Three ways to get file extension in php

The code is as follows:

<?php  
//方法一:  
function extend_1($file_name)  
{  
$retval="";  
$pt=strrpos($file_name, ".");  
if ($pt) $retval=substr($file_name, $pt+1, strlen($file_name) - $pt);  
return ($retval);  
}  

//方法二  
function extend_2($file_name)  
{  
$extend = pathinfo($file_name);  
$extend = strtolower($extend["extension"]);  
return $extend;  
}  

//方法三  
function extend_3($file_name)  
{  
$extend =explode("." , $file_name);  
$va=count($extend)-1; 
return $extend[$va];  
}  
?>

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