JSON Processing in C++: Libraries, Parsing and Data Serialization

JSON Processing in C++: Libraries, Parsing and Examples

JSON (JavaScript Object Notation) is one of the most popular data exchange formats. Although C++ does not have built-in JSON support, there are several powerful libraries that allow you to easily parse, generate, and modify JSON data. In this article, we will look at three main libraries: nlohmann/json, RapidJSON, and Boost.PropertyTree, and provide practical examples of their use.

Why do you need a JSON library in C++?

C++ is a compiled language focused on performance. Manually parsing JSON using regular expressions or string operations is a labor-intensive and error-prone task. Specialized libraries provide:

• High parsing and serialization speed.
• An intuitive API (often in STL style).
• Support for JSON standards (including nested objects, arrays, null, Unicode).
• Minimal dependencies (often header-only).

1. nlohmann/json Library (JSON for Modern C++)

The most popular and easy-to-use library. Distributed as header-only (a single header file). Ideal for educational projects and small applications.

Installation

Download the json.hpp file from the nlohmann/json repository and include it:

#include "json.hpp"using json = nlohmann::json;

Example: parsing JSON from a string

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

int main() {    std::string json_str = R"({        "name": "PythonLib",        "year": 2025,        "tags": ["C++", "JSON", "education"],        "active": true    })";

    json data = json::parse(json_str);

    std::cout << "Name: " << data["name"] << "";    std::cout << "Year: " << data["year"] << "";    std::cout << "First tag: " << data["tags"][0] << "";    std::cout << "Active: " << data["active"] << "";

    return 0;}

Example: creating and serializing JSON

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

int main() {    json obj;    obj["title"] = "JSON in C++";    obj["pages"] = 42;    obj["chapters"] = {"intro", "basics", "advanced"};    obj["metadata"]["author"] = "PythonLib Team";

    std::string serialized = obj.dump(4); // 4 — indentation for pretty printing    std::cout << serialized << "";

    return 0;}

2. RapidJSON Library

RapidJSON is a high-performance library focused on speed and minimal memory consumption. Often used in games, server applications, and embedded systems. Supports SAX-style (streaming parsing) and DOM-style.

Installation

Download the archive from GitHub and include the header files:

#include "rapidjson/document.h"#include "rapidjson/writer.h"#include "rapidjson/stringbuffer.h"

Example: parsing and reading

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

int main() {    const char* json = "{\\"project\\":\\"PythonLib\\",\\"version\\":2.0}";    rapidjson::Document doc;    doc.Parse(json);

    if (doc.HasParseError()) {        std::cerr << "Parse error!";        return 1;    }

    std::cout << "Project: " << doc["project"].GetString() << "";    std::cout << "Version: " << doc["version"].GetDouble() << "";

    return 0;}

Example: generating JSON

#include <iostream>#include "rapidjson/docume