It also enables the cookie engine, making libcurl parse and send cookies on subsequent requests with this handle.
Given an empty or non-existing file or by passing the empty string ("") to this option, you can enable the cookie engine without reading any initial cookies. If you tell libcurl the file name is "-" (just a single minus sign), libcurl will instead read from stdin.
This option only reads cookies. To make libcurl write cookies to file,
Exercise caution if you are using this option and multiple transfers may occur. If you use the Set-Cookie format and don't specify a domain then the cookie is sent for any domain (even after redirects are followed) and cannot be modified by a server-set cookie. If a server sets a cookie of the same name then both will be sent on a future transfer to that server, likely not what you intended. To address these issues set a domain in Set-Cookie (doing that will include sub-domains) or use the Netscape format.
If you use this option multiple times, you just add more files to read. Subsequent files will add more cookies.