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List<T>.LastIndexOf Method (T, Int32, 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 contains the specified number of elements and ends at the specified index.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)
public int LastIndexOf(
	T item,
	int index,
	int count
)

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.
count
Type: System.Int32
The number of elements in the section to 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 contains count number of elements and ends at index, if found; otherwise, –1.
ExceptionCondition
ArgumentOutOfRangeException

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

-or-

count is less than 0.

-or-

index and count do not specify a valid section in the List<T>.

The List<T> is searched backward starting at index and ending at index minus count plus 1, if count is greater than 0.

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 count.

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 4 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
 */


.NET Framework

Supported in: 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

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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