BinarySearch Method (Array, Object)

Array.BinarySearch Method (Array, Object)

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Searches an entire one-dimensional sorted Array for a specific element, using the IComparable interface implemented by each element of the Array and by the specified object.

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

'Declaration
Public Shared Function BinarySearch ( _
	array As Array, _
	value As Object _
) As Integer

Parameters

array
Type: System.Array
The sorted one-dimensional Array to search.
value
Type: System.Object
The object to search for.

Return Value

Type: System.Int32
The index of the specified value in the specified array, if value is found. If value is not found and value is less than one or more elements in array, a negative number which is the bitwise complement of the index of the first element that is larger than value. If value is not found and value is greater than any of the elements in array, a negative number which is the bitwise complement of (the index of the last element plus 1).

ExceptionCondition
ArgumentNullException

array is Nothing.

RankException

array is multidimensional.

ArgumentException

value is of a type that is not compatible with the elements of array.

InvalidOperationException

value does not implement the IComparable interface, and the search encounters an element that does not implement the IComparable interface.

array must be sorted before calling this method.

If the Array does not contain the specified value, the method returns a negative integer. You can apply the bitwise complement operator (~) to the negative result (in Visual Basic, Xor the negative result with -1) to produce an index. If this index is greater than or equal to the size of the array, there are no elements larger than value in the array. Otherwise, it is the index of the first element that is larger than value.

Either value or every element of array must implement the IComparable interface, which is used for comparisons. The elements of array must already be sorted in increasing value according to the sort order defined by the IComparable implementation; otherwise, the result might be incorrect.

NoteNote:

If value does not implement the IComparable interface, the elements of array are not tested for IComparable before the search begins. An exception is thrown if the search encounters an element that does not implement IComparable.

Duplicate elements are allowed. If the Array contains more than one element equal to value, the method returns the index of only one of the occurrences, and not necessarily the first one.

Nothing can always be compared with any other reference type; therefore, comparisons with Nothing do not generate an exception. When sorting, Nothing is considered to be less than any other object.

NoteNote:

   For every element tested, value is passed to the appropriate IComparable implementation, even if value is Nothing. That is, the IComparable implementation determines how a given element compares to Nothing.

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

The following code example shows how to use BinarySearch to locate a specific object in an Array.

NoteNote:

The array is created with its elements in ascending sort order. The BinarySearch method requires the array to be sorted in ascending order.



Public Class Example

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

      ' Creates and initializes a new Array.
      Dim myIntArray As Array = Array.CreateInstance(GetType(Int32), 5)
      Dim i As Integer
      For i = myIntArray.GetLowerBound(0) To myIntArray.GetUpperBound(0)
         myIntArray.SetValue(i * 2, i)
      Next i
      ' Do the required sort first
      Array.Sort(myIntArray)
      ' Displays the values of the Array.
      outputBlock.Text &= "The Int32 array contains the following:" & vbCrLf
      PrintValues(outputBlock, myIntArray)

      ' Locates a specific object that does not exist in the Array.
      Dim myObjectOdd As Object = 3
      FindMyObject(outputBlock, myIntArray, myObjectOdd)

      ' Locates an object that exists in the Array.
      Dim myObjectEven As Object = 6
      FindMyObject(outputBlock, myIntArray, myObjectEven)
   End Sub


   Public Shared Sub FindMyObject(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal myArr As Array, ByVal myObject As Object)
      Dim myIndex As Integer = Array.BinarySearch(myArr, myObject)
      If myIndex < 0 Then
         outputBlock.Text += String.Format("The object to search for ({0}) & vbCrLf is not found. " _
            + "The next larger object is at index {1}.", myObject, Not (myIndex))
      Else
         outputBlock.Text += String.Format("The object to search for ({0}) & vbCrLf is at index " _
            + "{1}.", myObject, myIndex)
      End If
   End Sub


   Public Shared Sub PrintValues(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal myArr As Array)
      Dim myEnumerator As System.Collections.IEnumerator = _
         myArr.GetEnumerator()
      Dim i As Integer = 0
      Dim cols As Integer = myArr.GetLength((myArr.Rank - 1))
      While myEnumerator.MoveNext()
         If i < cols Then
            i += 1
         Else
            outputBlock.Text &= vbCrLf
            i = 1
         End If
         outputBlock.Text += String.Format(ControlChars.Tab + "{0}", myEnumerator.Current)
      End While
      outputBlock.Text &= vbCrLf
   End Sub
End Class

' This code produces the following output.
' 
' The Int32 array contains the following:
'     0    2    4    6    8
' The object to search for (3) is not found. The next larger object is at index 2.
' The object to search for (6) is at index 3.  


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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