String.LastIndexOf Method (Char, Int32, Int32)
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Updated: October 2010
Reports the zero-based index position of the last occurrence of the specified Unicode character in a substring 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)
Syntax
'Declaration
<SecuritySafeCriticalAttribute> _
Public Function LastIndexOf ( _
value As Char, _
startIndex As Integer, _
count As Integer _
) As Integer
[SecuritySafeCriticalAttribute]
public int LastIndexOf(
char value,
int startIndex,
int count
)
Parameters
- value
Type: System.Char
A Unicode character to seek.
- startIndex
Type: System.Int32
The starting position of a substring within this instance.
- 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 character is found, or -1 if it is not found or if the current instance equals String.Empty.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | The current instance does not equal String.Empty, and startIndex is less than zero or greater than or equal to the length of this instance. -or- The current instance does not equal String.Empty, and startIndex - count + 1 is less than zero. |
Remarks
Index numbering starts from zero. That is, the first character in the string is at index 0 and the last is at Length - 1.
This method begins searching 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. The search is case-sensitive.
This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar value are the same. To perform a culture-sensitive search, use the CompareInfo.LastIndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature 'Æ' (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.
Examples
The following code example finds the index of all occurrences of a character in a substring, working from the end of the substring to the start of the substring.
' Sample for String.LastIndexOf(Char, 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 't' from position {0} to {1}.", start, [end]) & vbCrLf
outputBlock.Text &= String.Format("{1}{0}{2}{0}{3}{0}", vbCrLf, br1, br2, str) & vbCrLf
outputBlock.Text &= "The letter 't' 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("t"c, 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}", vbCrLf)
End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'All occurrences of 't' 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 letter 't' occurs at position(s): 64 55 44 41 33
'
'
// Sample for String.LastIndexOf(Char, Int32, Int32)
using System;
class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
string str = "Now is the time for all good men to come to the aid of their party.";
int start;
int at;
int count;
int end;
start = str.Length - 1;
end = start / 2 - 1;
outputBlock.Text += String.Format("All occurrences of 't' from position {0} to {1}.", start, end) + "\n";
outputBlock.Text += String.Format("{1}{0}{2}{0}{3}{0}", "\n", br1, br2, str) + "\n";
outputBlock.Text += "The letter 't' occurs at position(s): ";
count = 0;
at = 0;
while ((start > -1) && (at > -1))
{
count = start - end; //Count must be within the substring.
at = str.LastIndexOf('t', start, count);
if (at > -1)
{
outputBlock.Text += String.Format("{0} ", at);
start = at - 1;
}
}
outputBlock.Text += String.Format("{0}{0}{0}", "\n");
}
}
/*
This example produces the following results:
All occurrences of 't' 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 letter 't' occurs at position(s): 64 55 44 41 33
*/
Version Information
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
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
See Also
Reference
Change History
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. |