json.hpp:8955: multiple definition of function that is not defined twice or more.

Json version 2.1.1

Any code in this form:

// This file called "lib.hpp"
using json = nlohmann::json;

namespace someNS {
    someType someFunction(json file) {
        // ...
    }
}

...Returns this error:

lib.hpp.o: In function `std::iterator_traits<char const*>::iterator_category std::__iterator_category<char const*>(char const* const&)':
json.hpp:8955: multiple definition of `someNS::someFunction(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>)'
main.cpp.o:lib.hpp:7: first defined here

I cannot reproduce this with:

// lib.hpp

#include "json.hpp"

using json = nlohmann::json;

namespace someNS {
    std::string someFunction(json file) {
        return file.dump(4);
    }
}

// main.cpp

#include "lib.hpp"
#include <iostream>

int main()
{
    json j = {1,2,3};
    std::cout << someNS::someFunction(j) << std::endl;
}

and version 2.1.1.

Running

c++ -std=c++11    main.cpp   -o main
./main

yields

This looks a lot like a missing include guard, do you include json.hpp directly or through another of your own header files?

@theodelrieu

@theodelrieu I have included it.

Could you paste the contents of lib.hpp?

@theodelrieu

@theodelrieu

#include <SFML/Window.hpp>
#include "json.hpp"

using json = nlohmann::json;

namespace FB {
    std::vector<sf::Vector2f> praseTeams(json file) {
        std::vector<sf::Vector2f> ret;
        unsigned int retPos = 0;
        json tmp;
        std::string itV;
        for (json::iterator it = file.begin(); it != file.end(); ++it) {
            itV = it.value();
            tmp.parse(itV);
            ret[retPos].x = tmp["x"];
            ret[retPos].y = tmp["y"];
            retPos++;
            tmp = nullptr;
        }
        return ret;
    }
}

I guess this file is included multiple times, try to add a #pragma once at the very top of your file, this should work.

@theodelrieu

@theodelrieu Here is the code. The first one was older.
Also it does not work...

#pragma once
#include <SFML/Window.hpp>
#include "json.hpp"

using json = nlohmann::json;

namespace FB {
    std::vector<sf::Vector2f> praseTeams(json file) {
        std::vector<sf::Vector2f> ret;
        unsigned int retPos = 0;
        json tmp;
        std::string itV;
        for (json::iterator it = file.begin(); it != file.end(); ++it) {
            itV = it.value();
            tmp.parse(itV);
            ret[retPos].x = tmp["x"];
            ret[retPos].y = tmp["y"];
            retPos++;
            tmp = 0;
        }
        return ret;
    }
}

Oh I didn't realize, it's very simple in fact.

This has nothing to do with this library, you should not define a method in a header, unless:

It is marked inline (in your case this doesn't seem very judicious)
It is a function template
It is a member function

Thank you!

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json.hpp:8955: multiple definition of function that is not defined twice or more. #804

Json version 2.1.1

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json.hpp:8955: multiple definition of function that is not defined twice or more. #804

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Json version 2.1.1

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nlohmann commented on Oct 27, 2017

theodelrieu commented on Oct 27, 2017

nm17 commented on Oct 27, 2017

theodelrieu commented on Oct 27, 2017

nm17 commented on Oct 27, 2017

theodelrieu commented on Oct 27, 2017

nm17 commented on Oct 27, 2017

theodelrieu commented on Oct 27, 2017

nm17 commented on Oct 27, 2017

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