From 3f4392e05cb657cceb0a9eda681d935290f5d313 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Sun, 10 Jul 2022 16:30:30 +0700
Subject: [PATCH 1/6] Include <cmeow> instead of <meow.h>

---
 stl/inc/charconv                                     | 10 +++++-----
 stl/src/vector_algorithms.cpp                        |  2 +-
 stl/src/xonce2.cpp                                   |  2 +-
 stl/src/xxxprec.hpp                                  |  8 ++++----
 .../tests/Dev08_496675_iostream_int_reading/test.cpp |  2 +-
 tests/std/tests/Dev08_563686_ostream/test.cpp        |  6 ++++--
 tests/std/tests/Dev08_576265_list_remove/test.cpp    |  2 +-
 tests/std/tests/Dev08_584299_search_n/test.cpp       |  2 +-
 tests/std/tests/Dev09_012361_vector_swap/test.cpp    |  8 ++++----
 .../Dev09_052961_has_iterator_debugging_0/test.cpp   |  6 +++---
 tests/std/tests/Dev09_056375_locale_cleanup/test.cpp |  4 ++--
 .../tests/Dev09_056375_locale_cleanup/testdll.cpp    |  2 +-
 .../tests/Dev09_098637_stl_function_typeids/test.cpp |  2 +-
 .../Dev09_126254_persistent_aux_allocators/test.cpp  |  8 ++++----
 tests/std/tests/Dev09_130060_unique_copy/test.cpp    |  2 +-
 .../std/tests/Dev09_152755_tr1_nested_bind/test.cpp  |  4 ++--
 tests/std/tests/Dev09_153419_tr1_allocators/test.cpp | 10 +++++-----
 .../Dev09_154033_tr1_predicate_search_n/test.cpp     |  2 +-
 .../tests/Dev09_155328_tr1_vector_of_set/test.cpp    |  2 +-
 .../Dev09_158181_tr1_unordered_meow_swap/test.cpp    |  6 +++---
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp |  2 +-
 .../Dev09_171205_tr1_assign_pair_to_tuple/test.cpp   |  2 +-
 .../Dev09_172505_tr1_bind_reference_wrapper/test.cpp |  2 +-
 tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp  |  2 +-
 tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp |  6 +++---
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  4 ++--
 tests/std/tests/Dev09_182017_tr1_search_n/test.cpp   |  2 +-
 .../tests/Dev09_186118_stoullx_corner_cases/test.cpp |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../Dev10_441756_function_reference_wrapper/test.cpp |  2 +-
 tests/std/tests/Dev10_445289_make_shared/test.cpp    |  8 ++++----
 .../tests/Dev10_482830_header_only_string/test.cpp   |  2 +-
 .../tests/Dev10_491486_floating_point_hash/test.cpp  |  4 ++--
 .../tests/Dev10_492345_tr1_function_swap/test.cpp    |  4 ++--
 .../test.cpp                                         |  2 +-
 .../Dev10_500860_overloaded_address_of/test.cpp      |  6 +++---
 .../Dev10_544258_heterogeneous_comparisons/test.cpp  |  2 +-
 .../Dev10_555491_complex_linker_errors/test.cpp      |  6 +++---
 .../tests/Dev10_561430_list_and_tree_leaks/test.cpp  |  6 +++---
 tests/std/tests/Dev10_562056_tree_leak/test.cpp      |  2 +-
 .../test.cpp                                         |  4 ++--
 .../tests/Dev10_567556_move_from_empty_list/test.cpp |  4 ++--
 tests/std/tests/Dev10_579381_vector_grow_to/test.cpp |  2 +-
 tests/std/tests/Dev10_590599_hash_string/test.cpp    |  2 +-
 tests/std/tests/Dev10_617014_tuple_tie/test.cpp      |  2 +-
 tests/std/tests/Dev10_632876_regex_proxy/test.cpp    |  8 ++++----
 .../std/tests/Dev10_635436_shared_ptr_reset/test.cpp |  2 +-
 tests/std/tests/Dev10_639436_const_map_at/test.cpp   |  4 ++--
 .../tests/Dev10_646244_bad_alloc_message/test.cpp    |  4 ++--
 .../Dev10_646556_construct_tuple_from_const/test.cpp |  2 +-
 .../Dev10_654977_655012_shared_ptr_move/test.cpp     |  2 +-
 .../std/tests/Dev10_661739_tuple_copy_ctors/test.cpp |  2 +-
 .../tests/Dev10_682964_stable_sort_warnings/test.cpp |  4 ++--
 .../Dev10_689595_back_inserter_vector_bool/test.cpp  |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.compile.pass.cpp                            |  2 +-
 .../Dev10_729003_bind_reference_wrapper/test.cpp     |  2 +-
 .../std/tests/Dev10_766948_insert_ambiguity/test.cpp |  2 +-
 .../std/tests/Dev10_780098_movable_elements/test.cpp |  4 ++--
 .../tests/Dev10_783436_rvalue_string_plus/test.cpp   |  2 +-
 .../Dev10_809142_copy_n_istream_iterator/test.cpp    |  4 ++--
 .../test.cpp                                         |  6 +++---
 .../Dev10_816787_swap_vector_bool_elements/test.cpp  |  2 +-
 .../Dev10_847656_shared_ptr_is_convertible/test.cpp  |  2 +-
 .../test.cpp                                         |  2 +-
 tests/std/tests/Dev10_860410_bitset_ctors/test.cpp   |  4 ++--
 .../Dev10_860421_deque_push_back_pop_front/test.cpp  |  2 +-
 .../Dev10_881629_vector_erase_return_value/test.cpp  |  2 +-
 .../test.cpp                                         |  2 +-
 .../std/tests/Dev10_905461_is_sorted_until/test.cpp  |  2 +-
 .../tests/Dev10_908702_string_memory_leak/test.cpp   |  2 +-
 .../std/tests/Dev10_909646_stringstream_vd2/test.cpp |  2 +-
 .../Dev11_0000000_dual_range_algorithms/test.cpp     |  4 ++--
 .../Dev11_0000000_null_forward_iterators/test.cpp    |  4 ++--
 tests/std/tests/Dev11_0000000_quoted/test.cpp        |  2 +-
 tests/std/tests/Dev11_0000000_rotate_test/test.cpp   |  2 +-
 tests/std/tests/Dev11_0000000_tuple_cat/test.cpp     |  2 +-
 .../Dev11_0000000_user_defined_literals/test.cpp     |  2 +-
 .../tests/Dev11_0019127_singular_iterators/test.cpp  |  2 +-
 .../Dev11_0091392_string_erase_resize_perf/test.cpp  |  6 +++---
 .../tests/Dev11_0133625_locale0_implib_cpp/test.cpp  |  2 +-
 .../Dev11_0135139_vector_bool_comparisons/test.cpp   |  2 +-
 .../Dev11_0235721_async_and_packaged_task/test.cpp   |  4 ++--
 tests/std/tests/Dev11_0253803_debug_pointer/test.cpp |  2 +-
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  4 ++--
 tests/std/tests/Dev11_0302476_pair_move/test.cpp     |  2 +-
 .../Dev11_0314451_make_pair_make_tuple/test.cpp      |  2 +-
 .../Dev11_0316853_find_memchr_optimization/test.cpp  |  2 +-
 .../tests/Dev11_0376122_grand_theft_bind/test.cpp    |  2 +-
 .../test.cpp                                         |  2 +-
 .../tests/Dev11_0387701_container_equality/test.cpp  |  4 ++--
 .../tests/Dev11_0437519_container_behavior/test.cpp  |  4 ++--
 .../tests/Dev11_0447546_facet_allocation/test.cpp    |  2 +-
 .../test.compile.pass.cpp                            |  6 +++---
 .../Dev11_0485243_condition_variable_crash/test.cpp  |  4 ++--
 .../Dev11_0493504_error_category_lifetime/test.cpp   |  4 ++--
 .../tests/Dev11_0494593_time_put_wchar_t/test.cpp    |  4 ++--
 tests/std/tests/Dev11_0496153_locale_ctor/test.cpp   |  6 +++---
 .../std/tests/Dev11_0532622_minmax_element/test.cpp  |  2 +-
 .../tests/Dev11_0535636_functional_overhaul/test.cpp |  4 ++--
 .../Dev11_0555154_system_clock_to_time_t/test.cpp    |  4 ++--
 tests/std/tests/Dev11_0577418_random_seed_0/test.cpp |  2 +-
 .../test.cpp                                         |  6 +++---
 .../test.cpp                                         |  2 +-
 .../tests/Dev11_0617384_empty_std_function/test.cpp  |  2 +-
 .../std/tests/Dev11_0653897_codecvt_partial/test.cpp |  2 +-
 tests/std/tests/Dev11_0671816_list_splice/test.cpp   |  2 +-
 .../std/tests/Dev11_0696045_future_wait_for/test.cpp |  2 +-
 .../test.cpp                                         |  6 +++---
 .../test.cpp                                         |  8 ++++----
 .../tests/Dev11_0823534_transparent_lookup/test.cpp  |  4 ++--
 tests/std/tests/Dev11_0835323_to_string/test.cpp     |  4 ++--
 tests/std/tests/Dev11_0836436_get_time/test.cpp      |  4 ++--
 .../test.cpp                                         | 10 +++++-----
 .../Dev11_0863628_atomic_compare_exchange/test.cpp   |  8 ++++----
 .../tests/Dev11_0920385_list_sort_allocator/test.cpp |  6 +++---
 tests/std/tests/Dev11_1003120_search_test/test.cpp   |  6 +++---
 .../test.cpp                                         |  2 +-
 .../Dev11_1066931_filesystem_rename_noop/test.cpp    |  6 +++---
 tests/std/tests/Dev11_1074023_constexpr/test.cpp     |  4 ++--
 .../tests/Dev11_1086953_call_once_overhaul/test.cpp  |  6 +++---
 .../Dev11_1114006_condition_variable_pred/test.cpp   |  4 ++--
 .../tests/Dev11_1131212_uncaught_exceptions/test.cpp |  2 +-
 .../tests/Dev11_1137366_nested_exception/test.cpp    |  4 ++--
 .../test.cpp                                         |  2 +-
 tests/std/tests/Dev11_1150223_shared_mutex/test.cpp  |  2 +-
 .../tests/Dev11_1158803_regex_thread_safety/test.cpp |  2 +-
 .../Dev11_1180290_filesystem_error_code/test.cpp     |  2 +-
 .../tests/GH_000457_system_error_message/test.cpp    |  2 +-
 .../GH_000625_vector_bool_optimization/test.cpp      |  2 +-
 .../floating_point_utils.hpp                         |  2 +-
 .../GH_001010_filesystem_error_encoding/test.cpp     |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../P0024R2_parallel_algorithms_all_of/test.cpp      |  2 +-
 .../tests/P0024R2_parallel_algorithms_count/test.cpp |  2 +-
 .../tests/P0024R2_parallel_algorithms_equal/test.cpp |  2 +-
 .../test.cpp                                         |  2 +-
 .../tests/P0024R2_parallel_algorithms_find/test.cpp  |  2 +-
 .../P0024R2_parallel_algorithms_find_end/test.cpp    |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../P0024R2_parallel_algorithms_for_each/test.cpp    |  2 +-
 .../test.cpp                                         |  2 +-
 .../P0024R2_parallel_algorithms_is_heap/test.cpp     |  2 +-
 .../test.cpp                                         |  4 ++--
 .../P0024R2_parallel_algorithms_is_sorted/test.cpp   |  4 ++--
 .../P0024R2_parallel_algorithms_mismatch/test.cpp    |  2 +-
 .../P0024R2_parallel_algorithms_partition/test.cpp   |  2 +-
 .../P0024R2_parallel_algorithms_reduce/test.cpp      |  2 +-
 .../P0024R2_parallel_algorithms_remove/test.cpp      |  2 +-
 .../P0024R2_parallel_algorithms_replace/test.cpp     |  2 +-
 .../P0024R2_parallel_algorithms_search/test.cpp      |  4 ++--
 .../P0024R2_parallel_algorithms_search_n/test.cpp    |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../tests/P0024R2_parallel_algorithms_sort/test.cpp  |  2 +-
 .../P0024R2_parallel_algorithms_stable_sort/test.cpp |  2 +-
 .../P0024R2_parallel_algorithms_transform/test.cpp   |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../tests/P0035R4_over_aligned_allocation/test.cpp   |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.hpp                                         |  2 +-
 .../double_from_chars_test_cases.hpp                 |  2 +-
 .../P0067R5_charconv/float_from_chars_test_cases.hpp |  2 +-
 tests/std/tests/P0067R5_charconv/test.cpp            | 10 +++++-----
 tests/std/tests/P0067R5_charconv/test.hpp            |  2 +-
 .../tests/P0083R3_splicing_maps_and_sets/test.cpp    |  6 +++---
 tests/std/tests/P0092R1_polishing_chrono/test.cpp    |  4 ++--
 tests/std/tests/P0122R7_span_death/test.cpp          |  2 +-
 tests/std/tests/P0137R1_launder/test.cpp             |  2 +-
 .../test.cpp                                         |  4 ++--
 tests/std/tests/P0218R1_filesystem/test.cpp          |  6 +++---
 tests/std/tests/P0220R1_sample/test.cpp              |  4 ++--
 tests/std/tests/P0220R1_searchers/test.cpp           |  6 +++---
 tests/std/tests/P0220R1_string_view/test.cpp         |  4 ++--
 .../std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp  |  2 +-
 tests/std/tests/P0325R4_to_array/test.cpp            |  2 +-
 .../test.cpp                                         |  4 ++--
 tests/std/tests/P0356R5_bind_front/test.cpp          |  2 +-
 .../std/tests/P0414R2_shared_ptr_for_arrays/test.cpp |  2 +-
 tests/std/tests/P0415R1_constexpr_complex/test.cpp   |  2 +-
 .../std/tests/P0426R1_constexpr_char_traits/test.cpp |  2 +-
 tests/std/tests/P0433R2_deduction_guides/test.cpp    |  4 ++--
 tests/std/tests/P0448R4_spanstream/test.cpp          |  2 +-
 .../test.cpp                                         |  2 +-
 tests/std/tests/P0476R2_bit_cast/test.cpp            |  7 ++++---
 .../test.cpp                                         |  2 +-
 tests/std/tests/P0513R0_poisoning_the_hash/test.cpp  |  4 ++--
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 tests/std/tests/P0586R2_integer_comparison/test.cpp  |  4 ++--
 .../std/tests/P0595R2_is_constant_evaluated/test.cpp |  2 +-
 tests/std/tests/P0607R0_inline_variables/test.cpp    |  2 +-
 .../test.cpp                                         |  2 +-
 .../std/tests/P0616R0_using_move_in_numeric/test.cpp |  2 +-
 .../std/tests/P0645R10_text_formatting_args/test.cpp |  2 +-
 .../test.cpp                                         |  2 +-
 .../tests/P0645R10_text_formatting_death/test.cpp    |  2 +-
 .../test.cpp                                         |  4 ++--
 .../P0645R10_text_formatting_parse_contexts/test.cpp |  2 +-
 tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp |  4 ++--
 tests/std/tests/P0660R10_stop_token/test.cpp         |  4 ++--
 tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp   |  2 +-
 .../test.cpp                                         |  2 +-
 .../tests/P0769R2_shift_left_shift_right/test.cpp    |  2 +-
 tests/std/tests/P0784R7_library_machinery/test.cpp   |  2 +-
 .../test.cpp                                         |  6 +++---
 tests/std/tests/P0811R3_midpoint_lerp/test.cpp       | 10 +++++-----
 .../tests/P0896R4_ranges_iterator_machinery/test.cpp |  2 +-
 .../tests/P0896R4_ranges_range_machinery/test.cpp    |  2 +-
 tests/std/tests/P0896R4_ranges_to_address/test.cpp   |  2 +-
 tests/std/tests/P0898R3_concepts/test.cpp            |  2 +-
 tests/std/tests/P0898R3_identity/test.cpp            |  2 +-
 tests/std/tests/P0912R5_coroutine/test.cpp           |  2 +-
 .../P0919R3_heterogeneous_unordered_lookup/test.cpp  |  2 +-
 .../test.cpp                                         |  2 +-
 tests/std/tests/P1004R2_constexpr_vector/test.cpp    |  2 +-
 .../std/tests/P1004R2_constexpr_vector_bool/test.cpp |  2 +-
 tests/std/tests/P1007R3_assume_aligned/test.cpp      | 10 ++++++----
 .../P1020R1_smart_pointer_for_overwrite/test.cpp     |  2 +-
 .../tests/P1032R1_miscellaneous_constexpr/test.cpp   |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../P1502R1_standard_library_header_units/test.cpp   |  4 ++--
 tests/std/tests/P1645R1_constexpr_numeric/test.cpp   |  4 ++--
 .../test.cpp                                         |  2 +-
 .../tests/VSO_0000000_allocator_propagation/test.cpp |  6 +++---
 .../tests/VSO_0000000_any_calling_conventions/a.cpp  |  2 +-
 .../test.cpp                                         |  6 +++---
 .../test.cpp                                         |  6 +++---
 .../VSO_0000000_exception_ptr_rethrow_seh/test.cpp   |  8 ++++----
 tests/std/tests/VSO_0000000_has_static_rtti/test.cpp |  2 +-
 .../tests/VSO_0000000_initialize_everything/test.cpp |  6 +++---
 .../VSO_0000000_list_iterator_debugging/test.cpp     |  4 ++--
 .../VSO_0000000_list_unique_self_reference/test.cpp  |  4 ++--
 .../tests/VSO_0000000_matching_npos_address/test.cpp | 10 ++++++----
 .../VSO_0000000_more_pair_tuple_sfinae/test.cpp      |  2 +-
 .../tests/VSO_0000000_nullptr_stream_out/test.cpp    |  2 +-
 tests/std/tests/VSO_0000000_oss_workarounds/test.cpp |  2 +-
 .../tests/VSO_0000000_path_stream_parameter/test.cpp |  2 +-
 tests/std/tests/VSO_0000000_regex_interface/test.cpp |  4 ++--
 tests/std/tests/VSO_0000000_regex_use/test.cpp       |  4 ++--
 tests/std/tests/VSO_0000000_string_view_idl/test.cpp |  2 +-
 .../VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp     |  2 +-
 .../VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp |  4 ++--
 .../VSO_0095837_current_exception_dtor/test.cpp      |  4 ++--
 .../tests/VSO_0099869_pow_float_overflow/test.cpp    | 12 ++++++------
 .../std/tests/VSO_0102478_moving_allocators/test.cpp |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  6 +++---
 .../std/tests/VSO_0105317_expression_sfinae/test.cpp |  2 +-
 .../std/tests/VSO_0118461_min_max_noexcept/test.cpp  |  2 +-
 .../test.cpp                                         |  8 ++++----
 .../VSO_0121440_is_iterator_iterator_traits/test.cpp |  2 +-
 .../test.cpp                                         |  2 +-
 .../VSO_0135428_custom_char_traits_string/test.cpp   |  2 +-
 tests/std/tests/VSO_0144114_sleep_until/test.cpp     |  2 +-
 .../test.cpp                                         |  2 +-
 .../VSO_0149983_system_error_broken_pipe/test.cpp    |  2 +-
 tests/std/tests/VSO_0174871_string_replace/test.cpp  |  8 ++++----
 .../tests/VSO_0180466_algorithm_overhauls/test.cpp   |  2 +-
 tests/std/tests/VSO_0180469_fill_family/test.cpp     |  6 +++---
 .../test.cpp                                         |  4 ++--
 .../std/tests/VSO_0224478_scoped_allocator/test.cpp  |  2 +-
 tests/std/tests/VSO_0226079_mutex/test.cpp           |  6 +++---
 .../std/tests/VSO_0234888_num_get_overflows/test.cpp |  4 ++--
 .../VSO_0299624_checked_array_iterator_idl/test.cpp  |  6 +++---
 tests/std/tests/VSO_0397980_codecvt_length/test.cpp  |  2 +-
 .../VSO_0429900_fast_debug_range_based_for/test.cpp  |  2 +-
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  4 ++--
 .../VSO_0575109_string_ambiguous_overloads/test.cpp  |  2 +-
 tests/std/tests/VSO_0599804_seekg_zero/test.cpp      |  2 +-
 tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp   | 10 +++++-----
 .../tests/VSO_0664587_lcg_divide_by_zero/test.cpp    |  2 +-
 .../VSO_0677157_flist_merge_edge_cases/test.cpp      |  4 ++--
 .../tests/VSO_0735700_fstream_read_over_4k/test.cpp  |  4 ++--
 .../VSO_0736657_unordered_assign_rehash/test.cpp     |  2 +-
 .../test.cpp                                         |  4 ++--
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../test.cpp                                         |  2 +-
 .../std/tests/VSO_0961751_hash_range_erase/test.cpp  |  6 +++---
 .../tests/VSO_0971246_legacy_await_headers/test.cpp  |  2 +-
 tools/validate/validate.cpp                          |  8 ++++----
 297 files changed, 504 insertions(+), 497 deletions(-)

