Definition:
function do_action($tag, $arg = '') {}
Execute functions hooked on a specific action hook.
This function invokes all functions attached to action hook $tag. It is possible to create new action hooks by simply calling this function, specifying the name of the new hook using the <tt>$tag</tt> parameter.
Parameters
- string $tag: The name of the action to be executed.
- mixed $arg,…: Optional additional arguments which are passed on to the functions hooked to the action.
- $arg
Return values
returns:Will return null if $tag does not exist in $wp_filter array
Source code
function do_action($tag, $arg = '') {
global $wp_filter, $wp_actions, $merged_filters, $wp_current_filter;
if ( ! isset($wp_actions) )
$wp_actions = array();
if ( ! isset($wp_actions[$tag]) )
$wp_actions[$tag] = 1;
else
++$wp_actions[$tag];
// Do 'all' actions first
if ( isset($wp_filter['all']) ) {
$wp_current_filter[] = $tag;
$all_args = func_get_args();
_wp_call_all_hook($all_args);
}
if ( !isset($wp_filter[$tag]) ) {
if ( isset($wp_filter['all']) )
array_pop($wp_current_filter);
return;
}
if ( !isset($wp_filter['all']) )
$wp_current_filter[] = $tag;
$args = array();
if ( is_array($arg) && 1 == count($arg) && isset($arg[0]) && 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);
// Sort
if ( !isset( $merged_filters[ $tag ] ) ) {
ksort($wp_filter[$tag]);
$merged_filters[ $tag ] = true;
}
reset( $wp_filter[ $tag ] );
do {
foreach ( (array) current($wp_filter[$tag]) as $the_ )
if ( !is_null($the_['function']) )
call_user_func_array($the_['function'], array_slice($args, 0, (int) $the_['accepted_args']));
} while ( next($wp_filter[$tag]) !== false );
array_pop($wp_current_filter);
}
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February 11, 2011 


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