Pass a pointer to a linked list of HTTP headers to pass to the server and/or
proxy in your HTTP request. The same list can be used for both host and proxy
The linked list should be a fully valid list of struct curl_slist
structs properly filled in. Use curl_slist_append(3) to create the list
and curl_slist_free_all(3) to clean up an entire list. If you add a
header that is otherwise generated and used by libcurl internally, your added
one will be used instead. If you add a header with no content as in Accept:
(no data on the right side of the colon), the internally used header will get
disabled. With this option you can add new headers, replace internal headers
and remove internal headers. To add a header with no content (nothing to the
right side of the colon), use the form MyHeader; (note the ending
The headers included in the linked list must not be CRLF-terminated,
because libcurl adds CRLF after each header item. Failure to comply with this
will result in strange bugs because the server will most likely ignore part of
the headers you specified.
The first line in a request (containing the method, usually a GET or POST) is
not a header and cannot be replaced using this option. Only the lines
following the request-line are headers. Adding this method line in this list
of headers will only cause your request to send an invalid header. Use
CURLOPT_CUSTOMREQUEST(3) to change the method.
When this option is passed to curl_easy_setopt(3), libcurl will not copy
the entire list so you must keep it around until you no longer use this
handle for a transfer before you call curl_slist_free_all(3) on
Pass a NULL to this option to reset back to no custom headers.
The most commonly replaced headers have "shortcuts" in the options
CURLOPT_COOKIE(3), CURLOPT_USERAGENT(3) and
CURLOPT_REFERER(3). We recommend using those.
Theres an alternative option that sets or replaces headers only for requests
that are sent with CONNECT to a proxy: CURLOPT_PROXYHEADER(3). Use
CURLOPT_HEADEROPT(3) to control the behavior.
CURL *curl = curl_easy_init();
struct curl_slist *list = NULL;
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
list = curl_slist_append(list, "Shoesize: 10");
list = curl_slist_append(list, "Accept:");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);
curl_slist_free_all(list); /* free the list again */