When trying to execute a from_json and to_json to a struct I created, a linker problem arises

Question

I created a struct:

    {
        unsigned int id;
        std::string name;
        unsigned int maxPlayers;
        unsigned int numOfQuestionsInGame;
        unsigned int timePerQuestion;
        unsigned int isActive;
    } RoomData;

In my code, I have to create a vector of RoomData and then convert it into a json object (I'm using nlohmann, and unable to use any other method due to restrictions in my instructions), and to do so, i tried to create a from_json and to_json functions.

The code itself (this is the header file of the code):

#include <iostream>
#include <string>
#include <vector>
#include "LoggedUser.h"
#include "json.hpp"

namespace nh = nlohmann;

namespace rd {
    typedef struct RoomData
    {
        unsigned int id;
        std::string name;
        unsigned int maxPlayers;
        unsigned int numOfQuestionsInGame;
        unsigned int timePerQuestion;
        unsigned int isActive;
    } RoomData;

    void from_json(const nh::json& j, RoomData& val)
    {
        j.at("id").get_to(val.id);
        j.at("name").get_to(val.name);
        j.at("maxPlayers").get_to(val.maxPlayers);
        j.at("numOfQuestionsInGame").get_to(val.numOfQuestionsInGame);
        j.at("timePerQuestion").get_to(val.timePerQuestion);
        j.at("isActive").get_to(val.isActive);
    }
    
    void to_json(nh::json& j, const RoomData& val)
    {
        j["id"] = val.id;
        j["name"] = val.name;
        j["maxPlayers"] = val.maxPlayers;
        j["numOfQuestionsInGame"] = val.numOfQuestionsInGame;
        j["timePerQuestion"] = val.timePerQuestion;
        j["isActive"] = val.isActive;
    }
}

class Room
{
public:
    Room() = default;
    Room(const rd::RoomData& data);
    void addUser(LoggedUser);  // adds a user to the users vector
    void removeUser(LoggedUser);  // removes a user from the users vector
    std::vector<std::string> getAllUsers();  // return a vector of all the users

    // getters
    rd::RoomData getRoomData() const;

private:
    rd::RoomData m_metadata;  // the data of the room
    std::vector<LoggedUser> m_users;  // the vector of the users in the room
};

After trying to run it, a LNK2005 error arises. I know that the type I use and those functions have to be in the same namespace, did I do it wrong?

The exact error: "void cdecl to_json(class nlohmann::basic_json<class std::map,class std::vector,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,bool,int64,unsigned __int64,double,class std::allocator,struct nlohmann::adl_serializer,class std::vector<unsigned char,class std::allocator<unsigned char> > > &,struct RoomData const &)" (?to_json@@YAXAAV?$basic_json@Vmap@std@@Vvector@2@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@2@_N_J_KNVallocator@2@Uadl_serializer@nlohmann@@V?$vector@EV?$allocator@E@std@@@2@@nlohmann@@ABURoomData@@@Z) already defined in Communicator.obj

Side note: C++ learned a lot from C, and one of the things it learned was that `typedef struct RoomData { ... } RoomData;` trick. C++ baked it in, so all you need is `struct RoomData { ... };` — user4581301, May 18 '21 at 19:49
Can you post the exact text of the LNK error that arises? Or some example calling code that shows _how_ you're trying to use `from_json` and `to_json`? — Nathan Pierson, May 18 '21 at 20:04
@NathanPierson the project goes much beyond this file so many other classes are mentioned, but I'll update the question and include the exact error. — shubbbik, May 18 '21 at 20:09

score 0 · Answer 1 · answered May 18 '21 at 20:16

0

Apparently, to solve this kind of issue, all I had to do was adding "inline" at the start of the function. Example:

inline void to_json(nh::json& j, const RoomData& val)

My reference: https://github.com/nlohmann/json/issues/542

answered May 18 '21 at 20:16

shubbbik

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When trying to execute a from_json and to_json to a struct I created, a linker problem arises

1 Answers1