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List<T>.LastIndexOf Method (T, Int32)

Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that extends from the first element to the specified index.

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

public int LastIndexOf(
	T item,
	int index
)

Parameters

item
Type: T

The object to locate in the List<T>. The value can be null for reference types.

index
Type: System.Int32

The zero-based starting index of the backward search.

Return Value

Type: System.Int32
The zero-based index of the last occurrence of item within the range of elements in the List<T> that extends from the first element to index, if found; otherwise, –1.

ExceptionCondition
ArgumentOutOfRangeException

index is outside the range of valid indexes for the List<T>.

The List<T> is searched backward starting at index and ending at the first element.

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

This method performs a linear search; therefore, this method is an O(n) operation, where n is the number of elements from the beginning of the List<T> to index.

The following code example demonstrates all three overloads of the LastIndexOf method. A List<T> of strings is created, with one entry that appears twice, at index location 0 and index location 5. The LastIndexOf(T) method overload searches the entire list from the end, and finds the second occurrence of the string. The LastIndexOf(T, Int32) method overload is used to search the list backward beginning with index location 3 and continuing to the beginning of the list, so it finds the first occurrence of the string in the list. Finally, the LastIndexOf(T, Int32, Int32) method overload is used to search a range of four entries, beginning at index location 4 and extending backward (that is, it searches the items at locations 4, 3, 2, and 1); this search returns –1 because there are no instances of the search string in that range.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>();

        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Brachiosaurus");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Compsognathus");

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\"): {0}", 
            dinosaurs.LastIndexOf("Tyrannosaurus"));

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 3): {0}", 
            dinosaurs.LastIndexOf("Tyrannosaurus", 3));

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 4, 4): {0}", 
            dinosaurs.LastIndexOf("Tyrannosaurus", 4, 4));
    }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

LastIndexOf("Tyrannosaurus"): 5

LastIndexOf("Tyrannosaurus", 3): 0

LastIndexOf("Tyrannosaurus", 4, 4): -1
 */

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

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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