IComparer Interface


Exposes a method that compares two objects.

Namespace:   System.Collections
Assembly:  mscorlib (in mscorlib.dll)

public interface class IComparer

System_CAPS_pubmethodCompare(Object^, Object^)

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

This interface is used in conjunction with the Array::Sort and Array::BinarySearch methods. It provides a way to customize the sort order of a collection. See the Compare method for notes on parameters and return value.

The default implementation of this interface is the Comparer class. For the generic version of this interface, see System.Collections.Generic::IComparer<T>.

The following code example demonstrates the use of the IComparer interface to sort an ArrayList object. In this example, the IComparer interface is implemented using the CaseInsensitiveComparer class to reverse the order of the contents of the ArrayList.

using namespace System;
using namespace System::Collections;
void PrintIndexAndValues( IEnumerable^ myList );
ref class myReverserClass: public IComparer

   // Calls CaseInsensitiveComparer.Compare with the parameters reversed.
   virtual int Compare( Object^ x, Object^ y ) sealed = IComparer::Compare
      return ((gcnew CaseInsensitiveComparer)->Compare( y, x ));


int main()

   // Creates and initializes a new ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "The" );
   myAL->Add( "quick" );
   myAL->Add( "brown" );
   myAL->Add( "fox" );
   myAL->Add( "jumps" );
   myAL->Add( "over" );
   myAL->Add( "the" );
   myAL->Add( "lazy" );
   myAL->Add( "dog" );

   // Displays the values of the ArrayList.
   Console::WriteLine( "The ArrayList initially contains the following values:" );
   PrintIndexAndValues( myAL );

   // Sorts the values of the ArrayList using the default comparer.
   Console::WriteLine( "After sorting with the default comparer:" );
   PrintIndexAndValues( myAL );

   // Sorts the values of the ArrayList using the reverse case-insensitive comparer.
   IComparer^ myComparer = gcnew myReverserClass;
   myAL->Sort( myComparer );
   Console::WriteLine( "After sorting with the reverse case-insensitive comparer:" );
   PrintIndexAndValues( myAL );

void PrintIndexAndValues( IEnumerable^ myList )
   int i = 0;
   IEnumerator^ myEnum = myList->GetEnumerator();
   while ( myEnum->MoveNext() )
      Object^ obj = safe_cast<Object^>(myEnum->Current);
      Console::WriteLine( "\t[{0}]:\t{1}", i++, obj );


This code produces the following output.
The ArrayList initially contains the following values:
        [0]:    The
        [1]:    quick
        [2]:    brown
        [3]:    fox
        [4]:    jumps
        [5]:    over
        [6]:    the
        [7]:    lazy
        [8]:    dog

After sorting with the default comparer:
        [0]:    brown
        [1]:    dog
        [2]:    fox
        [3]:    jumps
        [4]:    lazy
        [5]:    over
        [6]:    quick
        [7]:    the
        [8]:    The

After sorting with the reverse case-insensitive comparer:
        [0]:    the
        [1]:    The
        [2]:    quick
        [3]:    over
        [4]:    lazy
        [5]:    jumps
        [6]:    fox
        [7]:    dog
        [8]:    brown 

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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