Modern C++ in the API World: REST, GraphQL, and gRPC in Practice

Working with APIs in C++: REST, GraphQL, gRPC

When it comes to creating or consuming APIs, many developers instinctively reach for Python, Node.js, or Go. But what if you need maximum performance, low-level memory control, or you work in a legacy system where C++ reigns supreme? The answer is simple: C++ is not just alive — it thrives in the API world. Let's break down three key approaches every C++ developer should know: classic REST, modern GraphQL, and high-performance gRPC.

This article is not a dry reference manual, but a practical guide written for those who want to write real code. We'll look at how these technologies are applied in C++, provide examples with popular libraries, and help you choose the right tool for your task.

1. REST API in C++: A Classic in a Modern Implementation

REST (Representational State Transfer) remains the most common API style. It is loved for its simplicity, human-readable JSON, and versatility. In C++, we have several powerful tools for working with REST, and one of the most popular is cpprestsdk (also known as Casablanca) from Microsoft.

Writing a REST Client in C++

Imagine we need to get weather data from a public API. Here's how it looks with cpprestsdk:

#include <cpprest/http_client.h>#include <cpprest/filestream.h>#include <iostream>

using namespace web;using namespace web::http;using namespace web::http::client;

int main() {    // Create an HTTP client    http_client client(U("https://api.openweathermap.org/data/2.5"));

    // Build a GET request with parameters    uri_builder builder(U("/weather"));    builder.append_query(U("q"), U("Moscow"));    builder.append_query(U("appid"), U("YOUR_API_KEY"));    builder.append_query(U("units"), U("metric"));

    // Send the request and get the response    client.request(methods::GET, builder.to_string())        .then([](http_response response) {            if (response.status_code() == status_codes::OK) {                return response.extract_json();            }            throw std::runtime_error("Failed to fetch data");        })        .then([](json::value jsonData) {            std::cout << "Temperature: "                       << jsonData[U("main")][U("temp")].as_double()                       << "°C" << std::endl;        })        .wait();

    return 0;}

Key points:

• Asynchrony: cpprestsdk uses PPL (Parallel Patterns Library) and futures, which is ideal for C++.
• Working with JSON: the built-in json::value parser makes it easy to manipulate data.
• Cross-platform: the library works on Windows, Linux, and macOS.

When to choose REST?

REST in C++ is ideal for:

• Simple CRUD operations
• Integration with web services (social networks, payment systems)
• Prototyping and low-load microservices

2. GraphQL: Query Flexibility in C++

GraphQL solves the main problem of REST — overfetching (getting unnecessary data) and underfetching (needing multiple requests to get complete information). In C++, the cppgraphql library is most commonly used for working with GraphQL, or developers write their own client based on libcurl.

Example of a GraphQL Query in C++

Suppose we need to get a user's profile and their latest posts — in REST this would require two requests, but in GraphQL it takes one:

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

using json = nlohmann::json;

static size_t WriteCallback(void *contents, size_t size, size_t nmemb, void *userp) {    ((std::string*)userp)->a