IComparable Interface


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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)

public interface class IComparable


Compares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.

This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo(Object^), 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.

The implementation of the CompareTo(Object^) method must return an Int32 that has one of three values, as shown in the following table.



Less than zero

The current instance precedes the object specified by the CompareTo method in the sort order.


This current instance occurs in the same position in the sort order as the object specified by the CompareTo method.

Greater than zero

This current instance follows the object specified by the CompareTo method in the sort order.

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 example 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>
   // The value holder
   Double m_value;

   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;

   // Sort ArrayList.

   for each (Temperature^ temp in temperatures)
   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

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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