CURLOPT\_DEBUGDATA(3) Library Functions Manual CURLOPT\_DEBUGDATA(3)

# [NAME](#NAME)

CURLOPT\_DEBUGDATA - pointer passed to the debug callback

# [SYNOPSIS](#SYNOPSIS)

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

# [DESCRIPTION](#DESCRIPTION)

Pass a *pointer* to whatever you want passed in to your [*CURLOPT\_DEBUGFUNCTION(3)*](/man/os/curl/CURLOPT_DEBUGFUNCTION.3) in the last void * argument. This pointer is not used by libcurl, it is only passed to the callback.

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#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 result;


  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/");


    result = curl_easy_perform(curl);


    /* always cleanup */


    curl_easy_cleanup(curl);


  }


  return 0;
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.9.6

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/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)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_DEBUGFUNCTION**(3)](/man/os/curl/CURLOPT_DEBUGFUNCTION.3), [**CURLOPT\_STDERR**(3)](/man/os/curl/CURLOPT_STDERR.3)

2026-10-19 libcurl

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Document: CURLOPT_DEBUGDATA(3) from curl 8.23.0-r1 (Chainguard OS)
Source: https://github.com/curl/curl.git