curl_global_init(). This is necessary because some underlying libraries that libcurl might be using need a call ahead to get setup and initialized properly.curl_global_cleanup() to free and clean up the associated global resources the init call allocated.curl_global_init() call, but it does so by calling it itself instead (if you did not do it before any actual file transfer starts) and it then uses its own defaults. But beware that it is still not thread safe even then, so it might cause some "interesting" side effects for you. It is much better to call curl_global_init() yourself in a controlled manner.