正則表達式，負向超前（？！？）找到<標籤沒有跟隨？

Question

如何找到<標籤後面沒有?

$htmlStr = " ba <div>b <? </div>n"; 
$regex1 = '#<#'; // finds 3 '<' 
$regex2 = '#<(?!?)#'; // does not find anyhting, although should find two '<' not followed by '?' 

Answer 1

?是一個特殊的字符在你的正則表達式模式，應該被轉義：

$htmlStr = " ba <div>b <? </div>n"; 
$regex2 = '#<(?!\?)#'; // <-- will find 2 matches