From: Erik Lindblad <eriklindblad3@...>
Date: 2009-09-13T17:21:36+09:00
Subject: Re: Using Data_Make_Struct for incomplete type

The wrapped package is a closed source package so there is no
equivalent to a -dev package available.

I have read up a bit on the problem and it is like I suspected. The
struct contains arrays of undeclared size and naturally the compiler
cannot guess the size. For now I have worked around it bu transferring
the struct data to VALUE instance variable, but that solution is not
as pretty as the option of wrapping the full struct.

On the other hand there are advantages of doing one "import" step at
creation and then have the struct data as Ruby VALUEs, so it is kind
of ok. I will hopefully release an alpha version of the bindings
within a week or so and I'd be happy to link to the source on github
at that time for input on how the incomplete struct might be completed
in a "best practice" way.

Thanks for the input so far.

Regards

Erik



On 13 Sep, 03:26, Joel VanderWerf <vj...@path.berkeley.edu> wrote:
> Erik Lindblad wrote:
> > On 12 Sep, 21:39, Joel VanderWerf <vj...@path.berkeley.edu> wrote:
> >> Erik Lindblad wrote:
> >>> Hi all
> >>> I am writing a Ruby wrapper for a C library. I can wrap some of the C
> >>> structs with Data_Make_Struct but for one of them I get "invalid
> >>> application of sizeof to incomplete type". I expect this has something
> >>> to do with that the compiler cannot find a definitive size of the
> >>> struct.
> >> Have you included all the relevant headers?
>
> >> --
> >>        vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
>
> > Yes, I can do both Data_Wrap_Struct for other structs in the same
> > library, and create "instances" of the struct in question. The struct
> > is defined in a lib that I only have as a binary so I cannot
> > experiment with the source.
>
> > I have tried both with Data_Make_Struct and with a construct I found
> > in a blog post:
>
> > struct_name* s = (struct_name*)malloc(sizeof(struct_name));
> > VALUE obj;
> > obj = Data_Wrap_Struct(klass, 0, terminate, s);
>
> > Both result in the same compile message:
>
> > invalid application of sizeof to incomplete type s
>
> > The struct contains arrays of pointers to other structs so my guess is
> > that it has something to do with that the compiler cannot figure out a
> > definitive size to use for the struct. If that is the case I have no
> > idea how to work around that.
>
> If you don't at least have the headers[1] it will be hard to do much
> with the struct, except pass it back in to the functions of the library.
> Maybe that's enough. In that case, if you can at least determine the
> size of the struct, you can define a dummy struct of that size, and that
> may work, in a fragile sort of way.
>
> [1]  Having the headers is not necessarily the same as having the full
> source. I'm assuming that in your case the problem will not be solved by
> installing the -dev package of the library?
>
> --
>        vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407