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Array.BinarySearch Method

Definition

Searches a one-dimensional sorted Array for a value, using a binary search algorithm.

Overloads

BinarySearch(Array, Object)

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.

BinarySearch(Array, Object, IComparer)

Searches an entire one-dimensional sorted array for a value using the specified IComparer interface.

BinarySearch(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.

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

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

BinarySearch<T>(T[], T)

Searches an entire one-dimensional sorted array for a specific element, using the IComparable<T> generic interface implemented by each element of the Array and by the specified object.

BinarySearch<T>(T[], T, IComparer<T>)

Searches an entire one-dimensional sorted array for a value using the specified IComparer<T> generic interface.

BinarySearch<T>(T[], Int32, Int32, T)

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

BinarySearch<T>(T[], Int32, Int32, T, IComparer<T>)

Searches a range of elements in a one-dimensional sorted array for a value, using the specified IComparer<T> generic interface.

BinarySearch(Array, Object)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

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.

C#
public static int BinarySearch(Array array, object value);
C#
public static int BinarySearch(Array array, object? value);

Parameters

array
Array

The sorted one-dimensional Array to search.

value
Object

The object to search for.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

array is multidimensional.

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.

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.

C#
using System;

public class SamplesArray
{
    public static void Main()
    {
        // Creates and initializes a new Array.
        Array myIntArray = Array.CreateInstance(typeof(int), 5);

        myIntArray.SetValue(8, 0);
        myIntArray.SetValue(2, 1);
        myIntArray.SetValue(6, 2);
        myIntArray.SetValue(3, 3);
        myIntArray.SetValue(7, 4);

        // Do the required sort first
        Array.Sort(myIntArray);

        // Displays the values of the Array.
        Console.WriteLine( "The int array contains the following:" );
        PrintValues(myIntArray);

        // Locates a specific object that does not exist in the Array.
        object myObjectOdd = 1;
        FindMyObject( myIntArray, myObjectOdd );

        // Locates an object that exists in the Array.
        object myObjectEven = 6;
        FindMyObject(myIntArray, myObjectEven);
    }

    public static void FindMyObject(Array myArr, object myObject)
    {
        int myIndex=Array.BinarySearch(myArr, myObject);
        if (myIndex < 0)
        {
            Console.WriteLine("The object to search for ({0}) is not found. The next larger object is at index {1}.", myObject, ~myIndex );
        }
        else
        {
            Console.WriteLine("The object to search for ({0}) is at index {1}.", myObject, myIndex );
        }
    }

    public static void PrintValues(Array myArr)
    {
        int i = 0;
        int cols = myArr.GetLength(myArr.Rank - 1);
        foreach (object o in myArr)
        {
            if ( i < cols )
            {
                i++;
            }
            else
            {
                Console.WriteLine();
                i = 1;
            }
            Console.Write( "\t{0}", o);
        }
        Console.WriteLine();
    }
}
// This code produces the following output.
//
//The int array contains the following:
//        2       3       6       7       8
//The object to search for (1) is not found. The next larger object is at index 0
//
//The object to search for (6) is at index 2.

Remarks

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.

Note

Ifvalue 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.

Note

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 Length of array.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch(Array, Object, IComparer)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

Searches an entire one-dimensional sorted array for a value using the specified IComparer interface.

C#
public static int BinarySearch(Array array, object value, System.Collections.IComparer comparer);
C#
public static int BinarySearch(Array array, object? value, System.Collections.IComparer? comparer);

Parameters

array
Array

The sorted one-dimensional Array to search.

value
Object

The object to search for.

comparer
IComparer

The IComparer implementation to use when comparing elements.

-or-

null to use the IComparable implementation of each element.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

array is multidimensional.

comparer is null, and value is of a type that is not compatible with the elements of array.

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

Remarks

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.

The comparer customizes how the elements are compared. For example, you can use a System.Collections.CaseInsensitiveComparer as the comparer to perform case-insensitive string searches.

If comparer is not null, 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.

Ifcomparer is null, 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 null 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.

