CURLOPT_HEADERDATA(3) Library Functions Manual CURLOPT_HEADERDATA(3)
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_WRITE-
FUNCTION(3) or CURLOPT_HEADERFUNCTION(3) if you set this option or you
might experience crashes.
DEFAULT
NULL
PROTOCOLS
This functionality affects all supported 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
Added in curl 7.10
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_HEADERFUNCTION(3), CURLOPT_WRITEFUNCTION(3), curl_easy_header(3)
libcurl 2026-07-12 CURLOPT_HEADERDATA(3)
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