Can't set cookie in Wordpress plugin after theme has started rendering

Question

When I set a cookie in a Wordpress plugin, I get the \"headers already sent\" error. Can someone suggest how I can fix this?

Warning: Cannot modify header

Answer 1

You're calling your set_cookies function too late. At the time you call it, output has already started. You need call it before any output has started, because cookies can not be set if output has already started (see as well: setcookieDocs).

In your case before header.php line 11 is being executed.

That's merely before the theme get's loaded.

Answer 2

You can avoid header modification warning messages by buffering your source, before it makes it to the browser. If you do not have access to php.ini you can add php_value output_buffering 4096 to your .htaccess or you can add ob_start("ob_gzhandler"); at the top and ob_end_flush() at the bottom of your wordpresses root index.php