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Table of Contents
? Basic Setup
? Step-by-Step Code Example
? Key Points Explained
? Tips
? Summary
Home Backend Development C++ How to make an HTTP GET request with libcurl in C

How to make an HTTP GET request with libcurl in C

Jul 26, 2025 am 02:08 AM
libcurl

To initiate an HTTP GET request in C using libcurl, you must first install and link the libcurl library, and then follow the following steps: 1. Call curl_easy_init() to initialize the CURL session; 2. Use curl_easy_setopt to set the target URL (CURLOPT_URL), callback function (CURLOPT_WRITEFUNCTION) and data pointer (CURLOPT_WRITEDATA) to capture the response; 3. Optional settings such as follow redirection (CURLOPT_FOLLOWLOCATION) and timeout (CURLOPT_TIMEOUT); 4. Call curl_easy_perform() to execute the request and check whether the return value is successful; 5. Use std::string to store response data and process it through callback function; 6. Finally, curl_easy_cleanup() is called to free up resources to avoid memory leaks. Although this method is more complex than Python's requests library, it is efficient and widely used in C projects. After completing the above steps, you can correctly send GET requests and get the response content.

How to make an HTTP GET request with libcurl in C

To make an HTTP GET request using libcurl in C , you need to initialize a CURL session, set the necessary options (like the URL), and perform the request. Here's a clear, practical guide to get it working.

How to make an HTTP GET request with libcurl in C

? Basic Setup

First, make sure you have libcurl installed and linked to your project. On Ubuntu/Debian:

 sudo apt-get install libcurl4-openssl-dev

When compiling, link with -lcurl :

How to make an HTTP GET request with libcurl in C
 g your_file.cpp -o your_program -lcurl

? Step-by-Step Code Example

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

// Callback function to handle data received from curl
size_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* response) {
    size_t totalSize = size * nmemb;
    response->append((char*)contents, totalSize);
    return totalSize;
}

int main() {
    // Initialize curl
    CURL* curl = curl_easy_init();
    std::string response_data;

    if (curl) {
        // Set the URL for the GET request
        curl_easy_setopt(curl, CURLOPT_URL, "https://httpbin.org/get");

        // Set the callback function to capture the response
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response_data);

        // Optional: follow redirects
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);

        // Optional: set timeout
        curl_easy_setopt(curl, CURLOPT_TIMEOUT, 10L);

        // Perform the request
        CURLcode res = curl_easy_perform(curl);

        // Check for errors
        if (res != CURLE_OK) {
            std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
        } else {
            // Print the response
            std::cout << "Response:\n" << response_data << std::endl;
        }

        // Clean up
        curl_easy_cleanup(curl);
    } else {
        std::cerr << "Failed to initialize curl" << std::endl;
    }

    return 0;
}

? Key Points Explained

  • curl_easy_init() – Starts a libcurl session.
  • CURLOPT_URL – Sets the target URL.
  • CURLOPT_WRITEFUNCTION – Specifies a function to handle incoming data.
  • CURLOPT_WRITEDATA – Passes your variable ( response_data ) to the callback.
  • curl_easy_perform() – Executes the request synchronously.
  • Always call curl_easy_cleanup() to avoid memory leaks.

? Tips

  • The callback function must match the expected signature ( size_t (*)(void*, size_t, size_t, void*) ).
  • You can use this same pattern for JSON APIs – just parse the response with a JSON library like nlohmann/json .
  • For HTTPS, ensure you have SSL support enabled in your libcurl build (usually default).
  • If you're getting certificate errors, you can (temporarily for testing) add:
     curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);

    ?? But never do this in production.


    ? Summary

    Making a GET request with libcurl in C involves:

    How to make an HTTP GET request with libcurl in C
    1. Initializing curl
    2. Setting options (URL, callback)
    3. Performing the request
    4. Handling the response and cleaning up

    It's not as simple as Python's requests.get() , but it's efficient and widely used in C applications.

    Basically just set up the callback, tell curl where to go, and read the result.

    The above is the detailed content of How to make an HTTP GET request with libcurl in C. For more information, please follow other related articles on the PHP Chinese website!

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