String.LastIndexOf Method (String, Int32, Int32, StringComparison)

Reports the zero-based index position of the last occurrence of a specified string within this instance. The search starts at a specified character position and proceeds backward toward the beginning of the string for the specified number of character positions. A parameter specifies the type of comparison to perform when searching for the specified string.

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

public int LastIndexOf(
	string value,
	int startIndex,
	int count,
	StringComparison comparisonType
)

Parameters

value
Type: System.String

The string to seek.

startIndex
Type: System.Int32

The search starting position. The search proceeds from startIndex toward the beginning of this instance.

count
Type: System.Int32

The number of character positions to examine.

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 found or if the current instance equals String.Empty. If value is String.Empty, the return value is the smaller of startIndex and the last index position in this instance.

ExceptionCondition
ArgumentNullException

value is null.

ArgumentOutOfRangeException

count is negative.

-or-

The current instance does not equal String.Empty, and startIndex is negative.

-or-

The current instance does not equal String.Empty, and startIndex is greater than the length of this instance.

-or-

The current instance does not equal String.Empty, and startIndex + 1 - count specifies a position that is not within this instance.

-or-

The current instance equals String.Empty and start is less than -1 or greater than zero.

-or-

The current instance equals String.Empty and count is greater than 1.

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 search begins at the startIndex character position and proceeds backward until either value is found or count character positions have been examined. For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string.

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.

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 comparisonType 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(String, Int32, Int32, StringComparison) method always returns startIndex, which is the character position at which the search begins.

In the following example, the LastIndexOf(String, Int32, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" in all but the first character position before the final "m" in two strings. Only one of the strings contains the required substring. If the example is run on the .NET Framework 4 or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. When it performs an ordinal comparison, however, it finds the substring only in the first string. Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m" when it performs a culture-sensitive comparison. The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

using System;

public class Example
{
   public static void Main()
   {
      string searchString = "\u00ADm";
      string s1 = "ani\u00ADmal" ;
      string s2 = "animal";
      int position;

      position = s1.LastIndexOf('m');
      if (position >= 1) {
         Console.WriteLine(s1.LastIndexOf(searchString, position, position, StringComparison.CurrentCulture));
         Console.WriteLine(s1.LastIndexOf(searchString, position, position, StringComparison.Ordinal));
      }      

      position = s2.LastIndexOf('m');
      if (position >= 1) { 
         Console.WriteLine(s2.LastIndexOf(searchString, position, position, StringComparison.CurrentCulture));
         Console.WriteLine(s2.LastIndexOf(searchString, position, position, StringComparison.Ordinal));
      }
   }
}
// The example displays the following output: 
//       4 
//       3 
//       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. 

using System;
using System.Threading;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the last occurrence of a character using different " + 
                   "values of StringComparison.";
    string resultFmt = "Comparison: {0,-28} Location: {1,3}";

// Define a string to search for. 
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE 
    string CapitalAWithRing = "\u00c5"; 

// 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). 
    string cat = "A Cheshire c" + "\u0061\u030a" + "t";
    int loc = 0;
    StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

// 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.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. Specify the  
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }
    }
}

/*
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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