正则表达式(2)

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原文链接：http://www.cnblogs.com/bo-bo/archive/2009/06/21/1507689.html

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本文介绍了.NET Framework中正则表达式的使用方法，包括Regex类、Match类、MatchCollection类、GroupCollection类、CaptureCollection类、Group类和Capture类的详细应用示例。

以下各节介绍 .NET Framework 正则表达式类。

Regex

类表示不可变（只读）正则表达式类。它还包含各种静态方法，允许在不显式创建其他类的实例的情况下使用其他正则表达式类。

以下代码示例创建了 Regex 类的实例并在初始化对象时定义一个简单的正则表达式。请注意，使用了附加的反斜杠作为转义字符，它将 \s 匹配字符类中的反斜杠指定为原义字符。

[Visual Basic]
    ' Declare object variable of type Regex.
    Dim r As Regex 
    ' Create a Regex object and define its regular expression.
    r = New Regex("\s2000")

[C#]
    // Declare object variable of type Regex.
    Regex r; 
    // Create a Regex object and define its regular expression.
    r = new Regex("\\s2000");

Match

类表示正则表达式匹配操作的结果。以下示例使用 Regex 类的 Match 方法返回 Match 类型的对象，以便找到输入字符串中的第一个匹配项。此示例使用 Match 类的属性来指示是否已找到匹配。

[Visual Basic]
    ' cCreate a new Regex object.
    Dim r As New Regex("abc") 
    ' Find a single match in the input string.
    Dim m As Match = r.Match("123abc456") 
    If m.Success Then
        ' Print out the character position where a match was found. 
        ' (Character position 3 in this case.)
        Console.WriteLine("Found match at position " & m.Index.ToString())
    End If

[C#]
    // Create a new Regex object.
    Regex r = new Regex("abc"); 
    // Find a single match in the string.
    Match m = r.Match("123abc456"); 
    if (m.Success) 
    {
        // Print out the character position where a match was found. 
        // (Character position 3 in this case.)
        Console.WriteLine("Found match at position " + m.Index);
    }

MatchCollection

类表示成功的非重叠匹配的序列。该集合为不可变（只读）的，并且没有公共构造函数。MatchCollection 的实例是由 Regex.Matches 属性返回的。

以下示例使用 Regex 类的方法，通过在输入字符串中找到的所有匹配填充 MatchCollection。该示例将此集合复制到一个字符串数组和一个整数数组中，其中字符串数组用以保存每个匹配项，整数数组用以指示每个匹配项的位置。

[Visual Basic]
    Dim mc As MatchCollection
    Dim results(20) As String
    Dim matchposition(20) As Integer

    ' Create a new Regex object and define the regular expression.
    Dim r As New Regex("abc")
    ' Use the Matches method to find all matches in the input string.
    mc = r.Matches("123abc4abcd")
    ' Loop through the match collection to retrieve all 
    ' matches and positions.
    Dim i As Integer
    For i = 0 To mc.Count - 1
        ' Add the match string to the string array.
        results(i) = mc(i).Value
        ' Record the character position where the match was found.
        matchposition(i) = mc(i).Index
    Next i

[C#]
    MatchCollection mc;
    String[] results = new String[20];
    int[] matchposition = new int[20];

    // Create a new Regex object and define the regular expression.
    Regex r = new Regex("abc"); 
    // Use the Matches method to find all matches in the input string.
    mc = r.Matches("123abc4abcd");
    // Loop through the match collection to retrieve all 
    // matches and positions.
    for (int i = 0; i < mc.Count; i++) 
    {
        // Add the match string to the string array.   
        results[i] = mc[i].Value;
        // Record the character position where the match was found.
        matchposition[i] = mc[i].Index;   
    }

GroupCollection

类表示捕获的组的集合并返回单个匹配中捕获的组的集合。该集合为不可变（只读）的，并且没有公共构造函数。GroupCollection 的实例在 Match.Groups 属性返回的集合中返回。

以下控制台应用程序示例查找并输出由正则表达式捕获的组的数目。有关如何提取组集合的每一成员中的各个捕获项的示例，请参见下面一节的 Capture Collection 示例。