diff --git a/stl/inc/charconv b/stl/inc/charconv
index 080b5107fbe..09271706f25 100644
--- a/stl/inc/charconv
+++ b/stl/inc/charconv
@@ -804,8 +804,8 @@ _NODISCARD inline bool _Multiply_by_power_of_ten(_Big_integer_flt& _Xval, const
 #if 0
 #include <algorithm>
 #include <charconv>
-#include <stdint.h>
-#include <stdio.h>
+#include <cstdint>
+#include <cstdio>
 #include <tuple>
 #include <vector>
 using namespace std;
@@ -2444,13 +2444,13 @@ _NODISCARD to_chars_result _Floating_to_chars_hex_shortest(
 // cl /EHsc /nologo /W4 /MT /O2 /std:c++17 generate_tables.cpp && generate_tables
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <charconv>
 #include <cmath>
+#include <cstdint>
+#include <cstdio>
 #include <limits>
 #include <map>
-#include <stdint.h>
-#include <stdio.h>
 #include <system_error>
 #include <type_traits>
 #include <vector>
diff --git a/stl/src/vector_algorithms.cpp b/stl/src/vector_algorithms.cpp
index 5214349b768..507a0fa8547 100644
--- a/stl/src/vector_algorithms.cpp
+++ b/stl/src/vector_algorithms.cpp
@@ -12,11 +12,11 @@
 
 #if (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_ARM64EC)
 
+#include <cstdint>
 #include <emmintrin.h>
 #include <immintrin.h>
 #include <intrin0.h>
 #include <isa_availability.h>
-#include <stdint.h>
 
 extern "C" long __isa_enabled;
 
diff --git a/stl/src/xonce2.cpp b/stl/src/xonce2.cpp
index a94fbaddc20..17c9a3c3a76 100644
--- a/stl/src/xonce2.cpp
+++ b/stl/src/xonce2.cpp
@@ -3,7 +3,7 @@
 
 #include <yvals_core.h>
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <synchapi.h>
 
 // This must be as small as possible, because its contents are
diff --git a/stl/src/xxxprec.hpp b/stl/src/xxxprec.hpp
index 0d9d30cfefc..dd8c6477684 100644
--- a/stl/src/xxxprec.hpp
+++ b/stl/src/xxxprec.hpp
@@ -27,15 +27,15 @@ _EXTERN_C
     } // STET
 
 #if 0
-#include <stdio.h>
+#include <cstdio>
 
 static void printit(const char* s, FTYPE* p, int n) { // print xp array
     int i;
-    printf(s);
+    std::printf(s);
     for (i = 0; i < n && (p[i] != FLIT(0.0) || i == 0); ++i) {
-        printf(" %La", static_cast<long double>(p[i]));
+        std::printf(" %La", static_cast<long double>(p[i]));
     }
-    printf("\n");
+    std::printf("\n");
 }
 #endif // 0
 
diff --git a/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp b/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
index c4d14581de8..4f1f187fd1f 100644
--- a/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
+++ b/tests/std/tests/Dev08_496675_iostream_int_reading/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 int main() {
diff --git a/tests/std/tests/Dev08_563686_ostream/test.cpp b/tests/std/tests/Dev08_563686_ostream/test.cpp
index 1b5d8b4bd46..45238c79abd 100644
--- a/tests/std/tests/Dev08_563686_ostream/test.cpp
+++ b/tests/std/tests/Dev08_563686_ostream/test.cpp
@@ -26,11 +26,13 @@
 
 #define CRTDBG_MAP_ALLOC
 #include <crtdbg.h>
+#include <cstdlib>
 #include <sstream>
-#include <stdlib.h>
 
 #include <Windows.h>
 
+using namespace std;
+
 int main() {
     // Track CRT blocks
     _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_CHECK_CRT_DF);
@@ -38,7 +40,7 @@ int main() {
     {
         // Allocate long lived objects in the CRT.
         // We don't want these objects to show up as leaks.
-        std::iostream s(nullptr);
+        iostream s(nullptr);
     }
 
     // Get memory state before creating iostream
diff --git a/tests/std/tests/Dev08_576265_list_remove/test.cpp b/tests/std/tests/Dev08_576265_list_remove/test.cpp
index 6604c0e870d..f941f74ebd2 100644
--- a/tests/std/tests/Dev08_576265_list_remove/test.cpp
+++ b/tests/std/tests/Dev08_576265_list_remove/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <list>
 
 struct Val {
diff --git a/tests/std/tests/Dev08_584299_search_n/test.cpp b/tests/std/tests/Dev08_584299_search_n/test.cpp
index f072ce2925d..332ea5cbc08 100644
--- a/tests/std/tests/Dev08_584299_search_n/test.cpp
+++ b/tests/std/tests/Dev08_584299_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <list>
 
 // This test makes sure that the search_n algorithm behaves correctly.
diff --git a/tests/std/tests/Dev09_012361_vector_swap/test.cpp b/tests/std/tests/Dev09_012361_vector_swap/test.cpp
index 1d1487c2150..79f2a0380b7 100644
--- a/tests/std/tests/Dev09_012361_vector_swap/test.cpp
+++ b/tests/std/tests/Dev09_012361_vector_swap/test.cpp
@@ -85,14 +85,14 @@
 // deque<int>::iterator: Previously 12, 16, 16, 12, 8. Now 12, 8, 8, 8, 8.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
 #include <deque>
 #include <iterator>
 #include <list>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp b/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
index cead3da600f..66e8a30dc47 100644
--- a/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
+++ b/tests/std/tests/Dev09_052961_has_iterator_debugging_0/test.cpp
@@ -49,9 +49,9 @@
 // correctness to all known cases, and also increases efficiency (as iterator destructors
 // in debug mode with iterator debugging disabled now perform no extra work).
 
-#include <assert.h>
-#include <stdio.h>
-#include <string.h>
+#include <cassert>
+#include <cstdio>
+#include <cstring>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
index b495ef5fd1d..ce23d39c16c 100644
--- a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
+++ b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <locale>
-#include <stdio.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp b/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
index 51e338de533..b890a5b02ab 100644
--- a/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
+++ b/tests/std/tests/Dev09_056375_locale_cleanup/testdll.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 
 #include <Windows.h>
diff --git a/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp b/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
index b2a11425779..c36becdb829 100644
--- a/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
+++ b/tests/std/tests/Dev09_098637_stl_function_typeids/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 #include <typeinfo>
 
diff --git a/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp b/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
index fdcd0adb812..ea278e06e2a 100644
--- a/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
+++ b/tests/std/tests/Dev09_126254_persistent_aux_allocators/test.cpp
@@ -1,16 +1,16 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <new>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
diff --git a/tests/std/tests/Dev09_130060_unique_copy/test.cpp b/tests/std/tests/Dev09_130060_unique_copy/test.cpp
index 416e6c5a21f..fec2b1f9db1 100644
--- a/tests/std/tests/Dev09_130060_unique_copy/test.cpp
+++ b/tests/std/tests/Dev09_130060_unique_copy/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp b/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
index f8e9613c174..433e7edb3c2 100644
--- a/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
+++ b/tests/std/tests/Dev09_152755_tr1_nested_bind/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cmath>
 #include <functional>
-#include <math.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp b/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
index 50abbf12489..4bfb2c260e0 100644
--- a/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
+++ b/tests/std/tests/Dev09_153419_tr1_allocators/test.cpp
@@ -12,14 +12,14 @@
 // Big is 7 * 64 bits to disable the Small Functor Optimization.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <functional>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp b/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
index 6b726c80d3b..16ff6ea8e46 100644
--- a/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
+++ b/tests/std/tests/Dev09_154033_tr1_predicate_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <vector>
 
 struct X {
diff --git a/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp b/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
index 1c45dccac4c..90e7d20d9c5 100644
--- a/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
+++ b/tests/std/tests/Dev09_155328_tr1_vector_of_set/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <set>
 #include <vector>
 
diff --git a/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp b/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
index 8692ce252ce..4c53a27b8d2 100644
--- a/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
+++ b/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <climits>
 #include <cmath>
-#include <limits.h>
+#include <cstdlib>
 #include <stdexcept>
-#include <stdlib.h>
 #include <unordered_set>
 #include <utility>
 
diff --git a/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp b/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
index 1c2aa9b9537..0ffe77aa7f8 100644
--- a/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
+++ b/tests/std/tests/Dev09_158457_tr1_mem_fn_calling_conventions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <type_traits>
 
diff --git a/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp b/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
index 7baefd4aec8..92284ee339e 100644
--- a/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
+++ b/tests/std/tests/Dev09_161106_tr1_bind_templated_fxn_call_operator/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp b/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
index 51f10300091..9e3287e07fd 100644
--- a/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
+++ b/tests/std/tests/Dev09_165853_tr1_tuple_swap/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp b/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
index 34d3f6ad7ef..d93ec83a81f 100644
--- a/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
+++ b/tests/std/tests/Dev09_171205_tr1_assign_pair_to_tuple/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <utility>
 
diff --git a/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp b/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
index 02bbce83167..068993f7d86 100644
--- a/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev09_172505_tr1_bind_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp b/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
index 293625f488b..c57ae88c8be 100644
--- a/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
+++ b/tests/std/tests/Dev09_172666_tr1_tuple_odr/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <__msvc_all_public_headers.hpp>
-#include <assert.h>
+#include <cassert>
 
 namespace fs = std::experimental::filesystem;
 
