Date sent: Wed, 25 May 2005 09:29:00 +0200
From: Søren Ager <[EMAIL PROTECTED]>
To: FPC-Pascal users discussions
<fpc-pascal@lists.freepascal.org>
Subject: [fpc-pascal] cdecl calling and const parameters - was
SizeOf(File)
<> SizeOf(FileRec)
Send reply to: FPC-Pascal users discussions
<fpc-pascal@lists.freepascal.org>
<mailto:[EMAIL PROTECTED]>
<mailto:[EMAIL PROTECTED]>
> > I believe the C const construct (const declaration in a call marked
> > as cdecl) is wrongly used in so32dll.connect (the meaning of this
> > construct in C is different from the Pascal "const" modifier).
>
> I am programming in Pascal so I can't see what C has to do with it ;-)
You expect them to behave the same way as you're used to from Pascal,
but ask FPC to call the function in a way compatible to C by using a
cdecl modifier. ;-) Yes, the meaning of a cdecl modifier is somewhat
different in FPC from some other Pascal compilers - but it's designed
so for better compatibility with those C compilers?
> I am only interested in changing the caling convention - not the
> meaning of the const which should be the same as var - with the
> exception that you are not allowed to change the parameter. So you are
> saying there is no way to make it behave like that? :-(
>
> > If address of the record should be passed, use either "var" modifier
>
> That works - but it is not optimal as I have to double buffer all
> calls in the standard units from const to var. Sockets.pas:
>
> Function Connect(Sock:Longint;const Addr; Addrlen:Longint):Boolean;
> var
> sa : so32dll.SockAddr;
> begin
> sa:=so32dll.SockAddr(Addr);
> Connect:=so32dll.Connect(Sock,sa,AddrLen)=0;
> if not Connect then
> SocketError:=so32dll.sock_errno
> else
> SocketError:=0;
> end;
My suggestion would be:
1) Provide the (relevant) library calls in so32dll.pas with two
(overloaded) versions, one with the more C-like approach using
pointers, the other more pascallish with var pointers.
2) Use the pointer version in sockets.pas - that's perfectly
compatible to the const parameters and is by the way the same what's
done for the Unix implementations using C library -
/rtl/inc/stdsock.inc (Unix implementations using kernel syscalls have
different calling convention).
> And it gets worse when I have an untyped buffer (as send does) - then
> I will have to allocate memory - copy the contents - call the dll -
> deallocate...
Actually, it gets better there. ;-) Parameters cannot be passed on
stack if they are untyped, so they are passed by reference as
expected by you. That's another potential solution to your issue,
although I wouldn't recommend discarding the types in declarations in
cases these are known (e.g. in Connect), because that would remove
the advantage of Pascal type checking.
Tomas
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-pascal
