List<T>.BinarySearchList<T>.BinarySearchList<T>.BinarySearchList<T>.BinarySearch Method

Definition

Uses a binary search algorithm to locate a specific element in the sorted List<T> or a portion of it.

 BinarySearch(T) BinarySearch(T) BinarySearch(T) BinarySearch(T) Searches the entire sorted List for an element using the default comparer and returns the zero-based index of the element. BinarySearch(T, IComparer) BinarySearch(T, IComparer) BinarySearch(T, IComparer) BinarySearch(T, IComparer) Searches the entire sorted List for an element using the specified comparer and returns the zero-based index of the element. BinarySearch(Int32, Int32, T, IComparer) BinarySearch(Int32, Int32, T, IComparer) BinarySearch(Int32, Int32, T, IComparer) BinarySearch(Int32, Int32, T, IComparer) Searches a range of elements in the sorted List for an element using the specified comparer and returns the zero-based index of the element.

BinarySearch(T)BinarySearch(T)BinarySearch(T)BinarySearch(T)

Searches the entire sorted List<T> for an element using the default comparer and returns the zero-based index of the element.

``````public:
int BinarySearch(T item);``````
``public int BinarySearch (T item);``
``member this.BinarySearch : 'T -> int``
``Public Function BinarySearch (item As T) As Integer``

Parameters

item
T T T T

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

Returns

The zero-based index of `item` in the sorted List<T>, 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

The default comparer Default cannot find an implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

Examples

The following example demonstrates the Sort() method overload and the BinarySearch(T) method overload. A List<T> 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.

``````using namespace System;
using namespace System::Collections::Generic;

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

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
*/
``````
``````using System;
using System.Collections.Generic;

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

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
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)

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
``````

Remarks

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

The List<T> must already be sorted according to the comparer implementation; otherwise, the result is incorrect.

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

If the List<T> 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 List<T> 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 List<T>, 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.

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

Searches the entire sorted List<T> for an element using the specified comparer and returns the zero-based index of the element.

``````public:
int BinarySearch(T item, System::Collections::Generic::IComparer<T> ^ comparer);``````
``public int BinarySearch (T item, System.Collections.Generic.IComparer<T> comparer);``
``member this.BinarySearch : 'T * System.Collections.Generic.IComparer<'T> -> int``
``Public Function BinarySearch (item As T, comparer As IComparer(Of T)) As Integer``

Parameters

item
T T T T

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

comparer
IComparer<T> IComparer<T> IComparer<T> IComparer<T>

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

-or-

`null` to use the default comparer Default.

Returns

The zero-based index of `item` in the sorted List<T>, 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

`comparer` is `null`, and the default comparer Default cannot find an implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

Examples

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

The example defines an alternative comparer for strings named DinoCompare, which implements the `IComparer<string>` (`IComparer(Of String)` in Visual Basic, `IComparer<String^>` in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for `null`, and a null reference is treated as less than a non-null. Second, the string lengths are compared, and the longer string is deemed to be greater. Third, if the lengths are equal, ordinary string comparison is used.

A List<T> of strings is created and populated with four strings, in no particular order. The list is displayed, sorted using the alternate comparer, and displayed again.

