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.
Assemblies: System.Text.RegularExpressions (in System.Text.RegularExpressions.dll)
System (in System.dll)
public string Replace( string input, MatchEvaluator evaluator, int count, int startat )
- Type: System.String
The string to search for a match.
- Type: System.Text.RegularExpressions.MatchEvaluator
A custom method that examines each match and returns either the original matched string or a replacement string.
- Type: System.Int32
The maximum number of times the replacement will occur.
- Type: System.Int32
The character position in the input string where the search begins.
Return ValueType: 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.
The 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 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.
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.