<?php
//获取文件扩展名
$file = 'youkud.com.php';

//方法1
$path_info = pathinfo($file);
//print_r($path_info);
//echo "<br>";
//echo $path_info['dirname'];
//echo "<br>";
//echo $path_info['basename'];
echo "<br>";
echo strtolower($path_info['extension']);

//方法2
echo "---------------------<br/>";
$p = strrpos($file,'.'); //得到最后一个点的位置
echo strtolower(substr($file,$p+1));

//方法3
echo "---------------------<br/>";
$arr = explode('.',$file);
echo strtolower($arr[count($arr)-1]);

//方法4
echo "---------------------<br/>";
$arr = explode('.',$file);
echo strtolower(end($arr));

//方法5
echo "---------------------<br/>";
preg_match('/\.(\w+)$/',$file,$extend);
echo  strtolower($extend['1']);

//方法6
echo "---------------------<br/>";
//strrchr($file,'.') 最后一次出现的位置开始到最后的字符串
echo strtolower(substr(strrchr($file,'.'),1));

//by http://www.youkud.com
?>