String.LastIndexOf Method (String, Int32, StringComparison)
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Updated: October 2010
Reports the zero-based index of the last occurrence of a specified string within the current String object. Parameters specify the starting search position in the current string, and type of search to use for the specified string.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Function LastIndexOf ( _
value As String, _
startIndex As Integer, _
comparisonType As StringComparison _
) As Integer
public int LastIndexOf(
string value,
int startIndex,
StringComparison comparisonType
)
Parameters
- value
Type: System.String
The string to seek.
- startIndex
Type: System.Int32
The search starting position.
- comparisonType
Type: System.StringComparison
One of the enumeration values that specifies the rules for the search.
Return Value
Type: System.Int32
The zero-based index position of the value parameter 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 the smaller of startIndex and the last index position in this instance.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | value is nulla null reference (Nothing in Visual Basic). |
| ArgumentOutOfRangeException | The current instance does not equal String.Empty, and startIndex is less than zero or greater than the length of the current instance. -or- The current instance equals String.Empty, and startIndex is greater than zero. |
| ArgumentException | comparisonType is not a valid System.StringComparison value. |
Remarks
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 comparisonType parameter specifies to search for the value parameter using the current or invariant culture, using a case-sensitive or case-insensitive search, and using word or ordinal comparison rules.
The search begins at the startIndex character position and proceeds backward until either value is found or the first character position has been examined. For example, if startIndex is Length - 1, the method searches every character from the last character in the string to the beginning.
Platform Notes
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Silverlight for Windows Phone
String.LastIndexOf(String, Int32, StringComparison) method returns incorrect values when the string contains Unicode characters.
Examples
The following code example demonstrates three overloads of the LastIndexOf method that find the last occurrence of a string within another string using different values of the StringComparison enumeration.
' This code example demonstrates the
' System.String.LastIndexOf(String, ..., StringComparison) methods.
Imports System.Threading
Imports System.Globalization
Class Example
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim intro As String = "Find the last occurrence of a character using different " & _
"values of StringComparison."
Dim resultFmt As String = "Comparison: {0,-28} Location: {1,3}"
' Define a string to search for.
' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
Dim CapitalAWithRing As String = "Å"
' Define a string to search.
' The result of combining the characters LATIN SMALL LETTER A and COMBINING
' RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character
' LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
Dim cat As String = "A Cheshire c" & "å" & "t"
Dim loc As Integer = 0
Dim scValues As StringComparison() = { _
StringComparison.CurrentCulture, _
StringComparison.CurrentCultureIgnoreCase, _
StringComparison.InvariantCulture, _
StringComparison.InvariantCultureIgnoreCase, _
StringComparison.Ordinal, _
StringComparison.OrdinalIgnoreCase}
Dim sc As StringComparison
' Display an introduction.
outputBlock.Text &= intro & vbCrLf
' Display the current culture because culture affects the result. For example,
' try this code example with the "sv-SE" (Swedish-Sweden) culture.
Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")
outputBlock.Text &= String.Format("The current culture is ""{0}"" - {1}.", _
Thread.CurrentThread.CurrentCulture.Name, _
Thread.CurrentThread.CurrentCulture.DisplayName) & vbCrLf
' Display the string to search for and the string to search.
outputBlock.Text &= String.Format("Search for the string ""{0}"" in the string ""{1}""", _
CapitalAWithRing, cat) & vbCrLf
outputBlock.Text &= vbCrLf
' Note that in each of the following searches, we look for
' LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains
' LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates
' the string was not found.
' Search using different values of StringComparsion. Specify the start
' index and count.
outputBlock.Text &= "Part 1: Start index and count are specified." & vbCrLf
For Each sc In scValues
loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc)
outputBlock.Text &= String.Format(resultFmt, sc, loc) & vbCrLf
Next sc
' Search using different values of StringComparsion. Specify the
' start index.
outputBlock.Text &= vbCrLf & "Part 2: Start index is specified." & vbCrLf
For Each sc In scValues
loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc)
outputBlock.Text &= String.Format(resultFmt, sc, loc) & vbCrLf
Next sc
' Search using different values of StringComparsion.
outputBlock.Text &= vbCrLf & "Part 3: Neither start index nor count is specified." & vbCrLf
For Each sc In scValues
loc = cat.LastIndexOf(CapitalAWithRing, sc)
outputBlock.Text &= String.Format(resultFmt, sc, loc) & vbCrLf
Next sc
End Sub 'Main
End Class 'Sample
'
'Note: This code example was executed on a console whose user interface
'culture is "en-US" (English-United States).
'
'This code example produces the following results:
'
'Find the last occurrence of a character using different values of StringComparison.
'The current culture is "en-US" - English (United States).
'Search for the string "Å" in the string "A Cheshire ca°t"
'
'Part 1: Start index and count are specified.
