CURLOPT_DEBUGDATA(3) - Man pages

CURLOPT_DEBUGDATA(3)        Library Functions Manual       CURLOPT_DEBUGDATA(3)

NAME
       CURLOPT_DEBUGDATA - pointer passed to the debug callback

SYNOPSIS
       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DEBUGDATA, void *pointer);

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

DEFAULT
       NULL

PROTOCOLS
       This functionality affects all supported protocols

EXAMPLE
       struct data {
         void *custom;
       };

       static int my_trace(CURL *handle, curl_infotype type,
                           char *data, size_t size,
                           void *clientp)
       {
         struct data *mine = clientp;
         printf("our ptr: %p\n", mine->custom);

         /* output debug info */
         return 0;
       }

       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;
       }

AVAILABILITY
       Added in curl 7.9.6

RETURN VALUE
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error  occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLOPT_DEBUGFUNCTION(3), CURLOPT_STDERR(3)

libcurl                            2026-07-12              CURLOPT_DEBUGDATA(3)

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