Store a private pointer
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PRIVATE, void *pointer);
Pass a void * as parameter, pointing to data that should be associated with this curl handle. The pointer can subsequently be retrieved using curl_easy_getinfo(3) with the CURLINFO_PRIVATE option. libcurl itself never does nothing with this data.
Added in 7.10.3
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.