---
name: "CURLOPT_TRAILERDATA"
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_TRAILERDATA"
---

# CURLOPT\_TRAILERDATA(3)

pointer passed to trailing headers callback

## NAME

CURLOPT\_TRAILERDATA - pointer passed to trailing headers callback

## SYNOPSIS

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

## DESCRIPTION

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

## DEFAULT

NULL

## PROTOCOLS

This functionality affects http only

## 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

Added in curl 7.64.0

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