Working with YAML in C++: yaml-cpp and rapidyaml libraries

Working with YAML in C++: yaml-cpp and rapidyaml libraries

YAML (YAML Ain't Markup Language) is a data serialization format widely used for configuration files, environment description files (Docker Compose, Kubernetes), and for data exchange between services. Unlike JSON, YAML is more human-readable thanks to indentation and support for comments.

C++ has no built-in YAML support, but excellent third-party libraries exist. In this article, we will look at the two most popular ones: yaml-cpp (classic, simple) and rapidyaml (modern, very fast). You will learn how to install the libraries, read a YAML file, create one programmatically, and handle typical errors.

1. yaml-cpp Library

yaml-cpp is the de facto standard library for working with YAML in C++. It provides a convenient API reminiscent of working with STL containers. The library supports the YAML 1.2 specification.

Installation

The easiest way is to use the vcpkg or Conan package manager. For Linux/macOS:

# Installation via vcpkgvcpkg install yaml-cpp

# Installation via Conanconan install yaml-cpp/0.7.0@

If you prefer to build manually, download the source code from GitHub and run:

mkdir build && cd buildcmake ..cmake --build .sudo cmake --install .

Parsing a YAML File

Suppose we have a configuration file config.yaml:

server:  host: "localhost"  port: 8080  debug: true

database:  driver: "postgresql"  connection_string: "host=localhost dbname=test"  pool_size: 10

Example of reading and accessing data in C++:

#include <yaml-cpp/yaml.h>#include <iostream>#include <string>

int main() {    try {        // Loading the file        YAML::Node config = YAML::LoadFile("config.yaml");

        // Accessing nested nodes        std::string host = config["server"]["host"].as<std::string>();        int port = config["server"]["port"].as<int>();        bool debug = config["server"]["debug"].as<bool>();

        std::cout << "Server: " << host << ":" << port                  << " (debug=" << (debug ? "on" : "off") << ")";

        // Checking if a key exists        if (config["database"]["pool_size"]) {            int pool = config["database"]["pool_size"].as<int>();            std::cout << "Pool size: " << pool << "";        }

        // Iterating over a sequence (list)        // Suppose the YAML has a field: hosts: ["alpha", "beta", "gamma"]        // for (const auto& h : config["hosts"]) {        //     std::cout << "Host: " << h.as<std::string>() << "";        // }

    } catch (const YAML::Exception& e) {        std::cerr << "YAML parsing error: " << e.what() << "";        return 1;    } catch (const std::exception& e) {        std::cerr << "General error: " << e.what() << "";        return 1;    }    return 0;}

Creating a YAML Document

With yaml-cpp, you can not only read but also generate YAML:

#include <yaml-cpp/yaml.h>#include <fstream>

int main() {    YAML::Emitter out;    out << YAML::BeginMap;    out << YAML::Key << "application";    out << YAML::Value << "MyApp";    out << YAML::Key << "version";    out << YAML::Value << 2.5;    out << YAML::Key << "features";    out << YAML::Value << YAML::BeginSeq;    out << "logging" << "auth" << "cache";    ou