curl/docs/libcurl/opts/CURLOPT_HEADERDATA.md

---

c: Copyright (C) Daniel Stenberg, daniel@haxx.se, et al. SPDX-License-Identifier: curl Title: CURLOPT_HEADERDATA Section: 3 Source: libcurl See-also:

• CURLOPT_HEADERFUNCTION (3)
• CURLOPT_WRITEFUNCTION (3)
• curl_easy_header (3) Protocol:
• All Added-in: 7.10 ---

NAME

CURLOPT_HEADERDATA - pointer to pass to header callback

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERDATA, void *pointer);

DESCRIPTION

Pass a pointer to be used to write the header part of the received data to.

If CURLOPT_WRITEFUNCTION(3) or CURLOPT_HEADERFUNCTION(3) is used, pointer is passed in to the respective callback.

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

If you are using libcurl as a Windows DLL, you MUST use a CURLOPT_WRITEFUNCTION(3) or CURLOPT_HEADERFUNCTION(3) if you set this option or you might experience crashes.

DEFAULT

NULL

%PROTOCOLS%

EXAMPLE

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 = userdata;
  printf("shoe size: %d\n", i->shoesize);
  /* now this callback can access the my_info struct */

  return nitems * size;
}

int main(void)
{
  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);
  }
}

%AVAILABILITY%

RETURN VALUE

Returns CURLE_OK