[Visual Basic]
    Imports System
    Imports System.Text.RegularExpressions

    Public Class RegexTest
        Public Shared Sub RunTest()
            ' Define groups "abc", "ab", and "b".
            Dim r As New Regex("(a(b))c") 
            Dim m As Match = r.Match("abdabc")
            Console.WriteLine("Number of groups found = " _
            & m.Groups.Count.ToString())
        End Sub    

        Public Shared Sub Main()
            RunTest()
        End Sub
    End Class

[C#]
    using System;
    using System.Text.RegularExpressions;

    public class RegexTest 
    {
        public static void RunTest() 
        {
            // Define groups "abc", "ab", and "b".
            Regex r = new Regex("(a(b))c"); 
            Match m = r.Match("abdabc");
            Console.WriteLine("Number of groups found = " + m.Groups.Count);
        }
        public static void Main() 
        {
            RunTest();
        }
    }

该示例产生下面的输出。

[Visual Basic]
    Number of groups found = 3

[C#]
    Number of groups found = 3

CaptureCollection

类表示捕获的子字符串的序列，并且返回由单个捕获组执行的捕获的集合。由于，捕获组可以在单个匹配中捕获多个字符串。Captures 属性（CaptureCollection 类的对象）是作为和类的成员提供的，以便于对捕获的子字符串的集合的访问。

例如，如果使用正则表达式 ((a(b))c)+（其中 + 限定符指定一个或多个匹配）从字符串“abcabcabc”中捕获匹配，则子字符串的每一匹配的 Group 的 CaptureCollection 将包含三个成员。

以下控制台应用程序示例使用正则表达式 (Abc)+ 来查找字符串“XYZAbcAbcAbcXYZAbcAb”中的一个或多个匹配。该示例阐释了使用 Captures 属性来返回多组捕获的子字符串。

[Visual Basic]
    Imports System
    Imports System.Text.RegularExpressions

    Public Class RegexTest
        Public Shared Sub RunTest()
            Dim counter As Integer
            Dim m As Match
            Dim cc As CaptureCollection
            Dim gc As GroupCollection
            ' Look for groupings of "Abc".
            Dim r As New Regex("(Abc)+") 
            ' Define the string to search.
            m = r.Match("XYZAbcAbcAbcXYZAbcAb")
            gc = m.Groups

            ' Print the number of groups.
            Console.WriteLine("Captured groups = " & gc.Count.ToString())

            ' Loop through each group.
            Dim i, ii As Integer
            For i = 0 To gc.Count - 1
                cc = gc(i).Captures
                counter = cc.Count

                ' Print number of captures in this group.
                Console.WriteLine("Captures count = " & counter.ToString())

                ' Loop through each capture in group.            
                For ii = 0 To counter - 1
                    ' Print capture and position.
                    Console.WriteLine(cc(ii).ToString() _
                        & "   Starts at character " & cc(ii).Index.ToString())
                Next ii
            Next i
        End Sub

        Public Shared Sub Main()
            RunTest()
         End Sub
    End Class

[C#]
    using System;
    using System.Text.RegularExpressions;

    public class RegexTest 
        {
        public static void RunTest() 
        {
            int counter;
            Match m;
            CaptureCollection cc;
            GroupCollection gc;

            // Look for groupings of "Abc".
            Regex r = new Regex("(Abc)+"); 
            // Define the string to search.
            m = r.Match("XYZAbcAbcAbcXYZAbcAb"); 
            gc = m.Groups;

            // Print the number of groups.
            Console.WriteLine("Captured groups = " + gc.Count.ToString());

            // Loop through each group.
            for (int i=0; i < gc.Count; i++) 
            {
                cc = gc[i].Captures;
                counter = cc.Count;

                // Print number of captures in this group.
                Console.WriteLine("Captures count = " + counter.ToString());

                // Loop through each capture in group.
                for (int ii = 0; ii < counter; ii++) 
                {
                    // Print capture and position.
                    Console.WriteLine(cc[ii] + "   Starts at character " + 
                        cc[ii].Index);
                }
            }
        }

        public static void Main() {
            RunTest();
        }
    }

此示例返回下面的输出结果。

[Visual Basic]
    Captured groups = 2
    Captures count = 1
    AbcAbcAbc   Starts at character 3
    Captures count = 3
    Abc   Starts at character 3
    Abc   Starts at character 6
    Abc   Starts at character 9

