define('DT_ROOT', str_replace("\\", '/', dirname(__FILE__)));$fp = fopen(DT_ROOT."/test.txt", "w");//文件被清空后再写入if($fp){    $count=0;    for($i=1;$i<=5;$i++)    {        $flag=fwrite($fp,"行".$i." : "."Hello World!\r\n");        if(!$flag)        {            echo "写入文件失败
";            break;        }        $count+=$flag;    }    echo "共写入".$count."个字符";}else{    echo "打开文件失败";}fclose($fp);