CURLOPT_XFERINFODATA (3) - Linux Manuals
CURLOPT_XFERINFODATA: custom pointer passed to the progress callback
NAME
CURLOPT_XFERINFODATA - custom pointer passed to the progress callbackSYNOPSIS
#include <curl/curl.h>CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFODATA, void *pointer);
DESCRIPTION
Pass a pointer that will be untouched by libcurl and passed as the first argument in the progress callback set with CURLOPT_XFERINFOFUNCTION(3).This is an alias for CURLOPT_PROGRESSDATA(3).