[C#]
    Captured groups = 2
    Captures count = 1
    AbcAbcAbc   Starts at character 3
    Captures count = 3
    Abc   Starts at character 3
    Abc   Starts at character 6
    Abc   Starts at character 9

Group

类表示来自单个捕获组的结果。因为 Group 可以在单个匹配中捕获零个、一个或更多的字符串（使用限定符），所以它包含 Capture 对象的集合。因为 Group 继承自 Capture，所以可以直接访问最后捕获的子字符串（Group 实例本身等价于 Captures 属性返回的集合的最后一项）。

Group 的实例是由 Match.Groups(groupnum) 属性返回的，或者在使用“(?<groupname>)”分组构造的情况下，是由 Match.Groups("groupname") 属性返回的。

以下代码示例使用嵌套的分组构造来将子字符串捕获到组中。

[Visual Basic]
    Dim matchposition(20) As Integer
    Dim results(20) As String
    ' Define substrings abc, ab, b.
    Dim r As New Regex("(a(b))c") 
    Dim m As Match = r.Match("abdabc")
    Dim i As Integer = 0
    While Not (m.Groups(i).Value = "")    
       ' Copy groups to string array.
       results(i) = m.Groups(i).Value     
       ' Record character position. 
       matchposition(i) = m.Groups(i).Index 
        i = i + 1
    End While

[C#]
    int[] matchposition = new int[20];
    String[] results = new String[20];
    // Define substrings abc, ab, b.
    Regex r = new Regex("(a(b))c"); 
    Match m = r.Match("abdabc");
    for (int i = 0; m.Groups[i].Value != ""; i++) 
    {
        // Copy groups to string array.
        results[i]=m.Groups[i].Value; 
        // Record character position.
        matchposition[i] = m.Groups[i].Index; 
    }

此示例返回下面的输出结果。

[Visual Basic]
    results(0) = "abc"   matchposition(0) = 3
    results(1) = "ab"    matchposition(1) = 3
    results(2) = "b"     matchposition(2) = 4

[C#]
    results[0] = "abc"   matchposition[0] = 3
    results[1] = "ab"    matchposition[1] = 3
    results[2] = "b"     matchposition[2] = 4

以下代码示例使用命名的分组构造，从包含“DATANAME:VALUE”格式的数据的字符串中捕获子字符串，正则表达式通过冒号“:”拆分数据。

[Visual Basic]
    Dim r As New Regex("^(?<name>\w+):(?<value>\w+)")
    Dim m As Match = r.Match("Section1:119900")

[C#]
    Regex r = new Regex("^(?<name>\\w+):(?<value>\\w+)");
    Match m = r.Match("Section1:119900");

此正则表达式返回下面的输出结果。

[Visual Basic]
    m.Groups("name").Value = "Section1"
    m.Groups("value").Value = "119900"

[C#]
    m.Groups["name"].Value = "Section1"
    m.Groups["value"].Value = "119900"

Capture

类包含来自单个子表达式捕获的结果。

以下示例在 Group 集合中循环，从 Group 的每一成员中提取 Capture 集合，并且将变量 posn 和 length 分别分配给找到每一字符串的初始字符串中的字符位置，以及每一字符串的长度。

[Visual Basic]
    Dim r As Regex
    Dim m As Match
    Dim cc As CaptureCollection
    Dim posn, length As Integer

    r = New Regex("(abc)*")
    m = r.Match("bcabcabc")
    Dim i, j As Integer
    i = 0
    While m.Groups(i).Value <> ""
        ' Grab the Collection for Group(i).
        cc = m.Groups(i).Captures
        For j = 0 To cc.Count - 1
            ' Position of Capture object.
            posn = cc(j).Index
            ' Length of Capture object.
            length = cc(j).Length
        Next j
        i += 1
    End While

[C#]
    Regex r;
    Match m;
    CaptureCollection cc;
    int posn, length;

    r = new Regex("(abc)*");
    m = r.Match("bcabcabc");
    for (int i=0; m.Groups[i].Value != ""; i++) 
    {
        // Capture the Collection for Group(i).
        cc = m.Groups[i].Captures; 
        for (int j = 0; j < cc.Count; j++) 
        {
            // Position of Capture object.
            posn = cc[j].Index; 
            // Length of Capture object.
            length = cc[j].Length; 
        }
    }