diff --git a/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp b/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
index 54abc22c893..203cbb82438 100644
--- a/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
+++ b/tests/std/tests/Dev09_173612_tr1_regex_leak/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <locale>
 #include <new>
 #include <regex>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp b/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
index 1b4ba4b844b..0d63cdb76fa 100644
--- a/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
+++ b/tests/std/tests/Dev09_174589_tr1_function_storing_pmf_called_with_reference_or_pointer/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <memory>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp b/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
index 4adb8ad5a7c..a37def59461 100644
--- a/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
+++ b/tests/std/tests/Dev09_175314_tr1_reference_wrapper_assignment/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp b/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
index dd096ed41a5..c656f958b2b 100644
--- a/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev09_175716_tr1_dereferencing_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp b/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
index 876abf9d4ef..4f6c672be71 100644
--- a/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
+++ b/tests/std/tests/Dev09_176467_tr1_make_tuple_from_string_literal/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp b/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
index 6696e3a4c14..87bbfa53f60 100644
--- a/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
+++ b/tests/std/tests/Dev09_176498_tr1_binding_functors_with_non_const_fxn_call_ops/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp b/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
index 0859477411d..9e59b41b723 100644
--- a/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
+++ b/tests/std/tests/Dev09_181509_tr1_inf_loop_uniform_int_ull/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <execution>
 #include <random>
-#include <stdint.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp b/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
index f68559a4194..b427372a05a 100644
--- a/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
+++ b/tests/std/tests/Dev09_182017_tr1_search_n/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp b/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
index edde4cf3d2e..3dc91e3c8a1 100644
--- a/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
+++ b/tests/std/tests/Dev09_186118_stoullx_corner_cases/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 int main() {
diff --git a/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp b/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
index 00e9cd27854..3e76543f177 100644
--- a/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
+++ b/tests/std/tests/Dev09_192736_tr1_prngs_not_copyconstructible/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <iterator>
 #include <random>
diff --git a/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp b/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
index 374d3dee433..d3f75aaa9d7 100644
--- a/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
+++ b/tests/std/tests/Dev09_196243_tr1_enable_shared_from_this_ops/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 
 using namespace std;
diff --git a/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp b/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
index 14c3fc14ca5..2d40860b020 100644
--- a/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
+++ b/tests/std/tests/Dev09_199123_tr1_mem_fun_abstract_classes/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp b/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
index 37dbe23b458..c1b1e2160d9 100644
--- a/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev10_441756_function_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <random>
 
diff --git a/tests/std/tests/Dev10_445289_make_shared/test.cpp b/tests/std/tests/Dev10_445289_make_shared/test.cpp
index a9d67228489..ba15fbdd1eb 100644
--- a/tests/std/tests/Dev10_445289_make_shared/test.cpp
+++ b/tests/std/tests/Dev10_445289_make_shared/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_482830_header_only_string/test.cpp b/tests/std/tests/Dev10_482830_header_only_string/test.cpp
index ad288fcdd4a..33ac64e5a33 100644
--- a/tests/std/tests/Dev10_482830_header_only_string/test.cpp
+++ b/tests/std/tests/Dev10_482830_header_only_string/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cctype>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp b/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
index 89e82bc5a6a..8d18750ea3f 100644
--- a/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
+++ b/tests/std/tests/Dev10_491486_floating_point_hash/test.cpp
@@ -3,9 +3,9 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <functional>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp b/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
index e635248152a..5b84891fd9e 100644
--- a/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
+++ b/tests/std/tests/Dev10_492345_tr1_function_swap/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <new>
-#include <stddef.h>
 #include <tuple>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp b/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
index 38f027d6930..eca03193fc3 100644
--- a/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
+++ b/tests/std/tests/Dev10_498944_enable_shared_from_this_auto_ptr/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _HAS_AUTO_PTR_ETC 1
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp b/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
index 912c2061392..93b4ead540d 100644
--- a/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
+++ b/tests/std/tests/Dev10_500860_overloaded_address_of/test.cpp
@@ -4,12 +4,12 @@
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
 #include <array>
-#include <stddef.h>
-#include <stdlib.h>
+#include <cstddef>
+#include <cstdlib>
 #ifndef _M_CEE_PURE
 #include <atomic>
 #endif // _M_CEE_PURE
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <exception>
 #include <forward_list>
diff --git a/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp b/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
index a2501ca712e..e6fd9ac5f9a 100644
--- a/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
+++ b/tests/std/tests/Dev10_544258_heterogeneous_comparisons/test.cpp
@@ -6,7 +6,7 @@
 // family of functions"
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp b/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
index 569adafec8c..4dbe0fed137 100644
--- a/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
+++ b/tests/std/tests/Dev10_555491_complex_linker_errors/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cmath>
 #include <complex>
+#include <cstdint>
+#include <cstring>
 #include <limits>
-#include <stdint.h>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp b/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
index 8d2f66b285f..7eb85025d3a 100644
--- a/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
+++ b/tests/std/tests/Dev10_561430_list_and_tree_leaks/test.cpp
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -10,8 +12,6 @@
 #include <memory>
 #include <regex>
 #include <set>
-#include <stddef.h>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/Dev10_562056_tree_leak/test.cpp b/tests/std/tests/Dev10_562056_tree_leak/test.cpp
index d6dcc08c929..1c921104efe 100644
--- a/tests/std/tests/Dev10_562056_tree_leak/test.cpp
+++ b/tests/std/tests/Dev10_562056_tree_leak/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <list>
 #include <map>
diff --git a/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp b/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
index aefed9da8dd..9479b7414ba 100644
--- a/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
+++ b/tests/std/tests/Dev10_563443_empty_vector_begin_plus_zero/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp b/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
index e804e8da022..0fd9c785dc5 100644
--- a/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
+++ b/tests/std/tests/Dev10_567556_move_from_empty_list/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <set>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp b/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
index d1779c52e51..b6e9b742535 100644
--- a/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
+++ b/tests/std/tests/Dev10_579381_vector_grow_to/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <list>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_590599_hash_string/test.cpp b/tests/std/tests/Dev10_590599_hash_string/test.cpp
index 14b0b5425df..7648542491c 100644
--- a/tests/std/tests/Dev10_590599_hash_string/test.cpp
+++ b/tests/std/tests/Dev10_590599_hash_string/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <string>
 
diff --git a/tests/std/tests/Dev10_617014_tuple_tie/test.cpp b/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
index f07d3ff9161..d3fd82a55e7 100644
--- a/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
+++ b/tests/std/tests/Dev10_617014_tuple_tie/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev10_632876_regex_proxy/test.cpp b/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
index 2f4f0626320..d7ced586811 100644
--- a/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
+++ b/tests/std/tests/Dev10_632876_regex_proxy/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <new>
 #include <regex>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp b/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
index 0dd30270dce..28f631bb2cc 100644
--- a/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
+++ b/tests/std/tests/Dev10_635436_shared_ptr_reset/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/Dev10_639436_const_map_at/test.cpp b/tests/std/tests/Dev10_639436_const_map_at/test.cpp
index c1a31b9fc91..3ba7d04418a 100644
--- a/tests/std/tests/Dev10_639436_const_map_at/test.cpp
+++ b/tests/std/tests/Dev10_639436_const_map_at/test.cpp
@@ -3,10 +3,10 @@
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <hash_map>
 #include <map>
-#include <stdlib.h>
 #include <unordered_map>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp b/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
index 90d2946e39e..ca319b0c07f 100644
--- a/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
+++ b/tests/std/tests/Dev10_646244_bad_alloc_message/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <new>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp b/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
index afcb3029eed..a837847d088 100644
--- a/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
+++ b/tests/std/tests/Dev10_646556_construct_tuple_from_const/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp b/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
index e2a197b78cb..654d609b903 100644
--- a/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
+++ b/tests/std/tests/Dev10_654977_655012_shared_ptr_move/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp b/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
index e71a41ef43b..42b86e6d01c 100644
--- a/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
+++ b/tests/std/tests/Dev10_661739_tuple_copy_ctors/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp b/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
index a8653938c60..ec4a1feaa90 100644
--- a/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
+++ b/tests/std/tests/Dev10_682964_stable_sort_warnings/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <random>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp b/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
index 7bccb57d5b9..6703352da5e 100644
--- a/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
+++ b/tests/std/tests/Dev10_689595_back_inserter_vector_bool/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <list>
 #include <vector>
diff --git a/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp b/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
index b60cebb776e..5addf960bdc 100644
--- a/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
+++ b/tests/std/tests/Dev10_709166_checked_and_unchecked_array_iterator/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp b/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
index a1a12d3bddb..8b660a2e572 100644
--- a/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
+++ b/tests/std/tests/Dev10_709168_marking_iterators_as_checked/test.compile.pass.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
+#include <cstddef>
 #include <deque>
 #include <filesystem>
 #include <forward_list>
@@ -10,7 +11,6 @@
 #include <map>
 #include <set>
 #include <span>
-#include <stddef.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp b/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
index ea7f59a476a..6e57a4a9969 100644
--- a/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
+++ b/tests/std/tests/Dev10_729003_bind_reference_wrapper/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <string>
 
diff --git a/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp b/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
index 8340d994fec..cea9cf2277c 100644
--- a/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
+++ b/tests/std/tests/Dev10_766948_insert_ambiguity/test.cpp
@@ -4,7 +4,7 @@
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <hash_map>
 #include <hash_set>
 #include <map>
diff --git a/tests/std/tests/Dev10_780098_movable_elements/test.cpp b/tests/std/tests/Dev10_780098_movable_elements/test.cpp
index c99688c5329..8e03ddc349e 100644
--- a/tests/std/tests/Dev10_780098_movable_elements/test.cpp
+++ b/tests/std/tests/Dev10_780098_movable_elements/test.cpp
@@ -1,7 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -9,7 +10,6 @@
 #include <list>
 #include <memory>
 #include <set>
-#include <stddef.h>
 #include <unordered_set>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp b/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
index 639bca1e632..5bbdf31a17e 100644
--- a/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
+++ b/tests/std/tests/Dev10_783436_rvalue_string_plus/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp b/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
index a3ee38ad55d..8af8f1deab4 100644
--- a/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
+++ b/tests/std/tests/Dev10_809142_copy_n_istream_iterator/test.cpp
@@ -3,13 +3,13 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <sstream>
-#include <stdlib.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp b/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
index 6b3ca253a43..ab6f047f9b6 100644
--- a/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
+++ b/tests/std/tests/Dev10_814245_regex_character_class_crash/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
 #include <regex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 
 #include <test_regex_support.hpp>
diff --git a/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp b/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
index 619ccd9a0f0..0bffce7a9dc 100644
--- a/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
+++ b/tests/std/tests/Dev10_816787_swap_vector_bool_elements/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp b/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
index b64b2b8031a..730f44cdaa7 100644
--- a/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
+++ b/tests/std/tests/Dev10_847656_shared_ptr_is_convertible/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp b/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
index 8bee3c01c23..460a4d2e4a1 100644
--- a/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
+++ b/tests/std/tests/Dev10_851347_weak_ptr_virtual_inheritance/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <utility>
 #ifndef _M_CEE_PURE // in /clr:pure we miss runtime coverage of weak_ptr converting constructor
diff --git a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
index b6516c7fadc..283dedc4a51 100644
--- a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
+++ b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <bitset>
+#include <cassert>
+#include <cstdlib>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp b/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
index c1857bde5ea..3a9e78d92c6 100644
--- a/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
+++ b/tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp b/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
index d7aa0dbcfde..861bba6b23b 100644
--- a/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
+++ b/tests/std/tests/Dev10_881629_vector_erase_return_value/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp b/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
index 3117a14d068..c3e00928f45 100644
--- a/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
+++ b/tests/std/tests/Dev10_904413_moved_from_function_should_be_empty/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <utility>
 
diff --git a/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp b/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
index 62b8690bc46..5ce8b908c5c 100644
--- a/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
+++ b/tests/std/tests/Dev10_905461_is_sorted_until/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp b/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
index 65ef7e531f7..674e2341c79 100644
--- a/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
+++ b/tests/std/tests/Dev10_908702_string_memory_leak/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <crtdbg.h>
 #include <locale>
 #include <new>
diff --git a/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp b/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
index 9be50018512..a3ba7218d93 100644
--- a/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
+++ b/tests/std/tests/Dev10_909646_stringstream_vd2/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp b/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
index 6f02556e5b1..72a9a632b3d 100644
--- a/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
+++ b/tests/std/tests/Dev11_0000000_dual_range_algorithms/test.cpp
@@ -3,13 +3,13 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <list>
-#include <stdlib.h>
 #include <string>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
index 35346dc1b61..f9ea851fcc1 100644
--- a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
+++ b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
@@ -5,7 +5,8 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <deque>
 #include <experimental/filesystem>
 #include <filesystem>
@@ -17,7 +18,6 @@
 #include <regex>
 #include <set>
 #include <span>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/Dev11_0000000_quoted/test.cpp b/tests/std/tests/Dev11_0000000_quoted/test.cpp
index b2f0e43c8a0..ef08817a425 100644
--- a/tests/std/tests/Dev11_0000000_quoted/test.cpp
+++ b/tests/std/tests/Dev11_0000000_quoted/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <iomanip>
 #include <iostream>
 #include <sstream>
diff --git a/tests/std/tests/Dev11_0000000_rotate_test/test.cpp b/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
index 253c1d2ad36..91f203095f2 100644
--- a/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
+++ b/tests/std/tests/Dev11_0000000_rotate_test/test.cpp
@@ -17,7 +17,7 @@
 // -5- Complexity: At most last - first swaps.
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp b/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
index 6ed6101118d..4258b875f6d 100644
--- a/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
+++ b/tests/std/tests/Dev11_0000000_tuple_cat/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <string>
diff --git a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
index 545da00ef0a..4e94f1105cf 100644
--- a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
+++ b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
@@ -8,7 +8,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <complex>
 #include <cstddef>
diff --git a/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp b/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
index ab6d5f6ef06..674940b1ed1 100644
--- a/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
+++ b/tests/std/tests/Dev11_0019127_singular_iterators/test.cpp
@@ -14,7 +14,7 @@
 // a value-initialized iterator as the source of a copy or move operation."
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <forward_list>
 #include <list>
diff --git a/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp b/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
index c6035cd7e1f..39e3a7f5604 100644
--- a/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
+++ b/tests/std/tests/Dev11_0091392_string_erase_resize_perf/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <stdexcept>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp b/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
index e4a542d6304..e5af4b6949d 100644
--- a/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
+++ b/tests/std/tests/Dev11_0133625_locale0_implib_cpp/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp b/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
index 43dfd67165b..44927210742 100644
--- a/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
+++ b/tests/std/tests/Dev11_0135139_vector_bool_comparisons/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <random>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp b/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
index 69a285092b6..3a63b9b5984 100644
--- a/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
+++ b/tests/std/tests/Dev11_0235721_async_and_packaged_task/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdlib>
 #include <functional>
 #include <future>
 #include <memory>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
 #include <thread>
diff --git a/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp b/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
index 6e66216ced3..63aa3516a4f 100644
--- a/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
+++ b/tests/std/tests/Dev11_0253803_debug_pointer/test.cpp
@@ -4,7 +4,7 @@
 // DevDiv-253803 "<algorithm>: merge() asserts when given null src/dest"
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp b/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
index fa050292eb5..dd67957c7ba 100644
--- a/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
+++ b/tests/std/tests/Dev11_0289403_partition_point_complexity/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp b/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
index e5d7ba58b18..664fe80360e 100644
--- a/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
+++ b/tests/std/tests/Dev11_0299014_exception_ptr_requirements/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <new>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0302476_pair_move/test.cpp b/tests/std/tests/Dev11_0302476_pair_move/test.cpp
index a0d34d45590..479294924d6 100644
--- a/tests/std/tests/Dev11_0302476_pair_move/test.cpp
+++ b/tests/std/tests/Dev11_0302476_pair_move/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <tuple>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp b/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
index f46def52bc3..a3adc62e703 100644
--- a/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
+++ b/tests/std/tests/Dev11_0314451_make_pair_make_tuple/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <tuple>
diff --git a/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp b/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
index 88bb3637ad3..266509eb65c 100644
--- a/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
+++ b/tests/std/tests/Dev11_0316853_find_memchr_optimization/test.cpp
@@ -15,7 +15,7 @@
 #endif // __clang__
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <climits>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp b/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
index 6ed18c2416f..2fbf27bb441 100644
--- a/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
+++ b/tests/std/tests/Dev11_0376122_grand_theft_bind/test.cpp
@@ -8,7 +8,7 @@
 // [...]
 // - otherwise, the value is tid and its type Vi is TiD cv &.
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 
diff --git a/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp b/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
index d1c0d64c9f7..23b90ea4213 100644
--- a/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
+++ b/tests/std/tests/Dev11_0377755_thread_ctor_move_only_types/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <future>
 #include <memory>
diff --git a/tests/std/tests/Dev11_0387701_container_equality/test.cpp b/tests/std/tests/Dev11_0387701_container_equality/test.cpp
index 6d00e3d2b52..ee733eb0e0e 100644
--- a/tests/std/tests/Dev11_0387701_container_equality/test.cpp
+++ b/tests/std/tests/Dev11_0387701_container_equality/test.cpp
@@ -5,7 +5,8 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -15,7 +16,6 @@
 #include <map>
 #include <random>
 #include <set>
-#include <stddef.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0437519_container_behavior/test.cpp b/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
index 1d6751311dd..8a6e1f238dd 100644
--- a/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
+++ b/tests/std/tests/Dev11_0437519_container_behavior/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp b/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
index fe73ee5ddd0..b9b08f29ec0 100644
--- a/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
+++ b/tests/std/tests/Dev11_0447546_facet_allocation/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <codecvt>
 #include <locale>
 #include <new>
diff --git a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
index a323504ec10..e5c9102828c 100644
--- a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
+++ b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <list>
 #include <map>
 #include <set>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
@@ -25,11 +25,11 @@ struct simple_allocator : Base {
     simple_allocator(simple_allocator<U, UB> const&) {}
 
