Regex.Replace Method (String, MatchEvaluator)

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 RegexMatchTimeoutException exception is thrown if the execution time of the replacement operation exceeds the time-out interval specified by the Regex.Regex(String, RegexOptions, TimeSpan) constructor. If you do not set a time-out interval when you call the constructor, the exception is thrown if the operation exceeds any time-out value established for the application domain in which the Regex object is created. If no time-out is defined in the Regex constructor call or in the application domain's properties, or if the time-out value is Regex.InfiniteMatchTimeout, no exception is thrown

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

.NET Framework Client Profile

Portable Class Library

.NET for Windows Store apps

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Reference

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