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.


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 Regular Expressions as a Language and Regular Expression Language Elements topics in the .NET Framework documentation.

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

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;
string text = "The threaded application ate up the thread pool as it executed.";
MatchCollection matches;

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

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


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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