     value_type* allocate(std::size_t n) {
-        return static_cast<value_type*>(malloc(n * sizeof(value_type)));
+        return static_cast<value_type*>(std::malloc(n * sizeof(value_type)));
     }
 
     void deallocate(value_type* p, std::size_t) {
-        free(p);
+        std::free(p);
     }
 };
 
diff --git a/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp b/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
index 465c1b4c166..07b770d5983 100644
--- a/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
+++ b/tests/std/tests/Dev11_0485243_condition_variable_crash/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
 #include <crtdbg.h>
+#include <cstdlib>
 #include <functional>
 #include <list>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp b/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
index 88009970591..59aa7eea9b9 100644
--- a/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
+++ b/tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
-#include <ctype.h>
+#include <cassert>
+#include <cctype>
 #include <ios>
 #include <system_error>
 
diff --git a/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp b/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
index ca4304f61b0..9e147d89e32 100644
--- a/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
+++ b/tests/std/tests/Dev11_0494593_time_put_wchar_t/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <ctime>
 #include <iterator>
 #include <locale>
 #include <sstream>
 #include <string>
-#include <time.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
index f4c61f86cbe..c7ac08d39eb 100644
--- a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
+++ b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <clocale>
+#include <cstdio>
 #include <exception>
-#include <locale.h>
 #include <locale>
 #include <sstream>
-#include <stdio.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/Dev11_0532622_minmax_element/test.cpp b/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
index eacba1e0e2c..1a2964283d5 100644
--- a/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
+++ b/tests/std/tests/Dev11_0532622_minmax_element/test.cpp
@@ -16,7 +16,7 @@
 // where M is the last iterator in [first,last) such that no iterator in the range refers to a larger element."
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp b/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
index 3650ebf1625..c61226c1f32 100644
--- a/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
+++ b/tests/std/tests/Dev11_0535636_functional_overhaul/test.cpp
@@ -6,10 +6,10 @@
 #define _SILENCE_CXX17_ADAPTOR_TYPEDEFS_DEPRECATION_WARNING
 #define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <memory>
-#include <stdlib.h>
 #include <string>
 #include <type_traits>
 #include <typeinfo>
diff --git a/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp b/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
index f2c04f61e72..9e4be783a62 100644
--- a/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
+++ b/tests/std/tests/Dev11_0555154_system_clock_to_time_t/test.cpp
@@ -7,9 +7,9 @@
 // restricted to the coarser of the precisions of time_t and time_point. It is
 // implementation defined whether values are rounded or truncated to the required precision."
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
-#include <stdint.h>
+#include <cstdint>
 
 using namespace std;
 using namespace std::chrono;
diff --git a/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp b/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
index 8cd793c4175..6cff3d0e2d8 100644
--- a/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
+++ b/tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <random>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp b/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
index 3b3fdfe4862..e9beb782f24 100644
--- a/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
+++ b/tests/std/tests/Dev11_0579795_inplace_merge_out_of_memory/test.cpp
@@ -3,10 +3,10 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
 #include <new>
-#include <stdint.h>
-#include <stdlib.h>
 
 #if _HAS_CXX17 && !defined(_M_CEE)
 #define HAS_PARALLEL_ALGORITHMS 1
diff --git a/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp b/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
index 76ee02195ea..1189dd0359e 100644
--- a/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
+++ b/tests/std/tests/Dev11_0607540_pair_tuple_rvalue_references/test.cpp
@@ -22,7 +22,7 @@
 // tuple(const tuple&) = default;
 // tuple(tuple&&) = default;
 
-#include <assert.h>
+#include <cassert>
 #include <tuple>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp b/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
index e0e0c218f88..16ae8abdb4b 100644
--- a/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
+++ b/tests/std/tests/Dev11_0617384_empty_std_function/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp b/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
index 31800797307..0cf5fb7d511 100644
--- a/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
+++ b/tests/std/tests/Dev11_0653897_codecvt_partial/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <locale>
 #include <sstream>
 #include <string>
diff --git a/tests/std/tests/Dev11_0671816_list_splice/test.cpp b/tests/std/tests/Dev11_0671816_list_splice/test.cpp
index 29679a5918a..a6f5cc8b586 100644
--- a/tests/std/tests/Dev11_0671816_list_splice/test.cpp
+++ b/tests/std/tests/Dev11_0671816_list_splice/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp b/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
index d8a4987cb98..59445210f11 100644
--- a/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
+++ b/tests/std/tests/Dev11_0696045_future_wait_for/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <future>
 
diff --git a/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp b/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
index ca7ba6f3c8d..7572be3adf8 100644
--- a/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
+++ b/tests/std/tests/Dev11_0732166_unordered_strong_guarantee/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <map>
 #include <new>
 #include <set>
-#include <stddef.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
index 268721302d3..4dd0833a6c0 100644
--- a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
+++ b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
@@ -3,13 +3,13 @@
 
 #define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <crtdbg.h>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
 #include <functional>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp b/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
index 5d4eaf1a289..07c66ed99ba 100644
--- a/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
+++ b/tests/std/tests/Dev11_0823534_transparent_lookup/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <map>
 #include <set>
-#include <stddef.h>
 #include <string>
 #include <tuple>
 
diff --git a/tests/std/tests/Dev11_0835323_to_string/test.cpp b/tests/std/tests/Dev11_0835323_to_string/test.cpp
index e57504dc870..10d52236e79 100644
--- a/tests/std/tests/Dev11_0835323_to_string/test.cpp
+++ b/tests/std/tests/Dev11_0835323_to_string/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cmath>
+#include <cstdlib>
 #include <limits>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0836436_get_time/test.cpp b/tests/std/tests/Dev11_0836436_get_time/test.cpp
index 1143bf5365c..5f784c3d694 100644
--- a/tests/std/tests/Dev11_0836436_get_time/test.cpp
+++ b/tests/std/tests/Dev11_0836436_get_time/test.cpp
@@ -1,16 +1,16 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdio>
 #include <cstdlib>
+#include <ctime>
 #include <iomanip>
 #include <ios>
 #include <locale>
 #include <sstream>
 #include <streambuf>
 #include <string>
-#include <time.h>
 #include <tuple>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp b/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
index ee421c1135e..57c08b074cb 100644
--- a/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
+++ b/tests/std/tests/Dev11_0845312_comprehensive_floating_point/test.cpp
@@ -7,14 +7,14 @@
 // improvements. This test verifies scanf-printf round-tripping of a set of
 // diverse floating point values (both single and double precision).
 
-#include <assert.h>
-#include <float.h>
+#include <cassert>
+#include <cfloat>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
 #include <iomanip>
 #include <ios>
-#include <math.h>
 #include <sstream>
-#include <stdint.h>
-#include <stdio.h>
 
 #include <floating_point_test_cases.hpp>
 
diff --git a/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp b/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
index 63ee746546e..cf069ef66d8 100644
--- a/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
+++ b/tests/std/tests/Dev11_0863628_atomic_compare_exchange/test.cpp
@@ -6,13 +6,13 @@
 // Regress\intrin\atomic.cpp
 //
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
 #include <limits>
 #include <new>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 
 
diff --git a/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp b/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
index d1c74c1e5ad..1be18dcf82d 100644
--- a/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
+++ b/tests/std/tests/Dev11_0920385_list_sort_allocator/test.cpp
@@ -7,7 +7,9 @@
 #define _SILENCE_CXX17_OLD_ALLOCATOR_MEMBERS_DEPRECATION_WARNING
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -19,8 +21,6 @@
 #include <random>
 #include <regex>
 #include <set>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/Dev11_1003120_search_test/test.cpp b/tests/std/tests/Dev11_1003120_search_test/test.cpp
index b0f904a2ae1..b65aa27e4f1 100644
--- a/tests/std/tests/Dev11_1003120_search_test/test.cpp
+++ b/tests/std/tests/Dev11_1003120_search_test/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stdlib.h>
-#include <string.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp b/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
index f6a42a36eec..b2a61f0d57a 100644
--- a/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
+++ b/tests/std/tests/Dev11_1066589_shared_ptr_atomic_deadlock/test.cpp
@@ -3,8 +3,8 @@
 
 #define _SILENCE_CXX20_OLD_SHARED_PTR_ATOMIC_SUPPORT_DEPRECATION_WARNING
 
+#include <cstdlib>
 #include <memory>
-#include <stdlib.h>
 
 #ifndef _M_CEE_PURE
 #include <atomic>
diff --git a/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp b/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
index e4f6a4f33d0..27300609c41 100644
--- a/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
+++ b/tests/std/tests/Dev11_1066931_filesystem_rename_noop/test.cpp
@@ -3,13 +3,13 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdint>
+#include <cstdio>
 #include <experimental/filesystem>
 #include <filesystem>
 #include <fstream>
-#include <stdint.h>
-#include <stdio.h>
 #include <string>
 #include <system_error>
 
diff --git a/tests/std/tests/Dev11_1074023_constexpr/test.cpp b/tests/std/tests/Dev11_1074023_constexpr/test.cpp
index 5bd52e78b6a..1386ab3c221 100644
--- a/tests/std/tests/Dev11_1074023_constexpr/test.cpp
+++ b/tests/std/tests/Dev11_1074023_constexpr/test.cpp
@@ -9,7 +9,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #ifndef _M_CEE_PURE
 #include <atomic>
 #endif // _M_CEE_PURE
@@ -29,12 +29,12 @@
 #ifndef _M_CEE
 #include <mutex>
 #endif // _M_CEE
+#include <cstdint>
 #include <new>
 #include <numeric>
 #include <random>
 #include <ratio>
 #include <regex>
-#include <stdint.h>
 #include <string>
 #include <system_error>
 #include <tuple>
diff --git a/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp b/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
index 35c969fc237..071ad45f307 100644
--- a/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
+++ b/tests/std/tests/Dev11_1086953_call_once_overhaul/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <chrono>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <functional>
 #include <intrin0.h>
 #include <mutex>
 #include <stdexcept>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <thread>
 #include <vector>
diff --git a/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp b/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
index 0af65eccf50..d740068deca 100644
--- a/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
+++ b/tests/std/tests/Dev11_1114006_condition_variable_pred/test.cpp
@@ -3,11 +3,11 @@
 
 // Test DevDiv-1114006 "[+ VS2015] conditional_variable with predicate does not behave according to the standard".
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdlib>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 
 using namespace std;
diff --git a/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp b/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
index 1c5ad910d27..f02b0aafb60 100644
--- a/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
+++ b/tests/std/tests/Dev11_1131212_uncaught_exceptions/test.cpp
@@ -6,7 +6,7 @@
 // This test validates the implementation of std::uncaught_exceptions by recursively
 // throwing exceptions from a destructor.
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 
 class awesome_exception {};
diff --git a/tests/std/tests/Dev11_1137366_nested_exception/test.cpp b/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
index 8b8d96c3992..7e72d736353 100644
--- a/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
+++ b/tests/std/tests/Dev11_1137366_nested_exception/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <type_traits>
 #include <typeinfo>
diff --git a/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp b/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
index 927c27c68ae..4e47fdb70f3 100644
--- a/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
+++ b/tests/std/tests/Dev11_1140665_unique_ptr_array_conversions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp b/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
index 721a217a1fa..55d463d44de 100644
--- a/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
+++ b/tests/std/tests/Dev11_1150223_shared_mutex/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
 #include <mutex>
 #include <shared_mutex>
diff --git a/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp b/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
index b0c51f8e08c..6da04e5bb1d 100644
--- a/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
+++ b/tests/std/tests/Dev11_1158803_regex_thread_safety/test.cpp
@@ -1,8 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <regex>
 #include <thread>
 #include <vector>
diff --git a/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp b/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
index ae25b358015..d6c7d2d200d 100644
--- a/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
+++ b/tests/std/tests/Dev11_1180290_filesystem_error_code/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <experimental/filesystem>
 #include <fstream>
diff --git a/tests/std/tests/GH_000457_system_error_message/test.cpp b/tests/std/tests/GH_000457_system_error_message/test.cpp
index 234115aa39e..76c65980b82 100644
--- a/tests/std/tests/GH_000457_system_error_message/test.cpp
+++ b/tests/std/tests/GH_000457_system_error_message/test.cpp
@@ -4,7 +4,7 @@
 #include <yvals.h>
 
 #include <__msvc_system_error_abi.hpp>
-#include <assert.h>
+#include <cassert>
 
 int main() {
     char example[] = "test string \r\n\t\0 test test";
diff --git a/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp b/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
index 4b6f623d19e..7e9d8f395a0 100644
--- a/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
+++ b/tests/std/tests/GH_000625_vector_bool_optimization/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstdlib>
 #include <vector>
 
diff --git a/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp b/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
index 48f83b781a0..4c43feebe40 100644
--- a/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
+++ b/tests/std/tests/GH_000935_complex_numerical_accuracy/floating_point_utils.hpp
@@ -5,8 +5,8 @@
 
 #include <cassert>
 #include <cfenv>
+#include <cfloat>
 #include <cmath>
-#include <float.h>
 #include <type_traits>
 #include <xutility>
 
diff --git a/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp b/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
index a823c2599a2..656b95c5d68 100644
--- a/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
+++ b/tests/std/tests/GH_001010_filesystem_error_encoding/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 #include <filesystem>
 #include <string_view>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
index ef17b13b40f..ac14629d80e 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_difference/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <numeric>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
index fdf114291e6..2cdf0d54415 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_adjacent_find/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
index fbf511c823b..0206f7025df 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_all_of/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
index 3d277ccf3fc..6252f6e4633 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_count/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <list>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
index 9e1cadc49e3..45fd84742e7 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_equal/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
index fb168c1e154..08939a1b966 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_exclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
index 97aa3f3e072..6f6de1ed091 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
index b3f4597ebbf..1e269d1bf31 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find_end/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
index 3983d045321..e4516709d29 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_find_first_of/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <list>
 #include <numeric>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
index f3dc7a969c3..014fa457449 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_for_each/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
index 9e9c6276882..f391c140a12 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_inclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
index ed8fd50cdf3..25f8464e982 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_heap/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <numeric>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
index 8b0181988df..c3d08f94e6c 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_partitioned/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
-#include <stddef.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
index cf131436133..b733540f210 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_is_sorted/test.cpp
@@ -2,7 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <deque>
 #include <execution>
 #include <forward_list>
@@ -10,7 +11,6 @@
 #include <iterator>
 #include <list>
 #include <numeric>
-#include <stddef.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
index 40340d755db..cac22c3ab70 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_mismatch/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
index 345f2c21715..1a3b53c758f 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_partition/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
index 3d8cc29fe75..c168a294f23 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_reduce/test.cpp
@@ -3,7 +3,7 @@
 
