.NET Framework Class Library
IComparable<(Of <(T>)>)..::.CompareTo Method

Compares the current object with another object of the same type.

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

Visual Basic (Declaration)
Function CompareTo ( _
    other As T _
) As Integer
Visual Basic (Usage)
Dim instance As IComparable
Dim other As T
Dim returnValue As Integer

returnValue = instance.CompareTo(other)
C#
int CompareTo(
    T other
)
Visual C++
int CompareTo(
    T other
)
JScript
function CompareTo(
    other : T
) : int

Parameters

other
Type: T
An object to compare with this object.

Return Value

Type: System..::.Int32
A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has the following meanings:

Value

Meaning

Less than zero

This object is less than the other parameter.

Zero

This object is equal to other.

Greater than zero

This object is greater than other.

Remarks

CompareTo provides a strongly typed comparison method for ordering members of a generic collection object. Because of this, it is usually not called directly from developer code. Instead, it is called automatically by methods such as List<(Of <(T>)>)..::.Sort()()() and Add.

This method is only a definition and must be implemented by a specific class or value type to have effect. The meaning of the comparisons, "less than," "equal to," and "greater than," depends on the particular implementation.

By definition, any object compares greater than nullNothingnullptra null reference (Nothing in Visual Basic), and two null references compare equal to each other.

Notes to Implementers:

For objects A, B, and C, the following must be true:

A.CompareTo(A) is required to return zero.

If A.CompareTo(B) returns zero, then B.CompareTo(A) is required to return zero.

If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) is required to return zero.

If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) is required to return a value of the opposite sign.

If A.CompareTo(B) returns a value x that is not equal to zero, and B.CompareTo(C) returns a value y of the same sign as x, then A.CompareTo(C) is required to return a value of the same sign as x and y.

Notes to Callers:

Use the CompareTo method to determine the ordering of instances of a class.

Examples

The following code example illustrates the implementation of IComparable for a simple Temperature object. The example creates a SortedList<(Of <(TKey, TValue>)>) collection of strings with Temperature object keys, and adds several pairs of temperatures and strings to the list out of sequence. In the call to the Add method, the SortedList<(Of <(TKey, TValue>)>) collection uses the IComparable<(Of <(T>)>) implementation to sort the list entries, which are then displayed in order of increasing temperature.

Visual Basic
Imports System
Imports System.Collections.Generic

Public Class Temperature
    Implements IComparable(Of Temperature)

    ' Implement the generic CompareTo method. In the Implements statement,
    ' specify the Temperature class for the type parameter of the
    ' generic IComparable interface. Use that type for the parameter
    ' of the CompareTo method.
    '
    Public Overloads Function CompareTo(ByVal other As Temperature) As Integer _
        Implements IComparable(Of Temperature).CompareTo

        ' The temperature comparison depends on the comparison of the
        ' the underlying Double values. Because the CompareTo method is
        ' strongly typed, it is not necessary to test for the correct
        ' object type.
        Return m_value.CompareTo(other.m_value)
    End Function

    ' The underlying temperature value.
    Protected m_value As Double = 0.0

    Public ReadOnly Property Celsius() As Double
        Get
            Return m_value - 273.15
        End Get
    End Property

    Public Property Kelvin() As Double
        Get
            Return m_value
        End Get
        Set(ByVal Value As Double)
            If value < 0.0 Then 
                Throw New ArgumentException("Temperature cannot be less than absolute zero.")
            Else
                m_value = Value
            End If
        End Set
    End Property

    Public Sub New(ByVal degreesKelvin As Double)
        Me.Kelvin = degreesKelvin 
    End Sub
End Class

Public Class Example
    Public Shared Sub Main()
        Dim temps As New SortedList(Of Temperature, String)

        ' Add entries to the sorted list, out of order.
        temps.Add(New Temperature(2017.15), "Boiling point of Lead")
        temps.Add(New Temperature(0), "Absolute zero")
        temps.Add(New Temperature(273.15), "Freezing point of water")
        temps.Add(New Temperature(5100.15), "Boiling point of Carbon")
        temps.Add(New Temperature(373.15), "Boiling point of water")
        temps.Add(New Temperature(600.65), "Melting point of Lead")

        For Each kvp As KeyValuePair(Of Temperature, String) In temps
            Console.WriteLine("{0} is {1} degrees Celsius.", kvp.Value, kvp.Key.Celsius)
        Next
    End Sub
End Class

