.NET Framework Class Library
ListTBinarySearch Method (T)

Searches the entire sorted ListT for an element using the default comparer and returns the zero-based index of the element.

Namespace:   System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Public Function BinarySearch ( _
	item As T _
) As [%$TOPIC/w4e7fxsh_en-us_VS_110_2_0_0_0_0%]
public [%$TOPIC/w4e7fxsh_en-us_VS_110_2_0_1_0_0%] BinarySearch(
	T item
)
public:
[%$TOPIC/w4e7fxsh_en-us_VS_110_2_0_2_0_0%] BinarySearch(
	T item
)
member BinarySearch : 
        item:'T -> [%$TOPIC/w4e7fxsh_en-us_VS_110_2_0_3_0_0%]
public function BinarySearch(
	item : T
) : [%$TOPIC/w4e7fxsh_en-us_VS_110_2_0_4_0_0%]

Parameters

item
Type: T

The object to locate. The value can be for reference types.

Return Value

Type: SystemInt32
The zero-based index of item in the sorted ListT, if item is found; otherwise, a negative number that is the bitwise complement of the index of the next element that is larger than item or, if there is no larger element, the bitwise complement of Count.
Exceptions
ExceptionCondition
InvalidOperationException

The default comparer ComparerTDefault cannot find an implementation of the IComparableT generic interface or the IComparable interface for type T.

Remarks

This method uses the default comparer ComparerTDefault for type T to determine the order of list elements. The ComparerTDefault property checks whether type T implements the IComparableT generic interface and uses that implementation, if available. If not, ComparerTDefault checks whether type T implements the IComparable interface. If type T does not implement either interface, ComparerTDefault throws an InvalidOperationException.

The ListT must already be sorted according to the comparer implementation; otherwise, the result is incorrect.

Comparing with any reference type is allowed and does not generate an exception when using the IComparableT generic interface. When sorting, is considered to be less than any other object.

If the ListT contains more than one element with the same value, the method returns only one of the occurrences, and it might return any one of the occurrences, not necessarily the first one.

If the ListT does not contain the specified value, the method returns a negative integer. You can apply the bitwise complement operation (~) to this negative integer to get the index of the first element that is larger than the search value. When inserting the value into the ListT, this index should be used as the insertion point to maintain the sort order.

This method is an O(log n) operation, where n is the number of elements in the range.

Examples

The following example demonstrates the Sort method overload and the BinarySearch(T) method overload. A ListT of strings is created and populated with four strings, in no particular order. The list is displayed, sorted, and displayed again.

The BinarySearch(T) method overload is then used to search for two strings that are not in the list, and the Insert method is used to insert them. The return value of the BinarySearch(T) method is negative in each case, because the strings are not in the list. Taking the bitwise complement (the ~ operator in C# and Visual C++, Xor -1 in Visual Basic) of this negative number produces the index of the first element in the list that is larger than the search string, and inserting at this location preserves the sort order. The second search string is larger than any element in the list, so the insertion position is at the end of the list.

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

        dinosaurs.Add("Pachycephalosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Deinonychus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & "Sort")
        dinosaurs.Sort

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & _
            "BinarySearch and Insert ""Coelophysis"":")
        Dim index As Integer = dinosaurs.BinarySearch("Coelophysis")
        If index < 0 Then
            index = index Xor -1
            dinosaurs.Insert(index, "Coelophysis")
        End If

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & _
            "BinarySearch and Insert ""Tyrannosaurus"":")
        index = dinosaurs.BinarySearch("Tyrannosaurus")
        If index < 0 Then
            index = index Xor -1
            dinosaurs.Insert(index, "Tyrannosaurus")
        End If

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next 

    End Sub 
End Class 

' This code example produces the following output: 
' 
'Pachycephalosaurus 
'Amargasaurus 
'Mamenchisaurus 
'Deinonychus 
' 
'Sort 
' 
'Amargasaurus 
'Deinonychus 
'Mamenchisaurus 
'Pachycephalosaurus 
' 
'BinarySearch and Insert "Coelophysis": 
' 
'Amargasaurus 
'Coelophysis 
'Deinonychus 
'Mamenchisaurus 
'Pachycephalosaurus 
' 
'BinarySearch and Insert "Tyrannosaurus": 
' 
'Amargasaurus 
'Coelophysis 
'Deinonychus 
'Mamenchisaurus 
'Pachycephalosaurus 
'Tyrannosaurus
using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>();

        dinosaurs.Add("Pachycephalosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Deinonychus");

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

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

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

        Console.WriteLine("\nBinarySearch and Insert \"Coelophysis\":");
        int index = dinosaurs.BinarySearch("Coelophysis");
        if (index < 0)
        {
            dinosaurs.Insert(~index, "Coelophysis");
        }

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

        Console.WriteLine("\nBinarySearch and Insert \"Tyrannosaurus\":");
        index = dinosaurs.BinarySearch("Tyrannosaurus");
        if (index < 0)
        {
            dinosaurs.Insert(~index, "Tyrannosaurus");
        }

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

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort

Amargasaurus
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaurus":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus
Tyrannosaurus
 */
using namespace System;
using namespace System::Collections::Generic;

void main()
{
    List<String^>^ dinosaurs = gcnew List<String^>();

    dinosaurs->Add("Pachycephalosaurus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Mamenchisaurus");
    dinosaurs->Add("Deinonychus");

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nSort");
    dinosaurs->Sort();

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nBinarySearch and Insert \"Coelophysis\":");
    int index = dinosaurs->BinarySearch("Coelophysis");
    if (index < 0)
    {
        dinosaurs->Insert(~index, "Coelophysis");
    }

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nBinarySearch and Insert \"Tyrannosaurus\":");
    index = dinosaurs->BinarySearch("Tyrannosaurus");
    if (index < 0)
    {
        dinosaurs->Insert(~index, "Tyrannosaurus");
    }

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort

Amargasaurus
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaurus":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus
Tyrannosaurus
 */
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8