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Capture Class

Updated: August 2009

Represents the results from a single subexpression capture.

Namespace:  System.Text.RegularExpressions
Assembly:  System (in System.dll)

[SerializableAttribute]
public class Capture

A Capture object is immutable and has no public constructor. Instances are returned through the CaptureCollection object, which is returned by the Match.Captures and Group.Captures properties. However, the Match.Captures property provides information about the same match as the Match object.

If you do not apply a quantifier to a capturing group, the Group.Captures property returns a CaptureCollection with a single Capture object that provides information about the same capture as the Group object. If you do apply a quantifier to a capturing group, the Group.Index, Group.Length, and Group.Value properties provide information only about the last captured group, whereas the Capture objects in the CaptureCollection provide information about all subexpression captures. The example provides an illustration.

The following example defines a regular expression that matches sentences that contain no punctuation except for a period (".").

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Main()
   {
      string input = "Yes. This dog is very friendly.";
      string pattern = @"((\w+)[\s.])+";
      foreach (Match match in Regex.Matches(input, pattern))
      {
         Console.WriteLine("Match: {0}", match.Value);
         for (int groupCtr = 0; groupCtr < match.Groups.Count; groupCtr++)
         {
            Group group = match.Groups[groupCtr];
            Console.WriteLine("   Group {0}: {1}", groupCtr, group.Value);
            for (int captureCtr = 0; captureCtr < group.Captures.Count; captureCtr++)
               Console.WriteLine("      Capture {0}: {1}", captureCtr, 
                                 group.Captures[captureCtr].Value);
         }                      
      }
   }
}
// The example displays the following output: 
//       Match: Yes. 
//          Group 0: Yes. 
//             Capture 0: Yes. 
//          Group 1: Yes. 
//             Capture 0: Yes. 
//          Group 2: Yes 
//             Capture 0: Yes 
//       Match: This dog is very friendly. 
//          Group 0: This dog is very friendly. 
//             Capture 0: This dog is very friendly. 
//          Group 1: friendly. 
//             Capture 0: This 
//             Capture 1: dog 
//             Capture 2: is 
//             Capture 3: very 
//             Capture 4: friendly. 
//          Group 2: friendly 
//             Capture 0: This 
//             Capture 1: dog 
//             Capture 2: is 
//             Capture 3: very 
//             Capture 4: friendly

The regular expression pattern ((\w+)[\s.])+ is defined as shown in the following table. Note that in this regular expression, a quantifier is applied to the entire regular expression.

Pattern

Description

(\w+)

Match one or more word characters. This is the second capturing group.

[\s.])

Match a white-space character or period (".").

((\w+)[\s.])

Match one or more word characters followed by a white-space character or period ("."). This is the first capturing group.

((\w+)[\s.])+

Match one or more occurrences of a word character or characters followed by a white-space character or period (".").

In this example, the input string consists of two sentences. As the output shows, because the first sentence consists of only one word, the CaptureCollection object has a single Capture object that represents the same capture as the Group object. Because the second sentence consists of multiple words, the Group objects only contain information about the last matched subexpression. Group 1, which represents the first capture, contains the last word in the sentence with a closing period. Group 2, which represents the second capture, contains the last word in the sentence. However, the Capture objects in the group's CaptureCollection object capture each subexpression match. The Capture objects in the first capturing group's collection of captures contain information about each captured word and white-space character or period. The Capture objects in the second capturing group's collection of captures contain information about each captured word.

System.Object
  System.Text.RegularExpressions.Capture
    System.Text.RegularExpressions.Group

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

August 2009

Expanded the Remarks section and replaced the example.

Customer feedback.

July 2008

Standardized the example and example output for all languages.

Content bug fix.

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