root/tags/2.1/wp-includes/plugin.php

<?php

//
// Filter functions, the core of the WP plugin architecture.
//

function add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
    global $wp_filter;

    // check that we don't already have the same filter at the same priority
    if ( isset($wp_filter[$tag]["$priority"]) ) {
        foreach ( $wp_filter[$tag]["$priority"] as $filter ) {
            // uncomment if we want to match function AND accepted_args
            // if ( $filter == array($function, $accepted_args) ) {
            if ( $filter['function'] == $function_to_add )
                return true;
        }
    }

    // So the format is wp_filter['tag']['array of priorities']['array of ['array (functions, accepted_args)]']
    $wp_filter[$tag]["$priority"][] = array('function'=>$function_to_add, 'accepted_args'=>$accepted_args);
    return true;
}

function apply_filters($tag, $string) {
    global $wp_filter;

    $args = array();
    for ( $a = 2; $a < func_num_args(); $a++ )
        $args[] = func_get_arg($a);

    merge_filters($tag);

    if ( !isset($wp_filter[$tag]) )
        return $string;

    foreach ( (array) $wp_filter[$tag] as $priority => $functions ) {
        if ( !is_null($functions) ) {
            foreach ( (array) $functions as $function ) {
                $function_name = $function['function'];
                $accepted_args = $function['accepted_args'];
                $the_args = $args;
                array_unshift($the_args, $string);
                if ( $accepted_args > 0 )
                    $the_args = array_slice($the_args, 0, $accepted_args);
                elseif ( 0 == $accepted_args )
                    $the_args = NULL;
                $string = call_user_func_array($function_name, $the_args);
            }
        }
    }
    return $string;
}

function merge_filters($tag) {
    global $wp_filter;
    if ( isset($wp_filter['all']) ) {
        foreach ( (array) $wp_filter['all'] as $priority => $functions ) {
            if ( isset($wp_filter[$tag][$priority]) )
                $wp_filter[$tag][$priority] = array_merge($wp_filter['all'][$priority], $wp_filter[$tag][$priority]);
            else
                $wp_filter[$tag][$priority] = array_merge($wp_filter['all'][$priority], array());
            $wp_filter[$tag][$priority] = array_unique($wp_filter[$tag][$priority]);
        }
    }

    if ( isset($wp_filter[$tag]) )
        uksort( $wp_filter[$tag], "strnatcasecmp" );
}

function remove_filter($tag, $function_to_remove, $priority = 10, $accepted_args = 1) {
    global $wp_filter;

    // rebuild the list of filters
    if ( isset($wp_filter[$tag]["$priority"]) ) {
        $new_function_list = array();
        foreach ( (array) $wp_filter[$tag]["$priority"] as $filter ) {
            if ( $filter['function'] != $function_to_remove )
                $new_function_list[] = $filter;
        }
        $wp_filter[$tag]["$priority"] = $new_function_list;
    }
    return true;
}

//
// Action functions
//

function add_action($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
    add_filter($tag, $function_to_add, $priority, $accepted_args);
}

function do_action($tag, $arg = '') {
    global $wp_filter, $wp_actions;

    $args = array();
    if ( is_array($arg) && 1 == count($arg) && is_object($arg[0]) ) // array(&$this)
        $args[] =& $arg[0];
    else
        $args[] = $arg;
    for ( $a = 2; $a < func_num_args(); $a++ )
        $args[] = func_get_arg($a);

    merge_filters($tag);

    if ( !isset($wp_filter[$tag]) )
        return;

    foreach ( (array) $wp_filter[$tag] as $priority => $functions ) {
        if ( !is_null($functions) ) {
            foreach ( (array) $functions as $function ) {
                $function_name = $function['function'];
                $accepted_args = $function['accepted_args'];

                if ( $accepted_args > 0 )
                    $the_args = array_slice($args, 0, $accepted_args);
                elseif ( $accepted_args == 0 )
                    $the_args = NULL;
                else
                    $the_args = $args;

                call_user_func_array($function_name, $the_args);
            }
        }
    }

    if ( is_array($wp_actions) )
        $wp_actions[] = $tag;
    else
        $wp_actions = array($tag);
}

// Returns the number of times an action has been done
function did_action($tag) {
    global $wp_actions;

    return count(array_keys($wp_actions, $tag));
}

function do_action_ref_array($tag, $args) {
    global $wp_filter, $wp_actions;

    if ( !is_array($wp_actions) )
        $wp_actions = array($tag);
    else
        $wp_actions[] = $tag;

    merge_filters($tag);

    if ( !isset($wp_filter[$tag]) )
        return;

    foreach ( (array) $wp_filter[$tag] as $priority => $functions ) {
        if ( !is_null($functions) ) {
            foreach ( (array) $functions as $function ) {
                $function_name = $function['function'];
                $accepted_args = $function['accepted_args'];
                if ( $accepted_args > 0 )
                    $the_args = array_slice($args, 0, $accepted_args);
                elseif ( 0 == $accepted_args )
                    $the_args = NULL;
                else
                    $the_args = $args;

                call_user_func_array($function_name, $the_args);
            }
        }
    }
}

function remove_action($tag, $function_to_remove, $priority = 10, $accepted_args = 1) {
    remove_filter($tag, $function_to_remove, $priority, $accepted_args);
}

//
// Functions for handling plugins.
//

function plugin_basename($file) {
    $file = preg_replace('|\\\\+|', '\\\\', $file);
    $file = preg_replace('/^.*wp-content[\\\\\/]plugins[\\\\\/]/', '', $file);
    return $file;
}

function register_activation_hook($file, $function) {
    $file = plugin_basename($file);
    add_action('activate_' . $file, $function);
}

function register_deactivation_hook($file, $function) {
    $file = plugin_basename($file);
    add_action('deactivate_' . $file, $function);
}

?>