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String.LastIndexOf Method (Char)

Updated: October 2008

Reports the 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

A 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.

ExceptionCondition
ArgumentNullException

value is null.

Index numbering starts from 0 (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;
      }
   }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

October 2008

Replaced the example.

Customer feedback.

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