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

Note

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 Length of array.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch(Array, Int32, Int32, Object)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

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.

C#
public static int BinarySearch(Array array, int index, int length, object value);
C#
public static int BinarySearch(Array array, int index, int length, object? value);

Parameters

array
Array

The sorted one-dimensional Array to search.

index
Int32

The starting index of the range to search.

length
Int32

The length of the range to search.

value
Object

The object to search for.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

array is multidimensional.

index is less than the lower bound of array.

-or-

length is less than zero.

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

-or-

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.

Remarks

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.

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.

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

Note

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.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

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

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

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

C#
public static int BinarySearch(Array array, int index, int length, object value, System.Collections.IComparer comparer);
C#
public static int BinarySearch(Array array, int index, int length, object? value, System.Collections.IComparer? comparer);

Parameters

array
Array

The sorted one-dimensional Array to search.

index
Int32

The starting index of the range to search.

length
Int32

The length of the range to search.

value
Object

The object to search for.

comparer
IComparer

The IComparer implementation to use when comparing elements.

-or-

null to use the IComparable implementation of each element.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

array is multidimensional.

index is less than the lower bound of array.

-or-

length is less than zero.

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

-or-

comparer is null, and value is of a type that is not compatible with the elements of array.

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

Remarks

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.

The comparer customizes how the elements are compared. For example, you can use a System.Collections.CaseInsensitiveComparer as the comparer to perform case-insensitive string searches.

If comparer is not null, 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 null, 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 null 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.

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

Note

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.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch<T>(T[], T)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

Searches an entire one-dimensional sorted array for a specific element, using the IComparable<T> generic interface implemented by each element of the Array and by the specified object.

C#
public static int BinarySearch<T>(T[] array, T value);

Type Parameters

T

The type of the elements of the array.

Parameters

array
T[]

The sorted one-dimensional, zero-based Array to search.

value
T

The object to search for.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

T does not implement the IComparable<T> generic interface.

Examples

The following code example demonstrates the Sort<T>(T[]) generic method overload and the BinarySearch<T>(T[], T) generic method overload. An array of strings is created, in no particular order.

The array is displayed, sorted, and displayed again. Arrays must be sorted in order to use the BinarySearch method.

Note

The calls to the Sort and BinarySearch generic methods do not look any different from calls to their nongeneric counterparts, because Visual Basic, F#, C#, and C++ infer the type of the generic type parameter from the type of the first argument. If you use the Ildasm.exe (IL Disassembler) to examine the Microsoft intermediate language (MSIL), you can see that the generic methods are being called.

The BinarySearch<T>(T[], T) generic method overload is then used to search for two strings, one that is not in the array and one that is. The array and the return value of the BinarySearch method are passed to the ShowWhere generic method (the showWhere function in the F# example), which displays the index value if the string is found, and otherwise the elements the search string would fall between if it were in the array. The index is negative if the string is not in the array, so the ShowWhere method takes the bitwise complement (the ~ operator in C# and Visual C++, the ~~~ operator in F#, Xor-1 in Visual Basic) to obtain the index of the first element in the list that is larger than the search string.

C#
using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = {"Pachycephalosaurus",
                              "Amargasaurus",
                              "Tyrannosaurus",
                              "Mamenchisaurus",
                              "Deinonychus",
                              "Edmontosaurus"};

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nSort");
        Array.Sort(dinosaurs);

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nBinarySearch for 'Coelophysis':");
        int index = Array.BinarySearch(dinosaurs, "Coelophysis");
        ShowWhere(dinosaurs, index);

        Console.WriteLine("\nBinarySearch for 'Tyrannosaurus':");
        index = Array.BinarySearch(dinosaurs, "Tyrannosaurus");
        ShowWhere(dinosaurs, index);
    }

    private static void ShowWhere<T>(T[] array, int index)
    {
        if (index<0)
        {
            // If the index is negative, it represents the bitwise
            // complement of the next larger element in the array.
            //
            index = ~index;

