为什么正则表达式中的组无法正常工作 [英] Why are groups in regex doesn't works correctly

问题描述

Match match = Regex.Match(textBox1.Text, @"(\d)*(\d)");
         MessageBox.Show(match.Groups[1].Value.ToString());
             double x2 = Convert.ToDouble(match.Groups[1].Value.ToString());
             double x1 = Convert.ToInt32(match.Groups[2].Value.ToString());

             textBox1.Text = Regex.Replace(textBox1.Text, @"\d*\d", (x1 * x2).ToString());

我的尝试：



我一直在尝试编写数学解析器，我遇到了正则表达式组的问题，例如



textBox.Text = 2 * 2


和match.Groups [1] .Value为空。

What I have tried:

I have been trying to write a math parser and I catch a problem with regex groups for example

textBox.Text = 2*2

and match.Groups[1].Value is empty.

推荐答案

Quote：

为什么正则表达式中的组无法正常工作

Why are groups in regex doesn't works correctly

因为*在RegEx中有特殊含义，当你想要使用时它是文字的。你需要逃避*到\ *。



只是一些有趣的链接来帮助构建和调试RegEx。

这是一个链接到RegEx文档：

perlre - perldoc.perl.org [ ^ ]

以下是帮助构建RegEx和调试的工具的链接他们：

.NET Regex Tester - Regex Storm [ ^ ]

Expresso正则表达式工具 [ ^ ]

RegExr：Learn，Build，&测试RegEx [ ^ ]

在线正则表达式测试器和调试器：PHP，PCRE，Python，Golang和JavaScript [ ^ ]

这个显示RegEx是一个很好的图表，它非常有助于理解RegEx的作用： Debuggex：在线可视正则表达式测试器。 JavaScript，Python和PCRE。 [ ^ ]

此网站还在一个漂亮的图表中显示正则表达式，但无法测试与RegEx匹配的内容： Regexper [ ^ ]

Because * have a special meaning in RegEx, when you want to use it as literal. You need to escape * to \* .

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx: Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
This site also show the Regex in a nice graph but can't test what match the RegEx: Regexper[^]

为了更好地理解

For your better understanding

using System;
using System.Text.RegularExpressions;

namespace myApp
{
	class Program
	{
		static void Main(string[] args)
		{
			String chk = "5*6";
			Match match = Regex.Match(chk, @"(\d)\*(\d)");
			Console.WriteLine(match.Groups[0]);
			Console.WriteLine(match.Groups[1]);
			Console.WriteLine(match.Groups[2]);
		}
	}
}

结果：

Result:

myApp

dotnet run
5 * 6
5
6

dotnet run 5*6 5 6

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