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Replace Method (String, MatchEvaluator, Int32, Int32)

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

In 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
Assemblies:   System.Text.RegularExpressions (in System.Text.RegularExpressions.dll)
  System (in System.dll)

public string Replace(
	string input,
	MatchEvaluator evaluator,
	int count,
	int startat
)

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.

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. If the regular expression pattern is not matched in the current instance, the method returns the current instance unchanged.

ExceptionCondition
ArgumentNullException

input or evaluator is null.

ArgumentOutOfRangeException

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

RegexMatchTimeoutException

A time-out occurred. For more information about time-outs, see the Remarks section.

The Regex.Replace(String, MatchEvaluator, Int32, Int32) 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, Int32) method and passing the first count Match 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 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

Because the method returns input unchanged if there is no match, you can use the Object.ReferenceEquals method to determine whether the method has made any replacements to the input string.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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