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String.LastIndexOf Method (String)

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

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
public int LastIndexOf(
	string value
)

Parameters

value
Type: System.String

The string to seek.

Return Value

Type: System.Int32
The zero-based starting index position of value 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 null.

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 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.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

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, 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(String) method always returns String.Length – 1, which represents the last index position in the current instance. In the following example, the LastIndexOf(String) 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, in each case, because the soft hyphen is an ignorable character, the result is the same as if the soft hyphen had not been included in value. When searching for a soft hyphen only, the method returns 6 and 5. These values correspond to the index of the last character in the two strings.

using System;

public class Example
{
   public static void Main()
   {
      string s1 = "ani\u00ADmal";
      string s2 = "animal";

      // Find the index of the last soft hyphen.
      Console.WriteLine(s1.LastIndexOf("\u00AD"));
      Console.WriteLine(s2.LastIndexOf("\u00AD"));

      // Find the index of the last soft hyphen followed by "n".
      Console.WriteLine(s1.LastIndexOf("\u00ADn"));
      Console.WriteLine(s2.LastIndexOf("\u00ADn"));

      // Find the index of the last soft hyphen followed by "m".
      Console.WriteLine(s1.LastIndexOf("\u00ADm"));
      Console.WriteLine(s2.LastIndexOf("\u00ADm"));
   }
}
// The example displays the following output: 
//       6 
//       5 
//       1 
//       1 
//       4 
//       3

Notes to Callers

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To find the last index of a substring within a string instance by using the comparison rules of the current culture, call the LastIndexOf(String, StringComparison) method overload with a value of StringComparison.CurrentCulture for its comparisonType parameter.

The following example removes opening and closing HTML tags from a string if the tags begin and end the string. If a string ends with a closing bracket character (">"), the example uses the LastIndexOf method to locate the start of the end tag.

using System;

public class Example 
{
   public static void Main() 
   {
      string[] strSource = { "<b>This is bold text</b>", "<H1>This is large Text</H1>",
               "<b><i><font color=green>This has multiple tags</font></i></b>",
               "<b>This has <i>embedded</i> tags.</b>",
               "This line ends with a greater than symbol and should not be modified>" };

      // Strip HTML start and end tags from each string if they are present. 
      foreach (string s in strSource)
      {
         Console.WriteLine("Before: " + s);
         string item = s;
         // Use EndsWith to find a tag at the end of the line. 
         if (item.Trim().EndsWith(">")) 
         {
            // Locate the opening tag. 
            int endTagStartPosition = item.LastIndexOf("</");
            // Remove the identified section, if it is valid. 
            if (endTagStartPosition >= 0 )
               item = item.Substring(0, endTagStartPosition);

            // Use StartsWith to find the opening tag. 
            if (item.Trim().StartsWith("<"))
            {
               // Locate the end of opening tab. 
               int openTagEndPosition = item.IndexOf(">");
               // Remove the identified section, if it is valid. 
               if (openTagEndPosition >= 0)
                  item = item.Substring(openTagEndPosition + 1);
            }      
         }
         // Display the trimmed string.
         Console.WriteLine("After: " + item);
         Console.WriteLine();
      }                   
   }
}
// The example displays the following output: 
//    Before: <b>This is bold text</b> 
//    After: This is bold text 
//     
//    Before: <H1>This is large Text</H1> 
//    After: This is large Text 
//     
//    Before: <b><i><font color=green>This has multiple tags</font></i></b> 
//    After: <i><font color=green>This has multiple tags</font></i> 
//     
//    Before: <b>This has <i>embedded</i> tags.</b> 
//    After: This has <i>embedded</i> tags. 
//     
//    Before: This line ends with a greater than symbol and should not be modified> 
//    After: This line ends with a greater than symbol and should not be modified>

.NET Framework

Supported in: 4.5.1, 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

.NET for Windows Phone apps

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

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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