(PHP 5 >= 5.2.0)
filter_list — Returns a list of all supported filters
Returns an array of names of all supported filters, empty array if there are no such filters. Indexes of this array are not filter IDs, they can be obtained with filter_id() from a name instead.
Example #1 A filter_list() example 以上例程的输出类似于：
<?php
print_r(filter_list());
?>
Array
(
[0] => int
[1] => boolean
[2] => float
[3] => validate_regexp
[4] => validate_url
[5] => validate_email
[6] => validate_ip
[7] => string
[8] => stripped
[9] => encoded
[10] => special_chars
[11] => unsafe_raw
[12] => email
[13] => url
[14] => number_int
[15] => number_float
[16] => magic_quotes
[17] => callback
)