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String.LastIndexOf Method (Char)

 

Reports the zero-based index position of the last occurrence of a specified Unicode character within this instance.

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

Public Function LastIndexOf (
	value As Char
) As Integer

Parameters

value
Type: System.Char

The Unicode character to seek.

Return Value

Type: System.Int32

The zero-based index position of value if that character is found, or -1 if it is not.

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

This method begins searching 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. 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 values 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.

The following example defines an ExtractFilename method that uses the LastIndexOf(Char) method to find the last directory separator character in a string and to extract the string's file name. If the file exists, the method returns the file name without its path.

Imports System.IO

Public Module Test
   Public Sub Main()
      Dim filename As String 

      filename = ExtractFilename("C:\temp\")
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))

      filename = ExtractFilename("C:\temp\delegate.txt") 
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))

      filename = ExtractFilename("delegate.txt")      
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))

      filename = ExtractFilename("C:\temp\notafile.txt")
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))
   End Sub

   Public Function ExtractFilename(filepath As String) As String
      ' If path ends with a "\", it's a path only so return String.Empty.
      If filepath.Trim().EndsWith("\") Then Return String.Empty

      ' Determine where last backslash is.
      Dim position As Integer = filepath.LastIndexOf("\"c)
      ' If there is no backslash, assume that this is a filename.
      If position = -1 Then
         ' Determine whether file exists in the current directory.
         If File.Exists(Environment.CurrentDirectory + Path.DirectorySeparatorChar + filepath) Then
            Return filepath
         Else
            Return String.Empty
         End If
      Else
         ' Determine whether file exists using filepath.
         If File.Exists(filepath) Then
            ' Return filename without file path.
            Return filepath.Substring(position + 1)
         Else
            Return String.Empty
         End If                     
      End If
   End Function
End Module 
' The example displays the following output:
'        <none>
'        delegate.txt
'        <none>
'        <none>

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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