3种通过php获取文件后缀的方法：

<?php
$filename1='http://www.100sucai.com/logo.gif';
$filename2='http://www.100sucai.com/logo.png';
$filename3='http://www.100sucai.com/logo.jpg';
//获取文件后缀方法1,输出后缀是gif
function extend_1($name)
 {
 $retval="";
 $pt=strrpos($name, ".");
 if ($pt) $retval=substr($name, $pt+1, strlen($name) - $pt);
 return ($retval);
 }
 echo extend_1($filename1)."<p>";
//获取文件后缀方法2,输出后缀是png
 function extend_2($name)
 {
 $extend = pathinfo($name);
 $extend = strtolower($extend["extension"]);
 return $extend;
 }
 echo extend_2($filename2)."<p>";
//获取文件后缀方法3,输出后缀是jpg
 function extend_3($name)
 {
 $extend =explode("." , $name);
 $va=count($extend)-1;
 return $extend[$va];
 }
 echo extend_3($filename3);
?>