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Regex.IsMatch Method (String, Int32)

Updated: September 2009

Indicates whether the regular expression specified in the Regex constructor finds a match in the input string beginning at the specified starting position in the string.

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

public bool IsMatch(
	string input,
	int startat


Type: System.String

The string to search for a match.

Type: System.Int32

The character position at which to start the search.

Return Value

Type: System.Boolean
true if the regular expression finds a match; otherwise, false.


input is null.


startat cannot be less than zero or greater than the length of input.

The IsMatch method is typically used to validate a string or to ensure that a string conforms to a particular pattern without retrieving that string for subsequent manipulation. To determine whether one or more strings match a regular expression pattern and to retrieve them for subsequent manipulation, call the Match or Matches method.

The following example illustrates the use of the IsMatch(String, Int32) method to determine whether a string is a valid part number. It searches for a part number that follows a colon (:) character in a string. The IndexOf(Char) method is used to determine the position of the colon character, which is then passed to the IsMatch(String, Int32) method. The regular expression assumes that the part number has a specific format that consists of three sets of characters separated by hyphens. The first set, which contains four characters, must consist of an alphanumeric character followed by two numeric characters followed by an alphanumeric character. The second set, which consists of three characters, must be numeric. The third set, which consists of four characters, must have three numeric characters followed by an alphanumeric character.

using System;
using System.Text.RegularExpressions;

public class Example
   public static void Main()
      string[] partNumbers= { "Part Number: 1298-673-4192", "Part No: A08Z-931-468A", 
                              "_A90-123-129X", "123K-000-1230", 
                              "SKU: 0919-2893-1256" };
      Regex rgx = new Regex(@"[a-zA-Z0-9]\d{2}[a-zA-Z0-9](-\d{3}){2}[A-Za-z0-9]$");
      foreach (string partNumber in partNumbers)
         int start = partNumber.IndexOf(':');
         if (start >= 0)
            Console.WriteLine("{0} {1} a valid part number.", 
                              rgx.IsMatch(partNumber, start) ? "is" : "is not");
            Console.WriteLine("Cannot find starting position in {0}.", partNumber);
// The example displays the following output: 
//       Part Number: 1298-673-4192 is a valid part number. 
//       Part No: A08Z-931-468A is a valid part number. 
//       Cannot find starting position in _A90-123-129X. 
//       Cannot find starting position in 123K-000-1230. 
//       SKU: 0919-2893-1256 is not a valid part number.

The regular expression pattern is:


The following table shows how the regular expression pattern is interpreted.




Match a single alphabetic character (a through z or A through Z) or numeric character.


Match two numeric characters.


Match a single alphabetic character (a through z or A through Z) or numeric character.


Match a hyphen.


Match exactly three numeric characters.


Find a hyphen followed by three numeric characters, and match two occurrences of this pattern.


Match a single alphabetic character (a through z or A through Z) or numeric character.


End the match at the end of the line.

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.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0




September 2009

Modified the regular expression in the example.

Customer feedback.

February 2009

Added remarks and an example.

Customer feedback.