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.TH CURLOPT_HEADERDATA 3 "September 16, 2020" "libcurl 7.73.0" "curl_easy_setopt options"

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

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