| Description |
The Packed keyword tells Delphi to minimise the storage taken up by the defined object.
Normally, complex data types, such as records have their elements aligned to 2, 4 or 8 byte boundaries, as appropriate to the data type. For example, a Word field would be aligned to a 4 byte boundary.
Records are also padded to ensure that they end on a 4 byte boundary.
These alignments ensure optimal access performance.
The Packed overrides this, compressing the data into the smallest storage, albeit with consequential reduced access performance.
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| Notes |
Examples of unpacked alignments :
Word = 2 bytes
LongWord = 4 bytes
Single = 4 bytes
Double = 8 bytes
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| Related commands |
| $Align |
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Determines whether data is aligned or packed |
| Array |
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A data type holding indexable collections of data |
| Class |
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Starts the declaration of a type of object class |
| Object |
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Allows a subroutine data type to refer to an object method |
| Record |
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A structured data type - holding fields of data |
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| Example code : Packing a record to reduce storage |
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
SysUtils,
Forms, Dialogs;
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;
var
Form1: TForm1;
implementation
{$R *.dfm} // Include form definitions
procedure TForm1.FormCreate(Sender: TObject);
type
// Declare an unpacked record
TDefaultRecord = Record
name1 : string[4];
floater : single;
name2 : char;
int : Integer;
end;
// Declare a packed record
TPackedRecord = Packed Record
name1 : string[4];
floater : single;
name2 : char;
int : Integer;
end;
var
defaultRec : TDefaultRecord;
packedRec : TPackedRecord;
begin
ShowMessage('Default record size = '+IntToStr(SizeOf(defaultRec)));
ShowMessage('Packed record size = '+IntToStr(SizeOf(packedRec)));
end;
end.
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| Hide full unit code |
Default record size = 20
Packed record size = 14
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