| Description |
The Subtract method does two very different things :
1. Returns a TimeSpan value as the difference between the current DateTime value and the Value DateTime value. The TimeSpan value contains a day and time value - the value is a total elapsed time, not a point in time.
2. Returns a DateTime value. You provide a day/time span, which gets subtracted from the current DateTime value to give the return value.
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| Microsoft MSDN Links |
System
System.DateTime
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| A simple example illustrating both methods |
// Full Unit code.
// -------------------------------------------------------------
// Create a new WinForm application, double click the form to
// create an OnLoad event, and then replace the WinForm unit
// with this text.
unit WinForm;
interface
uses
System.Drawing, System.Collections, System.ComponentModel,
System.Windows.Forms, System.Data;
type
TWinForm = class(System.Windows.Forms.Form)
\{REGION 'Designer Managed Code'\} // Note that REGION and ENREGION should be prefixed by a dollar sign
strict private
///
/// Required designer variable.
///
Components: System.ComponentModel.Container;
///
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
///
procedure InitializeComponent;
procedure TWinForm_Load(sender: System.Object; e: System.EventArgs);
{ENDREGION}
strict protected
///
/// Clean up any resources being used.
///
procedure Dispose(Disposing: Boolean); override;
private
{ Private Declarations }
public
constructor Create;
end;
[assembly: RuntimeRequiredAttribute(TypeOf(TWinForm))]
implementation
\{REGION 'Windows Form Designer generated code'\}
///
/// Required method for Designer support -- do not modify
/// the contents of this method with the code editor.
///
procedure TWinForm.InitializeComponent;
begin
//
// TWinForm
//
Self.AutoScaleBaseSize := System.Drawing.Size.Create(5, 13);
Self.ClientSize := System.Drawing.Size.Create(292, 266);
Self.Name := 'TWinForm';
Self.Text := 'WinForm';
Include(Self.Load, Self.TWinForm_Load);
end;
{ENDREGION}
procedure TWinForm.Dispose(Disposing: Boolean);
begin
if Disposing then
begin
if Components <> nil then
Components.Dispose();
end;
inherited Dispose(Disposing);
end;
constructor TWinForm.Create;
begin
inherited Create;
//
// Required for Windows Form Designer support
//
InitializeComponent;
//
// TODO: Add any constructor code after InitializeComponent call
//
end;
procedure TWinForm.TWinForm_Load(sender: System.Object; e: System.EventArgs);
program Project1;
{$APPTYPE CONSOLE}
var
dateTime1, dateTime2 : DateTime;
timeSpan1 : TimeSpan;
begin
dateTime1 := DateTime.Create(2004, 6, 20); // 00:00:00 on 20 June 2004
dateTime2 := DateTime.Create(2004, 7, 11); // 00:00:00 on 11 July 2004
Console.WriteLine('dateTime1 = {0:F}', dateTime1);
Console.WriteLine('dateTime2 = {0:F}', dateTime2);
Console.WriteLine;
Console.WriteLine('Subtracting dateTime2 from dateTime1');
Console.WriteLine;
timeSpan1 := dateTime2.Subtract(dateTime1);
Console.WriteLine('Gives time span = {0:F}', timeSpan1);
Console.WriteLine;
Console.WriteLine('Subtracting this time span from dateTime1');
Console.WriteLine;
dateTime1 := dateTime1.Subtract(timeSpan1);
Console.WriteLine('dateTime1 now = {0:F}', dateTime1);
Console.ReadLine;
end.
end. | | Hide full unit code | dateTime1 = 20 June 2004 00:00:00
dateTime2 = 11 July 2004 00:00:00
Subtracting dateTime2 from dateTime1
Gives time span = 21.00:00:00
Subtracting this time span from dateTime1
dateTime1 now = 30 May 2004 00:00:00
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