Sending SMS in C++: API Libraries libcurl and cpprestsdk

Sending SMS in C++: API Libraries libcurl and cpprestsdk

In modern C++ development, there is often a need to integrate with external services, including sending SMS messages. Although the C++ standard library does not provide built-in tools for working with HTTP requests, there are powerful third-party libraries that solve this problem. In this article, we will look at two popular libraries — libcurl (CURL) and cpprestsdk (Casablanca) — and show how to use them to send SMS via the APIs of popular SMS providers.

Why do you need a library for sending SMS in C++?

Sending SMS via C++ is a typical task for server applications, monitoring systems, notifications, or automation. Direct work with sockets and the HTTP protocol in C++ is complex and error-prone. Libraries such as libcurl and cpprestsdk abstract this complexity, providing a convenient interface for making HTTP requests (GET, POST, PUT) and processing JSON/XML responses.

We will use the API of an SMS provider (e.g., Twilio, SMS.ru, or any other that supports a REST API). In the examples below, replace YOUR_API_KEY, YOUR_SENDER, and YOUR_PHONE with your actual data.

Library 1: libcurl (CURL)

libcurl is a time-tested library for working with URLs, supporting many protocols (HTTP, HTTPS, FTP, etc.). It is written in C but has excellent C++ bindings. To use it in a C++ project, simply include the header file curl/curl.h and link against libcurl.

Installing libcurl

• Linux (Ubuntu/Debian): sudo apt-get install libcurl4-openssl-dev
• Windows: download pre-built binaries from the official website or use vcpkg: vcpkg install curl
• macOS: brew install curl

Example of sending SMS via libcurl (C++ syntax)

In this example, we use a simple POST request with data in JSON format. The libcurl library handles HTTP headers and the request body.

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

// Callback function for writing the server responsesize_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {    size_t totalSize = size * nmemb;    output->append((char*)contents, totalSize);    return totalSize;}

bool sendSMS_via_libcurl(const std::string& phone, const std::string& message) {    CURL* curl = curl_easy_init();    if (!curl) return false;

    std::string response;    std::string url = "https://api.sms-provider.com/v1/send"; // Replace with your provider's URL    std::string jsonData = R"({        "api_key": "YOUR_API_KEY",        "sender": "YOUR_SENDER",        "phone": ")" + phone + R"(",        "text": ")" + message + R"("    })";

    struct curl_slist* headers = nullptr;    headers = curl_slist_append(headers, "Content-Type: application/json");

    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, jsonData.c_str());    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);

    CURLcode res = curl_easy_perform(curl);    curl_slist_free_all(headers);    curl_easy_cleanup(curl);

    if (res != CURLE_OK) {        std::cerr << "curl error: " << curl_easy_strerror(res) << std::endl;        return false;    }

    std::cout << "Server response: " << response << std::endl;    return true;}

int main() {    curl_global_init(CURL_GLOBAL_DEF