curl_formfree (3) - Linux Man Pages
curl_formfree: free a previously build multipart/formdata HTTP POST chain
NAMEcurl_formfree - free a previously build multipart/formdata HTTP POST chain
DESCRIPTIONcurl_formfree() is used to clean up data previously built/appended with curl_formadd(3). This must be called when the data has been used, which typically means after curl_easy_perform(3) has been called.
The pointer to free is the same pointer you passed to the CURLOPT_HTTPPOST option, which is the firstitem pointer from the curl_formadd(3) invoke(s).
form is the pointer as returned from a previous call to curl_formadd(3) and may be NULL.