System.Array.BinarySearch Method

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.

[System.Runtime.ConstrainedExecution.ReliabilityContract(System.Runtime.ConstrainedExecution.Consistency.WillNotCorruptState, System.Runtime.ConstrainedExecution.Cer.MayFail)]

public static int**BinarySearch** (Array array, object value)

public static int

array- The sorted one-dimensional Array to search.
value- The object to search for.

The index of the specified

valuein the specifiedarray, ifvalueis found. Ifvalueis not found andvalueis less than one or more elements inarray, a negative number which is the bitwise complement of the index of the first element that is larger thanvalue. Ifvalueis not found andvalueis greater than any of the elements inarray, a negative number which is the bitwise complement of (the index of the last element plus 1).

Type Reason ArgumentException Both

valueand at least one element ofarraydo not implement the IComparable interface.-or-

valueis not assignment-compatible with at least one element ofarray.-or-

array.UpperBound == int.MaxValue.ArgumentNullException arrayisnull.RankException arrayhas more than one dimension.InvalidOperationException Both valueand at least one element ofarraydo 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 the Array.Length of *array*.