FILTER_CALLBACK constant in PHP

The FILTER_CALLBACK constant calls a user defined function to filter the value.

Return

The FILTER_CALLBACK constant does not return anything.

Example

The following is an example that converts the case of a string. Here, existing function in PHP is taken.

<?php
   $string = "DEMO TEXT!";
   echo filter_var($string, FILTER_CALLBACK,array("options" = >"strtolower"));
?>

Output

The following is the output.

demo text!