            Console.Write("Not found. Sorts between: ");

            if (index == 0)
                Console.Write("beginning of array and ");
            else
                Console.Write("{0} and ", array[index-1]);

            if (index == array.Length)
                Console.WriteLine("end of array.");
            else
                Console.WriteLine("{0}.", array[index]);
        }
        else
        {
            Console.WriteLine("Found at index {0}.", index);
        }
    }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Tyrannosaurus
Mamenchisaurus
Deinonychus
Edmontosaurus

Sort

Amargasaurus
Deinonychus
Edmontosaurus
Mamenchisaurus
Pachycephalosaurus
Tyrannosaurus

BinarySearch for 'Coelophysis':
Not found. Sorts between: Amargasaurus and Deinonychus.

BinarySearch for 'Tyrannosaurus':
Found at index 5.
 */

Remarks

This method does not support searching arrays that contain negative indexes. array must be sorted before calling this method.

If 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 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.

T 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.

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.

Note

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 the Length of array.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch<T>(T[], T, IComparer<T>)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

Searches an entire one-dimensional sorted array for a value using the specified IComparer<T> generic interface.

C#
public static int BinarySearch<T>(T[] array, T value, System.Collections.Generic.IComparer<T> comparer);
C#
public static int BinarySearch<T>(T[] array, T value, System.Collections.Generic.IComparer<T>? comparer);

Type Parameters

T

The type of the elements of the array.

Parameters

array
T[]

The sorted one-dimensional, zero-based Array to search.

value
T

The object to search for.

comparer
IComparer<T>

The IComparer<T> implementation to use when comparing elements.

-or-

null to use the IComparable<T> implementation of each element.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

comparer is null, and value is of a type that is not compatible with the elements of array.

comparer is null, and T does not implement the IComparable<T> generic interface

Examples

The following example demonstrates the Sort<T>(T[], IComparer<T>) generic method overload and the BinarySearch<T>(T[], T, IComparer<T>) generic method overload.

The code example defines an alternative comparer for strings, named ReverseCompare, which implements the IComparer<string> (IComparer(Of String) in Visual Basic, IComparer<String^> in Visual C++) generic interface. The comparer calls the CompareTo(String) method, reversing the order of the comparands so that the strings sort high-to-low instead of low-to-high.

The array is displayed, sorted, and displayed again. Arrays must be sorted in order to use the BinarySearch method.

Note

The calls to the Sort<T>(T[], IComparer<T>) and BinarySearch<T>(T[], T, IComparer<T>) generic methods do not look any different from calls to their nongeneric counterparts, because Visual Basic, C#, and C++ infer the type of the generic type parameter from the type of the first argument. If you use the Ildasm.exe (IL Disassembler) to examine the Microsoft intermediate language (MSIL), you can see that the generic methods are being called.

The BinarySearch<T>(T[], T, IComparer<T>) generic method overload is then used to search for two strings, one that is not in the array and one that is. The array and the return value of the BinarySearch<T>(T[], T, IComparer<T>) method are passed to the ShowWhere generic method (the showWhere function in the F# example), which displays the index value if the string is found, and otherwise the elements the search string would fall between if it were in the array. The index is negative if the string is not n the array, so the ShowWhere method takes the bitwise complement (the ~ operator in C# and Visual C++, the ~~~ operator in F#, Xor -1 in Visual Basic) to obtain the index of the first element in the list that is larger than the search string.

C#
using System;
using System.Collections.Generic;

public class ReverseComparer: IComparer<string>
{
    public int Compare(string x, string y)
    {
        // Compare y and x in reverse order.
        return y.CompareTo(x);
    }
}

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = {"Pachycephalosaurus",
                              "Amargasaurus",
                              "Tyrannosaurus",
                              "Mamenchisaurus",
                              "Deinonychus",
                              "Edmontosaurus"};

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        ReverseComparer rc = new ReverseComparer();

        Console.WriteLine("\nSort");
        Array.Sort(dinosaurs, rc);

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nBinarySearch for 'Coelophysis':");
        int index = Array.BinarySearch(dinosaurs, "Coelophysis", rc);
        ShowWhere(dinosaurs, index);

