/**
* 5种方式获取文件后缀名
* 这道题其实就是考函数substr() strrchr() array_pop() strrpos() strpos() strrev() explode() pathinfo()
* @param string $filename 要处理的文件名 1.jpg/1.png/1.html/1.php
* @return string .php/php 
*/
function get_ext1($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";
/**
* 遍历目录(递归)
* @param string $dir 目录名且最后没有/
* @return array $files 整个目录结构
*/
function myScandir($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));