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 int LastIndexOf(
	char value
)

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.

using System;
using System.IO;

public class TestLastIndexOf
{
   public static void Main()
   {
      string filename;

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

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

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

      filename = ExtractFilename(@"C:\temp\notafile.txt");
      Console.WriteLine("{0}", String.IsNullOrEmpty(filename) ? "<none>" : filename);
   }

   public static string ExtractFilename(string filepath)
   {
      // If path ends with a "\", it's a path only so return String.Empty.
      if (filepath.Trim().EndsWith(@"\"))
         return String.Empty;

      // Determine where last backslash is. 
      int position = filepath.LastIndexOf('\\');
      // If there is no backslash, assume that this is a filename. 
      if (position == -1)
      {
         // Determine whether file exists in the current directory. 
         if (File.Exists(Environment.CurrentDirectory + Path.DirectorySeparatorChar + filepath)) 
            return filepath;
         else 
            return String.Empty;
      }
      else
      {
         // Determine whether file exists using filepath. 
         if (File.Exists(filepath))
            // Return filename without file path. 
            return filepath.Substring(position + 1);
         else 
            return String.Empty;
      }
   }
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: 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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