Let's implement the function to send an HTTP GET request to the API. For this task, we'll use libcurl - a popular C library for transferring data specified with URLs. ### Prerequisites Before we begin, ensure you have: 1. Set up your C++ project in your preferred IDE 2. Installed and included libcurl library 3. Familiarity with basic C++ programming concepts ### Understanding libcurl libcurl is a library that provides functionality for transferring data with URLs. It supports: - HTTP/HTTPS - FTP - SCP - SFTP - TFTP For our weather program, we'll use its HTTP capabilities. ### Steps to Implement HTTP GET Request #### 1. Include Necessary Headers First, include the libcurl header file in your source code: ```cpp #include ``` #### 2. Initialize libcurl Before making any requests, initialize libcurl: ```cpp curl_global_init(CURL_GLOBAL_DEFAULT); ``` This function initializes the libcurl library. It must be called once before any other libcurl functions are used. #### 3. Construct the API URL Create a function that constructs the API URL with your location parameter. For example, using OpenWeatherMap API: ```cpp std::string constructApiUrl(const std::string& location, const std::string& apiKey) { return "http://api.openweathermap.org/data/2.5/weather?q=" + location + "&units=metric&appid=" + apiKey; } ``` #### 4. Set Up curl Options Set up the curl options to configure the request: ```cpp curl *curl; curl = curl_easy_init(); if(curl) { // Set URL to use std::string apiUrl = constructApiUrl(location, apiKey); curl_easy_setopt(curl, CURLOPT_URL, apiUrl.c_str()); // Set callback function to write memory curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeMemoryCallback); // Pass pointer to our buffer to callback function curl_easy_setopt(curl, CURLOPT_WRITEDATA, &responseBuffer); // Set user agent curl_easy_setopt(curl, CURLOPT_USERAGENT, "WeatherProgram/1.0"); } ``` #### 5. Write Memory Callback Function The callback function that handles the received data: ```cpp static size_t writeMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp) { std::string &response = *reinterpret_cast(userp); response.assign(contents, size * nmemb); return size * nmemb; } ``` #### 6. Execute the Request Perform the request and check for errors: ```cpp CURLcode res; res = curl_easy_perform(curl); if(res != CURLE_OK) { std::cerr << "cURL error: " << curl_easy_strerror(res) << std::endl; return ""; } ``` #### 7. Cleanup After the request completes, always cleanup: ```cpp curl_easy_cleanup(curl); curl_global_cleanup(); ``` ### Complete Code Example Here's the complete function that sends an HTTP GET request: ```cpp #include #include #include static size_t writeMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp) { std::string &response = *reinterpret_cast(userp); response.assign(contents, size * nmemb); return size * nmemb; } std::string fetchWeatherData(const std::string& location, const std::string& apiKey) { curl_global_init(CURL_GLOBAL_DEFAULT); curl *curl; curl = curl_easy_init(); if(curl) { std::string apiUrl = "http://api.openweathermap.org/data/2.5/weather?q=" + location + "&units=metric&appid=" + apiKey; curl_easy_setopt(curl, CURLOPT_URL, apiUrl.c_str()); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeMemoryCallback); curl_easy_setopt(curl, CURLOPT_WRITEDATA, new std::string()); curl_easy_setopt(curl, CURLOPT_USERAGENT, "WeatherProgram/1.0"); CURLcode res = curl_easy_perform(curl); if(res != CURLE_OK) { std::cerr << "cURL error: " << curl_easy_strerror(res) << std::endl; return ""; } std::string *response = reinterpret_cast(curl_easy_getinfo(curl, CURLINFO_EFFECTIVE_URL)); curl_easy_cleanup(curl); curl_global_cleanup(); return *response; } return ""; } ``` ### Error Handling libcurl provides various error codes through `curl_easy_strerror()` function. Always check the return code of `curl_easy_perform()` to handle errors properly. ### Next Steps After successfully implementing this function, you'll move on to: 1. Parsing the JSON response 2. Displaying weather information 3. Handling errors gracefully ### Additional Resources - [libcurl Documentation](https://curl.se/libcurl/libcurl-tutorial.html) - [OpenWeatherMap API Documentation](https://openweathermap.org/api) - [curl_easy_setopt() Options](https://curl.se/libcurl/c/curl_easy_setopt.html)