class FileIterator implements Iterator
{
    private  $fp;
    private  $line_num;
    private  $line;

    public function __construct($filename) 
    {   
        $fp = @fopen($filename, ‘r‘);
        if (!$fp) {
            throw new Exception("file ".$filename." is not exists"); 
        }   
        $this->fp = $fp;
    }   

    public function key()
    {   
        return $this->line_num;
    }   

    public function current()
    {   
        return $this->line;
    }   

    public function rewind()
    {   
        rewind($this->fp);
    }   

    public function next()
    {   
    }   

    public function valid()
    {   
        $this->line = fgets($this->fp);
        $this->line_num++;
        return $this->line != false;
    }

}

foreach(new fileIterator(‘./test.txt‘) as $k => $line) {
        echo $k."->".$line;
}