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Regex.Split Method (String, Int32, Int32)

Updated: July 2009

Splits the specified input string a specified maximum number of times at the positions defined by a regular expression specified in the Regex constructor. The search for the regular expression pattern starts at a specified character position in the input string.

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

public string[] Split(
	string input,
	int count,
	int startat
)

Parameters

input
Type: System.String

The string to be split.

count
Type: System.Int32

The maximum number of times the split can occur.

startat
Type: System.Int32

The character position in the input string where the search will begin.

Return Value

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

ExceptionCondition
ArgumentNullException

input is null.

ArgumentOutOfRangeException

startat is less than zero or greater than the length of input.

The Regex.Split methods are similar to the String.Split method, except this method splits the string at a delimiter determined by a regular expression instead of a set of characters. The count parameter specifies the maximum number of substrings into which the input string is split; the last string contains the unsplit remainder of the string. A count value of zero provides the default behavior of splitting as many times as possible. The startat parameter defines the point at which the search for the first delimiter begins (this can be used for skipping leading white space).

If no matches are found from the count+1 position in the string, the method returns a one-element array that contains the input string. If one or more matches are found, the first element of the returned array contains the first portion of the string from the first character up to one character before the match.

If multiple matches are adjacent to one another and the number of matches found is at least two less than count, an empty string is inserted into the array. That is, empty strings that result from adjacent matches are counted in determining whether the number of matched substrings equals count.

If capturing parentheses are used in a regular expression, any captured text is included in the array of split strings. However, any array elements that contain captured text are not counted in determining whether the number of matches has reached count. For example, splitting the string '"apple-apricot-plum-pear-pomegranate-pineapple-peach" into a maximum of four substrings beginning at character 15 in the string results in a seven-element array, as the following code shows.

string pattern = "(-)";
string input = "apple-apricot-plum-pear-pomegranate-pineapple-peach";

// Split on hyphens from 15th character on
Regex regex = new Regex(pattern);    
// Split on hyphens from 15th character on
string[] substrings = regex.Split(input, 4, 15);
foreach (string match in substrings)
{
   Console.WriteLine("'{0}'", match);
}
// The method writes the following to the console: 
//    'apple-apricot-plum' 
//    '-' 
//    'pear' 
//    '-' 
//    'pomegranate' 
//    '-' 
//    'pineapple-peach'      

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 .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 individual words in a string. The first set of capturing parentheses captures the hyphen, while the second set captures the vertical bar. If the sample code is compiled and run under the .NET Framework 1.0 or 1.1, it excludes the vertical bar characters; if it is compiled and run under the .NET Framework 2.0, it includes them.

string pattern = "(-)|([|])";     // possible delimiters found in string
string input = "apple|apricot|plum|pear|pomegranate|pineapple|peach";

Regex regex = new Regex(pattern);    
// Split on delimiters from 15th character on
string[] substrings = regex.Split(input, 4, 15);
foreach (string match in substrings)
{
   Console.WriteLine("'{0}'", match);
}
// In .NET 2.0, the method returns an array of 
// 7 elements, as follows: 
//    apple|apricot|plum' 
//    '|' 
//    'pear' 
//    '|' 
//    'pomegranate' 
//    '|' 
//    'pineapple|peach' 
// In .NET 1.0 and 1.1, the method returns an array of 
// 4 elements, as follows: 
//    'apple|apricot|plum' 
//    'pear' 
//    'pomegranate' 
//    'pineapple|peach'

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. The following example splits the string "characters" into as many elements as the input string contains, starting with the character "a". Because the null string matches the end of the input string, a null string is inserted at the end of the returned array.

string input = "characters";
Regex regex = new Regex("");
string[] substrings = regex.Split(input, input.Length, input.IndexOf("a"));
Console.Write("{");
for(int ctr = 0; ctr < substrings.Length; ctr++)
{
   Console.Write(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, rs}

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

Included additional exception information.

Content bug fix.

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