CURLOPT_TRAILERDATA(3) Library Functions Manual CURLOPT_TRAILERDATA(3) NAME CURLOPT_TRAILERDATA - pointer passed to trailing headers callback SYNOPSIS #include 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) returns a CURLcode indicating success or error. CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3). SEE ALSO CURLOPT_TRAILERFUNCTION(3), CURLOPT_WRITEFUNCTION(3) libcurl 2025-06-04 CURLOPT_TRAILERDATA(3)