Array.BinarySearch<T> Method (T, Int32, Int32, T)
Assembly: mscorlib (in mscorlib.dll)
The type of the elements of the array.
- Type: 
The sorted one-dimensional, zero-based Array to search.
- Type: System.Int32
The starting index of the range to search.
- Type: System.Int32
The length of the range to search.
The object to search for.
Return ValueType: 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).
array is null.
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.
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<T> generic 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<T> implementation; otherwise, the result might be incorrect.
If value does not implement the IComparable<T> generic interface, the elements of array are not tested for IComparable<T> before the search begins. An exception is thrown if the search encounters an element that does not implement IComparable<T>.
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. When sorting, null is considered to be less than any other object.
For every element tested, value is passed to the appropriate IComparable<T> implementation, even if value is null. That is, the IComparable<T> implementation determines how a given element compares to null.
This method is an O(log n) operation, where n is length.
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