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IComparable Interface

Updated: July 2008

Defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.

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

[ComVisibleAttribute(true)]
public interface class IComparable

This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo, that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. The instance's IComparable implementation is called automatically by methods such as Array::Sort and ArrayList::Sort.

All numeric types (such as Int32 and Double) implement IComparable, as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable to enable object instances to be ordered or sorted.

The following code sample illustrates the implementation of IComparable and the requisite CompareTo method.

using namespace System;
using namespace System::Collections;

public ref class Temperature: public IComparable {
   /// <summary> 
   /// IComparable.CompareTo implementation. 
   /// </summary> 
protected:
   // The value holder
   Double m_value;

public:
   virtual Int32 CompareTo( Object^ obj ) {

      if (obj == nullptr) return 1;

      if ( obj->GetType() == Temperature::typeid ) {
         Temperature^ temp = dynamic_cast<Temperature^>(obj);

         return m_value.CompareTo( temp->m_value );
      }
      throw gcnew ArgumentException(  "object is not a Temperature" );
   }

   property Double Value {
      Double get() {
         return m_value;
      }
      void set( Double value ) {
         m_value = value;
      }
   }

   property Double Celsius  {
      Double get() {
         return (m_value - 32) / 1.8;
      }
      void set( Double value ) {
         m_value = (value * 1.8) + 32;
      }
   }
};

int main()
{
   ArrayList^ temperatures = gcnew ArrayList;
   // Initialize random number generator.
   Random^ rnd = gcnew Random;

   // Generate 10 temperatures between 0 and 100 randomly. 
   for (int ctr = 1; ctr <= 10; ctr++)
   {
      int degrees = rnd->Next(0, 100);
      Temperature^ temp = gcnew Temperature;
      temp->Value = degrees;
      temperatures->Add(temp);
   }

   // Sort ArrayList.
   temperatures->Sort();

   for each (Temperature^ temp in temperatures)
      Console::WriteLine(temp->Value);
   return 0;
}
// The example displays the following output to the console (individual 
// values may vary because they are randomly generated): 
//       2 
//       7 
//       16 
//       17 
//       31 
//       37 
//       58 
//       66 
//       72 
//       95

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

July 2008

Added detail on usage by the common language runtime and information for implementors.

Customer feedback.

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