Reading only JSON from begin+end containers

[AbitTheGray]

Hi, I have found a major difference between nlohmann::basic_json::parse and nlohmann::operator>>(basic_json) - it is not possible to parse only the JSON from a container.

When reading from the stream, it stops after the JSON is completed but with parse, it says "expected end of input".
Is there a way (callback, toggle...) to say "read just the valid JSON and give me iterator/pointer after it" ?

I've started it as discussion as I am not sure if there is someone else who would like this functionality as, as shown below, it can be done with little code around it.

Example

#include <string>
#include <iostream>
#include <sstream>
#include <nlohmann/json.hpp>

int main()
{
    const std::string input = "{ \"a\": 123 }asdf...";

    // This block is OK as it uses std::stream
    {
        std::stringstream ss(input);
        nlohmann::json j;
        ss >> j;
        std::string str;
        ss >> str;
        std::cout << "Parsed: " << j.dump() << std::endl;
        std::cout << "Remaining: " << str << std::endl;
        std::cout << "Full Stream: " << ss.str() << std::endl;
    }
    // This failes after reading the JSON as there are still some data but the object is over
    {
        const auto j = nlohmann::json::parse(input.begin(), input.end());
        std::cout << "Parsed2: " << j.dump() << std::endl;
    }
}

Parsed: {"a":123}
Remaining: asdf...
Full Stream: { "a": 123 }asdf...
terminate called after throwing an instance of 'nlohmann::json_v3_11_1::detail::parse_error'
  what():  [json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid literal; last read: '123 }a'; expected end of input
Program terminated with signal: SIGSEGV

[gregmarr]

Internally, there is a flag to the parser to say whether or not it is an error to have leftover data at the end. This is set to true when using the parse function and false when using the streams.
https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/input/parser.hpp#L93