How to use json c++ with my own object? - c++

Question

I am planning to use json c++ at https://github.com/nlohmann/json#examples . After reading its simple examples, I still have no idea how to use it with my own object? For example, I have a class
class Student
{
public:
Student(int id, string const& name)
: m_id(id), m_name(name)
{}
private:
int m_id;
string m_name;
};
How to use json to read and write (deserialize and serialize) a Student object?

Answer 1

this is another way to do the conversion from json to custom class, that actually fits the best practices defined in the official repo from nlohmann here
https://github.com/nlohmann/json#arbitrary-types-conversions
h:
#ifndef STUDENT_H
#define STUDENT_H
#include<string>
#include "json.hpp"
class Student
{
public:
Student();
Student(int id, const std::string &name);
int getId() const;
void setId(int newId);
std::string getName() const;
void setName(const std::string &newName);
private:
int m_id;
std::string m_name;
};
//json serialization
inline void to_json(nlohmann::json &j, const Student &s)
{
j["id"] = s.getId();
j["name"] = s.getName();
}
inline void from_json(const nlohmann::json &j, Student &s)
{
s.setId((j.at("id").get<int>()));
s.setName(j.at("name").get<std::string>());
}
#endif // STUDENT_H
cpp:
#include "Student.h"
#include<string>
Student::Student() : Student(0, "")
{
}
Student::Student(int id, const std::string &name) : m_id{id}, m_name{name}
{
}
int Student::getId() const
{
return this->m_id;
}
void Student::setId(int newId)
{
m_id = newId;
}
std::string Student::getName() const
{
return this->m_name;
}
void Student::setName(const std::string &newName)
{
this->m_name = newName;
}
example:
Student s{0, "x"};
nlohmann::json studentJson = s;
std::cout << "Student from object: " << s.getId() << std::endl;
std::cout << "Student from json: " << studentJson.at("id").get<int>() << std::endl;
//String
std::string jSt = studentJson.dump(); //{"id":0,"name":"x"}
Student s2 = studentJson;
Student s3 = nlohmann::json::parse(jSt);

Answer 2

This library doesnt seems to have any interaction with a class for serialization and deserialization.
But you can implement it yourself with a constructor and a getter.
using json = nlohmann::json;
class Student
{
public:
Student(int id, string const& name)
: m_id(id), m_name(name)
{}
Student(json data)
: m_id(data["id"]), m_name(data["name"])
{}
json getJson()
{
json student;
student["id"] = m_id;
student["name"] = m_name;
return student;
}
private:
int m_id;
string m_name;
};