 #pragma warning(disable : 4242 4244 4365) // test_case_incorrect_special_case_reasoning tests narrowing on purpose
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
index 324ff685efa..063b13817e4 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_remove/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
index d65b48cae89..1a4c38389ab 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_replace/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <random>
 #include <vector>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
index ab5e44b0b90..df56ffa6a36 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_search/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
index 46809e70ef7..dd7ed5433ab 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_search_n/test.cpp
@@ -2,14 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <forward_list>
 #include <iterator>
 #include <list>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <string_view>
 #include <vector>
 
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
index c641e892d4e..27cd4f78b20 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_set_difference/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <functional>
 #include <iostream>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
index 373c3997a13..713b6978ab2 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_set_intersection/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <execution>
 #include <functional>
 #include <iostream>
 #include <numeric>
 #include <random>
-#include <stdlib.h>
 #include <vector>
 
 #include <parallel_algorithms_utilities.hpp>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
index b3d614b1a20..c74a8c7fd51 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_sort/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <numeric>
 #include <random>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
index 0bf345291fd..2ffb6071602 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_stable_sort/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <list>
 #include <random>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
index 88a1775fe55..b901786db80 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <execution>
 #include <forward_list>
 #include <functional>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
index 256f6136494..816ef050365 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_exclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
index f048f2e236c..4b3666137b5 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_inclusive_scan/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp b/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
index 393e077b573..91418380195 100644
--- a/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
+++ b/tests/std/tests/P0024R2_parallel_algorithms_transform_reduce/test.cpp
@@ -3,7 +3,7 @@
 
 #pragma warning(disable : 4242 4244 4365) // test_case_incorrect_special_case_reasoning tests narrowing on purpose
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <execution>
 #include <functional>
 #include <iterator>
diff --git a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
index 7a21362fb2c..ac66ca4024a 100644
--- a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
+++ b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
@@ -7,7 +7,7 @@
 #define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp b/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
index 9502aa410cf..8acbe990af7 100644
--- a/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
+++ b/tests/std/tests/P0040R3_extending_memory_management_tools/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <memory>
 #include <new>
diff --git a/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp b/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
index beffa7170de..6ba46a24579 100644
--- a/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
+++ b/tests/std/tests/P0053R7_cpp_synchronized_buffered_ostream/test.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <ios>
diff --git a/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp b/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
index 7be213814d3..40c4778f6e2 100644
--- a/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
+++ b/tests/std/tests/P0067R5_charconv/double_from_chars_test_cases.hpp
@@ -5,7 +5,7 @@
 #define DOUBLE_FROM_CHARS_TEST_CASES_HPP
 
 #include <charconv>
-#include <stddef.h>
+#include <cstddef>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp b/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
index 0acbef16888..5bd6f23f881 100644
--- a/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
+++ b/tests/std/tests/P0067R5_charconv/float_from_chars_test_cases.hpp
@@ -5,7 +5,7 @@
 #define FLOAT_FROM_CHARS_TEST_CASES_HPP
 
 #include <charconv>
-#include <stddef.h>
+#include <cstddef>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0067R5_charconv/test.cpp b/tests/std/tests/P0067R5_charconv/test.cpp
index d58194240fe..400c1f62a53 100644
--- a/tests/std/tests/P0067R5_charconv/test.cpp
+++ b/tests/std/tests/P0067R5_charconv/test.cpp
@@ -5,10 +5,14 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <charconv>
 #include <chrono>
 #include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <fstream>
 #include <functional>
 #include <limits>
@@ -16,10 +20,6 @@
 #include <optional>
 #include <random>
 #include <set>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0067R5_charconv/test.hpp b/tests/std/tests/P0067R5_charconv/test.hpp
index 398533acfc8..8662971aa0b 100644
--- a/tests/std/tests/P0067R5_charconv/test.hpp
+++ b/tests/std/tests/P0067R5_charconv/test.hpp
@@ -5,8 +5,8 @@
 #define TEST_HPP
 
 #include <charconv>
+#include <cstddef>
 #include <limits>
-#include <stddef.h>
 #include <system_error>
 using namespace std;
 
diff --git a/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp b/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
index 64a8c05e22a..77054bb4ae6 100644
--- a/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
+++ b/tests/std/tests/P0083R3_splicing_maps_and_sets/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
 #include <functional>
 #include <initializer_list>
 #include <iterator>
 #include <map>
 #include <memory>
 #include <set>
-#include <stddef.h>
-#include <stdio.h>
 #include <type_traits>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/P0092R1_polishing_chrono/test.cpp b/tests/std/tests/P0092R1_polishing_chrono/test.cpp
index 90fef1c564c..f43668efa89 100644
--- a/tests/std/tests/P0092R1_polishing_chrono/test.cpp
+++ b/tests/std/tests/P0092R1_polishing_chrono/test.cpp
@@ -5,10 +5,10 @@
 // Tests the new functions added as part of P0092R1, "Polishing Chrono"
 //
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdint>
 #include <ratio>
-#include <stdint.h>
 
 using namespace std;
 using namespace std::chrono;
diff --git a/tests/std/tests/P0122R7_span_death/test.cpp b/tests/std/tests/P0122R7_span_death/test.cpp
index 619dae9b523..545b6729dec 100644
--- a/tests/std/tests/P0122R7_span_death/test.cpp
+++ b/tests/std/tests/P0122R7_span_death/test.cpp
@@ -4,8 +4,8 @@
 #define _CONTAINER_DEBUG_LEVEL 1
 
 #include <algorithm>
+#include <cstddef>
 #include <span>
-#include <stddef.h>
 #include <vector>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/P0137R1_launder/test.cpp b/tests/std/tests/P0137R1_launder/test.cpp
index 0eb5ef43363..8165c51d03e 100644
--- a/tests/std/tests/P0137R1_launder/test.cpp
+++ b/tests/std/tests/P0137R1_launder/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <new>
 
 using namespace std;
diff --git a/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp b/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
index d7615f245a5..dc51b5ce3f0 100644
--- a/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
+++ b/tests/std/tests/P0202R3_constexpr_algorithm_and_exchange/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/P0218R1_filesystem/test.cpp b/tests/std/tests/P0218R1_filesystem/test.cpp
index 9140c01a10d..96236069720 100644
--- a/tests/std/tests/P0218R1_filesystem/test.cpp
+++ b/tests/std/tests/P0218R1_filesystem/test.cpp
@@ -4,8 +4,10 @@
 #define _SILENCE_CXX20_U8PATH_DEPRECATION_WARNING
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdlib>
+#include <cstring>
 #include <cvt/cp1251>
 #include <cvt/sjis>
 #include <cvt/utf8_utf16>
@@ -18,8 +20,6 @@
 #include <memory>
 #include <optional>
 #include <sstream>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0220R1_sample/test.cpp b/tests/std/tests/P0220R1_sample/test.cpp
index ffe03d26356..007b9d52800 100644
--- a/tests/std/tests/P0220R1_sample/test.cpp
+++ b/tests/std/tests/P0220R1_sample/test.cpp
@@ -3,11 +3,11 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <iterator>
 #include <numeric>
 #include <random>
-#include <stdio.h>
 #include <type_traits>
 
 #include "adapterator.hpp"
diff --git a/tests/std/tests/P0220R1_searchers/test.cpp b/tests/std/tests/P0220R1_searchers/test.cpp
index a0cd15d29b7..85972030761 100644
--- a/tests/std/tests/P0220R1_searchers/test.cpp
+++ b/tests/std/tests/P0220R1_searchers/test.cpp
@@ -2,16 +2,16 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstddef>
+#include <cstdint>
 #include <forward_list>
 #include <functional>
 #include <initializer_list>
 #include <iostream>
 #include <iterator>
 #include <random>
-#include <stddef.h>
-#include <stdint.h>
 #include <string>
 #include <string_view>
 #include <utility>
diff --git a/tests/std/tests/P0220R1_string_view/test.cpp b/tests/std/tests/P0220R1_string_view/test.cpp
index 3a490ed7380..f7ffb3ee21f 100644
--- a/tests/std/tests/P0220R1_string_view/test.cpp
+++ b/tests/std/tests/P0220R1_string_view/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <deque>
 #include <sstream>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp b/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
index 51c990f9761..27949e667b2 100644
--- a/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
+++ b/tests/std/tests/P0295R0_gcd_lcm/test.compile.pass.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <limits.h>
+#include <climits>
 #include <numeric>
 
 using std::gcd;
diff --git a/tests/std/tests/P0325R4_to_array/test.cpp b/tests/std/tests/P0325R4_to_array/test.cpp
index 01673a8e8f6..6438e03befe 100644
--- a/tests/std/tests/P0325R4_to_array/test.cpp
+++ b/tests/std/tests/P0325R4_to_array/test.cpp
@@ -3,7 +3,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <type_traits>
diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
index 8639e40a72d..af9a59a56b6 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_formatting/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <clocale>
 #include <concepts>
+#include <cstdio>
 #include <format>
 #include <iostream>
 #include <locale>
 #include <sstream>
-#include <stdio.h>
 #include <string>
 #include <string_view>
 #include <type_traits>
diff --git a/tests/std/tests/P0356R5_bind_front/test.cpp b/tests/std/tests/P0356R5_bind_front/test.cpp
index 804c9c3bb6f..c6ad4e785de 100644
--- a/tests/std/tests/P0356R5_bind_front/test.cpp
+++ b/tests/std/tests/P0356R5_bind_front/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <string>
diff --git a/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp b/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
index b7443129dc1..b5378f8b238 100644
--- a/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
+++ b/tests/std/tests/P0414R2_shared_ptr_for_arrays/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <memory>
 #include <sstream>
diff --git a/tests/std/tests/P0415R1_constexpr_complex/test.cpp b/tests/std/tests/P0415R1_constexpr_complex/test.cpp
index e02267a93f2..12383dfc806 100644
--- a/tests/std/tests/P0415R1_constexpr_complex/test.cpp
+++ b/tests/std/tests/P0415R1_constexpr_complex/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <complex>
 #include <type_traits>
 using namespace std;
diff --git a/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp b/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
index 4a03e8e6b7f..c3153c7e86b 100644
--- a/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
+++ b/tests/std/tests/P0426R1_constexpr_char_traits/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/P0433R2_deduction_guides/test.cpp b/tests/std/tests/P0433R2_deduction_guides/test.cpp
index 37cd60f656e..db6aabc226c 100644
--- a/tests/std/tests/P0433R2_deduction_guides/test.cpp
+++ b/tests/std/tests/P0433R2_deduction_guides/test.cpp
@@ -2,10 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <chrono>
 #include <complex>
+#include <cstddef>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -21,7 +22,6 @@
 #include <set>
 #include <sstream>
 #include <stack>
-#include <stddef.h>
 #include <streambuf>
 #include <string>
 #include <string_view>
diff --git a/tests/std/tests/P0448R4_spanstream/test.cpp b/tests/std/tests/P0448R4_spanstream/test.cpp
index 4355df2f6dc..1dba07b485a 100644
--- a/tests/std/tests/P0448R4_spanstream/test.cpp
+++ b/tests/std/tests/P0448R4_spanstream/test.cpp
@@ -3,7 +3,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <ios>
 #include <limits>
 #include <span>
diff --git a/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp b/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
index f5cef24bced..f1ee5890b8a 100644
--- a/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
+++ b/tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp
@@ -1,6 +1,6 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/P0476R2_bit_cast/test.cpp b/tests/std/tests/P0476R2_bit_cast/test.cpp
index 4135f0f2ed0..f9cbbb28502 100644
--- a/tests/std/tests/P0476R2_bit_cast/test.cpp
+++ b/tests/std/tests/P0476R2_bit_cast/test.cpp
@@ -1,14 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <cmath>
+#include <cstddef>
+#include <cstring>
 #include <limits>
-#include <stddef.h>
-#include <string.h>
 #include <type_traits>
 #include <utility>
+using namespace std;
 
 // structure sizing depends on a packing of 8, which is the default
 
diff --git a/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp b/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
index edd29708600..00f8f4ae323 100644
--- a/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
+++ b/tests/std/tests/P0487R1_fixing_operator_shl_basic_istream_char_pointer/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <istream>
 #include <iterator>
 #include <sstream>
diff --git a/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp b/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
index 40edfba826f..a94452d8f62 100644
--- a/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
+++ b/tests/std/tests/P0513R0_poisoning_the_hash/test.cpp
@@ -4,12 +4,12 @@
 #define _HAS_DEPRECATED_ADAPTOR_TYPEDEFS 1
 #define _SILENCE_CXX17_ADAPTOR_TYPEDEFS_DEPRECATION_WARNING
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <memory>
 #include <optional>
-#include <stddef.h>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp b/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
index c73cccfa76b..2d924ccc9ff 100644
--- a/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
+++ b/tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <limits>
 
 using namespace std;
diff --git a/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp b/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
index 40bbfc0f000..983145ab428 100644
--- a/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
+++ b/tests/std/tests/P0556R3_bit_integral_power_of_two_operations/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#include <assert.h>
 #include <bit>
+#include <cassert>
 #include <limits>
 #include <utility>
 
diff --git a/tests/std/tests/P0586R2_integer_comparison/test.cpp b/tests/std/tests/P0586R2_integer_comparison/test.cpp
index 247172472ab..5522fe00a7c 100644
--- a/tests/std/tests/P0586R2_integer_comparison/test.cpp
+++ b/tests/std/tests/P0586R2_integer_comparison/test.cpp
@@ -5,9 +5,9 @@
 // Tests the new functions added as part of P0586R2, "Integer Comparison Functions"
 //
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <limits>
-#include <stdint.h>
 #include <utility>
 using namespace std;
 
diff --git a/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp b/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
index 1af2be04787..8f44b81f0ba 100644
--- a/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
+++ b/tests/std/tests/P0595R2_is_constant_evaluated/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 using namespace std;
 
diff --git a/tests/std/tests/P0607R0_inline_variables/test.cpp b/tests/std/tests/P0607R0_inline_variables/test.cpp
index cb28fc0b705..899d73728ed 100644
--- a/tests/std/tests/P0607R0_inline_variables/test.cpp
+++ b/tests/std/tests/P0607R0_inline_variables/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp b/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
index 59600dd93c8..b5f1f734c79 100644
--- a/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
+++ b/tests/std/tests/P0608R3_improved_variant_converting_constructor/test.cpp
@@ -3,8 +3,8 @@
 
 // Also tests for P1957R2: Converting from T* to bool should be considered narrowing
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <functional>
 #include <optional>
 #include <string>
diff --git a/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp b/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
index 58100b4314a..c89b53526ff 100644
--- a/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
+++ b/tests/std/tests/P0616R0_using_move_in_numeric/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <numeric>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/P0645R10_text_formatting_args/test.cpp b/tests/std/tests/P0645R10_text_formatting_args/test.cpp
index d5ba4e427f4..85a1784d7bc 100644
--- a/tests/std/tests/P0645R10_text_formatting_args/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_args/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <cstdint>
diff --git a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
index 78bcc07288f..39f946fa14c 100644
--- a/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_custom_formatting/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <format>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/P0645R10_text_formatting_death/test.cpp b/tests/std/tests/P0645R10_text_formatting_death/test.cpp
index e597f994cd4..e72fab0920f 100644
--- a/tests/std/tests/P0645R10_text_formatting_death/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_death/test.cpp
@@ -3,7 +3,7 @@
 
