How to Call libcurl from C on Ubuntu: A Step‑by‑Step Guide

Prerequisites

Install the libcurl development package on Ubuntu:

sudo apt-get update
sudo apt-get install libcurl4-openssl-dev

Source Code

Create curl_example.c with the following content. The program uses libcurl to perform a simple HTTP GET request and prints the response to standard output.

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

size_t write_callback(void *contents, size_t size, size_t nmemb, void *userp) {
    size_t real_size = size * nmemb;
    printf("%s", (char *)contents);
    return real_size;
}

int main(void) {
    CURL *curl;
    CURLcode res;

    curl_global_init(CURL_GLOBAL_ALL);
    curl = curl_easy_init();
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);
        res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed: %s
", curl_easy_strerror(res));
        }
        curl_easy_cleanup(curl);
    }
    curl_global_cleanup();
    return 0;
}

Compilation

Compile and link against libcurl: gcc curl_example.c -o curl_example -lcurl The -lcurl flag tells the linker to use the shared libcurl library, producing the executable curl_example.

Execution

Run the program: ./curl_example The program sends a GET request to http://example.com and prints the returned HTML to the console.