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IComparable.CompareTo Method

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

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

'Declaration
Function CompareTo ( _
	obj As Object _
) As Integer
'Usage
Dim instance As IComparable
Dim obj As Object
Dim returnValue As Integer

returnValue = instance.CompareTo(obj)
int CompareTo (
	Object obj
)
function CompareTo (
	obj : Object
) : int
Not applicable.

Parameters

obj

An object to compare with this instance.

Return Value

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

Value

Meaning

Less than zero

This instance is less than obj.

Zero

This instance is equal to obj.

Greater than zero

This instance is greater than obj.

Exception typeCondition

ArgumentException

obj is not the same type as this instance.

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 a null reference (Nothing in Visual Basic), and two null references compare equal to each other.

The parameter, obj, must be the same type as the class or value type that implements this interface; otherwise, an ArgumentException is thrown.

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 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.

The following code sample illustrates the use of CompareTo to compare a Temperature object implementing IComparable with another object. The Temperature object implements CompareTo by simply wrapping a call to the CompareTo method.

Public Class Temperature
    Implements IComparable

    ' The value holder
    Protected m_value As Double

    Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
        Implements IComparable.CompareTo

        If TypeOf obj Is Temperature Then
            Dim temp As Temperature = CType(obj, Temperature)
            Return m_value.CompareTo(temp.m_value)
        End If
        Throw New ArgumentException("object is not a Temperature")
    End Function

    Public Property Value() As Double
        Get
            Return m_value
        End Get
        Set(ByVal Value As Double)
            m_value = Value
        End Set
    End Property

    Public Property Celsius() As Double
        Get
            Return (m_value - 32) / 1.8
        End Get
        Set(ByVal Value As Double)
            m_value = (Value * 1.8) + 32
        End Set
    End Property
End Class

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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