什么是间和QUOT的差值;组＆QUOT;和＆QUOT;捕获＆QUOT;在.NET正EX pressions？ [英] What's the difference between "groups" and "captures" in .NET regular expressions?

问题描述

我对什么是组和捕捉之间的区别是，当涉及到.NET的正前pression语言有点模糊。请考虑下面的C＃code：

I'm a little fuzzy on what the difference between a "group" and a "capture" are when it comes to .NET's regular expression language. Consider the following C# code:

MatchCollection matches = Regex.Matches("{Q}", @"^\{([A-Z])\}$");

我预计这将导致对字母Q一个捕捉，但如果我打印的返回属性MatchCollection ，我看到：

matches.Count: 1
matches[0].Value: {Q}
        matches[0].Captures.Count: 1
                matches[0].Captures[0].Value: {Q}
        matches[0].Groups.Count: 2
                matches[0].Groups[0].Value: {Q}
                matches[0].Groups[0].Captures.Count: 1
                        matches[0].Groups[0].Captures[0].Value: {Q}
                matches[0].Groups[1].Value: Q
                matches[0].Groups[1].Captures.Count: 1
                        matches[0].Groups[1].Captures[0].Value: Q

究竟是怎么回事？据我所知，还有一个捕获了整场比赛，但如何在群体进来吗？为什么不比赛[0] .Captures 包括捕获的字母Q？

What exactly is going on here? I understand that there's also a capture for the entire match, but how do the groups come in? And why doesn't matches[0].Captures include the capture for the letter 'Q'?

推荐答案

您不会是第一谁是模糊了。这里是著名的杰弗里·弗里德尔有什么看法（页437 +）：

You won't be the first who's fuzzy about it. Here's what the famous Jeffrey Friedl has to say about it (pages 437+):

根据您的看法，它要么增加   到一个有趣的新维度   匹配的结果，或者增加了困惑和   膨胀。

Depending on your view, it either adds an interesting new dimension to the match results, or adds confusion and bloat.

和进一步上：

一组之间的主要区别   对象和一个捕捉对象是   每个组对象都包含一个   收集捕获重新presenting   所有的中间的的匹配   组在比赛期间，以及   所匹配的组最后文本。

The main difference between a Group object and a Capture object is that each Group object contains a collection of Captures representing all the intermediary matches by the group during the match, as well as the final text matched by the group.

和几页之后，这是他的结论是：

And a few pages later, this is his conclusion:

在过去获得了.NET   文档和实际   了解了这些对象添加，   我得对他们百感交集。上   一方面，这是一个有趣   创新[..]另一方面，它   似乎添加效率负担[..]   的，将不使用的官能   在大多数情况下的

After getting past the .NET documentation and actually understanding what these objects add, I've got mixed feelings about them. On one hand, it's an interesting innovation [..] on the other hand, it seems to add an efficiency burden [..] of a functionality that won't be used in the majority of cases

在换句话说：他们是非常相似的，但偶尔，因为它发生时，你会发现他们使用。在你成长的另外一个花白胡子，你甚至可以让酷爱的捕捉...

In other words: they are very similar, but occasionally and as it happens, you'll find a use for them. Before you grow another grey beard, you may even get fond of the Captures...

由于没有上述情况，也没有发生的事情在其他帖子说似乎真的来回答你的问题，考虑以下。想捕捉的是一种历史跟踪器。当正则表达式，使他的比赛，它通过字符串由左到右（忽略回溯了一会儿），它遇到一个匹配的捕获括号的时候，它会存储在 $ X （x是任意数字），比方说 $ 1 。

Since neither the above, nor what's said in the other post really seems to answer your question, consider the following. Think of Captures as a kind of history tracker. When the regex makes his match, it goes through the string from left to right (ignoring backtracking for a moment) and when it encounters a matching capturing parentheses, it will store that in $x (x being any digit), let's say $1.

普通的正则表达式引擎，当捕获括号要重复，就会扔掉电流 $ 1 ，并与新的值将取代。没有.NET，这将让这段历史，并将其放在捕获[0] 。

Normal regex engines, when the capturing parentheses are to be repeated, will throw away the current $1 and will replace it with the new value. Not .NET, which will keep this history and places it in Captures[0].

如果我们改变你的正则表达式如下所示：

If we change your regex to look as follows:

MatchCollection matches = Regex.Matches("{Q}{R}{S}", @"(\{[A-Z]\})+");

您会发现，第一个集团将有一个捕获（第一个总是被整场比赛组，即等于 $ 1,0 ），第二组将举行 {S} ，即只在最后一个匹配的组。然而，这里的渔获物，如果你想找到另外两个锁扣，他们在捕获，其中包含所有的中介捕获了 {Q } {R} 和 {S} 。

you will notice that the first Group will have one Captures (the first group always being the whole match, i.e., equal to $0) and the second group will hold {S}, i.e. only the last matching group. However, and here's the catch, if you want to find the other two catches, they're in Captures, which contains all intermediary captures for {Q} {R} and {S}.

如果你有没有想过你怎么能得到从多个捕获，这只能说明过去的比赛已经明显出现字符串中的单个捕获，您必须使用捕获。

If you ever wondered how you could get from the multiple-capture, which only shows last match to the individual captures that are clearly there in the string, you must use Captures.

你的最后一个问题的最后一句话：总比赛总是有一个总的捕捉，不要混用，与各分组。捕获是唯一感兴趣的内部组的。

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