echo $_SERVER['DOCUMENT_ROOT'];
这时输出当前文件所在的路径 D:/phpStudy/WWW/study/php&mysql
$_SERVER['DOCUMENT_ROOT']/orders.txt 这时候以为输出的路径为 D:/phpStudy/WWW/study/php&mysql/orders.txt
但是通过echo 输出的为结果为：
Notice: Use of undefined constant orders - assumed 'orders' in D:phpStudyWWWstudyphp&mysql est.php on line 9 Warning: Division by zero in D:phpStudyWWWstudyphp&mysql est.php on line 9 Notice: Use of undefined constant txt - assumed 'txt' in D:phpStudyWWWstudyphp&mysql est.php on line 9 txt
我们给 orders.txt 两边加上双引号试试，变成
$_SERVER['DOCUMENT_ROOT'].”/orders.txt“
这时才能正确识别orders.txt的地址
D:/phpStudy/WWW/study/php&mysql/orders.txt
还有一种方式就是给 $_SERVER['DOCUMENT_ROOT'] 两边加上大括号，然后总的路径打上双引号
"{$_SERVER['DOCUMENT_ROOT']}/orders.txt"
这样也能正确输出orders.txt的地址