'Comparison: CurrentCulture Location: -1
'Comparison: CurrentCultureIgnoreCase Location: 12
'Comparison: InvariantCulture Location: -1
'Comparison: InvariantCultureIgnoreCase Location: 12
'Comparison: Ordinal Location: -1
'Comparison: OrdinalIgnoreCase Location: -1
'
'Part 2: Start index is specified.
'Comparison: CurrentCulture Location: -1
'Comparison: CurrentCultureIgnoreCase Location: 12
'Comparison: InvariantCulture Location: -1
'Comparison: InvariantCultureIgnoreCase Location: 12
'Comparison: Ordinal Location: -1
'Comparison: OrdinalIgnoreCase Location: -1
'
'Part 3: Neither start index nor count is specified.
'Comparison: CurrentCulture Location: -1
'Comparison: CurrentCultureIgnoreCase Location: 12
'Comparison: InvariantCulture Location: -1
'Comparison: InvariantCultureIgnoreCase Location: 12
'Comparison: Ordinal Location: -1
'Comparison: OrdinalIgnoreCase Location: -1
'
// This code example demonstrates the
// System.String.LastIndexOf(String, ..., StringComparison) methods.
using System;
using System.Threading;
using System.Globalization;
class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
string intro = "Find the last occurrence of a character using different " +
"values of StringComparison.";
string resultFmt = "Comparison: {0,-28} Location: {1,3}";
// Define a string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
string CapitalAWithRing = "\u00c5";
// Define a string to search.
// The result of combining the characters LATIN SMALL LETTER A and COMBINING
// RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character
// LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
string cat = "A Cheshire c" + "\u0061\u030a" + "t";
int loc = 0;
StringComparison[] scValues = {
StringComparison.CurrentCulture,
StringComparison.CurrentCultureIgnoreCase,
StringComparison.InvariantCulture,
StringComparison.InvariantCultureIgnoreCase,
StringComparison.Ordinal,
StringComparison.OrdinalIgnoreCase };
// Display an introduction.
outputBlock.Text += intro + "\n";
// Display the current culture because culture affects the result. For example,
// try this code example with the "sv-SE" (Swedish-Sweden) culture.
Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
outputBlock.Text += String.Format("The current culture is \"{0}\" - {1}.",
Thread.CurrentThread.CurrentCulture.Name,
Thread.CurrentThread.CurrentCulture.DisplayName) + "\n";
// Display the string to search for and the string to search.
outputBlock.Text += String.Format("Search for the string \"{0}\" in the string \"{1}\"",
CapitalAWithRing, cat) + "\n";
outputBlock.Text += "\n";
// Note that in each of the following searches, we look for
// LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains
// LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates
// the string was not found.
// Search using different values of StringComparsion. Specify the start
// index and count.
outputBlock.Text += "Part 1: Start index and count are specified." + "\n";
foreach (StringComparison sc in scValues)
{
loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc);
outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
}
// Search using different values of StringComparsion. Specify the
// start index.
outputBlock.Text += "\nPart 2: Start index is specified." + "\n";
foreach (StringComparison sc in scValues)
{
loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc);
outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
}
// Search using different values of StringComparsion.
outputBlock.Text += "\nPart 3: Neither start index nor count is specified." + "\n";
foreach (StringComparison sc in scValues)
{
loc = cat.LastIndexOf(CapitalAWithRing, sc);
outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n";
}
}
}
/*
Note: This code example was executed on a console whose user interface
culture is "en-US" (English-United States).
This code example produces the following results:
Find the last occurrence of a character using different values of StringComparison.
The current culture is "en-US" - English (United States).
Search for the string "Å" in the string "A Cheshire ca°t"
Part 1: Start index and count are specified.
Comparison: CurrentCulture Location: -1
Comparison: CurrentCultureIgnoreCase Location: 12
Comparison: InvariantCulture Location: -1
Comparison: InvariantCultureIgnoreCase Location: 12
Comparison: Ordinal Location: -1
Comparison: OrdinalIgnoreCase Location: -1
Part 2: Start index is specified.
Comparison: CurrentCulture Location: -1
Comparison: CurrentCultureIgnoreCase Location: 12
Comparison: InvariantCulture Location: -1
Comparison: InvariantCultureIgnoreCase Location: 12
Comparison: Ordinal Location: -1
Comparison: OrdinalIgnoreCase Location: -1
Part 3: Neither start index nor count is specified.
Comparison: CurrentCulture Location: -1
Comparison: CurrentCultureIgnoreCase Location: 12
Comparison: InvariantCulture Location: -1
Comparison: InvariantCultureIgnoreCase Location: 12
Comparison: Ordinal Location: -1
Comparison: OrdinalIgnoreCase Location: -1
*/
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.
Change History
Date |
History |
Reason |
|---|---|---|
October 2010 |
Noted that an exception is not thrown for an empty string if the index parameter is invalid. |
Content bug fix. |