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Array.IndexOf<T> Method (T[], T)

Searches for the specified object and returns the index of its first occurrence in a one-dimensional array.

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

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

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.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of value in the entire array, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

array is null.

This method searches all the elements of a one-dimensional array for value. To determine whether value exists in array, the method performs an equality comparison by calling the T.Equals method on every element. This means that if T overrides the Equals method, that override is called.

This method is an O(n) operation, where n is the Length of array.

The following example demonstrates all three generic overloads of the IndexOf method. An array of strings is created, with one entry that appears twice, at index location 0 and index location 5. The IndexOf<T>(T[], T) method overload searches the array from the beginning, and finds the first occurrence of the string. The IndexOf<T>(T[], T, Int32) method overload is used to search the array beginning with index location 3 and continuing to the end of the array, and finds the second occurrence of the string. Finally, the IndexOf<T>(T[], T, Int32, Int32) method overload is used to search a range of two entries, beginning at index location two; it returns –1 because there are no instances of the search string in that range.

using System;

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = { "Tyrannosaurus",
            "Amargasaurus",
            "Mamenchisaurus",
            "Brachiosaurus",
            "Deinonychus",
            "Tyrannosaurus",
            "Compsognathus" };

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

        Console.WriteLine(
            "\nArray.IndexOf(dinosaurs, \"Tyrannosaurus\"): {0}", 
            Array.IndexOf(dinosaurs, "Tyrannosaurus"));

        Console.WriteLine(
            "\nArray.IndexOf(dinosaurs, \"Tyrannosaurus\", 3): {0}", 
            Array.IndexOf(dinosaurs, "Tyrannosaurus", 3));

        Console.WriteLine(
            "\nArray.IndexOf(dinosaurs, \"Tyrannosaurus\", 2, 2): {0}", 
            Array.IndexOf(dinosaurs, "Tyrannosaurus", 2, 2));
    }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

Array.IndexOf(dinosaurs, "Tyrannosaurus"): 0

Array.IndexOf(dinosaurs, "Tyrannosaurus", 3): 5

Array.IndexOf(dinosaurs, "Tyrannosaurus", 2, 2): -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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