CURLOPT_PROGRESSFUNCTIONbut the modern and preferred callback is set with
xfer_callbackfunction must match this prototype:
CURLOPT_NOPROGRESSis set to 0 (zero), this callback function gets called by libcurl with a frequent interval. While data is being transferred it will be called frequently, and during slow periods like when nothing is being transferred it can slow down to about one call per second.
dltotalis the total number of bytes libcurl expects to download in this transfer.
dlnowis the number of bytes downloaded so far.
ultotalis the total number of bytes libcurl expects to upload in this transfer.
ulnowis the number of bytes uploaded so far.
CURLOPT_PROGRESSFUNCTIONworked identically but instead of taking arguments of type
curl_off_t, it used