Q: When I received an illegal string,How the program knows?

[huluBrother]

std::string body = "";//illegal
std::string body = "a"//illegal
nlohmann::json reqContext = nlohmann::json::parse(body);

how the program knows?

Of course, the premise is that the program cannot crash.
Thanks

[nlohmann]

You can use accept() instead of parse which returns a bool. There is also a parameter allow_exceptions for parse to suppress exceptions, see https://nlohmann.github.io/json/doxygen/classnlohmann_1_1basic__json_a4c734aac1ea36f4b62f25308b6c6784a.html#a4c734aac1ea36f4b62f25308b6c6784a

[huluBrother]

You can use accept() instead of parse which returns a bool. There is also a parameter allow_exceptions for parse to suppress exceptions, see https://nlohmann.github.io/json/doxygen/classnlohmann_1_1basic__json_a4c734aac1ea36f4b62f25308b6c6784a.html#a4c734aac1ea36f4b62f25308b6c6784a
Sorry, I understand what you mean, but I did not understand how to pass this parameter, can you give an example?

[nlohmann]

Instead of calling

auto result = json::parse(body);

do this:

auto result = json::parse(body, nullptr, false);

[huluBrother]

Instead of calling

auto result = json::parse(body);

do this:

auto result = json::parse(body, nullptr, false);

The content returned by this result is a discard?
How can I tell if parse is successful?

[nlohmann]

From the documentation:

Returns: deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

[huluBrother]

From the documentation:

Returns: deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

value_t::discarded. In which file, how do I refer to this variable

[nlohmann]

You can check with result.is_discarded() whether the value is discarded. Or result == json::value_t::discarded.

[huluBrother]

You can check with result.is_discarded() whether the value is discarded. Or result == json::value_t::discarded.

	std::string body = "a";
	auto result = nlohmann::json::parse(body, nullptr, false);

	if (result == nlohmann::json::value_t::discarded) {
		std::cout << "nlohmann::json::value_t::discarded" << std::endl;
	}
	if (result.is_discarded()) {
		std::cout << "is_discard" << std::endl;
	}

Thank you very much, I solved the problem.
but result == nlohmann::json::value_t::discarded return false,

[nlohmann]

Sorry, I did not check my code example.

This works:

    if (result.type() == nlohmann::json::value_t::discarded) {
        std::cout << "nlohmann::json::value_t::discarded" << std::endl;
    }

[nlohmann]

Do you need further assistance with this issue?

[huluBrother]

Do you need further assistance with this issue?

Thanks, this has satisfied my needs, let me close this issue