Article
11/18/2011

Array.BinarySearch Method (Array, Int32, Int32, Object, IComparer)

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Searches a range of elements in a one-dimensional sorted Array for a value, using the specified IComparer interface.

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

Syntax

'Declaration
<SecuritySafeCriticalAttribute> _
Public Shared Function BinarySearch ( _
    array As Array, _
    index As Integer, _
    length As Integer, _
    value As Object, _
    comparer As IComparer _
) As Integer

[SecuritySafeCriticalAttribute]
public static int BinarySearch(
    Array array,
    int index,
    int length,
    Object value,
    IComparer comparer
)

Parameters

array
Type: System.Array
The sorted one-dimensional Array to search.

index
Type: System.Int32
The starting index of the range to search.

length
Type: System.Int32
The length of the range to search.

value
Type: System.Object
The object to search for.

comparer
Type: System.Collections.IComparer
The IComparer implementation to use when comparing elements.
-or-
nulla null reference (Nothing in Visual Basic) to use the IComparable implementation of each element.

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.
ArgumentOutOfRangeException	index is less than the lower bound of array. -or- length is less than zero.
ArgumentException	index and length do not specify a valid range in array. -or- comparer is nulla null reference (Nothing in Visual Basic), and value is of a type that is not compatible with the elements of array.
InvalidOperationException	comparer is nulla null reference (Nothing in Visual Basic), value does not implement the IComparable interface, and the search encounters an element that does not implement the IComparable interface.

Remarks

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.

The comparer customizes how the elements are compared.

If comparer is not nulla null reference (Nothing in Visual Basic), the elements of array are compared to the specified value using the specified IComparer implementation. The elements of array must already be sorted in increasing value according to the sort order defined by comparer; otherwise, the result might be incorrect.

If comparer is nulla null reference (Nothing in Visual Basic), the comparison is done using the IComparable implementation provided by the element itself or by the specified value. 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.

Note:
If comparer is nulla null reference (Nothing in Visual Basic) and 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 using IComparable. 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 length.

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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