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Regex.Replace Method (String, MatchEvaluator)

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)

public string Replace(
	string input,
	MatchEvaluator evaluator
)

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.

ExceptionCondition
ArgumentNullException

input or evaluator is null.

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.


public string MatchEvaluatorMethod(Match match)


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

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.


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 + "]");
    }
}
// The example displays the following output:
//       text=[four score and seven years ago]
//       result=[Four Score And Seven Years Ago]


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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