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String.LastIndexOf Method (String, StringComparison)

Reports the zero-based index of the last occurrence of a specified string within the current String object. A parameter specifies the type of search to use for the specified string.

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

'Declaration
Public Function LastIndexOf ( _
	value As String, _
	comparisonType As StringComparison _
) As Integer

Parameters

value
Type: System.String

The string to seek.

comparisonType
Type: System.StringComparison

One of the enumeration values that specifies the rules for the search.

Return Value

Type: System.Int32
The zero-based starting index position of the value parameter if that string is found, or -1 if it is not. If value is String.Empty, the return value is the last index position in this instance.

ExceptionCondition
ArgumentNullException

value is Nothing.

ArgumentException

comparisonType is not a valid System.StringComparison value.

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 last character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined.

Notes to Callers

Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. In a culture-sensitive search (that is, if options is not StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase), if value contains an ignorable character, the result is equivalent to searching with that character removed. If value consists only of one or more ignorable characters, the LastIndexOf method always returns String.Length – 1, which represents the last index position in the current instance.

In the following example, the LastIndexOf(String, StringComparison) method is used to find three substrings (a soft hyphen (U+00AD), a soft hyphen followed by "n", and a soft hyphen followed by "m") in two strings. Only one of the strings contains a soft hyphen. If the example is run on the .NET Framework 4 or later, because the soft hyphen is an ignorable character, a culture-sensitive search returns the same value that it would return if the soft hyphen were not included in the search string. An ordinal search, however, successfully finds the soft hyphen in one string and reports that it is absent from the second string.

Module Example
   Public Sub Main()
      Dim softHyphen As String = ChrW(&h00AD)
      Dim s1 As String = "ani" + softHyphen + "mal" 
      Dim s2 As String = "animal"

      Console.WriteLine("Culture-sensitive comparison:")
      ' Use culture-sensitive comparison to find the last soft hyphen.
      Console.WriteLine(s1.LastIndexOf(softHyphen, StringComparison.CurrentCulture))
      Console.WriteLine(s2.LastIndexOf(softHyphen, StringComparison.CurrentCulture))

      ' Use culture-sensitive comparison to find the last soft hyphen followed by "n".
      Console.WriteLine(s1.LastIndexOf(softHyphen + "n", StringComparison.CurrentCulture))
      Console.WriteLine(s2.LastIndexOf(softHyphen + "n", StringComparison.CurrentCulture))

      ' Use culture-sensitive comparison to find the last soft hyphen followed by "m".
      Console.WriteLine(s1.LastIndexOf(softHyphen + "m", StringComparison.CurrentCulture))
      Console.WriteLine(s2.LastIndexOf(softHyphen + "m", StringComparison.CurrentCulture))

      Console.WriteLine("Ordinal comparison:")
      ' Use ordinal comparison to find the last soft hyphen.
      Console.WriteLine(s1.LastIndexOf(softHyphen, StringComparison.Ordinal))
      Console.WriteLine(s2.LastIndexOf(softHyphen, StringComparison.Ordinal))

      ' Use ordinal comparison to find the last soft hyphen followed by "n".
      Console.WriteLine(s1.LastIndexOf(softHyphen + "n", StringComparison.Ordinal))
      Console.WriteLine(s2.LastIndexOf(softHyphen + "n", StringComparison.Ordinal))

      ' Use ordinal comparison to find the last soft hyphen followed by "m".
      Console.WriteLine(s1.LastIndexOf(softHyphen + "m", StringComparison.Ordinal))
      Console.WriteLine(s2.LastIndexOf(softHyphen + "m", StringComparison.Ordinal))
   End Sub 
End Module 
' The example displays the following output: 
'       6 
'       5 
'       1 
'       1 
'       4 
'       3 
'       Ordinal comparison: 
'       3 
'       -1 
'       -1 
'       -1 
'       3 
'       -1

The following 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
Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        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

        ' Clear the screen and display an introduction.
        Console.Clear()
        Console.WriteLine(intro)

        ' 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")
        Console.WriteLine("The current culture is ""{0}"" - {1}.", _
                           Thread.CurrentThread.CurrentCulture.Name, _
                           Thread.CurrentThread.CurrentCulture.DisplayName)

        ' Display the string to search for and the string to search.
        Console.WriteLine("Search for the string ""{0}"" in the string ""{1}""", _
                           CapitalAWithRing, cat)
        Console.WriteLine()

        ' 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. 
        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc

        ' Search using different values of StringComparsion. Specify the  
        ' start index. 
        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc

        ' Search using different values of StringComparsion. 
        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, sc)
            Console.WriteLine(resultFmt, sc, loc)
        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 
'

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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