C++ API Request Examples: Making HTTP Calls

Introduction

In today’s software landscape, APIs (Application Programming Interfaces) serve as crucial gateways for applications to communicate with each other. Using C++ to interact with APIs allows developers to leverage the performance and efficiency of the language while accessing external data or services. Below are three diverse and practical examples of using C++ with APIs, specifically focusing on making HTTP requests.

Example 1: Basic GET Request Using cURL

Context: This example demonstrates how to perform a basic GET request to retrieve data from a public API using the cURL library, which is widely used for making HTTP requests in C++.

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

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* curl;
    CURLcode res;
    std::string readBuffer;

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "https://api.example.com/data");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
    }

    std::cout << "Response: " << readBuffer << std::endl;
    return 0;
}

Notes: Ensure you have the cURL library installed and linked in your C++ project. You can install it via package managers like apt or vcpkg.

Example 2: POST Request with JSON Payload

Context: This example illustrates how to send a POST request with a JSON payload to an API endpoint. It uses the nlohmann/json library to handle JSON data conveniently.

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

using json = nlohmann::json;

int main() {
    CURL* curl;
    CURLcode res;
    curl = curl_easy_init();

    if(curl) {
        json payload = { {"key1", "value1"}, {"key2", "value2"} };
        std::string jsonData = payload.dump();

        curl_easy_setopt(curl, CURLOPT_URL, "https://api.example.com/data");
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, jsonData.c_str());
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, NULL);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
    }

    return 0;
}

Notes: Make sure to include the nlohmann/json library in your project. You can find it on GitHub or through package managers. Set the appropriate headers for content type if needed.

Example 3: Handling API Responses with Error Checking

Context: This example expands on the previous ones by adding error checking and response handling, which is essential when dealing with APIs.

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

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* curl;
    CURLcode res;
    std::string readBuffer;

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "https://api.example.com/data");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
        res = curl_easy_perform(curl);

        if(res != CURLE_OK) {
            std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
        } else {
            std::cout << "Response: " << readBuffer << std::endl;
        }
        curl_easy_cleanup(curl);
    }

    return 0;
}

Notes: This example showcases how to handle errors effectively. Always check the return value of curl_easy_perform() to ensure a successful request. You can further enhance error handling by inspecting HTTP response codes.

By exploring these examples of using C++ with APIs, you can build robust applications that leverage external data and services efficiently.