[Fwd: [omniORB] Repost: Why this call failed in dll?]

[Bing Zhang]

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Message-ID: <36362648.569F11CC@sohar.com>
Date: Tue, 27 Oct 1998 12:00:08 -0800
From: Bing Zhang <bzhang@sohar.com>
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To: Sai-Lai Lo <S.Lo@orl.co.uk>
Subject: Re: [omniORB] Repost: Why this call failed in dll?
References: <3634E786.C8FB2F7A@sohar.com> <3oemru9ths.fsf@neem.cam-orl.co.uk>
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Sai-Lai,

you are right. Actually  I realized this last evening after I sent out the
message. This is what I did.

The orginal services.h is
class ServiceClass {
...
 };
 extern ServiceClass Service;

Original file service.cc,
....
ServiceClass Service;

Now the services.h and services.cc compiled into DLL is:
class __declspec(dllexport) ServiceClass {
...
 };
//extern ServiceClass Service;  //Got compilation error if not commented out

 file service.cc,
....
__declspec(dllexport) ServiceClass Service;

The services.h compiled with application is
class __declspec(dllimport) ServiceClass {
...
 };
__declspec(dllimport) ServiceClass Service;

Everything works now.

>From your post, it seems to me that I do not have to change anything in file
services.h and services.cc compiled into dll, the services.h compiled with
application should only be

class ServiceClass {
...
 };
__declspec(dllimport) ServiceClass Service;

only place needs to be changed. Is this right? BTW: I did not find the
_OMNIORB_NTDLL_IMPORT in any omniORB2 file.

If the global variable is used both by other files in the dll and application
code, how do I declare them? Since if I had

class __declspec(dllexport) ServiceClass {
...
 };
extern ServiceClass Service;
in file services.h. Then I got compilation error if services.cc is
.....
__declspec(dllexport) ServiceClass Service;

This dll crap is really not that easy for a UNIX programmer trying to step into
the Window world. :)

Thanks

Bing

In the
Sai-Lai Lo wrote:

> I think the problem is that you have not qualified "extern ServiceClass
> Service" with a __declspec(dllimport) when your application code is
> compiled. In omniORB2 all global variables in the DLLs that have to be
> accessed in the application code are prefixed with the macro
> _OMNIORB_NTDLL_IMPORT which translate into __declspec(dllimport) when the
> header files are included in the application code.
>
> Don't just take my word for it. Please read up on the MSVC++ dllimport
> crap..
>
> Regards,
>
> Sai-Lai
>
> >>>>> Bing Zhang writes:
>
> > I have a very simple class in file services.h:
> > class ServiceClass {
> >    unsigned long caminStartTime;
> > public:
> >   ServiceClass();
> >  resetStartTime(unsigned long delta);
> >  unsigned long currentTime();
> > };
> > extern ServiceClass Service;
>
> > In file service.cc,
>
> > ServiceClass::ServiceClass() {
> >   caminStartTime = (unsigned long) timeGetTime();
> > }
> > ServiceClass::resetStartTime(unsigned long delta) {
> >         caminStartTime = delta;
> > }
> > unsigned long ServiceClass::currentTime() {
> >       return (unsinged long) timeGetTime();
> > }
> > ServiceClass Service;
>
> > In my main(), I call
>
> > Service.resetStartTime(0);
>
> > This works fine if I compile my main, application codes and omniORB2
> > source code (I modified some part of omniORB codes to suit our
> > situation) together with service.cc.
>
> > But when I put the service.cc along with omniORB source code in a dll
> > and link my application code to this
> > dll, every time this call is made, it throws out a "The instruction at
> > xxxxxx reference memory at xxxxxxx. The memory can not be wrriten" error
>
> > when  the statement
>
> > caminStartTime = delta;
>
> > is executed. But the call Service.currentTime() runs ok. So I think the
> > system does not want me to modify the member variable of Service, which
> > is
> > now a global variable inside the dll.
>
> > I am using vc++ 5.0 and omniORB 2.4. I built the dll by adding my source
>
> > codes to the dir.mk of omniORB.
>
> > What is wrong?
>
> --
> Dr. Sai-Lai Lo                          |       Research Scientist
>                                         |
> E-mail:         S.Lo@orl.co.uk          |       Olivetti & Oracle Research Lab
>                                         |       24a Trumpington Street
> Tel:            +44 223 343000          |       Cambridge CB2 1QA
> Fax:            +44 223 313542          |       ENGLAND




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