The BinarySearch(T, IComparer<T>) method overload is then used to search for several strings that are not in the list, employing the alternate comparer. The Insert method is used to insert the strings. These two methods are located in the function named `SearchAndInsert`, along with code to take the bitwise complement (the ~ operator in C# and Visual C++, `Xor` -1 in Visual Basic) of the negative number returned by BinarySearch(T, IComparer<T>) and use it as an index for inserting the new string.

``````using namespace System;
using namespace System::Collections::Generic;

public ref class DinoComparer: IComparer<String^>
{
public:
virtual int Compare(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// If x is null and y is null, they're
// equal.
return 0;
}
else
{
// If x is null and y is not null, y
// is greater.
return -1;
}
}
else
{
// If x is not null...
//
if (y == nullptr)
// ...and y is null, x is greater.
{
return 1;
}
else
{
// ...and y is not null, compare the
// lengths of the two strings.
//
int retval = x->Length.CompareTo(y->Length);

if (retval != 0)
{
// If the strings are not of equal length,
// the longer string is greater.
//
return retval;
}
else
{
// If the strings are of equal length,
// sort them with ordinary string comparison.
//
return x->CompareTo(y);
}
}
}
}
};

void SearchAndInsert(List<String^>^ list, String^ insert,
DinoComparer^ dc)
{
Console::WriteLine("\nBinarySearch and Insert \"{0}\":", insert);

int index = list->BinarySearch(insert, dc);

if (index < 0)
{
list->Insert(~index, insert);
}
};

void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
Console::WriteLine(s);
}
};

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

DinoComparer^ dc = gcnew DinoComparer();

Console::WriteLine("\nSort with alternate comparer:");
dinosaurs->Sort(dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Coelophysis", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Oviraptor", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Tyrannosaur", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, nullptr, dc);
Display(dinosaurs);
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort with alternate comparer:

Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Oviraptor":

Oviraptor
Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaur":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus
*/
``````
``````using System;
using System.Collections.Generic;

public class DinoComparer: IComparer<string>
{
public int Compare(string x, string y)
{
if (x == null)
{
if (y == null)
{
// If x is null and y is null, they're
// equal.
return 0;
}
else
{
// If x is null and y is not null, y
// is greater.
return -1;
}
}
else
{
// If x is not null...
//
if (y == null)
// ...and y is null, x is greater.
{
return 1;
}
else
{
// ...and y is not null, compare the
// lengths of the two strings.
//
int retval = x.Length.CompareTo(y.Length);

if (retval != 0)
{
// If the strings are not of equal length,
// the longer string is greater.
//
return retval;
}
else
{
// If the strings are of equal length,
// sort them with ordinary string comparison.
//
return x.CompareTo(y);
}
}
}
}
}

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

DinoComparer dc = new DinoComparer();

Console.WriteLine("\nSort with alternate comparer:");
dinosaurs.Sort(dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Coelophysis", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Oviraptor", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Tyrannosaur", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, null, dc);
Display(dinosaurs);
}

private static void SearchAndInsert(List<string> list,
string insert, DinoComparer dc)
{
Console.WriteLine("\nBinarySearch and Insert \"{0}\":", insert);

int index = list.BinarySearch(insert, dc);

if (index < 0)
{
list.Insert(~index, insert);
}
}

private static void Display(List<string> list)
{
Console.WriteLine();
foreach( string s in list )
{
Console.WriteLine(s);
}
}
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort with alternate comparer:

Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Oviraptor":

Oviraptor
Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaur":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class DinoComparer
Implements IComparer(Of String)

Public Function Compare(ByVal x As String, _
ByVal y As String) As Integer _
Implements IComparer(Of String).Compare

If x Is Nothing Then
If y Is Nothing Then
' If x is Nothing and y is Nothing, they're
' equal.
Return 0
Else
' If x is Nothing and y is not Nothing, y
' is greater.
Return -1
End If
Else
' If x is not Nothing...
'
If y Is Nothing Then
' ...and y is Nothing, x is greater.
Return 1
Else
' ...and y is not Nothing, compare the
' lengths of the two strings.
'
Dim retval As Integer = _
x.Length.CompareTo(y.Length)

If retval <> 0 Then
' If the strings are not of equal length,
' the longer string is greater.
'
Return retval
Else
' If the strings are of equal length,
' sort them with ordinary string comparison.
'
Return x.CompareTo(y)
End If
End If
End If
End Function
End Class

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)
Display(dinosaurs)

Dim dc As New DinoComparer

Console.WriteLine(vbLf & "Sort with alternate comparer:")
dinosaurs.Sort(dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Coelophysis", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Oviraptor", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Tyrannosaur", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, Nothing, dc)
Display(dinosaurs)
End Sub

Private Shared Sub SearchAndInsert( _
ByVal lis As List(Of String), _
ByVal insert As String, ByVal dc As DinoComparer)

Console.WriteLine(vbLf & _
"BinarySearch and Insert ""{0}"":", insert)

Dim index As Integer = lis.BinarySearch(insert, dc)

If index < 0 Then
index = index Xor -1
lis.Insert(index, insert)
End If
End Sub

Private Shared Sub Display(ByVal lis As List(Of String))
Console.WriteLine()
For Each s As String In lis
Console.WriteLine(s)
Next
End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'Sort with alternate comparer:
'
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Coelophysis":
'
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Oviraptor":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Tyrannosaur":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "":
'
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
``````

Remarks

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

If `comparer` is provided, the elements of the List<T> are compared to the specified value using the specified IComparer<T> implementation.

If `comparer` is `null`, the default comparer Comparer<T>.Default checks whether type `T` implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type `T` implements the IComparable interface. If type `T` does not implement either interface, Comparer<T>.Default throws InvalidOperationException.

