1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_HEADERDATA
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_HEADERFUNCTION (3)
9  - CURLOPT_WRITEFUNCTION (3)
10  - curl_easy_header (3)
11Protocol:
12  - All
13Added-in: 7.10
14---
15
16# NAME
17
18CURLOPT_HEADERDATA - pointer to pass to header callback
19
20# SYNOPSIS
21
22~~~c
23#include <curl/curl.h>
24
25CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERDATA, void *pointer);
26~~~
27
28# DESCRIPTION
29
30Pass a *pointer* to be used to write the header part of the received data
31to.
32
33If CURLOPT_WRITEFUNCTION(3) or CURLOPT_HEADERFUNCTION(3) is used,
34*pointer* is passed in to the respective callback.
35
36If neither of those options are set, *pointer* must be a valid FILE * and
37it is used by a plain fwrite() to write headers to.
38
39If you are using libcurl as a Windows DLL, you **MUST** use a
40CURLOPT_WRITEFUNCTION(3) or CURLOPT_HEADERFUNCTION(3) if you set
41this option or you might experience crashes.
42
43# DEFAULT
44
45NULL
46
47# %PROTOCOLS%
48
49# EXAMPLE
50
51~~~c
52struct my_info {
53  int shoesize;
54  char *secret;
55};
56
57static size_t header_callback(char *buffer, size_t size,
58                              size_t nitems, void *userdata)
59{
60  struct my_info *i = userdata;
61  printf("shoe size: %d\n", i->shoesize);
62  /* now this callback can access the my_info struct */
63
64  return nitems * size;
65}
66
67int main(void)
68{
69  CURL *curl = curl_easy_init();
70  if(curl) {
71    struct my_info my = { 10, "the cookies are in the cupboard" };
72    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
73
74    curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);
75
76    /* pass in custom data to the callback */
77    curl_easy_setopt(curl, CURLOPT_HEADERDATA, &my);
78
79    curl_easy_perform(curl);
80  }
81}
82~~~
83
84# %AVAILABILITY%
85
86# RETURN VALUE
87
88Returns CURLE_OK
89