Regex.Replace中的MatchEvaluator如何工作？ [英] How does MatchEvaluator in Regex.Replace work?

问题描述

这是输入字符串 23x * y34x2 。我想在每个数字后跟字母，以及在每个字母后跟数字后插入 * （用空格包围的星号）。因此，我的输出字符串如下所示： 23 * x * y * 34 * x * 2 。

This is the input string 23x * y34x2. I want to insert " * " (star surrounded by whitespaces) after every number followed by letter, and after every letter followed by number. So my output string would look like this: 23 * x * y * 34 * x * 2.

此是执行此操作的正则表达式： @ \d（？= [az]）| [az]（？= \d） 。这是我编写的插入 * 的函数。

This is the regex that does the job: @"\d(?=[a-z])|[a-z](?=\d)". This is the function that I wrote that inserts the " * ".

Regex reg = new Regex(@"\d(?=[a-z])|[a-z](?=\d)");   
MatchCollection matchC;
matchC = reg.Matches(input);
int ii = 1;
foreach (Match element in matchC)//foreach match I will find the index of that match
{
    input = input.Insert(element.Index + ii, " * ");//since I' am inserting " * " ( 3 characters )
    ii += 3;                                        //I must increment index by 3
}
return input; //return modified input

我的问题是如何使用.net做相同的工作 MatchEvaluator ？我是regex的新手，所以不理解用 MatchEvaluator 来代替它是不错的选择。这是我尝试编写的代码：

My question how to do same job using .net MatchEvaluator? I am new to regex and don't understand good replacing with MatchEvaluator. This is the code that I tried to wrote:

{
    Regex reg = new Regex(@"\d(?=[a-z])|[a-z](?=\d)");
    MatchEvaluator matchEval = new MatchEvaluator(ReplaceStar);
    input = reg.Replace(input, matchEval);
    return input;
}
public string ReplaceStar( Match match )
{
    //return What??
}

推荐答案

A MatchEvaluator 是接受Match的委托对象，并返回应替换而不是匹配的字符串。您也可以参考比赛中的组。您可以按以下方式重写代码：

A MatchEvaluator is a delegate that takes a Match object and returns a string that should be replaced instead of the match. You can also refer to groups from the match. You can rewrite your code as follows:

string input = "23x * y34x2";
Regex reg = new Regex(@"\d(?=[a-z])|[a-z](?=\d)");
string result = reg.Replace(input, delegate(Match m) {
    return m.Value + " * ";
});

举一个这样的例子，第一次调用该委托时，Match参数将是字符串 3 上的匹配项。在这种情况下，委托被定义为将匹配本身返回为由 * 连接的字符串。因此，第一个 3 被替换为 3 * 。

To give an example of how this works, the first time the delegate is called, Match parameter will be a match on the string "3". The delegate in this case is defined to return the match itself as a string concatenated with " * ". So the first "3" is replaced with "3 * ".

此过程将以这种方式继续进行，对于原始字符串中的每个匹配项，都会调用一次委托。

The process continues in this way, with delegate being called once for each match in the original string.

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