Sending SMS in C++ using the libcurl API library

Sending SMS in C++ using the libcurl library

In modern development, integration with external services for sending SMS messages is often required. In C++, this task can be efficiently solved using the libcurl library — a powerful tool for working with HTTP/HTTPS protocols. The libcurl library provides a simple and flexible API for making requests to REST services, including sending SMS via provider APIs.

What is libcurl?

libcurl is a cross-platform library for data transfer over various protocols (HTTP, HTTPS, FTP, SMTP, and others). It is widely used in C++ projects due to its stability, performance, and extensive documentation. For sending SMS, we will need the functionality of HTTP POST requests with JSON or URL-encoded data transmission.

Installing libcurl

In most Linux distributions, libcurl can be installed via the package manager:

sudo apt-get install libcurl4-openssl-dev  # Ubuntu/Debiansudo yum install libcurl-devel             # CentOS/RHEL

For Windows, you can use vcpkg or download pre-built binaries from the official curl.se website.

Basic example: sending SMS via HTTP POST

Let's consider sending SMS using the API of a popular service (e.g., Twilio, Nexmo, or a Russian equivalent). In the example below, we send a POST request with JSON data containing the recipient's phone number and the message text.

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

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

bool sendSms(const std::string& apiKey, const std::string& phone, const std::string& message) {    CURL* curl;    CURLcode res;    std::string response;        curl_global_init(CURL_GLOBAL_DEFAULT);    curl = curl_easy_init();        if(curl) {        // API endpoint URL (replace with yours)        curl_easy_setopt(curl, CURLOPT_URL, "https://api.smsprovider.com/v1/send");                // Headers: content type and authorization        struct curl_slist* headers = NULL;        headers = curl_slist_append(headers, "Content-Type: application/json");        std::string authHeader = "Authorization: Bearer " + apiKey;        headers = curl_slist_append(headers, authHeader.c_str());        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);                // Form the JSON request body        std::string jsonData = "{";        jsonData += "\\"phone\\":\\"" + phone + "\\",";        jsonData += "\\"message\\":\\"" + message + "\\"";        jsonData += "}";                curl_easy_setopt(curl, CURLOPT_POSTFIELDS, jsonData.c_str());        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);                // Perform the request        res = curl_easy_perform(curl);                // Check the result        if(res != CURLE_OK) {            std::cerr << "curl error: " << curl_easy_strerror(res) << std::endl;            curl_easy_cleanup(curl);            curl_global_cleanup();            return false;        }                // Get the HTTP response code        long httpCode;        curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &httpCode);                curl_easy_cleanup(curl);        curl_global_cleanup();                if(httpCode == 200 || httpCode == 201) {            std::cout << "SMS sent successfully. Response: " << response << std::endl;            return true;        } else {            std::cerr << "Server error. HTTP " << httpCode << ": " << response << std::endl;