PHP stream_wrapper_register

 <?php
 /**
  * 引用：http://php.net/manual/en/function.stream-wrapper-register.php
  * 把变量当成文件读写的协议
  *
  * Class VariableStream
  */
 class VariableStream
 {
     private $postition;   // 当前的位置
     private $varname;     // 变量的名字

     /**
      * 打开
      *
      * @param $path
      * @param $mode
      * @param $options
      * @param $opened_path
      * @return bool
      */
     public function stream_open($path, $mode, $options, &$opened_path)
     {
         $url = parse_url($path);

         $this->varname   = $url['host'];
         $this->postition = 0;

         return true;
     }

     /**
      * 读取
      *
      * @param $count
      * @return string
      */
     public function stream_read($count)
     {

         $p   = $this->postition;
         $ret = substr($GLOBALS[$this->varname], $p,$count);
         $p  += $count;
         return $ret;
     }

     /**
      * 写入
      *
      * @param $data
      * @return int
      */
     public function stream_write($data)
     {
         $v = &$GLOBALS[$this->varname];
         $l = strlen($data);
         $p = &$this->postition;
         $v = substr($v,0,$p) .$data.substr($v,$p+=$l);

         return $l;
     }

     /**
      * 返回位置
      *
      * @return mixed
      */
     public function stream_tell()
     {
         return $this->postition;
     }

     /**
      * 寻位
      *
      * @param $offset
      * @param $whence
      * @return bool
      */
     public function stream_seek($offset, $whence)
     {
         $dp = $p = &$this->postition;
         $l  = strlen($GLOBALS[$this->varname]);

         switch($whence)
         {
             case SEEK_SET:
                 $p = 0;
                 break;
             case SEEK_END:
                 $p = $l;
                 break;
             default:
                 return false;
         }
         $p += $offset;
         $ret = ($p >= 0 || $p <= $l);
         if(!$ret)
             $this->postition = $dp;
         return $ret;
     }

     public function stream_eof()
     {
         return strlen($GLOBALS[$this->varname])== $this->postition;
     }
 }

 // 撤销已注册的同名协议
 if(in_array('var',stream_get_wrappers()))
 {
     stream_wrapper_unregister('var');
 }
 // 注册自己的协议
 stream_wrapper_register('var','VariableStream') or die('Failed to register protocol');

 $myvar = "";
 $fp = fopen('var://myvar','r+');
 if(!$fp){
     die('Failed to open the file!');
 }
 $str = "Hello the world!";
 fwrite($fp,$str,strlen($str));

 echo 'The length of the string is ' .strlen($myvar) ."\n";
 echo 'The value of variable ,$myvar,is :' .$myvar ."\n";
 echo 'The position of the cursor is :' .ftell($fp) ."\n";
 echo 'Is at the end of the file :' .(feof($fp) ? 'true':'false') ."\n";
 if(fseek($fp,-16,SEEK_END))
 {
     echo 'Now,the position is :' .ftell($fp);
 }