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

Searches for the specified object and returns the index of the first occurrence within the range of elements in the Array that starts at the specified index and contains the specified number of elements.

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

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

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 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 first occurrence of value within the range of elements in array that starts at startIndex and contains the number of elements specified in count, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

array is null.

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for array.

-or-

count is less than zero.

-or-

startIndex and count do not specify a valid section in array.

The Array is searched forward starting at startIndex and ending at startIndex plus count minus 1, if count is greater than 0.

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 property of the array as the startindex parameter results in a return value of -1; passing values greater than Length raises an ArgumentOutOfRangeException.

This method is an O(n) operation, where n is count.

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>(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 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
 */


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

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

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