c++jsonboostboost-propertytree

How to convert class object to json string using boost library in C++?


I am fairly new to C++ and I apologise beforehand if you find this very easy.

I have the following files POST1.h

#ifndef POST1_HH
#define POST1_HH

#include <iostream>

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

using namespace std ;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

#include "DBAccess2.h"

class POST1
{

    public:
    string TokenNo;
    string CommandStatus;
    string CommandID;
    string CPUID;
    string ISEncrypted;
    string JSON_Cmnd_String;

    void POST_Device_Status(sqliteDB & DB_OBJ);

};

#endif

Below is POST1.cpp

#include <iostream>
#include <sstream>

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

#include "DBAccess2.h"
#include "POST1.h"

using namespace std ;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

void POST1::POST_Device_Status(sqliteDB & DB_OBJ)
{
    POST1 POST_OBJ;

    POST_OBJ.TokenNo = "1122";
    POST_OBJ.CommandStatus = "0";
    POST_OBJ.CommandID = "00";
    POST_OBJ.CPUID = "A1234B1234";
    POST_OBJ.ISEncrypted = "0";
    POST_OBJ.JSON_Cmnd_String = DB_OBJ.dump(DB_OBJ);
}

NOTE:-

(1) sqliteDB is another class declared in a .cpp file.

(2) the output of function dump() is a json string. this get stored into JSON_Cmnd_string.

So, I want to convert the class object into JSON string, How can I do that ? Do I have to first put these object into a container (like vector or list) and then write it into JSON?


Solution

  • This is not "fairly easy", because C++ doesn't have JSON support.

    Neither does Boost:

    That said, this appears to be what you want:

    So, I want to convert the class object into JSON string, How can I do that ? Do I have to first put these object into a container (like vector or list) and then write it into JSON?

    Yes, you put them into a tree container, namely boost::property_tree::ptree:

    Live On Coliru

    #include <boost/property_tree/json_parser.hpp>
    #include <boost/property_tree/ptree.hpp>
    #include <iostream>
    #include <sstream>
    using boost::property_tree::ptree;
    
    namespace Entities {
    
        struct POST1 {
            std::string TokenNo;
            std::string CommandStatus;
            std::string CommandID;
            std::string CPUID;
            std::string ISEncrypted;
    
        };
    
        std::string to_json(POST1 const& o) {
            ptree out;
            out.put("POST1.TokenNo",          o.TokenNo);
            out.put("POST1.CommandStatus",    o.CommandStatus);
            out.put("POST1.CommandID",        o.CommandID);
            out.put("POST1.CPUID",            o.CPUID);
            out.put("POST1.ISEncrypted",      o.ISEncrypted);
    
            std::ostringstream oss;
            boost::property_tree::write_json(oss, out);
            return oss.str();
        }
    }
    
    // ADL trigger; `using Entities::to_json` would be roughly equivalent, but not
    // make it clear that ADL is happening
    void to_json();
    
    int main() {
        Entities::POST1 obj { "1122", "0", "00", "A1234B1234", "0" };
        std::cout << to_json(obj);
    }
    

    Output:

    {
        "POST1": {
            "TokenNo": "1122",
            "CommandStatus": "0",
            "CommandID": "00",
            "CPUID": "A1234B1234",
            "ISEncrypted": "0"
        }
    }