---
name: "CURLOPT_DEBUGDATA"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_DEBUGDATA"
---

# CURLOPT\_DEBUGDATA(3)

pointer passed to the debug callback

## 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\_DEBUGFUNCTION(3)](/CURLOPT_DEBUGFUNCTION/3.md)* 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 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

Added in curl 7.9.6

## RETURN VALUE

*[curl\_easy\_setopt(3)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_DEBUGFUNCTION**(3)](/CURLOPT_DEBUGFUNCTION/3.md), [**CURLOPT\_STDERR**(3)](/CURLOPT_STDERR/3.md)