How is the json library used in C++?

The JSON library in C++ is used to handle JSON data, providing classes and functions for parsing, generating, and manipulating JSON objects. Here are some common JSON libraries and their usage:

1. RapidJSON: RapidJSON is a high-performance C++ JSON library that can be used for parsing and generating JSON data. It offers a DOM-style API for representing and manipulating JSON objects. Here is an example of parsing a JSON string using RapidJSON:

#include <iostream>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"

int main() {
    const char* json = "{\"name\":\"John\", \"age\":30, \"city\":\"New York\"}";

    rapidjson::Document document;
    document.Parse(json);

    std::string name = document["name"].GetString();
    int age = document["age"].GetInt();
    std::string city = document["city"].GetString();

    std::cout << "Name: " << name << std::endl;
    std::cout << "Age: " << age << std::endl;
    std::cout << "City: " << city << std::endl;

    return 0;
}

nlohmann/json is a modern C++ JSON library that offers a simple and intuitive way to handle JSON data. Below is an example of parsing a JSON string using the nlohmann/json library.

#include <iostream>
#include <nlohmann/json.hpp>

int main() {
    std::string json = "{\"name\":\"John\", \"age\":30, \"city\":\"New York\"}";

    nlohmann::json data = nlohmann::json::parse(json);

    std::string name = data["name"];
    int age = data["age"];
    std::string city = data["city"];

    std::cout << "Name: " << name << std::endl;
    std::cout << "Age: " << age << std::endl;
    std::cout << "City: " << city << std::endl;

    return 0;
}

JsonCpp is a C++ library for working with JSON data, providing an easy way to handle and manipulate JSON data. Here is an example of using the JsonCpp library to parse a JSON string:

#include <iostream>
#include <json/json.h>

int main() {
    std::string json = "{\"name\":\"John\", \"age\":30, \"city\":\"New York\"}";

    Json::Value value;
    Json::Reader reader;
    reader.parse(json, value);

    std::string name = value["name"].asString();
    int age = value["age"].asInt();
    std::string city = value["city"].asString();

    std::cout << "Name: " << name << std::endl;
    std::cout << "Age: " << age << std::endl;
    std::cout << "City: " << city << std::endl;

    return 0;
}

These libraries offer various ways to parse, generate, and manipulate JSON data, so you can choose the one that best fits your needs.