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Regex Constructor (String, RegexOptions)

Initializes and compiles a new instance of the Regex class for the specified regular expression, with options that modify the pattern.

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

public Regex(
	string pattern,
	RegexOptions options


Type: System.String
The regular expression pattern to match.
Type: System.Text.RegularExpressions.RegexOptions
A bitwise combination of the enumeration values that modify the regular expression.


A regular expression parsing error occurred.


pattern is null.


options contains an invalid flag.

The pattern parameter consists of various regular expression language elements that symbolically describe the string to match. For more information about regular expressions, see the .NET Framework Regular Expressions and Regular Expression Language - Quick Reference topics.

A Regex object is immutable, which means that it can be used only for the match parameters defined when it is created. However, it can be used any number of times without being recompiled.

The following example illustrates how to use this constructor to instantiate a regular expression that matches any word that begins with the letters "a" or "t".

string pattern = @"\b[at]\w+";
RegexOptions options = RegexOptions.IgnoreCase | RegexOptions.Compiled;
string text = "The threaded application ate up the thread pool as it executed.";
MatchCollection matches;

Regex optionRegex = new Regex(pattern, options);
Console.WriteLine("Parsing '{0}' with options {1}:", text, options.ToString());
// Get matches of pattern in text
matches = optionRegex.Matches(text);
// Iterate matches
for (int ctr = 0; ctr < matches.Count; ctr++)
   Console.WriteLine("{0}. {1}", ctr, matches[ctr].Value);

Note that the match collection includes the word "The" that begins the text because the options parameter has defined case-insensitive comparisons.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.