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.\" generated by cd2nroff 0.1 from CURLOPT_HEADER.md
.TH CURLOPT_HEADER 3 "2025-06-27" libcurl
.SH NAME
CURLOPT_HEADER \- pass headers to the data stream
.SH SYNOPSIS
.nf
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADER, long onoff);
.fi
.SH DESCRIPTION
Pass the long value \fIonoff\fP set to 1 to ask libcurl to include the headers
in the write callback (\fICURLOPT_WRITEFUNCTION(3)\fP). This option is
relevant for protocols that actually have headers or other meta\-data (like
HTTP and FTP).
When asking to get the headers passed to the same callback as the body, it is
not possible to accurately separate them again without detailed knowledge
about the protocol in use.
Further: the \fICURLOPT_WRITEFUNCTION(3)\fP callback is limited to only ever
get a maximum of \fICURL_MAX_WRITE_SIZE\fP bytes passed to it (16KB), while a
header can be longer and the \fICURLOPT_HEADERFUNCTION(3)\fP supports getting
called with headers up to \fICURL_MAX_HTTP_HEADER\fP bytes big (100KB).
It is often better to use \fICURLOPT_HEADERFUNCTION(3)\fP to get the header
data separately.
While named confusingly similar, \fICURLOPT_HTTPHEADER(3)\fP is used to set
custom HTTP headers.
.SH DEFAULT
0
.SH PROTOCOLS
This functionality affects ftp, http, imap, pop3 and smtp
.SH EXAMPLE
.nf
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
curl_easy_setopt(curl, CURLOPT_HEADER, 1L);
curl_easy_perform(curl);
}
}
.fi
.SH AVAILABILITY
Added in curl 7.1
.SH RETURN VALUE
\fIcurl_easy_setopt(3)\fP returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non\-zero means an error occurred, see
\fIlibcurl\-errors(3)\fP.
.SH SEE ALSO
.BR CURLOPT_HEADERFUNCTION (3),
.BR CURLOPT_HTTPHEADER (3)