Hi
I have the following question: how are open array parameters currently implemented in FPC? The reason I am asking is that I am using DLL functions in C which rely on borland's syntax, that is,

void __cdecl SomeProc(const double *coords, const int high) (in C++ Builder)

is equivallet to either of the following Delphi constructs:

procedure SomeProc1(const coords: array of Double); cdecl;

or

PDouble = ^Double;
procedure SomeProc2(const coords: PDouble; const high: Integer); cdecl;

This allows seamless integration of Delphi functions with open arrays into C++ code and vice versa.

I know that fpc does not like open array functions declared with cdecl. So I am wondering wath is the internal representation and are such functions binary equivalent to the above C++ example?

For more information, see bug:
http://www.freepascal.org/mantis/view.php?id=6940

Peter Popov

Hi,

You should use
PDouble = ^Double;
procedure SomeProc2(const coords: PDouble; const high: Integer); cdecl;

The reason is simple, it's equal to C's code...

Open arrays are voodoo magic, specially for C\++ compilers..

Ido

Are you saying that a delphi open array is binary compatible to a FPC open array?

Peter

Voodoo or not, code should be binary compatible.

It's the same in FPC. However as you say, that's "currently". You should not rely on internal implementations, it's a recipe for disaster.

Jonas

Peter Popov wrote

Are you saying that a delphi open array is binary compatible to a FPC open array?

No-one has investigated this, as far as I know.

Peter Voodoo or not, code should be binary compatible.

In order to work, yes.

But FPC code is not by definition binary compatible with Delphi's. Not always, at least.

Michael.

Well, what I mean is that C++ Builder specifically specifies how Delphi (Object Pascal) open array parameters should be viewed from C++. If this is the current FPC standard this is good. On the other hand FPC does not allow cdecl functions with open arrays (see
http://www.freepascal.org/mantis/view.php?id=6940), which is exactly what you would need to interface with a C++ library.

Peter

I agree with Ido the only proper way is to explicitly encode this view in your parameter declaration. There are more compilers than C+ +Builder and more Pascal compilers than just FPC (and more platforms than Win32/i386).

E.g. simply changing from a 32 to 64 bit platform may already break things otherwise (because e.g. the C "int" remains 32 bit while the implicit high parameter becomes 64 bit, or vice versa -- I don't know by heart what the size is of the high parameter on FPC 64 bit platforms, but I guess it's 64 bit).

Jonas