File name to store cookies to
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_COOKIEJAR, char *filename);
Pass a filename as char *, zero terminated. This will make libcurl write all internally known cookies to the specified file when curl_easy_cleanup(3) is called. If no cookies are known, no file will be created. Specify "-" as filename to instead have the cookies written to stdout. Using this option also enables cookies for this session, so if you for example follow a location it will make matching cookies get sent accordingly.
Note that libcurl doesn't read any cookies from the cookie jar. If you want to read cookies from a file, use CURLOPT_COOKIEFILE(3).
If the cookie jar file can't be created or written to (when the curl_easy_cleanup(3) is called), libcurl will not and cannot report an error for this. Using CURLOPT_VERBOSE(3) or CURLOPT_DEBUGFUNCTION(3) will get a warning to display, but that is the only visible feedback you get about this possibly lethal situation.
Along with HTTP
Returns CURLE_OK if HTTP is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.