Re: Problems with FFI

--- In [email protected], Chris Double <chris.double@d...> wrote:
> I don't have Corman Lisp handy to run so the following comments are
untested, 
> but I'm pretty sure their right.
> 
> > } OPENFILENAME, *LPOPENFILENAME;
> 
> There are two types defined here. One is OPENFILENAME which will
have the size 
> of the structure. The other is LPOPENFILENAME which is a pointer
type and is 
> only of the size of the pointer.
> 
> >     (let ((lpOFN  (malloc (sizeof 'LPOPENFILENAME))))
> 
> Here you are mallocing a size of the pointer type. I think this
should be 
> (sizeof 'OPENFILENAME). What do (sizeof 'OPENFILENAME) and (sizeof 
> 'LPOPENFILENAME) return?
> 
> >         (with-c-struct (strct lpOFN OPENFILENAME)
> 
> You are offsetting into the memory allocated as if it was a fully
allocated 
> OPENFILENAME, but it is only a few bytes big. You will be
overwriting memory 
> here. Fix the malloc above it and this should be fine.
> 
> >                     lpstrFile         (malloc (* (sizeof 'LPTSTR)
260))
> 
> Here you probably mean to allocate a string of 260 characteres.
(malloc 260) 
> would be sufficient. I believe what you are actually saying here is
malloc 
> something 260 * the sizeof a pointer (again that LP indicates a pointer 
> type). So you are allocating more than needed, not really a problem.
> 
> >                     nMaxFile          260
> 
> This indicates you really did want (malloc 260) before.
> 
> Try those fixes and see how things go.
> 
> Chris.

You're right, I changed the (malloc (sizeof 'LPOPENFILENAME)) to
(malloc (sizeof 'OPENFILENAME)) and that seems to be working just
fine. And I thought I knew C!!

I guess what thouroughly confuses me is the occasions when a
declaration does look like (malloc (Sizeof 'somepointer)). It doesn't
make sense because all pointers are 4 bytes on the Windows platform.
Is this merely so that when the resulting (cref somepointer ptr 0) is
called the lisp knows what to do?




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