[fpc-pascal] Syntax to select constant or variable with function call

[Sven Barth]

On 24.09.2017 21:07, James Richters wrote:
> Thank you for explaining how to achieve this.  
> I am curious about the meaning behind the prefixes you used:
>>  TVGA256Array = Array[0..255] of VGARGBRec;  
>>  PVGA256Array = ^TVGA256Array;
> Do the T and P in front of VGA256Array have a special meaning or significance?   I see things like that all the time, but never really understood why there are these designations.

"T" and "P" are simply the typical Hungarian notations in Pascal for
ordinary types and pointer types respectively.

> I should have mentioned that not all my arrays are [0..255], Most are, but I have some that are [0..15] and one that is [1..14] Is there a way to implement a variable size array and somehow use the array minimum and maximum element in the for loop?

If you use open array parameters you can do that. E.g.

=== code begin ===

program tdynarr;

const
  Array1: array[0..3] of LongInt = (1, 2, 3, 4);
  Array2: array[2..6] of LongInt = (1, 2, 3, 4, 5);

{ Important: a dynamic array type (aka "TArray = array of LongInt") for
the array parameter will only work with 0 based array constants (in this
case Array1) }
procedure DoArray(aArr: array of LongInt);
begin
  Writeln(Low(aArr), '..', High(aArr));
end;

begin
  DoArray(Array1);
  DoArray(Array2);
end.

=== code end ===

Please note that an open array is always zero based so the output of the
above example will be:

=== output begin ===

0..3
0..4

=== output end ===

Regards,
Sven