interface_exists
    (PHP 5 >= 5.0.2)
interface_exists -- Checks if the interface has been defined
Description
bool 
interface_exists ( string interface_name [, bool autoload] )
     This function returns TRUE if the interface given by
     interface_name has been defined,
     FALSE otherwise.
    
     
Example 1. interface_exists() example 
<?php // Check the interface exists before trying to use it if (interface_exists('MyInterface')) {     class MyClass implements MyInterface     {         // Methods     } }
  ?>
 |  
  | 
    
     interface_exists() will attempt to call __autoload by
     default, if you don't want interface_exists() to 
     call __autoload, you can set the parameter autoload
     to FALSE.
    
     See also class_exists().