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Regex.Split Method (String, String)

Updated: July 2009

Splits the input string at the positions defined by a regular expression pattern.

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

public static string[] Split(
	string input,
	string pattern
)

Parameters

input
Type: System.String

The string to split.

pattern
Type: System.String

The regular expression pattern to match.

Return Value

Type: System.String[]
An array of strings.

ExceptionCondition
ArgumentException

A regular expression parsing error has occurred.

ArgumentNullException

input is null.

-or-

pattern is null.

The Regex.Split methods are similar to the String.Split method, except Split splits the string at a delimiter determined by a regular expression instead of a set of characters. The input string is split as many times as possible. If pattern is not found in the input string, the return value contains one element whose value is the original input parameter string.

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.

Important noteImportant Note:

Compiled regular expressions used in calls to static Split methods are automatically cached. To manage the lifetime of compiled regular expressions yourself, use the instance Split methods.

If multiple matches are adjacent to one another, an empty string is inserted into the array. For example, splitting a string on a single hyphen causes the returned array to include an empty string in the position where two adjacent hyphens are found, as the following code shows.

string input = "plum--pear";
string pattern = "-";            // Split on hyphens

string[] substrings = Regex.Split(input, pattern);
foreach (string match in substrings)
{
   Console.WriteLine("'{0}'", match);
}
// The method writes the following to the console: 
//    'plum' 
//    '' 
//    'pear'      

If capturing parentheses are used in a Regex.Split expression, any captured text is included in the resulting string array. For example, splitting the string " plum-pear" on a hyphen placed within capturing parentheses adds a string element that contains the hyphen to the returned array.

string input = "plum-pear";
string pattern = "(-)";

string[] substrings = Regex.Split(input, pattern);    // Split on hyphens 
foreach (string match in substrings)
{
   Console.WriteLine("'{0}'", match);
}
// The method writes the following to the console: 
//    'plum' 
//    '-' 
//    'pear'      

However, when the regular expression pattern includes multiple sets of capturing parentheses, the behavior of this method depends on the version of the .NET Framework. In the .NET Framework versions 1.0 and 1.1, if a match is not found within the first set of capturing parentheses, captured text from additional capturing parentheses is not included in the returned array. In the .NET Framework version 2.0, all captured text is also added to the returned array. For example, the following code uses two sets of capturing parentheses to extract the elements of a date, including the date delimiters, from a date string. The first set of capturing parentheses captures the hyphen, while the second set captures the forward slash. If the sample code is compiled and run under the .NET Framework 1.0 or 1.1, it excludes the slash characters; if it is compiled and run under the .NET Framework 2.0, it includes them.

string input = @"07/14/2007";   
string pattern = @"(-)|(/)";

foreach (string result in Regex.Split(input, pattern)) 
{
   Console.WriteLine("'{0}'", result);
}
// In .NET 1.0 and 1.1, the method returns an array of 
// 3 elements, as follows: 
//    '07' 
//    '14' 
//    '2007' 
// 
// In .NET 2.0, the method returns an array of 
// 5 elements, as follows: 
//    '07' 
//    '/' 
//    '14' 
//    '/' 
//    '2007' 

If the regular expression can match the empty string, Split will split the string into an array of single-character strings because the empty string delimiter can be found at every location. For example:

string input = "characters";
string[] substrings = Regex.Split(input, "");
Console.Write("{");
for(int ctr = 0; ctr < substrings.Length; ctr++)
{
   Console.Write("'{0}'", substrings[ctr]);
   if (ctr < substrings.Length - 1)
      Console.Write(", ");
}
Console.WriteLine("}");
// The example produces the following output:    
//    {'', 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r', 's', ''}

Note that the returned array also includes an empty string at the beginning and end of the array.

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

Date

History

Reason

July 2009

Added exception information.

Content bug fix.

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