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

# [NAME](#NAME)

CURLOPT\_TRAILERDATA - pointer passed to trailing headers callback

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERDATA, void *userdata);
```

# [DESCRIPTION](#DESCRIPTION)

Data pointer to be passed to the HTTP trailer callback function.

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http only

# [EXAMPLE](#EXAMPLE)

```
struct MyData {


  void *custom;
};
int main(void)
{


  CURL *curl = curl_easy_init();


  if(curl) {


    struct MyData data;


    curl_easy_setopt(curl, CURLOPT_TRAILERDATA, &data);


  }
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.64.0

# [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\_TRAILERFUNCTION**(3)](/man/os/curl/CURLOPT_TRAILERFUNCTION.3), [**CURLOPT\_WRITEFUNCTION**(3)](/man/os/curl/CURLOPT_WRITEFUNCTION.3)

2026-10-01 libcurl

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Document: CURLOPT_TRAILERDATA(3) from curl 8.22.0-r4 (Chainguard OS)
Source: https://github.com/curl/curl.git