CURLOPT_DEBUGDATA

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DEBUGDATA, void *pointer);

Pass a pointer to whatever you want passed in to your CURLOPT_DEBUGFUNCTION(3) in the last void * argument. This pointer is not used by libcurl, it is only passed to the callback.

NULL

All

int main(void)
{
  CURL *curl;
  CURLcode res;
  struct data my_tracedata;
  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, my_trace);
    curl_easy_setopt(curl, CURLOPT_DEBUGDATA, &my_tracedata);
    /* the DEBUGFUNCTION has no effect until we enable VERBOSE */
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    res = curl_easy_perform(curl);
    /* always cleanup */
    curl_easy_cleanup(curl);
  }
  return 0;
}

Always

Returns CURLE_OK

CURLOPT_STDERR(3), CURLOPT_DEBUGFUNCTION(3),