在正则表达式的上下文中，“懒惰"和“贪婪"是什么意思? [英] What do 'lazy' and 'greedy' mean in the context of regular expressions?

问题描述

有人可以用一种可以理解的方式解释这两个术语吗?

Could someone explain these two terms in an understandable way?

推荐答案

Greedy将消耗尽可能多的东西.在 http://www.regular-expressions.info/repeat.html 中，我们看到了尝试将HTML标签与<.+>匹配的示例.假设您具有以下条件:

Greedy will consume as much as possible. From http://www.regular-expressions.info/repeat.html we see the example of trying to match HTML tags with <.+>. Suppose you have the following:

<em>Hello World</em>

您可能会认为<.+>(.表示任何非换行符，而+表示一个或多个)只会与<em>和</em>，实际上它会非常贪婪，并且从第一个<到最后一个>.这意味着它将匹配<em>Hello World</em>而不是您想要的.

You may think that <.+> (. means any non newline character and + means one or more) would only match the <em> and the </em>, when in reality it will be very greedy, and go from the first < to the last >. This means it will match <em>Hello World</em> instead of what you wanted.

使它变懒(<.+?>)将防止这种情况.通过在+之后添加?，我们告诉它重复尽可能少，因此遇到的第一个>是我们要停止匹配的位置.

Making it lazy (<.+?>) will prevent this. By adding the ? after the +, we tell it to repeat as few times as possible, so the first > it comes across, is where we want to stop the matching.

我建议您下载 RegExr ，这是一个很好的工具，可帮助您探索正则表达式-我一直都在用.

I'd encourage you to download RegExr, a great tool that will help you explore Regular Expressions - I use it all the time.

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