How do you make a HTTP request with C++?

Making HTTP requests in C++ typically requires third-party libraries, as the standard C++ library lacks direct support for network programming. The following sections introduce two popular libraries: C++ REST SDK (also known as Casablanca) and cURL, to demonstrate how to make HTTP requests in C++.

1. Using C++ REST SDK (Casablanca)

C++ REST SDK is a Microsoft-maintained project designed to simplify HTTP client and server programming. Below is a basic example of using C++ REST SDK to perform an HTTP GET request:

First, install the C++ REST SDK. If you are using Visual Studio, you can install it via the NuGet package manager.

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

using namespace utility;                    // Common utilities like string conversions
using namespace web;                        // Common features like URIs.
using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features
using namespace concurrency::streams;       // Asynchronous streams

int main() {
    // Create HTTP client object
    http_client client(U("http://example.com"));

    // Build request
    uri_builder builder(U("/api/data"));
    builder.append_query(U("key"), U("value"));

    // Send GET request
    client.request(methods::GET, builder.to_string())
    .then([](http_response response) {
        // Check response status code
        if (response.status_code() == status_codes::OK) {
            return response.extract_string();
        }
        return pplx::task_from_result(utility::string_t());
    })
    .then([](const utility::string_t& body) {
        std::wcout << body << std::endl;
    })
    .wait();

    return 0;
}

2. Using cURL

cURL is a powerful library for handling URLs, supporting multiple protocols including HTTP and HTTPS. An example of using cURL for HTTP requests is shown below:

First, ensure the cURL library is installed on your system.

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

size_t write_callback(void *contents, size_t size, size_t nmemb, void *userp) {
    ((std::string*)userp)->append((char*)contents, size * nmemb);
    return size * nmemb;
}

int main() {
    CURL *curl;
    CURLcode res;
    std::string readBuffer;

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/api/data?key=value");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
        
        res = curl_easy_perform(curl);
        if(res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
        } else {
            std::cout << readBuffer << std::endl;
        }

        curl_easy_cleanup(curl);
    }

    return 0;
}

Both approaches are effective for making HTTP requests in C++. The choice of library depends on project requirements: C++ REST SDK offers a modern, asynchronous API, while cURL is valued for its stability and broad protocol support.