HTTP Client in C++: Making Requests the Right Way

Introduction: Why Write an HTTP Client in C++?

In modern development, interacting with web services has become an integral part of almost any application. Even if you are writing a desktop program in C++, sooner or later you will need to send data to a server or receive it from there. Unlike scripting languages, C++ does not have built-in tools for working with HTTP — but this is not a problem. There are several proven ways to implement an HTTP client in C++, and we will look at them from simple to complex.

In this article, we will cover:

• How to use the libcurl library — the gold standard for working with HTTP in C++
• How to send GET and POST requests with headers and body
• How to process the received response and parse JSON
• How to avoid common mistakes when working with network requests

All code examples can be used immediately in your projects. Let's go!

1. Choosing a Library: libcurl as the Main Tool

Writing an HTTP client in C++ from scratch is a thankless task. You will have to work with sockets, manually form headers, parse responses, and handle a bunch of edge cases. Fortunately, there is libcurl — a powerful, stable, and cross-platform library that does all the dirty work for you.

To get started, install libcurl. On Ubuntu, this is done with one command:

sudo apt-get install libcurl4-openssl-dev

On Windows, you can use vcpkg or download pre-built binaries. After installation, link the library in your CMakeLists.txt or simply link manually with the -lcurl flags.

The basic structure of working with libcurl is always the same:

1. Initialize the global context by calling curl_global_init()
2. Create a session handle curl_easy_init()
3. Set request parameters (URL, headers, method, etc.)
4. Execute the request curl_easy_perform()
5. Clean up resources

Sounds simple? Let's move on to the code.

2. Sending GET and POST Requests: Practical Examples

2.1 Simple GET Request

Let's start with a classic — get data from a public API. Suppose we want to know the current Bitcoin to Dollar exchange rate:

#include <iostream>#include <string>#include <curl/curl.h>

// Callback function for writing data to a stringstatic size_t WriteCallback(void* contents, size_t size, size_t nmemb, void* userp) {    ((std::string*)userp)->append((char*)contents, size * nmemb);    return size * nmemb;}

int main() {    curl_global_init(CURL_GLOBAL_DEFAULT);    CURL* curl = curl_easy_init();    std::string response;        if (curl) {        curl_easy_setopt(curl, CURLOPT_URL, "https://api.coindesk.com/v1/bpi/currentprice.json");        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);                CURLcode res = curl_easy_perform(curl);        if (res != CURLE_OK) {            std::cerr << "Error: " << curl_easy_strerror(res) << std::endl;        } else {            std::cout << "Server response:" << response << std::endl;        }        curl_easy_cleanup(curl);    }    curl_global_cleanup();    return 0;}

Note the callback function WriteCallback. libcurl does not know where to save the data, so we pass a pointer to a string and write to it as data arrives. This is a standard pattern.

2.2 POST Request with JSON Body

Now let's send data to the server. Suppose we are registering a user:

#include <iostream>#include <string>#include <curl/curl.h>

int main() {    curl_global_init(CURL_GLOBAL_DEFAULT);    CURL* curl = curl