type Name = Packed array[...] of ...;
type Name = Packed class ... end;
type Name = Packed object ... end;
type Name = Packed record ... end;
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.
Notes
Examples of unpacked alignments :
Word = 2 bytes
LongWord = 4 bytes
Single = 4 bytes
Double = 8 bytes
Related commands
$Align Determines whether data is aligned or packed
Array A data type holding indexable collections of data
Class Starts the declaration of a type of object class
Object Allows a subroutine data type to refer to an object method
Record A structured data type - holding fields of data
Example code : Packing a record to reduce storage
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;
Show full unit code
Default record size = 20
Packed record size = 14