Article
11/18/2011

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

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

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

Syntax

'Declaration
Public Shared Function IndexOf(Of T) ( _
    array As T(), _
    value As T, _
    startIndex As Integer _
) As Integer

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

Type Parameters

T
The type of the elements of the array.

Parameters

array
Type: array<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 search.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of value within the range of elements in array that extends from startIndex to the last element, if found; otherwise, –1.

Exceptions

Exception	Condition
ArgumentNullException	array is nulla null reference (Nothing in Visual Basic).
ArgumentOutOfRangeException	startIndex is outside the range of valid indexes for array.

Remarks

The Array is searched forward starting at startIndex and ending at the last 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.

Passing the Length of the array as the startindex will result in a return value of -1, while values greater than Length will raise an ArgumentOutOfRangeException.

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

Examples

The following code 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>(array<T[], T) method overload searches the array from the beginning, and finds the first occurrence of the string. The IndexOf<T>(array<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>(array<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.


Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim dinosaurs() As String = {"Tyrannosaurus", _
          "Amargasaurus", _
          "Mamenchisaurus", _
          "Brachiosaurus", _
          "Deinonychus", _
          "Tyrannosaurus", _
          "Compsognathus"}

      outputBlock.Text &= vbCrLf
      For Each dinosaur As String In dinosaurs
         outputBlock.Text &= dinosaur & vbCrLf
      Next

      outputBlock.Text &= String.Format(vbLf & _
          "Array.IndexOf(dinosaurs, ""Tyrannosaurus""): {0}", _
          Array.IndexOf(dinosaurs, "Tyrannosaurus")) & vbCrLf

      outputBlock.Text &= String.Format(vbLf & _
          "Array.IndexOf(dinosaurs, ""Tyrannosaurus"", 3): {0}", _
          Array.IndexOf(dinosaurs, "Tyrannosaurus", 3)) & vbCrLf

      outputBlock.Text &= String.Format(vbLf & _
          "Array.IndexOf(dinosaurs, ""Tyrannosaurus"", 2, 2): {0}", _
          Array.IndexOf(dinosaurs, "Tyrannosaurus", 2, 2)) & vbCrLf

   End Sub
End Class

' 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

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.IndexOf(dinosaurs, \"Tyrannosaurus\"): {0}",
          Array.IndexOf(dinosaurs, "Tyrannosaurus")) + "\n";

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

      outputBlock.Text += String.Format(
          "\nArray.IndexOf(dinosaurs, \"Tyrannosaurus\", 2, 2): {0}",
          Array.IndexOf(dinosaurs, "Tyrannosaurus", 2, 2)) + "\n";
   }
}

/* 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
 */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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