正则表达式引擎是否会跳过比模式短的字符串？

我想循环一组字符串。在每个字符串上，我想循环遍历一组正则表达式，以确定哪些表达式与我所在的字符串匹配。但是，如果字符串长度短于模式字符串的最大可能长度，我希望正则表达式引擎跳过它。

例如，假设我停在字符串“abc”上 并用这个正则表达式测试它。

(?i)[A-Z]{3}

它匹配。然后我要测试的下一个表达式就像

(?i)[A-Z]+(?=123)

即使第二种情况永远不会匹配，引擎是否仍会从头开始检查字符串？

如果是这种情况，有没有办法让它跳过不满足最小长度要求的字符串？

当您了解实现细节并且源代码可用时，最好的判断方法就是简单地查看它。 :)

简短的回答是：不完全是.

.NET 正则表达式实现中实现的优化是博耶-摩尔字符串搜索作为匹配的第一阶段如果可能。看看源代码对于血淋淋的细节。

从代码本身来看：

// The RegexBoyerMoore object precomputes the Boyer-Moore
// tables for fast string scanning. These tables allow
// you to scan for the first occurance of a string within
// a large body of text without examining every character.
// The performance of the heuristic depends on the actual
// string and the text being searched, but usually, the longer
// the string that is being searched for, the fewer characters
// need to be examined.

这需要一个锚定prefix，其搜索方式为这个功能，其评论说：

/*
 * This is the one of the only two functions that should be called from outside.
 * It takes a RegexTree and computes the set of chars that can start it.
 */

匹配算法包含返回一个no match如果输入字符串短于计算的前缀，则立即结果。

请注意，它也在寻找anchors当然，并针对这些进行优化。

I did not find a minimum length optimization in the code, but I admit I didn't read it thoroughly _{(gotta do that one day)}. But I know other regex implementations which do this kind of optimization (PCRE comes to mind). Anyway, the .NET implementation has its own way of optimizing things, you should rely on that.