The List<T> must already be sorted according to the comparer implementation; otherwise, the result is incorrect.

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

If the List<T> 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 List<T> 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 List<T>, 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.

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

Searches a range of elements in the sorted List<T> for an element using the specified comparer and returns the zero-based index of the element.

``````public:
int BinarySearch(int index, int count, T item, System::Collections::Generic::IComparer<T> ^ comparer);``````
``public int BinarySearch (int index, int count, T item, System.Collections.Generic.IComparer<T> comparer);``
``member this.BinarySearch : int * int * 'T * System.Collections.Generic.IComparer<'T> -> int``
``Public Function BinarySearch (index As Integer, count As Integer, item As T, comparer As IComparer(Of T)) As Integer``

Parameters

index
Int32 Int32 Int32 Int32

The zero-based starting index of the range to search.

count
Int32 Int32 Int32 Int32

The length of the range to search.

item
T T T T

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

comparer
IComparer<T> IComparer<T> IComparer<T> IComparer<T>

The IComparer<T> implementation to use when comparing elements, or `null` to use the default comparer Default.

Returns

The zero-based index of `item` in the sorted List<T>, 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

`index` is less than 0.

-or-

`count` is less than 0.

`index` and `count` do not denote a valid range in the List<T>.

`comparer` is `null`, and the default comparer Default cannot find an implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

Examples

The following example demonstrates the Sort(Int32, Int32, IComparer<T>) method overload and the BinarySearch(Int32, Int32, T, IComparer<T>) method overload.

The example defines an alternative comparer for strings named DinoCompare, which implements the `IComparer<string>` (`IComparer(Of String)` in Visual Basic, `IComparer<String^>` in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for `null`, and a null reference is treated as less than a non-null. Second, the string lengths are compared, and the longer string is deemed to be greater. Third, if the lengths are equal, ordinary string comparison is used.

A List<T> of strings is created and populated with the names of five herbivorous dinosaurs and three carnivorous dinosaurs. Within each of the two groups, the names are not in any particular sort order. The list is displayed, the range of herbivores is sorted using the alternate comparer, and the list is displayed again.

The BinarySearch(Int32, Int32, T, IComparer<T>) method overload is then used to search only the range of herbivores for "Brachiosaurus". The string is not found, and the bitwise complement (the ~ operator in C# and Visual C++, `Xor` -1 in Visual Basic) of the negative number returned by the BinarySearch(Int32, Int32, T, IComparer<T>) method is used as an index for inserting the new string.

``````using namespace System;
using namespace System::Collections::Generic;

public ref class DinoComparer: IComparer<String^>
{
public:
virtual int Compare(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// If x is null and y is null, they're
// equal.
return 0;
}
else
{
// If x is null and y is not null, y
// is greater.
return -1;
}
}
else
{
// If x is not null...
//
if (y == nullptr)
// ...and y is null, x is greater.
{
return 1;
}
else
{
// ...and y is not null, compare the
// lengths of the two strings.
//
int retval = x->Length.CompareTo(y->Length);

if (retval != 0)
{
// If the strings are not of equal length,
// the longer string is greater.
//
return retval;
}
else
{
// If the strings are of equal length,
// sort them with ordinary string comparison.
//
return x->CompareTo(y);
}
}
}
}
};

void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
Console::WriteLine(s);
}
};

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

int herbivores = 5;
Display(dinosaurs);

DinoComparer^ dc = gcnew DinoComparer();

Console::WriteLine("\nSort a range with the alternate comparer:");
dinosaurs->Sort(0, herbivores, dc);
Display(dinosaurs);

Console::WriteLine("\nBinarySearch a range and Insert \"{0}\":",
"Brachiosaurus");

int index = dinosaurs->BinarySearch(0, herbivores, "Brachiosaurus", dc);

if (index < 0)
{
dinosaurs->Insert(~index, "Brachiosaurus");
herbivores++;
}

Display(dinosaurs);
}

/* This code example produces the following output:

Pachycephalosaurus
Parasauralophus
Amargasaurus
Galimimus
Mamenchisaurus
Deinonychus
Oviraptor
Tyrannosaurus

Sort a range with the alternate comparer:

Galimimus
Amargasaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus

BinarySearch a range and Insert "Brachiosaurus":

