使用Regex解析C样式注释，避免回溯 [英] Parse C-Style Comments with Regex, avoid Backtracking

问题描述

我想匹配JavaScript文件中的所有块和多行注释(这些是C样式注释).我有一个运作良好的模式.但是，它会产生一些回溯，从而大大降低速度，尤其是在较大的文件上.

I want to match all block and multiline comments in a JavaScript file (these are C-Style comments). I have a pattern that works well. However, it creates some backtracking which slows it down significantly, especially on larger files.

模式:\/\*(?:.|[\r\n])*?\*\/|(?:\/\/.*)

示例: https://www.regex101.com/r/pR6eH6/2

如何避免回溯?

推荐答案

由于交替，您的回溯很重.您可以考虑使用字符类[\s\S]代替(?:.|[\r\n])，从而将性能显着提高:

You have heavy backtracking because of the alternation. Instead of the (?:.|[\r\n]), you may consider using a character class [\s\S] that boosts performance to a noticeable extent:

\/\*[\s\S]*?\*\/|\/\/.*

请参见演示

在Python中，您也可以使用re.S/re.DOTALL修饰符使.匹配换行符(请注意，单行注释模式应与\/\/[^\r\n]*匹配):

In Python, you can use the re.S/re.DOTALL modifier to make . match line breaks, too (note that the single line comment pattern should be matched with \/\/[^\r\n]* then):

/\*.*?\*/|//[^\r\n]*

请参见另一个演示

但是，由于*? 惰性量词也会导致类似于贪婪量词所引起的开销，因此对于 C样式多行注释-/\*[^*]*\*+(?:[^/*][^*]*\*+)*/，以及整个正则表达式现在看起来像:

However, since *? lazy quantifier will also cause an overhead similar to the one caused by greedy quantifiers, you should consider using a much more optimal pattern for C style multiline comments - /\*[^*]*\*+(?:[^/*][^*]*\*+)*/, and the whole regex will now look like:

/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//.*

请参见另一个演示

详细信息:

• /\*-一个/*
• [^*]*-除*
之外的零个或多个字符
• \*+-一个或多个星号
• (?:[^/*][^*]*\*+)*-零个或多个序列:
  • [^/*]-除/和*
  以外的其他符号
  • [^*]*-除*
  以外的零个或多个符号
  • \*+-1个以上星号
  • /\* - a /*
  • [^*]* - zero or more chars other than *
  • \*+ - one or more asterisks
  • (?:[^/*][^*]*\*+)* - zero or more sequences of:
    • [^/*] - a symbol other than / and *
    • [^*]* - zero or more symbols other than *
    • \*+ - 1+ asterisks

    只是要注意，在Python中，您不需要转义/(在JS中，使用RegExp构造函数声明正则表达式时，您无需转义/).

    Just wanted to note that in Python, you do not need to escape / (in JS, you do not need to escape / when declaring a regex using the RegExp constuctor).

    注意:最后一个模式不允许简单地捕获/*和*/内部的内容，但是由于该模式比其他模式更稳定，因此我建议即使在以下情况下也要使用它:您需要使用尾随*-/\*([^*]*\*+(?:[^/*][^*]*\*+)*)/|//(.*)-捕获内容，然后需要从.group(1)中删除最后一个字符.

    NOTE: The last pattern does not allow simple capturing what is inside /* and */, but since the pattern is more stable than the rest, I'd advise using it even when you need to capture the contents with the trailing * - /\*([^*]*\*+(?:[^/*][^*]*\*+)*)/|//(.*) - and then you'd need to remove the last char from .group(1).

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