 #define _CONTAINER_DEBUG_LEVEL 1
 
-#include <assert.h>
+#include <cassert>
 #include <format>
 #include <string_view>
 
diff --git a/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp b/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
index c68b91a0c12..224282a9e72 100644
--- a/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_grapheme_clusterization/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <format>
 #include <iterator>
 #include <span>
-#include <stddef.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp b/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
index c587832f85c..d0ec2134ce5 100644
--- a/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_parse_contexts/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <format>
diff --git a/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp b/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
index 5606ea85920..58bbf2049fb 100644
--- a/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
+++ b/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
 #include <mutex>
-#include <stdio.h>
 #include <thread>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/P0660R10_stop_token/test.cpp b/tests/std/tests/P0660R10_stop_token/test.cpp
index eaf5cdc24e0..a44555626dd 100644
--- a/tests/std/tests/P0660R10_stop_token/test.cpp
+++ b/tests/std/tests/P0660R10_stop_token/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
+#include <cstdio>
 #include <optional>
-#include <stdio.h>
 #include <stop_token>
 #include <thread>
 #include <utility>
diff --git a/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp b/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
index 76acd3e30ab..809eeb0fd9e 100644
--- a/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
+++ b/tests/std/tests/P0718R2_atomic_smart_ptrs/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdint>
 #include <memory>
 #include <thread>
diff --git a/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp b/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
index bdcd7dae5cd..f77bc7a19be 100644
--- a/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
+++ b/tests/std/tests/P0753R2_manipulators_for_cpp_synchronized_buffered_ostream/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <ios>
 #include <memory>
 #include <sstream>
diff --git a/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp b/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
index b7c702b420c..8c5d165ab9b 100644
--- a/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
+++ b/tests/std/tests/P0769R2_shift_left_shift_right/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <forward_list>
 #include <iterator>
 #include <list>
diff --git a/tests/std/tests/P0784R7_library_machinery/test.cpp b/tests/std/tests/P0784R7_library_machinery/test.cpp
index 4fe86b10e09..abd47bf44d7 100644
--- a/tests/std/tests/P0784R7_library_machinery/test.cpp
+++ b/tests/std/tests/P0784R7_library_machinery/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp b/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
index 7fae144a0cf..a91077e6c84 100644
--- a/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
+++ b/tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
 #include <limits>
 #include <memory>
 #include <span>
-#include <stddef.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <utility>
diff --git a/tests/std/tests/P0811R3_midpoint_lerp/test.cpp b/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
index da12486f640..23236f2dc8c 100644
--- a/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
+++ b/tests/std/tests/P0811R3_midpoint_lerp/test.cpp
@@ -2,18 +2,18 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
 #include <bit>
+#include <cassert>
+#include <cfenv>
 #include <charconv>
 #include <cmath>
-#include <fenv.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <iterator>
 #include <limits>
 #include <numeric>
 #include <optional>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <type_traits>
 
 using namespace std;
diff --git a/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp b/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
index 41d766f6248..245478e9cd0 100644
--- a/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_iterator_machinery/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <compare>
 #include <concepts>
 #include <iterator>
diff --git a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
index 730369c1d8d..76d3a4c93c1 100644
--- a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <compare>
 #include <concepts>
 #include <cstddef>
diff --git a/tests/std/tests/P0896R4_ranges_to_address/test.cpp b/tests/std/tests/P0896R4_ranges_to_address/test.cpp
index 34070d36885..c9bda4a2525 100644
--- a/tests/std/tests/P0896R4_ranges_to_address/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_to_address/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <string>
 #include <type_traits>
diff --git a/tests/std/tests/P0898R3_concepts/test.cpp b/tests/std/tests/P0898R3_concepts/test.cpp
index 1336525845b..42d04247f85 100644
--- a/tests/std/tests/P0898R3_concepts/test.cpp
+++ b/tests/std/tests/P0898R3_concepts/test.cpp
@@ -9,8 +9,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <assert.h>
 #include <bitset>
+#include <cassert>
 #include <concepts>
 #include <cstddef>
 #include <cstdio>
diff --git a/tests/std/tests/P0898R3_identity/test.cpp b/tests/std/tests/P0898R3_identity/test.cpp
index d3f34f26d7b..11e9a722f23 100644
--- a/tests/std/tests/P0898R3_identity/test.cpp
+++ b/tests/std/tests/P0898R3_identity/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <vector>
 
diff --git a/tests/std/tests/P0912R5_coroutine/test.cpp b/tests/std/tests/P0912R5_coroutine/test.cpp
index 76a81601fc6..5c9d13a5dee 100644
--- a/tests/std/tests/P0912R5_coroutine/test.cpp
+++ b/tests/std/tests/P0912R5_coroutine/test.cpp
@@ -4,7 +4,7 @@
 #include <version> // TRANSITION, Clang 14 coroutine support
 #ifdef __cpp_lib_coroutine // TRANSITION, Clang 14 coroutine support
 
-#include <assert.h>
+#include <cassert>
 #include <coroutine>
 #include <exception>
 using namespace std;
diff --git a/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp b/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
index 090e25fbe05..7926284594b 100644
--- a/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
+++ b/tests/std/tests/P0919R3_heterogeneous_unordered_lookup/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <hash_map>
 #include <hash_set>
diff --git a/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp b/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
index 7f5d00ebdae..4b77954ce96 100644
--- a/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
+++ b/tests/std/tests/P0966R1_string_reserve_should_not_shrink/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_CXX20_STRING_RESERVE_WITHOUT_ARGUMENT_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/P1004R2_constexpr_vector/test.cpp b/tests/std/tests/P1004R2_constexpr_vector/test.cpp
index 4549f9068cb..12a8d2ea664 100644
--- a/tests/std/tests/P1004R2_constexpr_vector/test.cpp
+++ b/tests/std/tests/P1004R2_constexpr_vector/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <iterator>
 #include <memory>
diff --git a/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp b/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
index 4a155ad2cbb..17c3d03e80c 100644
--- a/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
+++ b/tests/std/tests/P1004R2_constexpr_vector_bool/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cstddef>
 #include <iterator>
 #include <limits>
diff --git a/tests/std/tests/P1007R3_assume_aligned/test.cpp b/tests/std/tests/P1007R3_assume_aligned/test.cpp
index a878589d1fb..d2333fd98f2 100644
--- a/tests/std/tests/P1007R3_assume_aligned/test.cpp
+++ b/tests/std/tests/P1007R3_assume_aligned/test.cpp
@@ -1,18 +1,20 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <memory>
-#include <stddef.h>
+
+using namespace std;
 
 constexpr void can_change_value_via_assume_aligned(int* p) {
-    int* p1 = std::assume_aligned<256>(p);
+    int* p1 = assume_aligned<256>(p);
     p1[0]   = 10;
     p1[1]   = -15;
 }
 
 constexpr int can_read_value_via_assume_aligned_and_sum_it(int const* p, size_t size) {
-    int const* p1 = std::assume_aligned<256>(p);
+    int const* p1 = assume_aligned<256>(p);
     int result    = 0;
     for (size_t i = 0; i < size; ++i) {
         result += p1[i];
diff --git a/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp b/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
index c6ee3f4c3c9..39371d080e4 100644
--- a/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
+++ b/tests/std/tests/P1020R1_smart_pointer_for_overwrite/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
diff --git a/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp b/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
index b66ebf80fc1..f2ff62aa6e2 100644
--- a/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
+++ b/tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <memory>
-#include <stddef.h>
 #include <string_view>
 #include <tuple>
 #include <utility>
diff --git a/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp b/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
index 746969b8729..f583785499a 100644
--- a/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
+++ b/tests/std/tests/P1165R1_consistently_propagating_stateful_allocators/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <memory>
-#include <stddef.h>
 #include <stdexcept>
 #include <string>
 #include <utility>
diff --git a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
index 6c7525d7d08..1340df7d2fd 100644
--- a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
+++ b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
@@ -94,8 +94,8 @@ import <vector>;
 import <version>;
 // clang-format on
 
-#include <assert.h>
-#include <stdio.h>
+#include <cassert>
+#include <cstdio>
 
 #include <force_include.hpp>
 using namespace std;
diff --git a/tests/std/tests/P1645R1_constexpr_numeric/test.cpp b/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
index 20ffd6fbab1..8a5842a193e 100644
--- a/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
+++ b/tests/std/tests/P1645R1_constexpr_numeric/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <iterator>
 #include <numeric>
-#include <stddef.h>
 #include <utility>
 
 using namespace std;
diff --git a/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp b/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
index 79b16fa6919..77ab2d93b01 100644
--- a/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
+++ b/tests/std/tests/P2231R1_complete_constexpr_optional_variant/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <initializer_list>
 #include <optional>
 #include <type_traits>
diff --git a/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp b/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
index 627143040e7..b220fc08da0 100644
--- a/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
+++ b/tests/std/tests/VSO_0000000_allocator_propagation/test.cpp
@@ -2,7 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -12,8 +14,6 @@
 #include <map>
 #include <new>
 #include <set>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 #include <type_traits>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp b/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
index 942a4d4d0e5..89fcc3e5206 100644
--- a/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
+++ b/tests/std/tests/VSO_0000000_any_calling_conventions/a.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <any>
-#include <assert.h>
+#include <cassert>
 #include <utility>
 
 #include "ab.hpp"
diff --git a/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp b/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
index 22a4e69a802..8555e30670a 100644
--- a/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
+++ b/tests/std/tests/VSO_0000000_condition_variable_any_exceptions/test.cpp
@@ -1,14 +1,14 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <thread>
 #include <utility>
 
diff --git a/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp b/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
index 8a00c071f43..12d0d3811af 100644
--- a/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
+++ b/tests/std/tests/VSO_0000000_container_allocator_constructors/test.cpp
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -11,8 +13,6 @@
 #include <map>
 #include <new>
 #include <set>
-#include <stdio.h>
-#include <stdlib.h>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp b/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
index 03399bb6676..6052ab4a493 100644
--- a/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
+++ b/tests/std/tests/VSO_0000000_exception_ptr_rethrow_seh/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <excpt.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp b/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
index 00f5423fcf8..f3c0d19a44d 100644
--- a/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
+++ b/tests/std/tests/VSO_0000000_has_static_rtti/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <exception>
 #include <functional>
 #include <memory>
diff --git a/tests/std/tests/VSO_0000000_initialize_everything/test.cpp b/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
index c594c46baec..779e47ba36a 100644
--- a/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
+++ b/tests/std/tests/VSO_0000000_initialize_everything/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
 #include <initializer_list>
 #include <memory>
 #include <new>
-#include <stddef.h>
-#include <string.h>
 #include <string>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp b/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
index a688a5b8bf2..0b75fea6365 100644
--- a/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
+++ b/tests/std/tests/VSO_0000000_list_iterator_debugging/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <stdexcept>
-#include <stdlib.h>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp b/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
index c86c4fc27d8..33bb2deb78e 100644
--- a/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
+++ b/tests/std/tests/VSO_0000000_list_unique_self_reference/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <forward_list>
 #include <initializer_list>
 #include <list>
 #include <set>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
index c0588a85e3f..ff8b56b13d8 100644
--- a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
+++ b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
@@ -1,15 +1,17 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
-#include <stddef.h>
+#include <cassert>
+#include <cstddef>
 #include <string>
 
+using namespace std;
+
 extern "C" {
 extern const size_t* other_npos_address;
 }
 
 int main() {
-    static_assert(std::string::npos == static_cast<size_t>(-1), "");
-    assert(&std::string::npos == other_npos_address);
+    static_assert(string::npos == static_cast<size_t>(-1), "");
+    assert(&string::npos == other_npos_address);
 }
diff --git a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
index b563f091d70..bcf23d0edbd 100644
--- a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
+++ b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #ifndef _M_CEE
 #include <mutex>
diff --git a/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp b/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
index 3646a6e51b9..52e074acd43 100644
--- a/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
+++ b/tests/std/tests/VSO_0000000_nullptr_stream_out/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <iosfwd>
 #include <istream>
 #include <ostream>
diff --git a/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp b/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
index 495b9de28ac..9b11b5c280e 100644
--- a/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
+++ b/tests/std/tests/VSO_0000000_oss_workarounds/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_FPOS_SEEKPOS_DEPRECATION_WARNING
-#include <assert.h>
+#include <cassert>
 #include <iosfwd>
 
 int main() {
diff --git a/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp b/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
index 024d6152f2a..53b9f6576f4 100644
--- a/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
+++ b/tests/std/tests/VSO_0000000_path_stream_parameter/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
-#include <assert.h>
+#include <cassert>
 #include <experimental/filesystem>
 #include <fstream>
 #include <ios>
diff --git a/tests/std/tests/VSO_0000000_regex_interface/test.cpp b/tests/std/tests/VSO_0000000_regex_interface/test.cpp
index 337415b9132..0703637e4be 100644
--- a/tests/std/tests/VSO_0000000_regex_interface/test.cpp
+++ b/tests/std/tests/VSO_0000000_regex_interface/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <regex>
 #include <sstream>
-#include <stdio.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0000000_regex_use/test.cpp b/tests/std/tests/VSO_0000000_regex_use/test.cpp
index 65e792b6d2d..f5abd2955e7 100644
--- a/tests/std/tests/VSO_0000000_regex_use/test.cpp
+++ b/tests/std/tests/VSO_0000000_regex_use/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdio>
+#include <cstdlib>
 #include <regex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 
 #include <test_regex_support.hpp>
diff --git a/tests/std/tests/VSO_0000000_string_view_idl/test.cpp b/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
index a9d9449915a..f8b7b27f2df 100644
--- a/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
+++ b/tests/std/tests/VSO_0000000_string_view_idl/test.cpp
@@ -3,7 +3,7 @@
 
