[fpc-pascal] Array clearing

[Sven Barth]

On 04.04.2017 15:40, Ryan Joseph wrote:
> 
>> On Apr 4, 2017, at 7:17 PM, Sven Barth via fpc-pascal <fpc-pascal at 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.

SetLength() allocates a single block of memory, cause array access is
ordinary pointer arithmetic. However if you have an array of array then
the first array stores a pointer to each sub array.

E.g. the following would be valid, too:

=== code begin ===

var
  arr: array of array of Integer;
begin
  SetLength(arr, 10, 10);
  SetLength(arr[3], 5);
  arr[6] := Nil;
  SetLength(arr[8], 15);
end.

=== code end ===

Regards,
Sven