CURLOPT_DEBUGDATA - pointer passed to the debug callback

Added in curl 7.9.6

NULL

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.

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; }

CURLOPT_DEBUGDATA - pointer passed to the debug callback

This functionality affects all supported protocols

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).

CURLOPT_DEBUGFUNCTION(3), CURLOPT_STDERR(3) libcurl 2025-06-16 CURLOPT_DEBUGDATA(3)

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