Pointer to ARRAY in Delphi

[Ñuño Martínez]

System: Windows
Compiler/IDE: Lazarus & Delphi (trying multiplatform)
libraries: RTL

I'm using a DLL written in C. This library has several functions that use arrays. C uses pointers in most cases so I did something like this:[pascal]PROGRAM example;
TYPE
TLISTptr = ^TLIST;
TLIST = RECORD
Field: INTEGER;
Other: INTEGER;
END;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList[0]);
END.[/pascal]That compiles and runs perfect using Free Pascal but some users tells me that Delphi can't compile it. So I changed it by this:[pascal]PROGRAM example;
TYPE
TLIST_ITEMptr = ^TLIST_ITEM;
TLIST_ITEM = RECORD
Field: INTEGER;
Other: INTEGER;
END;

TLISTptr = ^TLIST;
TLIST = ARRAY OF TLIST_ITEM;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList^[0]);
END.[/pascal]Free Pascal compiles it but it returns a runtime 216 error. No idea about Delphi.

By the way this code seems to work both Delphi and FPC:[pascal]PROGRAM example;
TYPE
TLIST_ITEMptr = ^TLIST_ITEM;
TLIST_ITEM = RECORD
Field: INTEGER;
Other: INTEGER;
END;

TLISTptr = ^TLIST;
TLIST = ARRAY [0..80] OF TLIST_ITEM;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList^[0]);
END.[/pascal]But the returned list size may vary from 1 to infinite, so this isn't the solution

¬øAlny idea about how to work with a non-sized array pointer in Delphi?

Thanks

[Ñuño Martínez]

I've found the answer from another forum.

[pascal]PROGRAM example;
TYPE
TLIST_ITEMptr = ^TLIST_ITEM;
TLIST_ITEM = RECORD
Field: INTEGER;
Other: INTEGER;
END;

TLISTptr = ^TLIST;
TLIST = ARRAY [0..0] OF TLIST_ITEM;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList^[0]);
END.[/pascal]Note the use of [ 0..0 ] to prevent 'unfair use'.

It was sooooooo obvious... I'm embarassed... ops:

[JernejL]

@array is NOT SAME as @array[0] or @array[0, 0], it is simply not, just like string[0] is something else, for arrays you need to point your pointer AT THE DATA, NOT at the variable itself, the structure of the variable is not guaranteed to be same on all compilers, but the DATA is, so point at the data and not at the variable, because variable may contain internal structures to reprisent and hold the actual data.

If you have a dynamic 2d array of integers the data is not even guaranteed to be contigous, there may be internal data between each row of these arrays, not delphi not fpc or any other pascal compiler will guarantee that @array would ever point to data itself and the contigoucy of dynamic array internal structures.

[User137]

By the way this code seems to work both Delphi and FPC:[pascal]PROGRAM example;
TYPE
TLIST_ITEMptr = ^TLIST_ITEM;
TLIST_ITEM = RECORD
Field: INTEGER;
Other: INTEGER;
END;

TLISTptr = ^TLIST;
TLIST = ARRAY [0..80] OF TLIST_ITEM;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList^[0]);
END.[/pascal]But the returned list size may vary from 1 to infinite, so this isn't the solution

¬øAlny idea about how to work with a non-sized array pointer in Delphi?

Thanks

Wait, first you say "returned list size" but then you are asking to work with non-sized? How do you find out size of this list?

Even this should work and reserve same space as 0..0 when using it through pointers, but this allows compiler to access up to item[255] manually, where 0..0 only allows for [0] or through variable because of range checking:
TLIST = ARRAY [0..255] OF TLIST_ITEM;

[dmantione]

0..0 (with range checks disabled!!!) is the best solution. Delphi has no facilities for unbounded arrays.

[Jimmy Valavanis]

ry to declare TLISTptr as a pointer to array of TLIST items.

For example: (not tested)

 
PROGRAM example;
TYPE
TLIST = RECORD
Field: INTEGER;
Other: INTEGER;
END;
TLISTARRAY = array[0..$FFFF] of TLIST;
TLISTptr = ^TLISTARRAY;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
WriteLn (TheList[0]);
END.

[JSoftware]

Try to declare TLISTptr as a pointer to array of TLIST items.

For example: (not tested)

If that's going to work then you need to dereference the list pointer before indexation: ...^[0]

[Ñuño Martínez]

Wait, first you say "returned list size" but then you are asking to work with non-sized? How do you find out size of this list?

Well, I think the problem is that I'm not a native English speaker. I wanted to say "returned list with size"? not sure.

Anyway thanks for the comments.

I would use:[pascal]PROGRAM example;
TYPE
TLIST_ITEMptr = ^TLIST_ITEM;
TLIST_ITEM = RECORD
Field: INTEGER;
Other: INTEGER;
END;

TLISTptr = ^TLIST;
TLIST = ARRAY [0..0] OF TLIST_ITEM;

FUNCTION get_list: TLISTptr; CDECL; EXTERNAL 'lib.dll';

VAR
TheList: TLISTptr;
BEGIN
{ Somewhere }
TheList := get_list;
{$R-} { Don't check range. }
WriteLn (TheList^[0]); { Deference the pointer. }
{$R+}
END.[/pascal]Is that correct?

[Weps]

0..0 (with range checks disabled!!!) is the best solution. Delphi has no facilities for unbounded arrays.

[pascal]Type
TListItem = record
a,b,c: integer;
End;
TListArray = array of TListItem;[/pascal]


Doh!

[dmantione]

That is not an unbounded array, but a dynamic array. Stored on the heap, therefore not usefull in many circumstances.