On 04.04.2017 15:40, Ryan Joseph wrote:
>
>> On Apr 4, 2017, at 7:17 PM, Sven Barth via fpc-pascal
>> <fpc-pascal@lists.freepascal.org> wrote:
>>
>> If you want continuous memory areas you need to use static arrays or develop
>> your own dynamic data structure that uses array properties.
>>
>>
>
> I’m glad I asked because of arrays of pointers is bad news for performance.
> Does SetLength on a single level dynamic array not even allocate a continuous
> block of memory? I could use GetMem and array[0..0] but it seems like dynamic
> arrays should do basically that anyways if they’re not nested.
You could use something along these lines instead:
=== code begin ===
program tarrtest;
{$mode objfpc}
{$modeswitch advancedrecords}
type
generic TTwoDimArray<T> = record
private
fData: array of T;
{ Note: Length1 and Length2 are not initialized by default, but you
could use trunk's management operators for that }
fLength1,
fLength2: LongInt;
function GetElement(Index1, Index2: LongInt): T; inline;
procedure SetElement(Index1, Index2: LongInt; aValue: T); inline;
public
{ using SetLength() would lead to us needing to use
"System.SetLength()" for the array which in turn would complain
about usage of the static symtable; that's a problem that yet
needs to be solved inside generics, for non-generics that would
work however }
procedure AdjustLength(aLength1, aLength2: LongInt);
property Length1: LongInt read fLength1;
property Length2: LongInt read fLength2;
property Element[Index1, Index2: LongInt]: T read GetElement write
SetElement; default;
end;
{ TTwoDimArray }
function TTwoDimArray.GetElement(Index1, Index2: LongInt): T;
begin
{ ToDo: Length check }
Result := fData[Index1 * fLength1 + Index2];
end;
procedure TTwoDimArray.SetElement(Index1, Index2: LongInt; aValue: T);
begin
{ ToDo: Length check }
fData[Index1 * fLength1 + Index2] := aValue;
end;
procedure TTwoDimArray.AdjustLength(aLength1, aLength2: LongInt);
begin
SetLength(fData, aLength1 * aLength2);
fLength1 := aLength1;
fLength2 := aLength2;
end;
var
arr: specialize TTwoDimArray<LongInt>;
i: LongInt;
begin
arr.AdjustLength(10, 5);
i := arr[3, 2];
arr[7, 1] := i;
end.
=== code end ===
Regards,
Sven
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