Json: convert json value to std::string???

[Mamlesh]

how to convert json value to string ..

[nlohmann]

What did you try? Was there an error message? Did you have a look at the README?

[Mamlesh]

thanks for replay sir....
i need to convert the json value ....example

json jk; json jsd;
jk.pushback(jsd);

string str=jk;

want to use 'jk' value as string....

[whackashoe]

From README

You can also get a string representation of a JSON value (serialize):

// explicit conversion to string
std::string s = j.dump();    // {\"happy\":true,\"pi\":3.141}

// serialization with pretty printing
// pass in the amount of spaces to indent
std::cout << j.dump(4) << std::endl;
// {
//     "happy": true,
//     "pi": 3.141
// }

[nlohmann]

Can I close this issue?

[AOrazaev]

@nlohmann Probably not, looks like case with operator= messed up:

  json fail = R"({"foo": "bar"})"_json;
  // std::string barExpected;`
  // barExpected = fail["foo"]; // fails
  std::string barExpected = fail["foo"]; //works

[nlohmann]

@AOrazaev I cannot reproduce the error. Which compiler are you using? What is the error message?

[rue-ryuzaki]

Maybe like this?

std::string value = parser["value"].get<std::string>();

[AOrazaev]

@rue-ryuzaki Yep, I've worked around this like you said.

@nlohmann I compiled example from VS2017.
For some reason, when I'm compiling from developer console on small example using cl.exe I'm not getting this error, but from VS2017 actually I'm getting next:

Severity    Code    Description Project File    Line    Suppression State   Detail Description
Error (active)  E0350   more than one operator "=" matches these operands:  check_json  check_json.cpp  13                  function "std::basic_string<_Elem, _Traits, _Alloc>::operator=(std::basic_string<_Elem, _Traits, _Alloc> &&_Right) [with _Elem=char, _Traits=std::char_traits<char>, _Alloc=std::allocator<char>]"
            function "std::basic_string<_Elem, _Traits, _Alloc>::operator=(std::initializer_list<_Elem> _Ilist) [with _Elem=char, _Traits=std::char_traits<char>, _Alloc=std::allocator<char>]"
            operand types are: std::string = const nlohmann::basic_json<std::map, std::vector, std::string, bool, int64_t, uint64_t, double, std::allocator, nlohmann::adl_serializer>

Code I used to reproduce:

#include "json.hpp"
#include "stdafx.h" // only if using VS
#include <iostream>
#include <string>

using nlohmann::json;

struct JsonWrapper {
    std::string _foo;
public:
    JsonWrapper(const json& obj)
    {
        _foo = obj["foo"];
    }

    void log() {
        std::cout << "Foo: " << _foo << std::endl;
    }
};

int main() {
    json obj = R"({"foo": "bar"})"_json;
    JsonWrapper wrap{ obj };
    wrap.log();
    return 0;
}

[AOrazaev]

And if insead of:

    JsonWrapper(const json& obj)
    {
        _foo = obj["foo"];
    }

Use:

    JsonWrapper(const json& obj)
        : _foo(obj["foo"])
    {    }

It will fail in developer cmd with cl.exe too. complaining about

error C2668: 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>::basic_string': ambiguous call to overloaded function

[nlohmann]

@AOrazaev Your issue seems not related to the original comment.

[nlohmann]

@AOrazaev For https://github.com/nlohmann/json/issues/1061#issuecomment-385115936, using

JsonWrapper(const json& obj)
    : _foo(obj["foo"].get<std::string>())
{}

works though.

[AOrazaev]

I mean, probably topic starter tried his example in VS and hit issue I described before.

I personally worked around everything with get<std::string>, but bug is still there.

[nlohmann]

@Mamlesh Can I close this issue?