Array.BinarySearch Method (Array, Object)
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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)
Syntax
'Declaration
Public Shared Function BinarySearch ( _
array As Array, _
value As Object _
) As Integer
public static int BinarySearch(
Array array,
Object value
)
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).
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | array is nulla null reference (Nothing in Visual Basic). |
| 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. |
Remarks
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.
.gif "Note") Note: |
|---|
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.
nulla null reference (Nothing in Visual Basic) can always be compared with any other reference type; therefore, comparisons with nulla null reference (Nothing in Visual Basic) do not generate an exception. When sorting, nulla null reference (Nothing in Visual Basic) is considered to be less than any other object.
| Note: |
|---|
For every element tested, value is passed to the appropriate IComparable implementation, even if value is nulla null reference (Nothing in Visual Basic). That is, the IComparable implementation determines how a given element compares to nulla null reference (Nothing in Visual Basic). |
This method is an O(log n) operation, where n is the Length of array.
Examples
The following code example shows how to use BinarySearch to locate a specific object in an Array.
| Note: |
|---|
The array is created with its elements in ascending sort order. The BinarySearch method requires the array to be sorted in ascending order. |
| Note: |
|---|
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control. |
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.
using System;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
// Creates and initializes a new Array.
Array myIntArray = Array.CreateInstance(typeof(Int32), 5);
for (int i = myIntArray.GetLowerBound(0); i <= myIntArray.GetUpperBound(0); i++)
myIntArray.SetValue(i * 2, i);
// Do the required sort first
Array.Sort(myIntArray);
// Displays the values of the Array.
outputBlock.Text += "The Int32 array contains the following:" + "\n";
PrintValues(outputBlock, myIntArray);
// Locates a specific object that does not exist in the Array.
Object myObjectOdd = 3;
FindMyObject(outputBlock, myIntArray, myObjectOdd);
// Locates an object that exists in the Array.
Object myObjectEven = 6;
FindMyObject(outputBlock, myIntArray, myObjectEven);
}
public static void FindMyObject(System.Windows.Controls.TextBlock outputBlock, Array myArr, Object myObject)
{
int myIndex = Array.BinarySearch(myArr, myObject);
if (myIndex < 0)
outputBlock.Text += String.Format("The object to search for ({0}) is not found. The next larger object is at index {1}.", myObject, ~myIndex) + "\n";
else
outputBlock.Text += String.Format("The object to search for ({0}) is at index {1}.", myObject, myIndex) + "\n";
}
public static void PrintValues(System.Windows.Controls.TextBlock outputBlock, Array myArr)
{
System.Collections.IEnumerator myEnumerator = myArr.GetEnumerator();
int i = 0;
int cols = myArr.GetLength(myArr.Rank - 1);
while (myEnumerator.MoveNext())
{
if (i < cols)
{
i++;
}
else
{
outputBlock.Text += "\n";
i = 1;
}
outputBlock.Text += String.Format("\t{0}", myEnumerator.Current);
}
outputBlock.Text += "\n";
}
}
/*
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.
*/
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.