Updated: July 2008
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.
Namespace:
System
Assembly:
mscorlib (in mscorlib.dll)
Visual Basic (Declaration)
Function CompareTo ( _
obj As Object _
) As Integer
Dim instance As IComparable
Dim obj As Object
Dim returnValue As Integer
returnValue = instance.CompareTo(obj)
int CompareTo(
Object obj
)
int CompareTo(
Object^ obj
)
function CompareTo(
obj : Object
) : int
Return Value
Type:
System..::.Int32A 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. |
The CompareTo method is implemented by types whose values can be ordered or sorted. It is called automatically by methods of non-generic collection objects, such as Array..::.Sort, to order each member of the array. If a custom class or structure does not implement IComparable, its members cannot be ordered and the sort operation can throw an InvalidOperationException.
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.
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 Int32..::.CompareTo method.
Imports System.Collections
Public Class Temperature
Implements IComparable
' The temperature value
Protected temperatureF As Double
Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
Implements IComparable.CompareTo
Dim otherTemperature As Temperature = TryCast(obj, Temperature)
If otherTemperature IsNot Nothing Then
Return Me.temperatureF.CompareTo(otherTemperature.temperatureF)
Else
Throw New ArgumentException("Object is not a Temperature")
End If
End Function
Public Property Fahrenheit() As Double
Get
Return temperatureF
End Get
Set(ByVal Value As Double)
Me.temperatureF = Value
End Set
End Property
Public Property Celsius() As Double
Get
Return (temperatureF - 32) * (5/9)
End Get
Set(ByVal Value As Double)
Me.temperatureF = (Value * 9/5) + 32
End Set
End Property
End Class
Public Module CompareTemperatures
Public Sub Main()
Dim temperatures As New ArrayList
' Initialize random number generator.
Dim rnd As New Random()
' Generate 10 temperatures between 0 and 100 randomly.
For ctr As Integer = 1 To 10
Dim degrees As Integer = rnd.Next(0, 100)
Dim temp As New Temperature
temp.Fahrenheit = degrees
temperatures.Add(temp)
Next
' Sort ArrayList.
temperatures.Sort()
For Each temp As Temperature In temperatures
Console.WriteLine(temp.Fahrenheit)
Next
End Sub
End Module
' 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
using System;
using System.Collections;
public class Temperature : IComparable
{
// The temperature value
protected double temperatureF;
public int CompareTo(object obj) {
Temperature otherTemperature = obj as Temperature;
if (otherTemperature != null)
return this.temperatureF.CompareTo(otherTemperature.temperatureF);
else
throw new ArgumentException("Object is not a Temperature");
}
public double Fahrenheit
{
get
{
return this.temperatureF;
}
set {
this.temperatureF = value;
}
}
public double Celsius
{
get
{
return (this.temperatureF - 32) * (5.0/9);
}
set
{
this.temperatureF = (value * 9.0/5) + 32;
}
}
}
public class CompareTemperatures
{
public static void Main()
{
ArrayList temperatures = new ArrayList();
// Initialize random number generator.
Random rnd = new Random();
// Generate 10 temperatures between 0 and 100 randomly.
for (int ctr = 1; ctr <= 10; ctr++)
{
int degrees = rnd.Next(0, 100);
Temperature temp = new Temperature();
temp.Fahrenheit = degrees;
temperatures.Add(temp);
}
// Sort ArrayList.
temperatures.Sort();
foreach (Temperature temp in temperatures)
Console.WriteLine(temp.Fahrenheit);
}
}
// 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
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->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
Reference
Date | History | Reason |
|---|
July 2008
| Added detail on usage by the common language runtime. |
Customer feedback.
|