Codex tools: Log in / create account
Contents |
Hooks a function to a specific filter action.
Filters are the hooks that WordPress launches to modify text of various types before adding it to the database or sending it to the browser screen. Plugins can specify that one or more of its PHP functions is executed to modify specific types of text at these times, using the Filter API. See the Plugin API for a list of filter hooks.
<?php add_filter( $tag, $function_to_add, $priority, $accepted_args ); ?>
The function returns true whether the attempted function hook fails or not. There is no test that the function exists nor whether the $function_to_add is even a string. It is up to you to take care and this is done for optimization purposes, so everything is as quick as possible.
You may need to supply a pointer to the function's namespace for some filter callbacks, e.g.
<?php add_filter('media_upload_newtab', array(&$this, 'media_upload_mycallback')); ?>
Otherwise WordPress looks in its own namespace for the function, which can cause abnormal behaviour.
In WordPress 1.5.1+, hooked functions can take extra arguments that are set when the matching do_action() or apply_filters() call is run. For example, the action comment_id_not_found will pass any functions that hook onto it the ID of the requested comment.
Since: 0.71
add_filter() is located in wp-includes/plugin.php.
Filters: add_filter, has_filters, apply_filters, remove_filter, remove_all_filters, current_filter, merge_filters