Dumping core when reading invalid file

[ilya1725]

Hello:

I have your module in my application. Compiled with exceptions disabled and -O2 optimization.
I was trying to read an invalid JSON file:

{ "sn": 1, "name": "First bird" "type": 1, "flags": { "tied_down": true } }

const std::ifstream config_file(argv[1]); nlohmann::json j; config_file >> j;

The application dumps core in the last line instead of returning an error:

Program received signal SIGABRT, Aborted. __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory. (gdb) bt #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 #1 0x00007f0de58f8899 in __GI_abort () at abort.c:79 #2 0x000055d061bb677d in nlohmann::detail::json_sax_dom_callback_parser<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long, unsigned long, double, std::allocator, nlohmann::adl_serializer> >::parse_error (this=<optimized out>, this=<optimized out>, ex=...) at /usr/include/c++/9/bits/basic_string.h:1936 #3 nlohmann::detail::json_sax_dom_parser<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long, unsigned long, double, std::allocator, nlohmann::adl_serializer> >::parse_error (this=<optimized out>, this=<optimized out>, ex=...) at /develop/build/_deps/nlohmann_json-src/single_include/nlohmann/json.hpp:4806 #4 nlohmann::detail::parser<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long, unsigned long, double, std::allocator, nlohmann::adl_serializer> >::sax_parse_internal<nlohmann::detail::json_sax_dom_parser<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long, unsigned long, double, std::allocator, nlohmann::adl_serializer> > > (this=<optimized out>, sax=<optimized out>) at /develop/build/_deps/nlohmann_json-src/single_include/nlohmann/json.hpp:8987 #5 0x000055d061bb6dbc in nlohmann::detail::parser<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long, unsigned long, double, std::allocator, nlohmann::adl_serializer> >::parse ( this=0x7fff73960a80, strict=<optimized out>, result=...) at /usr/include/c++/9/bits/stl_vector.h:94 #6 0x000055d061bb76c3 in nlohmann::operator>> (i=..., j=...) at /develop/build/_deps/nlohmann_json-src/single_include/nlohmann/json.hpp:9104 #7 0x000055d061ba888a in main (argc=2, argv=0x7fff73960ee8) at /develop/apps/apps/test_application/src/test_application.cpp:33

1. Is this expected behavior?
2. If yes, what is the proper usage of the class so that the application doesn't dump core and returns an error instead?

Thank you.

[t-b]

The following example https://godbolt.org/z/zpxg_c does not dump core. Any idea what I'm doing wrong?

[dota17]

Hi @ilya1725 , this core dumpedbehavior is expected, the reason is very simple: The input file should be attached when executing the code., like./a.out input_data.json

[ilya1725]

@dota17 , sorry, what? The JSON source file is attached fine. This isn't the problem.

@t-b: I've tried the code in the example and it dumps core just fine. The Compiler Explorer just doesn't show it. One way to avoid the direct core dump is to set the allow_exceptions = true. In this case, if there is an error, the return value will have the discarded flag set. It is not clear from the documentation how to handle this case. An example would have been nice. And this method only works with direct parse(). It won't work with the stream parsing.

[dota17]

@ilya1725 Hmmm, you're right, I got a hasty conclusion, my last point is really wrong, even though they are the same types of errors.
Using operator>> to parse invalid JSON from the stream will indeed directly lead to core dumped, and this cannot be controlled with flags.
The way to avoid application interruption is to use try-catch statements to catch exceptions.