取得文件扩展名方法

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变量 $file_name 可以来自上传域或者指定为其他

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

// 方法二 (php4.03 及更高版本 )
$extend = pathinfo($file_name);
$extend = strtolower($extend["extension"]);
echo $extend;
?>