 #define _CONTAINER_DEBUG_LEVEL 1
 
-#include <stddef.h>
+#include <cstddef>
 #include <string_view>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp b/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
index b6fefa1eca8..d6c36d48aeb 100644
--- a/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
+++ b/tests/std/tests/VSO_0000000_wchar_t_filebuf_xsmeown/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <fstream>
 #include <ios>
 #include <iterator>
diff --git a/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp b/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
index d482bb4c6a4..2c436aafeb2 100644
--- a/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
+++ b/tests/std/tests/VSO_0095468_clr_exception_ptr_bad_alloc/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <new>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp b/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
index 8a189dacc33..05f87751f80 100644
--- a/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
+++ b/tests/std/tests/VSO_0095837_current_exception_dtor/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstring>
 #include <exception>
 #include <stdexcept>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp b/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
index a4c11a09a2c..b70947cf887 100644
--- a/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
+++ b/tests/std/tests/VSO_0099869_pow_float_overflow/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cinttypes>
 #include <cmath>
-#include <inttypes.h>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <limits>
 #include <map>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0102478_moving_allocators/test.cpp b/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
index 14b5809fe37..c11a47b51b0 100644
--- a/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
+++ b/tests/std/tests/VSO_0102478_moving_allocators/test.cpp
@@ -4,8 +4,9 @@
 #define _USE_HETEROGENEOUS_ALLOCATOR_COMPARE_IN_INTERNAL_CHECK
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <cstdio>
+#include <cstdlib>
 #include <deque>
 #include <forward_list>
 #include <functional>
@@ -16,7 +17,6 @@
 #include <regex>
 #include <set>
 #include <stdexcept>
-#include <stdlib.h>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
diff --git a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
index 3b2b36556e2..1b1d7d23ef6 100644
--- a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
+++ b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
 #include <exception>
-#include <stddef.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
index 8046a6088d3..de2c60e1bd0 100644
--- a/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
+++ b/tests/std/tests/VSO_0104705_throwing_copy_in_current_exception_seh/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
 #include <exception>
 #include <excpt.h>
-#include <stdint.h>
-#include <stdio.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp b/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
index 2884e162cbf..563fd1401a7 100644
--- a/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
+++ b/tests/std/tests/VSO_0105317_expression_sfinae/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <type_traits>
diff --git a/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp b/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
index 3ce1d2604ae..e1f550f2fac 100644
--- a/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
+++ b/tests/std/tests/VSO_0118461_min_max_noexcept/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 
 using std::max;
 using std::min;
diff --git a/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp b/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
index 0e1e96bb23c..77be49b3f52 100644
--- a/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
+++ b/tests/std/tests/VSO_0121275_filesystem_canonical_should_handle_many_double_dots/test.cpp
@@ -4,13 +4,13 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <cwctype>
 #include <experimental/filesystem>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
-#include <wctype.h>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp b/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
index 6a8882fa0a7..e9f9c2df8bd 100644
--- a/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
+++ b/tests/std/tests/VSO_0121440_is_iterator_iterator_traits/test.cpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <array>
+#include <cstddef>
 #include <iterator>
-#include <stddef.h>
 #include <type_traits>
 #include <utility>
 #include <vector>
diff --git a/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp b/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
index 5a6eeb4ce5a..87d8f6f435c 100644
--- a/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
+++ b/tests/std/tests/VSO_0131167_associative_emplacement_allocations/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <memory>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp b/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
index 9b415725606..d39ac22c1a7 100644
--- a/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
+++ b/tests/std/tests/VSO_0135428_custom_char_traits_string/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 #include <utility>
 
diff --git a/tests/std/tests/VSO_0144114_sleep_until/test.cpp b/tests/std/tests/VSO_0144114_sleep_until/test.cpp
index 5c36b9ca81b..9c245daf55c 100644
--- a/tests/std/tests/VSO_0144114_sleep_until/test.cpp
+++ b/tests/std/tests/VSO_0144114_sleep_until/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
 #include <ratio>
 #include <thread>
diff --git a/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp b/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
index d4ac27c8746..d66559c6583 100644
--- a/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
+++ b/tests/std/tests/VSO_0144294_unordered_map_max_bucket_count/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
-#include <assert.h>
+#include <cassert>
 #include <hash_map>
 #include <hash_set>
 #include <unordered_map>
diff --git a/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp b/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
index 5a81f5cdc6e..1d5d69fffcb 100644
--- a/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
+++ b/tests/std/tests/VSO_0149983_system_error_broken_pipe/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <system_error>
 
 int main() {
diff --git a/tests/std/tests/VSO_0174871_string_replace/test.cpp b/tests/std/tests/VSO_0174871_string_replace/test.cpp
index 655be2763ff..e06149b2ef1 100644
--- a/tests/std/tests/VSO_0174871_string_replace/test.cpp
+++ b/tests/std/tests/VSO_0174871_string_replace/test.cpp
@@ -1,11 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <stdexcept>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp b/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
index 8bb2f274383..23cfc10e5dd 100644
--- a/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
+++ b/tests/std/tests/VSO_0180466_algorithm_overhauls/test.cpp
@@ -11,7 +11,7 @@
 
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <iterator>
 #include <string>
diff --git a/tests/std/tests/VSO_0180469_fill_family/test.cpp b/tests/std/tests/VSO_0180469_fill_family/test.cpp
index 6c3bef212b9..52bc0a41a5d 100644
--- a/tests/std/tests/VSO_0180469_fill_family/test.cpp
+++ b/tests/std/tests/VSO_0180469_fill_family/test.cpp
@@ -9,12 +9,12 @@
 // Note that this test *should* trigger 4365 inside STL headers, because it
 // calls std::fill and std::uninitialized_fill with (signed*, signed*, unsigned)
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <cmath>
 #include <cstddef>
+#include <cstdio>
+#include <cstdlib>
 #include <memory>
-#include <stdio.h>
-#include <stdlib.h>
 #include <vector>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp b/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
index 7c891d41fef..45f422af1a6 100644
--- a/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
+++ b/tests/std/tests/VSO_0204655_heap_algorithms_integer_overflow/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <iterator>
 #include <limits>
 #include <numeric>
 #include <random>
-#include <stdint.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp b/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
index f50095babe9..3da2e414070 100644
--- a/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
+++ b/tests/std/tests/VSO_0224478_scoped_allocator/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <new>
 #include <scoped_allocator>
diff --git a/tests/std/tests/VSO_0226079_mutex/test.cpp b/tests/std/tests/VSO_0226079_mutex/test.cpp
index c23eace4605..433e2bb9a2a 100644
--- a/tests/std/tests/VSO_0226079_mutex/test.cpp
+++ b/tests/std/tests/VSO_0226079_mutex/test.cpp
@@ -1,13 +1,13 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <chrono>
+#include <cstdio>
+#include <cstdlib>
 #include <exception>
 #include <mutex>
 #include <shared_mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <system_error>
 #include <thread>
diff --git a/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp b/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
index 245fcd5aac2..2bacb2b91a1 100644
--- a/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
+++ b/tests/std/tests/VSO_0234888_num_get_overflows/test.cpp
@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdint>
 #include <iostream>
 #include <limits>
 #include <locale>
 #include <sstream>
-#include <stdint.h>
 #include <string>
 #include <type_traits>
 
diff --git a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
index cc58553189e..8f1c1a4fef5 100644
--- a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
+++ b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
@@ -1,15 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstddef>
 #include <iterator>
-#include <stddef.h>
 
 #include <test_death.hpp>
 
 using namespace stdext;
 
 void test_case_construction_out_of_range() {
-    checked_array_iterator<int*> it(nullptr, 1, 0); // checked_array_iterator construction index out of range
+    checked_array_iterator<int*> it(std::nullptr, 1, 0); // checked_array_iterator construction index out of range
     (void) it;
 }
 
@@ -43,7 +43,7 @@ void test_case_operator_preincrement_value_initialized_iterator() {
 void test_case_operator_preincrement_off_end() {
     int arr[] = {1, 2};
     checked_array_iterator<int*> it(arr, 2);
-    for (size_t idx = 0; idx < 3; ++idx) {
+    for (std::size_t idx = 0; idx < 3; ++idx) {
         ++it; // cannot increment checked_array_iterator past end
     }
 }
diff --git a/tests/std/tests/VSO_0397980_codecvt_length/test.cpp b/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
index e1d23def999..7558dc5f4ec 100644
--- a/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
+++ b/tests/std/tests/VSO_0397980_codecvt_length/test.cpp
@@ -7,7 +7,7 @@
 #undef _ENFORCE_FACET_SPECIALIZATIONS
 #define _ENFORCE_FACET_SPECIALIZATIONS 0
 
-#include <assert.h>
+#include <cassert>
 #include <codecvt>
 #include <cstdlib>
 #include <iterator>
diff --git a/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp b/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
index dd2d14c1e30..238419a844d 100644
--- a/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
+++ b/tests/std/tests/VSO_0429900_fast_debug_range_based_for/test.cpp
@@ -3,7 +3,7 @@
 
 #define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
 #include <array>
-#include <assert.h>
+#include <cassert>
 #include <deque>
 #include <forward_list>
 #include <hash_map>
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
index 0cfde34d7be..e516b792c48 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
index 59087b8cc30..949a61e0aa3 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_noexcept_function_2/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp b/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
index 48709db21a6..065d264fde2 100644
--- a/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
+++ b/tests/std/tests/VSO_0512710_terminate_current_exception_from_unwind/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <exception>
 #include <stdexcept>
-#include <stdlib.h>
 
 using namespace std;
 
diff --git a/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp b/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
index e27e5da1b81..248d7f995be 100644
--- a/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
+++ b/tests/std/tests/VSO_0575109_string_ambiguous_overloads/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0599804_seekg_zero/test.cpp b/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
index a8f5bac24d4..af29247ed25 100644
--- a/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
+++ b/tests/std/tests/VSO_0599804_seekg_zero/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <sstream>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp b/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
index 84ea48905ea..4d44f6a00c7 100644
--- a/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
+++ b/tests/std/tests/VSO_0644691_utf_8_codecvt/test.cpp
@@ -3,15 +3,15 @@
 
 #define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <clocale>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <exception>
 #include <fstream>
 #include <iostream>
-#include <locale.h>
 #include <locale>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp b/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
index 8c32e486ad9..95252f6cdea 100644
--- a/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
+++ b/tests/std/tests/VSO_0664587_lcg_divide_by_zero/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <random>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp b/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
index 18e5cfb7770..9c1434ac49f 100644
--- a/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
+++ b/tests/std/tests/VSO_0677157_flist_merge_edge_cases/test.cpp
@@ -2,12 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdlib>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <stdexcept>
-#include <stdlib.h>
 #include <vector>
 
 #include <test_death.hpp>
diff --git a/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp b/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
index dcc4b800793..aab90b9a5e5 100644
--- a/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
+++ b/tests/std/tests/VSO_0735700_fstream_read_over_4k/test.cpp
@@ -2,10 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
+#include <cstdio>
 #include <fstream>
 #include <numeric>
-#include <stdio.h>
 #include <string>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp b/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
index 435eac07136..6896543ad3a 100644
--- a/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
+++ b/tests/std/tests/VSO_0736657_unordered_assign_rehash/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <unordered_set>
 
 using namespace std;
diff --git a/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp b/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
index 352e6a7fc64..d0050dba5c5 100644
--- a/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
+++ b/tests/std/tests/VSO_0744055_atomic_load_8_bytes_readonly/test.cpp
@@ -1,9 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
 #include <atomic>
-#include <stdio.h>
+#include <cassert>
+#include <cstdio>
 
 #include <Windows.h>
 
diff --git a/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp b/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
index 9fb4e1553f4..c2a56c6e1a9 100644
--- a/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
+++ b/tests/std/tests/VSO_0792651_unordered_set_rehash_invalidates_key/test.cpp
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
 #include <memory>
 #include <unordered_set>
 
diff --git a/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp b/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
index 06d4b746eee..afbd1e2ec1f 100644
--- a/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
+++ b/tests/std/tests/VSO_0830211_container_debugging_range_checks/test.cpp
@@ -4,8 +4,8 @@
 #define _CONTAINER_DEBUG_LEVEL 1
 
 #include <array>
+#include <cstddef>
 #include <deque>
-#include <stddef.h>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp b/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
index 407f0c7ae3c..3bd64870769 100644
--- a/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
+++ b/tests/std/tests/VSO_0849827_multicontainer_emplace_hint_position/test.cpp
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include <iterator>
 #include <map>
 #include <utility>
diff --git a/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp b/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
index 1b9c08527bd..d32563c5b14 100644
--- a/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
+++ b/tests/std/tests/VSO_0961751_hash_range_erase/test.cpp
@@ -2,13 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _STL_INTERNAL_CHECK_EXHAUSTIVE
-#include <assert.h>
+#include <cassert>
+#include <climits>
+#include <cstdlib>
 #include <functional>
 #include <iterator>
-#include <limits.h>
 #include <memory>
 #include <stdexcept>
-#include <stdlib.h>
 #include <type_traits>
 #include <unordered_set>
 #include <utility>
diff --git a/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp b/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
index a40349e6cb7..2c605d033de 100644
--- a/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
+++ b/tests/std/tests/VSO_0971246_legacy_await_headers/test.cpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstdio>
 #include <experimental/generator>
 #include <future>
 #include <optional>
-#include <stdio.h>
 #include <vector>
 
 using namespace std::experimental;
diff --git a/tools/validate/validate.cpp b/tools/validate/validate.cpp
index 9870cb6c0a2..e77d56dd9fc 100644
--- a/tools/validate/validate.cpp
+++ b/tools/validate/validate.cpp
@@ -4,11 +4,11 @@
 #define _CRT_SECURE_NO_WARNINGS
 #include <algorithm>
 #include <array>
-#include <assert.h>
+#include <cassert>
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
 #include <filesystem>
-#include <stdarg.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string>
 #include <string_view>
 #include <utility>

From 503567d7a007295e1d89e1234049203ca1311250 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Sun, 10 Jul 2022 17:24:03 +0700
Subject: [PATCH 2/6] nullptr, not std::nullptr

---
 tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
index 8f1c1a4fef5..bc0c7e5d3f0 100644
--- a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
+++ b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
@@ -9,7 +9,7 @@
 using namespace stdext;
 
 void test_case_construction_out_of_range() {
-    checked_array_iterator<int*> it(std::nullptr, 1, 0); // checked_array_iterator construction index out of range
+    checked_array_iterator<int*> it(nullptr, 1, 0); // checked_array_iterator construction index out of range
     (void) it;
 }
 

From d32dac5ce2adb8733d9bd9e856da1285b0a8f7a9 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Wed, 13 Jul 2022 23:12:56 +0700
Subject: [PATCH 3/6] remove `std::`

---
 stl/src/xxxprec.hpp                                       | 6 +++---
 .../test.compile.pass.cpp                                 | 8 ++++----
 .../tests/VSO_0299624_checked_array_iterator_idl/test.cpp | 2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/stl/src/xxxprec.hpp b/stl/src/xxxprec.hpp
index dd8c6477684..dc3a4491b43 100644
--- a/stl/src/xxxprec.hpp
+++ b/stl/src/xxxprec.hpp
@@ -31,11 +31,11 @@ _EXTERN_C
 
 static void printit(const char* s, FTYPE* p, int n) { // print xp array
     int i;
-    std::printf(s);
+    printf(s);
     for (i = 0; i < n && (p[i] != FLIT(0.0) || i == 0); ++i) {
-        std::printf(" %La", static_cast<long double>(p[i]));
+        printf(" %La", static_cast<long double>(p[i]));
     }
-    std::printf("\n");
+    printf("\n");
 }
 #endif // 0
 
diff --git a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
index e5c9102828c..1f7f3677694 100644
--- a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
+++ b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
@@ -24,12 +24,12 @@ struct simple_allocator : Base {
     template <typename U, typename UB>
     simple_allocator(simple_allocator<U, UB> const&) {}
 
-    value_type* allocate(std::size_t n) {
-        return static_cast<value_type*>(std::malloc(n * sizeof(value_type)));
+    value_type* allocate(size_t n) {
+        return static_cast<value_type*>(malloc(n * sizeof(value_type)));
     }
 
-    void deallocate(value_type* p, std::size_t) {
-        std::free(p);
+    void deallocate(value_type* p, size_t) {
+        free(p);
     }
 };
 
diff --git a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
index bc0c7e5d3f0..91aee8682f3 100644
--- a/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
+++ b/tests/std/tests/VSO_0299624_checked_array_iterator_idl/test.cpp
@@ -43,7 +43,7 @@ void test_case_operator_preincrement_value_initialized_iterator() {
 void test_case_operator_preincrement_off_end() {
     int arr[] = {1, 2};
     checked_array_iterator<int*> it(arr, 2);
-    for (std::size_t idx = 0; idx < 3; ++idx) {
+    for (size_t idx = 0; idx < 3; ++idx) {
         ++it; // cannot increment checked_array_iterator past end
     }
 }

From dea5b85b50871441a062d0d27ef7273a54ac74e2 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Wed, 13 Jul 2022 23:27:03 +0700
Subject: [PATCH 4/6] replace `#include <meow.h>` to `#include <cmeow>`

