Array.LastIndexOf<T> Method (T[], T, Int32)

July 28, 2014

Searches for the specified object and returns the index of the last occurrence within the range of elements in the Array that extends from the first element to the specified index.

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

public static int LastIndexOf<T>(
	T[] array,
	T value,
	int startIndex
)

Type Parameters

T

The type of the elements of the array.

Parameters

array
Type: T []
The one-dimensional, zero-based Array to search.
value
Type: T
The object to locate in array.
startIndex
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 value within the range of elements in array that extends from the first element to startIndex, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

array is null.

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for array.

The Array is searched backward starting at startIndex and ending at the first element.

The elements are compared to the specified value using the Object.Equals method. If the element type is a nonintrinsic (user-defined) type, the Equals implementation of that type is used.

This method is an O(n) operation, where n is the number of elements from the beginning of array to startIndex.

The following code example demonstrates all three generic overloads of the LastIndexOf method. An array of strings is created, with one entry that appears twice, at index location 0 and index location 5. The LastIndexOf<T>(T[], T) method overload searches the entire array from the end, and finds the second occurrence of the string. The LastIndexOf<T>(T[], T, Int32) method overload is used to search the array backward beginning with index location 3 and continuing to the beginning of the array, and finds the first occurrence of the string. Finally, the LastIndexOf<T>(T[], 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;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string[] dinosaurs = { "Tyrannosaurus",
            "Amargasaurus",
            "Mamenchisaurus",
            "Brachiosaurus",
            "Deinonychus",
            "Tyrannosaurus",
            "Compsognathus" };

      outputBlock.Text += "\n";
      foreach (string dinosaur in dinosaurs)
      {
         outputBlock.Text += dinosaur + "\n";
      }

      outputBlock.Text += String.Format(
          "\nArray.LastIndexOf(dinosaurs, \"Tyrannosaurus\"): {0}",
          Array.LastIndexOf(dinosaurs, "Tyrannosaurus")) + "\n";

      outputBlock.Text += String.Format(
          "\nArray.LastIndexOf(dinosaurs, \"Tyrannosaurus\", 3): {0}",
          Array.LastIndexOf(dinosaurs, "Tyrannosaurus", 3)) + "\n";

      outputBlock.Text += String.Format(
          "\nArray.LastIndexOf(dinosaurs, \"Tyrannosaurus\", 4, 4): {0}",
          Array.LastIndexOf(dinosaurs, "Tyrannosaurus", 4, 4)) + "\n";
   }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

Array.LastIndexOf(dinosaurs, "Tyrannosaurus"): 5

Array.LastIndexOf(dinosaurs, "Tyrannosaurus", 3): 0

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


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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