PB Wishlist - UDT Packing?

[Mark Newman]

How about adding additional options to specify the packing used
for UDTs? Something like VC++'s 'pragma pack N' option.

I'm currently moving a VB program to PB and it needs to call a
DLL written in VC++, but the DLL has been built with the
'pragma pack 1' option for VB compatibility. So I now have the
fun task of porting about 600 lines of UDTs to figure out the
padding needed for PB to call the DLL.

(I think this has been mentioned before, though I didn't find it
in a search. If it has, please add another tick!)

Thanks!


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Mark Newman

[Eric Pearson]

Mark --

Have you tried using the alignment options that are part of the TYPE syntax?...

TYPE MyType [BYTE|WORD|DWORD]

-- Eric


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[Mark Newman]

Eric -

I'm aware of the current TYPE alignment options, but I don't think
that they'll work in this instance of talking to the "VB-friendly"
DLL.

From reading the PB docs and the BBS it appears that the only way
to do this is to manually pad out the PB UDT to match what the
DLL expects for alignement, in this case the famous/infamous VB
"Natural" aligment.

Use a pure BYTE-based UDT would also work, but it'd be WAY too
much work to manually wrap & unwrap the UDT every time, as I have
multiple data types and UDTs within UDTs to deal with.

Hence my selfish wish to PB



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Mark Newman

[Cecil Williams]

That brings up the question, since VC++6 now packs structures
on 8-byte alignment(_Win32) as the default, how would PB relate to
this packing alignment (double type)?

Cheers,
Cecil

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[This message has been edited by Cecil Williams (edited January 05, 2001).]

[Tom Hanlin]

If the DLL was built with #pragma pack 1, it's already fully
compatible with PowerBASIC, which uses BYTE packing by default.

Note that VC++ uses the same curious half-packed "natural" alignment
scheme as VB, so the current VC++ default eight-byte alignment
doesn't leave as much empty space in a structure as you might guess.
Most Windows structures are built of LONGs, DWORDs, and pointers,
all 32-bit types that automatically fall into alignment in these
cases.

Yes, support for "natural" alignment is on the PowerBASIC wish list.

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Tom Hanlin
PowerBASIC Staff

[Cecil Williams]

Tom,

Thanks a lot for clarifing the 8-byte alignment scheme. I ran
into this when AutoCAD 2000 became a full blown Windows program.
All the headers now come with 8-byte declaration in the front
end of the file. I only use VC++6 for ARX apps running inside
of the cad program, and BTW, can ONLY be compiled with VC6. The
Borland compiler can't handle the funky function decorations
(aka mangling) used by VC++.

Previous versions used the "/Zp1" compiler switch which was
BYTE alignment. It's also interesting to note that a lot of the
core functions are now exported thru DLLs along with the EXE
file which now is a resounding 6.6Mb. If enough of the functions
reach DLL hood, then you can be sure that a PB interface
to AutoCAD WILL soon become available.

Cheers,
Cecil

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[This message has been edited by Cecil Williams (edited January 09, 2001).]

[Joseph W Murphy]

For a DLL to do the pack/unpack of UDT alignment for Visual Basic 4.0 through 6.0 check out this site:
http://www.softcircuits.com/sw_tools.htm

and download vbhlp32.zip. The zip file contains the dll, help file, and a VB Project to demonstrate how to use the DLL.

Joe Murphy



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[Mark Newman]

I've used that DLL from SoftCircuits for some VB stuff, it's
handy at times.

The problem that led to the original post was that I'm porting
an app from VB to PB that uses some include-type files. I have
the VB versions and the C header files, so between the two I was
able to build up the PB versions of the include files; time
consuming but not hard.

But if PB had native support for the MS "Natural" alignment I
could have zapped it in no time. Whine Whine Whine

The good news is that it's on the wishlist.

(Tom H: The thing about the 'pragma pack' option that threw me
was that it was set to 1, not 4 as I'd expect for VB usage. It
turns out that the DLL author aligned everything on 4-byte
boundaries by manipulating the structure def, so in truth the
'pragma pack' option could have used 1, 2 or 4 with the same
result.)



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Mark Newman