        Console.WriteLine("\nBinarySearch for 'Tyrannosaurus':");
        index = Array.BinarySearch(dinosaurs, "Tyrannosaurus", rc);
        ShowWhere(dinosaurs, index);
    }

    private static void ShowWhere<T>(T[] array, int index)
    {
        if (index<0)
        {
            // If the index is negative, it represents the bitwise
            // complement of the next larger element in the array.
            //
            index = ~index;

            Console.Write("Not found. Sorts between: ");

            if (index == 0)
                Console.Write("beginning of array and ");
            else
                Console.Write("{0} and ", array[index-1]);

            if (index == array.Length)
                Console.WriteLine("end of array.");
            else
                Console.WriteLine("{0}.", array[index]);
        }
        else
        {
            Console.WriteLine("Found at index {0}.", index);
        }
    }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Tyrannosaurus
Mamenchisaurus
Deinonychus
Edmontosaurus

Sort

Tyrannosaurus
Pachycephalosaurus
Mamenchisaurus
Edmontosaurus
Deinonychus
Amargasaurus

BinarySearch for 'Coelophysis':
Not found. Sorts between: Deinonychus and Amargasaurus.

BinarySearch for 'Tyrannosaurus':
Found at index 0.
 */

Remarks

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 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. For example, you can use a System.Collections.CaseInsensitiveComparer as the comparer to perform case-insensitive string searches.

If comparer is not null, the elements of array are compared to the specified value using the specified IComparer<T> generic interface 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 null, the comparison is done using the IComparable<T> generic interface implementation provided by T. 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.

Note

If comparer is null and 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.

Note

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 the Length of array.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch<T>(T[], Int32, Int32, T)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

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

C#
public static int BinarySearch<T>(T[] array, int index, int length, T value);

Type Parameters

T

The type of the elements of the array.

Parameters

array
T[]

The sorted one-dimensional, zero-based Array to search.

index
Int32

The starting index of the range to search.

length
Int32

The length of the range to search.

value
T

The object to search for.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

index is less than the lower bound of array.

-or-

length is less than zero.

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

-or-

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

T does not implement the IComparable<T> generic interface.

Remarks

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 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.

T 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.

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.

Note

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.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

BinarySearch<T>(T[], Int32, Int32, T, IComparer<T>)

Source:
Array.cs
Source:
Array.cs
Source:
Array.cs

Searches a range of elements in a one-dimensional sorted array for a value, using the specified IComparer<T> generic interface.

C#
public static int BinarySearch<T>(T[] array, int index, int length, T value, System.Collections.Generic.IComparer<T> comparer);
C#
public static int BinarySearch<T>(T[] array, int index, int length, T value, System.Collections.Generic.IComparer<T>? comparer);

Type Parameters

T

The type of the elements of the array.

Parameters

array
T[]

The sorted one-dimensional, zero-based Array to search.

index
Int32

The starting index of the range to search.

length
Int32

The length of the range to search.

value
T

The object to search for.

comparer
IComparer<T>

The IComparer<T> implementation to use when comparing elements.

-or-

null to use the IComparable<T> implementation of each element.

Returns

The index of the specified value in the specified array, if value is found; otherwise, a negative number. If value is not found and value is less than one or more elements in array, the negative number returned 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 all elements in array, the negative number returned is the bitwise complement of (the index of the last element plus 1). If this method is called with a non-sorted array, the return value can be incorrect and a negative number could be returned, even if value is present in array.

Exceptions

array is null.

index is less than the lower bound of array.

-or-

length is less than zero.

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

-or-

comparer is null, and value is of a type that is not compatible with the elements of array.

comparer is null, and T does not implement the IComparable<T> generic interface.

Remarks

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 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. For example, you can use a System.Collections.CaseInsensitiveComparer as the comparer to perform case-insensitive string searches.

If comparer is not null, the elements of array are compared to the specified value using the specified IComparer<T> generic interface 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 null, the comparison is done using the IComparable<T> generic interface implementation provided for type T. 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.

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 using IComparable<T>.

Note

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.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0