.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" * SPDX-License-Identifier: curl
.\" *
.\" **************************************************************************
.\"
.TH CURLOPT_HEADERDATA 3 "January 05, 2023" "libcurl 7.88.1" "curl_easy_setopt options"

.SH NAME
CURLOPT_HEADERDATA \- pointer to pass to header callback
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERDATA, void *pointer);
.fi
.SH DESCRIPTION
Pass a \fIpointer\fP to be used to write the header part of the received data
to.

If \fICURLOPT_WRITEFUNCTION(3)\fP or \fICURLOPT_HEADERFUNCTION(3)\fP is used,
\fIpointer\fP will be passed in to the respective callback.

If neither of those options are set, \fIpointer\fP must be a valid FILE * and
it will be used by a plain fwrite() to write headers to.

If you are using libcurl as a win32 DLL, you \fBMUST\fP use a
\fICURLOPT_WRITEFUNCTION(3)\fP or \fICURLOPT_HEADERFUNCTION(3)\fP if you set
this option or you will experience crashes.
.SH DEFAULT
NULL
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
struct my_info {
  int shoesize;
  char *secret;
};

static size_t header_callback(char *buffer, size_t size,
                              size_t nitems, void *userdata)
{
  struct my_info *i = (struct my_info *)userdata;

  /* now this callback can access the my_info struct */

  return nitems * size;
}

CURL *curl = curl_easy_init();
if(curl) {
  struct my_info my = { 10, "the cookies are in the cupboard" };
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

  curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);

  /* pass in custom data to the callback */
  curl_easy_setopt(curl, CURLOPT_HEADERDATA, &my);

  curl_easy_perform(curl);
}
.fi
.SH AVAILABILITY
Always
.SH RETURN VALUE
Returns CURLE_OK
.SH "SEE ALSO"
.BR CURLOPT_HEADERFUNCTION "(3), " CURLOPT_WRITEFUNCTION "(3), "