Working with JSON in C++: Parsing and Serialization of Data

Introduction to Working with JSON in C++

JSON (JavaScript Object Notation) is a lightweight data interchange format widely used in web development, configuration files, and APIs. Although C++ does not have built-in JSON support, there are many reliable libraries that simplify parsing and serialization of data. In this article, we will look at two popular libraries: nlohmann/json (recommended for beginners and modern projects) and Boost.PropertyTree (for those already using Boost). You will learn how to read, create, modify, and output JSON data in C++.

nlohmann/json Library: Installation and Basic Principles

The nlohmann/json library (often called "JSON for Modern C++") is one of the most popular due to its simplicity and intuitive API. It supports C++11 and later, has no external dependencies, and is distributed as a single header file json.hpp.

Installation

Download the json.hpp file from the GitHub repository and place it in your project folder. Then include it in your code:

#include <iostream>#include <fstream>#include "json.hpp" // Include the library

using json = nlohmann::json;

Parsing JSON from String and File

The library allows parsing JSON from a string, file, or input stream. Let's look at an example of parsing from a string:

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

using json = nlohmann::json;

int main() {    // JSON string    std::string jsonString = R"({        "name": "Alice",        "age": 30,        "isStudent": false,        "hobbies": ["reading", "coding"]    })";        // Parsing    json data = json::parse(jsonString);        // Accessing data    std::cout << "Name: " << data["name"] << std::endl;    std::cout << "Age: " << data["age"] << std::endl;    std::cout << "Is student: " << (data["isStudent"] ? "true" : "false") << std::endl;        // Iterating over an array    for (auto& hobby : data["hobbies"]) {        std::cout << "Hobby: " << hobby << std::endl;    }        return 0;}

To parse from a file, use json::parse(std::ifstream("data.json"));.

JSON Serialization

Creating a JSON object and serializing it to a string is done naturally:

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

using json = nlohmann::json;

int main() {    json person;    person["name"] = "Bob";    person["age"] = 25;    person["isStudent"] = true;    person["hobbies"] = {"gaming", "swimming"};        // Nested object    json address;    address["city"] = "Moscow";    address["street"] = "Tverskaya";    person["address"] = address;        // Serialization to string with indentation    std::string serialized = person.dump(4); // 4 spaces for formatting    std::cout << serialized << std::endl;        // Saving to file    std::ofstream file("output.json");    file << person.dump(2);    file.close();        return 0;}

The dump() method converts the object to a string. The parameter specifies the number of spaces for indentation (0 for compact output).

Boost.PropertyTree Library: An Alternative Approach

If your project already uses Boost, the Boost.PropertyTree library provides a convenient way to work with JSON and other formats (XML, INI). It is less specialized for JSON but integrates well with the Boost ecosystem.

Parsing JSON with Boost.PropertyTree

#include <iostream>#include <boost/property_tree/ptree.hpp>\