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MatchEvaluator Delegate

Represents the method that is called each time a regular expression match is found during a Replace method operation.

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

public delegate string MatchEvaluator(
	Match match


Type: System.Text.RegularExpressions.Match

The Match object that represents a single regular expression match during a Replace method operation.

Return Value

Type: System.String
A string returned by the method that is represented by the MatchEvaluator delegate.

You can use a MatchEvaluator delegate method to perform a custom verification or manipulation operation for each match found by a replacement method such as Regex.Replace(String, MatchEvaluator). For each matched string, the Replace method calls the MatchEvaluator delegate method with a Match object that represents the match. The delegate method performs whatever processing you prefer and returns a string that the Replace method substitutes for the matched string.

The following code example uses the MatchEvaluator delegate to replace every matched group of characters with the number of the match occurrence.

using System;
using System.Text.RegularExpressions;

class MyClass
   static void Main(string[] args)
      string sInput, sRegex;

      // The string to search.
      sInput = "aabbccddeeffcccgghhcccciijjcccckkcc";

      // A very simple regular expression.
      sRegex = "cc";

      Regex r = new Regex(sRegex);
      MyClass c = new MyClass();

      // Assign the replace method to the MatchEvaluator delegate.
      MatchEvaluator myEvaluator = new MatchEvaluator(c.ReplaceCC);
      // Write out the original string.

      // Replace matched characters using the delegate method.
      sInput = r.Replace(sInput, myEvaluator);

      // Write out the modified string.

   public string ReplaceCC(Match m)
   // Replace each Regex cc match with the number of the occurrence.
      return i.ToString() + i.ToString();		
   public static int i=0;
// The example displays the following output: 
//       aabbccddeeffcccgghhcccciijjcccckkcc 
//       aabb11ddeeff22cgghh3344iijj5566kk77

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