Regex.Replace Method (String, MatchEvaluator) (System.Text.RegularExpressions)

.NET Framework Class Library

Regex..::.Replace Method (String, MatchEvaluator)

Updated: April 2009

Within a specified input string, replaces all strings that match a specified regular expression with a string returned by a MatchEvaluator delegate.

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

Syntax

Visual Basic (Declaration)

Public Function Replace ( _
    input As String, _
    evaluator As MatchEvaluator _
) As String

Visual Basic (Usage)

Dim instance As Regex
Dim input As String
Dim evaluator As MatchEvaluator
Dim returnValue As String

returnValue = instance.Replace(input, _
    evaluator)

public string Replace(
    string input,
    MatchEvaluator evaluator
)

Visual C++

public:
String^ Replace(
    String^ input, 
    MatchEvaluator^ evaluator
)

JScript

public function Replace(
    input : String, 
    evaluator : MatchEvaluator
) : String

Parameters

input: Type: System..::.String
The string to search for a match.

evaluator: Type: System.Text.RegularExpressions..::.MatchEvaluator
A custom method that examines each match and returns either the original matched string or a replacement string.

Return Value

Type: System..::.String
A new string that is identical to the input string, except that a replacement string takes the place of each matched string.

Exceptions

Exception	Condition
ArgumentNullException	input is nullNothingnullptra null reference (Nothing in Visual Basic). -or- evaluator is nullNothingnullptra null reference (Nothing in Visual Basic).

Exception

Condition

ArgumentNullException

input is nullNothingnullptra null reference (Nothing in Visual Basic).

-or-

evaluator is nullNothingnullptra null reference (Nothing in Visual Basic).

Remarks

The Regex..::.Replace(String, MatchEvaluator) method is useful for replacing a regular expression match if any of the following conditions is true:

The replacement string cannot readily be specified by a regular expression replacement pattern.
The replacement string results from some processing done on the matched string.
The replacement string results from conditional processing.

The method is equivalent to calling the Regex..::.Matches(String) method and passing each Match object in the returned MatchCollection collection to the evaluator delegate.

The regular expression is the pattern defined by the constructor for the current Regex object.

The evaluator parameter is the delegate for a custom method that you define and that examines each match. The custom method must have the following signature to match the MatchEvaluator delegate.

Visual Basic

Public Function MatchEvaluatorMethod(match As Match) As String
   Return String.Empty
End Function

public string MatchEvaluatorMethod(Match match)
{
   return String.Empty;
}

Your custom method returns a string that replaces the matched input.

Examples

The following code example displays an original string, matches each word in the original string, converts the first character of each match to uppercase, then displays the converted string.

Visual Basic

Imports System
Imports System.Text.RegularExpressions

Module RegExSample
    Function CapText(ByVal m As Match) As String
        ' Get the matched string.
        Dim x As String = m.ToString()
        ' If the first char is lower case...
        If Char.IsLower(x.Chars(0)) Then
            ' Capitalize it.
            Return Char.ToUpper(x.Chars(0)) & x.Substring(1, x.Length - 1)
        End If
        Return x
    End Function

    Sub Main()
        Dim text As String = "four score and seven years ago"

        System.Console.WriteLine("text=[" & text & "]")

        Dim rx As New Regex("\w+")

        Dim result As String = rx.Replace(text, AddressOf RegExSample.CapText)

        System.Console.WriteLine("result=[" & result & "]")
    End Sub
End Module

using System;
using System.Text.RegularExpressions;

class RegExSample
{
    static string CapText(Match m)
    {
        // Get the matched string.
        string x = m.ToString();
        // If the first char is lower case...
        if (char.IsLower(x[0]))
        {
            // Capitalize it.
            return char.ToUpper(x[0]) + x.Substring(1, x.Length - 1);
        }
        return x;
    }

    static void Main()
    {
        string text = "four score and seven years ago";

        System.Console.WriteLine("text=[" + text + "]");

        Regex rx = new Regex(@"\w+");

        string result = rx.Replace(text, new MatchEvaluator(RegExSample.CapText));

        System.Console.WriteLine("result=[" + result + "]");
    }
}

Platforms

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.

Version Information