Galimimus
Amargasaurus
Brachiosaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus
*/
``````
``````using System;
using System.Collections.Generic;

public class DinoComparer: IComparer<string>
{
public int Compare(string x, string y)
{
if (x == null)
{
if (y == null)
{
// If x is null and y is null, they're
// equal.
return 0;
}
else
{
// If x is null and y is not null, y
// is greater.
return -1;
}
}
else
{
// If x is not null...
//
if (y == null)
// ...and y is null, x is greater.
{
return 1;
}
else
{
// ...and y is not null, compare the
// lengths of the two strings.
//
int retval = x.Length.CompareTo(y.Length);

if (retval != 0)
{
// If the strings are not of equal length,
// the longer string is greater.
//
return retval;
}
else
{
// If the strings are of equal length,
// sort them with ordinary string comparison.
//
return x.CompareTo(y);
}
}
}
}
}

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

int herbivores = 5;
Display(dinosaurs);

DinoComparer dc = new DinoComparer();

Console.WriteLine("\nSort a range with the alternate comparer:");
dinosaurs.Sort(0, herbivores, dc);
Display(dinosaurs);

Console.WriteLine("\nBinarySearch a range and Insert \"{0}\":",
"Brachiosaurus");

int index = dinosaurs.BinarySearch(0, herbivores, "Brachiosaurus", dc);

if (index < 0)
{
dinosaurs.Insert(~index, "Brachiosaurus");
herbivores++;
}

Display(dinosaurs);
}

private static void Display(List<string> list)
{
Console.WriteLine();
foreach( string s in list )
{
Console.WriteLine(s);
}
}
}

/* This code example produces the following output:

Pachycephalosaurus
Parasauralophus
Amargasaurus
Galimimus
Mamenchisaurus
Deinonychus
Oviraptor
Tyrannosaurus

Sort a range with the alternate comparer:

Galimimus
Amargasaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus

BinarySearch a range and Insert "Brachiosaurus":

Galimimus
Amargasaurus
Brachiosaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class DinoComparer
Implements IComparer(Of String)

Public Function Compare(ByVal x As String, _
ByVal y As String) As Integer _
Implements IComparer(Of String).Compare

If x Is Nothing Then
If y Is Nothing Then
' If x is Nothing and y is Nothing, they're
' equal.
Return 0
Else
' If x is Nothing and y is not Nothing, y
' is greater.
Return -1
End If
Else
' If x is not Nothing...
'
If y Is Nothing Then
' ...and y is Nothing, x is greater.
Return 1
Else
' ...and y is not Nothing, compare the
' lengths of the two strings.
'
Dim retval As Integer = _
x.Length.CompareTo(y.Length)

If retval <> 0 Then
' If the strings are not of equal length,
' the longer string is greater.
'
Return retval
Else
' If the strings are of equal length,
' sort them with ordinary string comparison.
'
Return x.CompareTo(y)
End If
End If
End If
End Function
End Class

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)

Dim herbivores As Integer = 5
Display(dinosaurs)

Dim dc As New DinoComparer

Console.WriteLine(vbLf & _
"Sort a range with the alternate comparer:")
dinosaurs.Sort(0, herbivores, dc)
Display(dinosaurs)

Console.WriteLine(vbLf & _
"BinarySearch a range and Insert ""{0}"":", _
"Brachiosaurus")

Dim index As Integer = _
dinosaurs.BinarySearch(0, herbivores, "Brachiosaurus", dc)

If index < 0 Then
index = index Xor -1
dinosaurs.Insert(index, "Brachiosaurus")
herbivores += 1
End If

Display(dinosaurs)

End Sub

Private Shared Sub Display(ByVal lis As List(Of String))
Console.WriteLine()
For Each s As String In lis
Console.WriteLine(s)
Next
End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Parasauralophus
'Amargasaurus
'Galimimus
'Mamenchisaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
'
'Sort a range with the alternate comparer:
'
'Galimimus
'Amargasaurus
'Mamenchisaurus
'Parasauralophus
'Pachycephalosaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
'
'BinarySearch a range and Insert "Brachiosaurus":
'
'Galimimus
'Amargasaurus
'Brachiosaurus
'Mamenchisaurus
'Parasauralophus
'Pachycephalosaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
``````

Remarks

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

If `comparer` is provided, the elements of the List<T> are compared to the specified value using the specified IComparer<T> implementation.

If `comparer` is `null`, the default comparer Comparer<T>.Default checks whether type `T` implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type `T` implements the IComparable interface. If type `T` does not implement either interface, Comparer<T>.Default throws InvalidOperationException.

The List<T> must already be sorted according to the comparer implementation; otherwise, the result is incorrect.

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

If the List<T> 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 List<T> 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 List<T>, 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.