/**
* 5種方式獲取文件后綴名
* 這道題其實就是考函數(shù)substr() strrchr() array_pop() strrpos() strpos() strrev() explode() pathinfo()
* @param string $filename 要處理的文件名 1.jpg/1.png/1.html/1.php
* @return string .php/php 
*/
function get_ext1($filename)
{
    return strrchr($filename,'.');
}
function get_ext2($filename){
    return substr($filename,strrpos($filename,'.'));
}
function get_ext3($filename){
    return array_pop(explode('.',$filename));
}
function get_ext4($filename){
    return pathinfo($filename,PATHINFO_EXTENSION);
}
function get_ext5($filename){
    return strrev(substr(strrev($filename),0,strpos(strrev($filename),'.')));
}
$filename = "1.php";
echo get_ext1($filename)."\n";
echo get_ext2($filename)."\n";
echo get_ext3($filename)."\n";
echo get_ext4($filename)."\n";
echo get_ext5($filename)."\n";
/**
* 遍歷目錄(遞歸)
* @param string $dir 目錄名且最后沒有/
* @return array $files 整個目錄結構
*/
function myScandir($dir)
{
    $files = array();
    if($handle = opendir($dir)){
        while (($file = readdir($handle)) != false){
            if($file != "." && $file != ".."){
                $newDir = $dir."/".$file;
                if(is_dir($newDir)){
                    $files[$file] = myScandir($newDir);
                }else{
                    $files[] = $file;
                }
            }
        }
        closedir($handle);
        return $files;
    }
}
$dir = "/dirname";
print_r(myScandir($dir));