Regex.Replace Method (String, MatchEvaluator, Int32, Int32)

Within a specified input substring, replaces a specified maximum number of strings that match a regular expression pattern with a string returned by a MatchEvaluator delegate.

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


Public Function Replace ( _
    input As String, _
    evaluator As MatchEvaluator, _
    count As Integer, _
    startat As Integer _
) As String
public string Replace(
    string input,
    MatchEvaluator evaluator,
    int count,
    int startat


  • count
    Type: System.Int32
    The maximum number of times the replacement will occur.
  • startat
    Type: System.Int32
    The character position in the input string where the search begins.

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.


Exception Condition

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


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


startat is less than zero or greater than the length of input.


The Regex.Replace 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 method and passing the first countMatch objects 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 Function MatchEvaluatorMethod(ByVal match As Match) As String
public string MatchEvaluatorMethod(Match match)

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

Version Information


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0


For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.