CURLOPT_TRAILERDATA(3) Library Functions Manual CURLOPT_TRAILERDATA(3)

CURLOPT_TRAILERDATA - pointer passed to trailing headers callback

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

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

NULL

This functionality affects http only

struct MyData {
  void *custom;
};
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    struct MyData data;
    curl_easy_setopt(curl, CURLOPT_TRAILERDATA, &data);
  }
}

Added in curl 7.64.0

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_TRAILERFUNCTION(3), CURLOPT_WRITEFUNCTION(3)

2025-06-04 libcurl