Regex.Replace Method (String, String, MatchEvaluator, RegexOptions)
Updated: September 2010
Within a specified input string, replaces all strings that match a specified regular expression with a string returned by a MatchEvaluator delegate. Specified options modify the matching operation.
Assembly: System (in System.dll)
public static function Replace( input : String, pattern : String, evaluator : MatchEvaluator, options : RegexOptions ) : String
- Type: System.String
The string to search for a match.
- Type: System.String
The regular expression pattern to 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.Text.RegularExpressions.RegexOptions
A bitwise OR combination of the enumeration values.
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.
A regular expression parsing error has occurred.
input is a null reference (Nothing in Visual Basic).
pattern is a null reference (Nothing in Visual Basic).
evaluator is a null reference (Nothing in Visual Basic).
options is not a valid bitwise combination of RegexOptions values.
The method is useful for replacing a regular expression match in 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 pattern parameter consists of various regular expression language elements that symbolically describe the string to match. For more information about regular expressions, see .NET Framework Regular Expressions and Regular Expression Language - Quick Reference.
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.
If the options parameter specifies the RightToLeft enumeration value, the search for matches begins from the end of the input string and proceeds from right to left; otherwise, the search begins from the start of the input string and proceeds from left to right.
The following example uses a regular expression to extract the individual words from a string, and then uses a MatchEvaluator delegate to call a method named WordScramble that scrambles the individual letters in the word. To do this, the WordScramble method creates an array that contains the characters in the match. It also creates a parallel array that it populates with random floating-point numbers. The arrays are sorted by calling the Array.Sort(TKey, TValue)(TKey, TValue, IComparer(TKey)) method, and the sorted array is provided as an argument to a String class constructor. This newly created string is then returned by the WordScramble method. The regular expression pattern \w+ matches one or more word characters; the regular expression engine will continue to add characters to the match until it encounters a non-word character, such as a white-space character. The call to the method includes the RegexOptions.IgnorePatternWhitespace option so that the comment in the regular expression pattern \w+ # Matches all the characters in a word. is ignored by the regular expression engine.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.