PHP:意外PREG_BACKTRACK_LIMIT_ERROR

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问题描述

function recursiveSplit($string, $layer) {
    $err = preg_match_all("/\{(([^{}]*|(?R))*)\}/",$string,$matches);
    echo "Elementi trovati: $err<br>";
    if($err == FALSE) echo "preg_match_all ERROR<br>";

    // iterate thru matches and continue recursive split
    if (count($matches) > 1) {
        for ($i = 0; $i < count($matches[1]); $i++) {
            if (is_string($matches[1][$i])) {
                if (strlen($matches[1][$i]) > 0) {
                    echo "<pre>Layer ".$layer.":   ".$matches[1][$i]."</pre><br />";
                    recursiveSplit($matches[1][$i], $layer + 1);
                }
            }
        }
    }
}

$buffer = "{aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa{aaaaaaaaaaaaaaaaaa{aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa}";
recursiveSplit($buffer, 0);

输出

Elementi trovati:
preg_match_all ERROR
Backtrack limit was exhausted!

这段代码给我一个PREG_BACKTRACK_LIMIT_ERROR错误...但是回溯限制设置为100.000.000.

this code gives me a PREG_BACKTRACK_LIMIT_ERROR error... but the backtrack limit is set to 100.000.000.

这是我第一次使用正则表达式，我真的不知道该如何解决.

This is my first time with regex, and I really do not know how to solve it.

非常感谢你，马可

推荐答案

灾难性的另一种经典案例回溯.今天必须是我的幸运日.

/\{(([^{}]*|(?R))*)\}/

仅在大括号正确嵌套的情况下匹配.当然，它们不在您的字符串中.

only matches if the braces are nested correctly. Which they aren't, of course, in your string.

现在的问题是，您的正则表达式需要找出可以使用106 a生成的所有可能的字符串组合，以找出原因，因为您有嵌套的量词((...)*)*).哪个(如果我错了，请纠正我)应该在106!的附近

Now the problem is that your regex needs to figure out all possible string combinations you can build with 106 as to figure that out because you have nested quantifiers ((...)*)*). Which (correct me if I'm wrong) should be somewhere in the vicinity of 106! which comes to

114628056373470835453434738414834942870388487424139673389282723476762012382449946252660360871841673476016298287096435143747350528228224302506311680000000000000000000000000

轻松击败您的PREG_BACKTRACK_LIMIT.

which easily beats your PREG_BACKTRACK_LIMIT.

如果您使用所有量词，以确保您永远不会回溯到您已经匹配的非大括号，那么您应该没问题:

If you use possessive quantifiers to make sure that you'll never backtrack into the non-braces you've already matched, then you should be OK:

/\{(([^{}]*+|(?R))*)\}/

这篇关于PHP:意外PREG_BACKTRACK_LIMIT_ERROR的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！