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String.LastIndexOf Method (String, Int32, Int32)

Updated: October 2010

Reports the zero-based index position of the last occurrence of a specified string within this instance. The search starts at a specified character position and examines a specified number of character positions.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Function LastIndexOf ( _
	value As String, _
	startIndex As Integer, _
	count As Integer _
) As Integer

Parameters

value
Type: System.String
The string to seek.
startIndex
Type: System.Int32
The search starting position.
count
Type: System.Int32
The number of character positions to examine.

Return Value

Type: System.Int32
The zero-based index position of value if that string is found, or -1 if it is not found or if the current instance equals String.Empty. If value is String.Empty, the return value is startIndex.

ExceptionCondition
ArgumentNullException

value is Nothing.

ArgumentOutOfRangeException

count is negative.

-or-

The current instance does not equal String.Empty, and startIndex is negative.

-or-

The current instance does not equal String.Empty, and startIndex is greater than the length of this instance.

-or-

The current instance does not equal String.Empty, and startIndex - count + 1 specifies a position that is not within this instance.

Index numbering starts from zero. That is, the first character in the string is at index zero and the last is at Length - 1.

The search begins at the startIndex character position of this instance and proceeds backward toward the beginning until either value is found or count character positions have been examined. For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture. The search begins at the startIndex character position of this instance and proceeds backward until either value is found or count character positions have been examined.

Notes to Callers

Starting in Silverlight 4, the behavior of the String.LastIndexOf(String, Int32, Int32) method has changed. In Silverlight 4, it performs a case-sensitive and culture-sensitive comparison using the current culture to find the last occurrence of value. This conforms to the behavior of the String.LastIndexOf(String, Int32, Int32) method in the full .NET Framework. In Silverlight 2 and Silverlight 3, String.LastIndexOf(String, Int32, Int32) performs an ordinal comparison. If the common language runtime determines that a Silverlight-based application was compiled against Silverlight 2 or Silverlight 2, it performs an ordinal comparison; otherwise, it performs a culture-sensitive comparison.

The following code example finds the index of all occurrences of a string in substring, working from the end of the substring to the start of the substring.


' Sample for String.LastIndexOf(String, Int32, Int32)
 _

Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456"
      Dim str As String = "Now is the time for all good men to come to the aid of their party."
      Dim start As Integer
      Dim at As Integer
      Dim count As Integer
      Dim [end] As Integer

      start = str.Length - 1
      [end] = start / 2 - 1
      outputBlock.Text += String.Format("All occurrences of 'he' from position {0} to {1}.", start, [end]) & vbCrLf
      outputBlock.Text += String.Format("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str) & vbCrLf
      outputBlock.Text &= "The string 'he' occurs at position(s): "

      count = 0
      at = 0
      While start > -1 And at > -1
         count = start - [end] 'Count must be within the substring.
         at = str.LastIndexOf("he", start, count)
         If at > -1 Then
            outputBlock.Text += String.Format("{0} ", at)
            start = at - 1
         End If
      End While
      outputBlock.Text += String.Format("{0}{0}{0}", Environment.NewLine)
   End Sub 'Main 
End Class 'Sample
'
'This example produces the following results:
'All occurrences of 'he' from position 66 to 32.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The string 'he' occurs at position(s): 56 45
'
'


Silverlight

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.

Date

History

Reason

October 2010

Noted that an exception is not thrown for an empty string if the index or length parameter is invalid.

Content bug fix.

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