' This code example produces the following output:
'
'Absolute zero is -273.15 degrees Celsius.
'Freezing point of water is 0 degrees Celsius.
'Boiling point of water is 100 degrees Celsius.
'Melting point of Lead is 327.5 degrees Celsius.
'Boiling point of Lead is 1744 degrees Celsius.
'Boiling point of Carbon is 4827 degrees Celsius.
'
C#
using System;
using System.Collections.Generic;

public class Temperature : IComparable<Temperature>
{
    // Implement the CompareTo method. For the parameter type, Use 
    // the type specified for the type parameter of the generic 
    // IComparable interface. 
    //
    public int CompareTo(Temperature other)
    {
        // The temperature comparison depends on the comparison of the
        // the underlying Double values. Because the CompareTo method is
        // strongly typed, it is not necessary to test for the correct
        // object type.
        return m_value.CompareTo(other.m_value);
    }

    // The underlying temperature value.
    protected double m_value = 0.0;

    public double Celsius    
    {
        get
        {
            return m_value - 273.15;
        }
    }

    public double Kelvin    
    {
        get
        {
            return m_value;
        }
        set
        {
            if (value < 0.0)
            {
                throw new ArgumentException("Temperature cannot be less than absolute zero.");
            }
            else
            {
                m_value = value;
            }
        }
    }

    public Temperature(double degreesKelvin)
    {
        this.Kelvin = degreesKelvin;
    }
}

public class Example
{
    public static void Main()
    {
        SortedList<Temperature, string> temps = 
            new SortedList<Temperature, string>();

        // Add entries to the sorted list, out of order.
        temps.Add(new Temperature(2017.15), "Boiling point of Lead");
        temps.Add(new Temperature(0), "Absolute zero");
        temps.Add(new Temperature(273.15), "Freezing point of water");
        temps.Add(new Temperature(5100.15), "Boiling point of Carbon");
        temps.Add(new Temperature(373.15), "Boiling point of water");
        temps.Add(new Temperature(600.65), "Melting point of Lead");

        foreach( KeyValuePair<Temperature, string> kvp in temps )
        {
            Console.WriteLine("{0} is {1} degrees Celsius.", kvp.Value, kvp.Key.Celsius);
        }
    }
}

/* This code example produces the following output:

Absolute zero is -273.15 degrees Celsius.
Freezing point of water is 0 degrees Celsius.
Boiling point of water is 100 degrees Celsius.
Melting point of Lead is 327.5 degrees Celsius.
Boiling point of Lead is 1744 degrees Celsius.
Boiling point of Carbon is 4827 degrees Celsius.

*/
Visual C++
#using <System.dll>

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

public ref class Temperature: public IComparable<Temperature^> {

protected:
   // The value holder
   Double m_value;

public:
   // Implement the CompareTo method. For the parameter type, Use 
   // the type specified for the type parameter of the generic 
   // IComparable interface. 
   //
   virtual Int32 CompareTo( Temperature^ other ) {

      // The temperature comparison depends on the comparison of the
      // the underlying Double values. Because the CompareTo method is
      // strongly typed, it is not necessary to test for the correct
      // object type.
      return m_value.CompareTo( other->m_value );
   }

   property Double Celsius {
      Double get() {
         return m_value + 273.15;
      }
   }

   property Double Kelvin {
      Double get() {
         return m_value;
      }
      void set( Double value ) {
         if (value < 0)
            throw gcnew ArgumentException("Temperature cannot be less than absolute zero.");
         else
            m_value = value;
      }
   }

   Temperature(Double degreesKelvin) {
      this->Kelvin = degreesKelvin;
   }
};

int main() {
   SortedList<Temperature^, String^>^ temps = 
      gcnew SortedList<Temperature^, String^>();

   // Add entries to the sorted list, out of order.
   temps->Add(gcnew Temperature(2017.15), "Boiling point of Lead");
   temps->Add(gcnew Temperature(0), "Absolute zero");
   temps->Add(gcnew Temperature(273.15), "Freezing point of water");
   temps->Add(gcnew Temperature(5100.15), "Boiling point of Carbon");
   temps->Add(gcnew Temperature(373.15), "Boiling point of water");
   temps->Add(gcnew Temperature(600.65), "Melting point of Lead");

   for each( KeyValuePair<Temperature^, String^>^ kvp in temps )
   {
      Console::WriteLine("{0} is {1} degrees Celsius.", kvp->Value, kvp->Key->Celsius);
   }
}

/* This code example productes the following output:

Absolute zero is 273.15 degrees Celsius.
Freezing point of water is 546.3 degrees Celsius.
Boiling point of water is 646.3 degrees Celsius.
Melting point of Lead is 873.8 degrees Celsius.
Boiling point of Lead is 2290.3 degrees Celsius.
Boiling point of Carbon is 5373.3 degrees Celsius.

*/
Platforms

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.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
See Also

Reference

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