use json construct std::string

[yuzeng2017]

• What is the issue you have?
  “std::basic_string<char,std::char_traits,std::allocator>::basic_string”: Overload function ambiguous.

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?
  json j;
  j["account"] = "123456";
  std::string account_text(j["account"]);
  vs2015 compile error.

• What is the expected behavior?

• And what is the actual behavior instead?

• Which compiler and operating system are you using? Is it a supported compiler?

• Did you use a released version of the library or the version from the develop branch?

• If you experience a compilation error: can you compile and run the unit tests?

[nlohmann]

Related: #1061

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jerryjiahaha]

I have similar problem under MSVC 2017 (clang and gcc works). I want to convert json results to std::string vector and here is what I tried:

#include "json.hpp"
#include <vector>
#include <iostream>
#include <fstream>

int main()
{
	nlohmann::json jConfig2 = R"(
		{
			"names": ["Tim", "Tom"],
			"nums": [1.2, 2.3]
		}
	)"_json;
	std::vector<float> iNums0;
	std::vector<std::string> sNames0;

	// Just work for float, but std::string failed
	iNums0 = std::vector<float>(jConfig2.at("nums").begin(), jConfig2.at("nums").end());
	for (auto i : iNums0) { std::cout << i << " "; } std::cout << std::endl;

	// Work around for MSVC 2017
	auto itseed = jConfig2.at("names").get<std::vector<std::string>>();
	sNames0 = std::vector<std::string>(itseed.begin(), itseed.end());

	// Compile ok, but run failed: "vector iterators in range are from different containers"
//	sNames0 = std::vector<std::string>(jConfig2.at("names").get<std::vector<std::string>>().begin(), jConfig2.at("names").get<std::vector<std::string>>().end());

	// Comiple failed: Error C2668 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>::basic_string': ambiguous call to overloaded
//	sNames0 = std::vector<std::string>(jConfig2.at("names").begin(), jConfig2.at("names").end());

	// Compile failed: Error C2593 'operator =' is ambiguous
//	sNames0 = jConfig2.at("names");

	// Compile failed: Error C2440 '<function-style-cast>': cannot convert from 'nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>' to 'std::vector<std::string,std::allocator<_Ty>>'
//	sNames0 = std::vector<std::string>(jConfig2.at("names"));

	//  It works, too
	std::vector<std::string> _names = jConfig2.at("names");
//	sNames0 = _names;

	for (auto i : sNames0) {
		std::cout << i << " ";
	}
	std::cout << std::endl;

	return 0;
}

The format

std::vector<Type>(jsontype.at("Key").begin(), jsontype.at("Key").end());

works for Type int, float but not works under std::string.

I also tried clang++ and g++ with -Wall. g++ compiled without warnning, clang++ gave me warning:

In file included from ConsoleApplication1.cpp:1:
./json.hpp:1799:1: warning: 'tuple_size' defined as a class template here but previously declared as a struct template
[-Wmismatched-tags]
class tuple_size<::nlohmann::detail::iteration_proxy_value>
^
/usr/sbin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/array:350:5: note: did you mean class
here?
struct tuple_size;
^
/usr/sbin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/utility:84:5: note: did you mean class
here?
struct tuple_size;
^
In file included from ConsoleApplication1.cpp:1:
./json.hpp:1803:1: warning: 'tuple_element' defined as a class template here but previously declared as a struct template
[-Wmismatched-tags]
class tuple_element<N, ::nlohmann::detail::iteration_proxy_value>
^
/usr/sbin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/array:359:5: note: did you mean class
here?
struct tuple_element;
^
/usr/sbin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/utility:110:5: note: did you mean class
here?
struct tuple_element;
^
2 warnings generated.

@yuzeng2017 For your problem 1462#issue-404674231. You could try:

	nlohmann::json j;
	j["account"] = "123456";
	std::string account_text = j["account"]; // OK
//	std::string account_text2(j["account"]); // FAIL
	std::string account_text3(j["account"].get<std::string>()); // OK
	std::cout << account_text << account_text3 << std::endl;

Just use .get<std::string>() for MSVC or use = (I forgot which the constructor type is it)

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.