Hello,

I recently wrote a binding to Ruby’s extension API , and today finished writing a simple extension using it. But I ran into something strange. (I also had a problem compiling the DLL since I use Tango, but searching the newsgroup yielded the solution.)

Ruby’s API has rb_cObject, rb_cString, etc. as global variables that it sets to the Object class, String class etc. In ruby.h, they are defined as

extern unsigned long rb_cObject;

so in my binding I have

extern uint rb_cObject;

But when I try to use rb_cObject from my extension, it is not the right value... I think rb_cObject should equal rb_eval_string("Object"), but it does not. (Using the wrong value causes an access violation.)

I produced an OMF import library for Ruby’s runtime DLL by using coff2omf on the COFF import library that ships with it. I'm linking my extension with this import library.

If I remove the extern from my binding, I get a multiple definition error, so I must be linking with the variable in the DLL? But it seems the value is wrong. I’ve worked around this by calling rb_eval_string("Object") instead, but I’m really curious what could be happening here. Using rb_cObject is the usual way of referring to the Object class in C extensions, and I want to make sure my binding is correct. Could it be because the DLL was compiled with Visual Studio and my extension is in D?

Any ideas?

On Sat, 17 Jan 2009 06:30:35 +0300, Jordan Miner <TheUndaunted@nospam.gmail.com> wrote:

> Hello,
>
> I recently wrote a binding to Ruby’s extension API , and today finished writing a simple extension using it. But I ran into something strange. (I also had a problem compiling the DLL since I use Tango, but searching the newsgroup yielded the solution.)
>
> Ruby’s API has rb_cObject, rb_cString, etc. as global variables that it sets to the Object class, String class etc. In ruby.h, they are defined as
>
> extern unsigned long rb_cObject;
>
> so in my binding I have
>
> extern uint rb_cObject;
>
> But when I try to use rb_cObject from my extension, it is not the right value... I think rb_cObject should equal rb_eval_string("Object"), but it does not. (Using the wrong value causes an access violation.)
>
> I produced an OMF import library for Ruby’s runtime DLL by using coff2omf on the COFF import library that ships with it. I'm linking my extension with this import library.
>
> If I remove the extern from my binding, I get a multiple definition error, so I must be linking with the variable in the DLL? But it seems the value is wrong. I’ve worked around this by calling rb_eval_string("Object") instead, but I’m really curious what could be happening here. Using rb_cObject is the usual way of referring to the Object class in C extensions, and I want to make sure my binding is correct. Could it be because the DLL was compiled with Visual Studio and my extension is in D?
>
> Any ideas?
>

Try the following:

extern(C) extern uint rb_cObject;

On 17.01.2009 04:30, Jordan Miner wrote:
> extern unsigned long rb_cObject;
>
> so in my binding I have
>
> extern uint rb_cObject;

For accessing variables in a DLL, you need to do it like this:

export extern (C) extern uint rb_cObject;

Denis Koroskin Wrote:

> Try the following:
> 
> extern(C) extern uint rb_cObject;
> 

I forgot to mention it, but I already have extern(C): at the beginning of the file.

torhu Wrote:

> On 17.01.2009 04:30, Jordan Miner wrote:
> > extern unsigned long rb_cObject;
> >
> > so in my binding I have
> >
> > extern uint rb_cObject;
> 
> For accessing variables in a DLL, you need to do it like this:
> 
> export extern (C) extern uint rb_cObject;
> 

That worked, thank you! I already had extern(C): at the top of the file, but I hadn't thought of adding export.