---
 benchmarks/inc/utility.hpp                         |  4 ++--
 benchmarks/src/std_copy.cpp                        |  4 ++--
 tests/std/include/constexpr_char_traits.hpp        |  4 ++--
 tests/std/include/fenv_prefix.hpp                  |  4 ++--
 tests/std/include/floating_point_test_cases.hpp    |  2 +-
 tests/std/include/instantiate_algorithms.hpp       | 14 +++++++-------
 tests/std/include/new_counter.hpp                  |  6 +++---
 .../std/include/parallel_algorithms_utilities.hpp  |  2 +-
 tests/std/include/test_atomic_wait.hpp             |  4 ++--
 tests/std/include/test_death.hpp                   |  6 +++---
 tests/std/include/test_filesystem_support.hpp      |  2 +-
 tests/std/include/test_regex_support.hpp           |  6 +++---
 tests/std/include/test_thread_support.hpp          |  4 ++--
 tests/std/tests/P0156R2_scoped_lock/test.cpp       |  4 ++--
 14 files changed, 33 insertions(+), 33 deletions(-)

diff --git a/benchmarks/inc/utility.hpp b/benchmarks/inc/utility.hpp
index a27e1bacea6..e407e2654c3 100644
--- a/benchmarks/inc/utility.hpp
+++ b/benchmarks/inc/utility.hpp
@@ -4,9 +4,9 @@
 #pragma once
 
 #include <algorithm>
+#include <cstddef>
+#include <cstdint>
 #include <random>
-#include <stddef.h>
-#include <stdint.h>
 #include <vector>
 
 #include <xoshiro.hpp>
diff --git a/benchmarks/src/std_copy.cpp b/benchmarks/src/std_copy.cpp
index a84d58d19d4..4cb80016f5a 100644
--- a/benchmarks/src/std_copy.cpp
+++ b/benchmarks/src/std_copy.cpp
@@ -3,8 +3,8 @@
 
 #include <algorithm>
 #include <benchmark/benchmark.h>
-#include <stddef.h>
-#include <string.h>
+#include <cstddef>
+#include <cstring>
 #include <type_traits>
 #include <vector>
 
diff --git a/tests/std/include/constexpr_char_traits.hpp b/tests/std/include/constexpr_char_traits.hpp
index 26ec4fc86e5..bb53fbf6a3f 100644
--- a/tests/std/include/constexpr_char_traits.hpp
+++ b/tests/std/include/constexpr_char_traits.hpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #pragma once
-#include <stdio.h>
-#include <wchar.h>
+#include <cstdio>
+#include <cwchar>
 
 struct constexpr_char_traits {
     typedef char char_type;
diff --git a/tests/std/include/fenv_prefix.hpp b/tests/std/include/fenv_prefix.hpp
index bd3055a41f7..642e44a01b1 100644
--- a/tests/std/include/fenv_prefix.hpp
+++ b/tests/std/include/fenv_prefix.hpp
@@ -40,7 +40,7 @@
 #endif // defined(FP_CONTRACT_MODE)
 
 #include <cassert>
-#include <float.h>
+#include <cfloat>
 
 struct fenv_initializer_t {
     fenv_initializer_t() {
@@ -54,7 +54,7 @@ struct fenv_initializer_t {
 
     ~fenv_initializer_t() = default;
 
-    fenv_initializer_t(const fenv_initializer_t&) = delete;
+    fenv_initializer_t(const fenv_initializer_t&)            = delete;
     fenv_initializer_t& operator=(const fenv_initializer_t&) = delete;
 };
 
diff --git a/tests/std/include/floating_point_test_cases.hpp b/tests/std/include/floating_point_test_cases.hpp
index d463fb8f3f7..20fb51551e8 100644
--- a/tests/std/include/floating_point_test_cases.hpp
+++ b/tests/std/include/floating_point_test_cases.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include <stdint.h>
+#include <cstdint>
 #include <utility>
 
 constexpr std::pair<const char*, uint64_t> floating_point_test_cases_double[] = {
diff --git a/tests/std/include/instantiate_algorithms.hpp b/tests/std/include/instantiate_algorithms.hpp
index 577a1487dd0..ae35649478b 100644
--- a/tests/std/include/instantiate_algorithms.hpp
+++ b/tests/std/include/instantiate_algorithms.hpp
@@ -6,13 +6,13 @@
 // Notably, all permutations of all iterator strengths are tested.
 
 #include <algorithm>
+#include <cstddef>
 #include <forward_list>
 #include <functional>
 #include <iterator>
 #include <list>
 #include <memory>
 #include <numeric>
-#include <stddef.h>
 #include <type_traits>
 
 #if _HAS_CXX17 && !defined(_M_CEE)
@@ -42,17 +42,17 @@ namespace std_testing {
         // mode perf.
 
         struct Immobile {
-            Immobile()                = default;
-            Immobile(const Immobile&) = delete;
+            Immobile()                           = default;
+            Immobile(const Immobile&)            = delete;
             Immobile& operator=(const Immobile&) = delete;
         };
 
         struct MoveOnly {
-            MoveOnly()                = default;
-            MoveOnly(const MoveOnly&) = delete;
-            MoveOnly(MoveOnly&&)      = default;
+            MoveOnly()                           = default;
+            MoveOnly(const MoveOnly&)            = delete;
+            MoveOnly(MoveOnly&&)                 = default;
             MoveOnly& operator=(const MoveOnly&) = delete;
-            MoveOnly& operator=(MoveOnly&&) = delete;
+            MoveOnly& operator=(MoveOnly&&)      = delete;
         };
 
         template <typename T>
diff --git a/tests/std/include/new_counter.hpp b/tests/std/include/new_counter.hpp
index 9ecb27607a5..a7875a6c231 100644
--- a/tests/std/include/new_counter.hpp
+++ b/tests/std/include/new_counter.hpp
@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include <assert.h>
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
 #include <new>
-#include <stddef.h>
-#include <stdlib.h>
 
 #pragma once
 #pragma warning(push)
diff --git a/tests/std/include/parallel_algorithms_utilities.hpp b/tests/std/include/parallel_algorithms_utilities.hpp
index 1319274c12e..f29185d05a6 100644
--- a/tests/std/include/parallel_algorithms_utilities.hpp
+++ b/tests/std/include/parallel_algorithms_utilities.hpp
@@ -3,7 +3,7 @@
 
 #pragma once
 #include <algorithm>
-#include <stddef.h>
+#include <cstddef>
 #include <thread>
 
 #ifdef EXHAUSTIVE
diff --git a/tests/std/include/test_atomic_wait.hpp b/tests/std/include/test_atomic_wait.hpp
index 740213067e8..9322cd5454a 100644
--- a/tests/std/include/test_atomic_wait.hpp
+++ b/tests/std/include/test_atomic_wait.hpp
@@ -3,11 +3,11 @@
 
 #pragma once
 
-#include <assert.h>
 #include <atomic>
+#include <cassert>
 #include <chrono>
+#include <cstring>
 #include <memory>
-#include <string.h>
 #include <thread>
 
 template <template <class> class Template, class UnderlyingType>
diff --git a/tests/std/include/test_death.hpp b/tests/std/include/test_death.hpp
index 521945a24b1..d88f63e9dab 100644
--- a/tests/std/include/test_death.hpp
+++ b/tests/std/include/test_death.hpp
@@ -3,9 +3,9 @@
 
 #pragma once
 #include <crtdbg.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <string>
 #include <vector>
 
diff --git a/tests/std/include/test_filesystem_support.hpp b/tests/std/include/test_filesystem_support.hpp
index 7abd5574430..3aa59865650 100644
--- a/tests/std/include/test_filesystem_support.hpp
+++ b/tests/std/include/test_filesystem_support.hpp
@@ -6,11 +6,11 @@
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <algorithm>
+#include <cstring>
 #include <experimental/filesystem>
 #include <filesystem>
 #include <iterator>
 #include <random>
-#include <string.h>
 #include <string>
 
 inline std::string get_test_directory_subname(const char* const testName, const size_t testNameLength) {
diff --git a/tests/std/include/test_regex_support.hpp b/tests/std/include/test_regex_support.hpp
index 5d9531d6f39..fc11c74929b 100644
--- a/tests/std/include/test_regex_support.hpp
+++ b/tests/std/include/test_regex_support.hpp
@@ -2,8 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #pragma once
+#include <cstdio>
 #include <regex>
-#include <stdio.h>
 #include <string>
 
 class regex_fixture {
@@ -189,7 +189,7 @@ class test_regex {
         std::regex_constants::syntax_option_type syntax = std::regex_constants::ECMAScript)
         : fixture(fixture), pattern(pattern), syntax(syntax), r(pattern, syntax) {}
 
-    test_regex(const test_regex&) = delete;
+    test_regex(const test_regex&)            = delete;
     test_regex& operator=(const test_regex&) = delete;
 
     void should_search_match(const std::string& subject, const std::string& expected,
@@ -252,7 +252,7 @@ class test_wregex {
         std::regex_constants::syntax_option_type syntax = std::regex_constants::ECMAScript)
         : fixture(fixture), pattern(pattern), syntax(syntax), r(pattern, syntax) {}
 
-    test_wregex(const test_wregex&) = delete;
+    test_wregex(const test_wregex&)            = delete;
     test_wregex& operator=(const test_wregex&) = delete;
 
     void should_search_match(const std::wstring& subject, const std::wstring& expected,
diff --git a/tests/std/include/test_thread_support.hpp b/tests/std/include/test_thread_support.hpp
index f92e7ec0294..a2e44363468 100644
--- a/tests/std/include/test_thread_support.hpp
+++ b/tests/std/include/test_thread_support.hpp
@@ -5,9 +5,9 @@
 
 #include <chrono>
 #include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
 #include <mutex>
-#include <stdio.h>
-#include <stdlib.h>
 #include <thread>
 
 #include <Windows.h>
diff --git a/tests/std/tests/P0156R2_scoped_lock/test.cpp b/tests/std/tests/P0156R2_scoped_lock/test.cpp
index 8e25b9c1129..1248533591a 100644
--- a/tests/std/tests/P0156R2_scoped_lock/test.cpp
+++ b/tests/std/tests/P0156R2_scoped_lock/test.cpp
@@ -2,9 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <atomic>
+#include <cstdlib>
 #include <iostream>
 #include <mutex>
-#include <stdlib.h>
 #include <thread>
 #include <type_traits>
 #include <utility>
@@ -108,7 +108,7 @@ class logging_thread {
         cout << "Started thread " << this->t.get_id() << endl;
     }
 
-    logging_thread(logging_thread const&) = delete;
+    logging_thread(logging_thread const&)            = delete;
     logging_thread& operator=(logging_thread const&) = delete;
 
     ~logging_thread() {

From 898b3ea4429102d0384df7d77b82b4fb799b8446 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@nuwen.net>
Date: Mon, 18 Jul 2022 19:29:57 -0700
Subject: [PATCH 5/6] Undo namespace changes.

---
 tests/std/tests/Dev08_563686_ostream/test.cpp               | 4 +---
 .../test.compile.pass.cpp                                   | 4 ++--
 tests/std/tests/P0476R2_bit_cast/test.cpp                   | 1 -
 tests/std/tests/P1007R3_assume_aligned/test.cpp             | 6 ++----
 tests/std/tests/VSO_0000000_matching_npos_address/test.cpp  | 6 ++----
 5 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/tests/std/tests/Dev08_563686_ostream/test.cpp b/tests/std/tests/Dev08_563686_ostream/test.cpp
index 45238c79abd..48935394f57 100644
--- a/tests/std/tests/Dev08_563686_ostream/test.cpp
+++ b/tests/std/tests/Dev08_563686_ostream/test.cpp
@@ -31,8 +31,6 @@
 
 #include <Windows.h>
 
-using namespace std;
-
 int main() {
     // Track CRT blocks
     _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_CHECK_CRT_DF);
@@ -40,7 +38,7 @@ int main() {
     {
         // Allocate long lived objects in the CRT.
         // We don't want these objects to show up as leaks.
-        iostream s(nullptr);
+        std::iostream s(nullptr);
     }
 
     // Get memory state before creating iostream
diff --git a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
index 1f7f3677694..a643e89601e 100644
--- a/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
+++ b/tests/std/tests/Dev11_0483851_vector_debug_allocator_use/test.compile.pass.cpp
@@ -24,11 +24,11 @@ struct simple_allocator : Base {
     template <typename U, typename UB>
     simple_allocator(simple_allocator<U, UB> const&) {}
 
-    value_type* allocate(size_t n) {
+    value_type* allocate(std::size_t n) {
         return static_cast<value_type*>(malloc(n * sizeof(value_type)));
     }
 
-    void deallocate(value_type* p, size_t) {
+    void deallocate(value_type* p, std::size_t) {
         free(p);
     }
 };
diff --git a/tests/std/tests/P0476R2_bit_cast/test.cpp b/tests/std/tests/P0476R2_bit_cast/test.cpp
index f9cbbb28502..612846b41f8 100644
--- a/tests/std/tests/P0476R2_bit_cast/test.cpp
+++ b/tests/std/tests/P0476R2_bit_cast/test.cpp
@@ -9,7 +9,6 @@
 #include <limits>
 #include <type_traits>
 #include <utility>
-using namespace std;
 
 // structure sizing depends on a packing of 8, which is the default
 
diff --git a/tests/std/tests/P1007R3_assume_aligned/test.cpp b/tests/std/tests/P1007R3_assume_aligned/test.cpp
index d2333fd98f2..aa8cae4d23d 100644
--- a/tests/std/tests/P1007R3_assume_aligned/test.cpp
+++ b/tests/std/tests/P1007R3_assume_aligned/test.cpp
@@ -5,16 +5,14 @@
 #include <cstddef>
 #include <memory>
 
-using namespace std;
-
 constexpr void can_change_value_via_assume_aligned(int* p) {
-    int* p1 = assume_aligned<256>(p);
+    int* p1 = std::assume_aligned<256>(p);
     p1[0]   = 10;
     p1[1]   = -15;
 }
 
 constexpr int can_read_value_via_assume_aligned_and_sum_it(int const* p, size_t size) {
-    int const* p1 = assume_aligned<256>(p);
+    int const* p1 = std::assume_aligned<256>(p);
     int result    = 0;
     for (size_t i = 0; i < size; ++i) {
         result += p1[i];
diff --git a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
index ff8b56b13d8..b6a7c779153 100644
--- a/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
+++ b/tests/std/tests/VSO_0000000_matching_npos_address/test.cpp
@@ -5,13 +5,11 @@
 #include <cstddef>
 #include <string>
 
-using namespace std;
-
 extern "C" {
 extern const size_t* other_npos_address;
 }
 
 int main() {
-    static_assert(string::npos == static_cast<size_t>(-1), "");
-    assert(&string::npos == other_npos_address);
+    static_assert(std::string::npos == static_cast<size_t>(-1), "");
+    assert(&std::string::npos == other_npos_address);
 }

From 38ed81748c2dd623bf556874973f20e0ffe1b9c8 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@nuwen.net>
Date: Mon, 18 Jul 2022 19:49:37 -0700
Subject: [PATCH 6/6] The Header Units test is special.

---
 .../std/tests/P1502R1_standard_library_header_units/test.cpp  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
index 4cf65bcb9f2..c7680044633 100644
--- a/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
+++ b/tests/std/tests/P1502R1_standard_library_header_units/test.cpp
@@ -92,8 +92,8 @@ import <vector>;
 import <version>;
 // clang-format on
 
-#include <cassert>
-#include <cstdio>
+#include <assert.h> // intentionally not <cassert>
+#include <stdio.h> // intentionally not <cstdio>
 
 #include <force_include.hpp>
 using namespace std;