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


Searches a range of elements in a one-dimensional sorted array for a value, using the IComparable interface implemented by each element of the array and by the specified value.

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

public static int BinarySearch(
	Array array,
	int index,
	int length,
	object value


Type: System.Array

The sorted one-dimensional Array to search.

Type: System.Int32

The starting index of the range to search.

Type: System.Int32

The length of the range to search.

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; otherwise, a negative number. If value is not found andvalue is less than one or more elements in array, the negative number returned is the bitwise complement of the indexof the first element that is larger than value. If value is not found and value is greater than allelements in array, the negative number returnedis the bitwise complement of (the index of the last element plus 1).If this method is called with a non-sorted array, the return valuecan be incorrect and a negative number could be returned, evenifvalueis present in array.

Exception Condition

array is null.


array is multidimensional.


index is less than the lower bound of array.


length is less than zero.


index and length do not specify a valid range in array.


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


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

This method does not support searching arrays that contain negative indexes. 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 (~ in C#, Not in Visual Basic) to the negative result to produce an index. If this index is one greater than the upper bound 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.


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.

null can always be compared with any other reference type; therefore, comparisons with null do not generate an exception.


   For every element tested, value is passed to the appropriate IComparable implementation, even if value is null. That is, the IComparable implementation determines how a given element compares to null.

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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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