apply_filters() – Call the functions added to a filter hook.

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Description

Call the functions added to a filter hook.

The callback functions attached to filter hook $tag are invoked by calling this function. This function can be used to create a new filter hook by simply calling this function with the name of the new hook specified using the $tag parameter. The function allows for additional arguments to be added and passed to hooks.

// Our filter callback function
function example_callback( $string, $arg1, $arg2 ) {
// (maybe) modify $string
return $string;
}
add_filter( 'example_filter', 'example_callback', 10, 3 );

/*
Apply the filters by calling the 'example_callback' function we
"hooked" to 'example_filter' using the add_filter() function above.
'example_filter' is the filter hook $tag
'filter me' is the value being filtered
$arg1 and $arg2 are the additional arguments passed to the callback.
$value = apply_filters( 'example_filter', 'filter me', $arg1, $arg2 );

Usage

$mixed = apply_filters( $tag, $value );

Parameters

$tag: ( string ) required – The name of the filter hook.
$value: ( mixed ) required – The value on which the filters hooked to $tag are applied on.

Returns

mixed The filtered value after all hooked functions are applied to it.

Source

File name: wordpress/wp-includes/plugin.php

Lines:

1 to 37 of 37

function apply_filters( $tag, $value ) {
  global $wp_filter, $wp_current_filter;

  $args = array();

  // Do 'all' actions first.
  if ( isset( $wp_filter['all'] ) ) {
    $wp_current_filter[] = $tag;
    $args                = func_get_args();
    _wp_call_all_hook( $args );
  }

  if ( ! isset( $wp_filter[ $tag ] ) ) {
    if ( isset( $wp_filter['all'] ) ) {
      array_pop( $wp_current_filter );
    }
    return $value;
  }

  if ( ! isset( $wp_filter['all'] ) ) {
    $wp_current_filter[] = $tag;
  }

  if ( empty( $args ) ) {
    $args = func_get_args();
  }

  // don't pass the tag name to WP_Hook
  array_shift( $args );

  $filtered = $wp_filter[ $tag ]->apply_filters( $value, $args );

  array_pop( $wp_current_filter );

  return $filtered;
}

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