<?php
// for filters that accept options, use this format
$options = array(
    'options' => array(
        'default' => 3, // value to return if the filter fails
        // other options here
        'min_range' => 0
    ),
    'flags' => FILTER_FLAG_ALLOW_OCTAL,
);
$var = filter_var('0755', FILTER_VALIDATE_INT, $options);

// for filter that only accept flags, you can pass them directly
$var = filter_var('oops', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);

// for filter that only accept flags, you can also pass as an array
$var = filter_var('oops', FILTER_VALIDATE_BOOLEAN,
                  array('flags' => FILTER_NULL_ON_FAILURE));

// callback filter
function foo($value)
{
    $ret = new stdClass;
    $ret->value = filter_var($value, FILTER_VALIDATE_BOOLEAN,
                             array('flags' => FILTER_NULL_ON_FAILURE));
    return $ret;
}
$var = filter_var('yes', FILTER_CALLBACK, array('options' => 'foo'));
?>