Re: [Boost-users] dll-interface problems

From: Andrej van der Zee (mavdzee_at_[hidden])
Date: 2008-07-28 22:44:32

Yes okay, but how do you then export these methods from the base class if they appear in an external library (boost::exception in this case), without changing the external library?
Cheers,
Andrej



----- Original Message ----
From: gast128 <gast128_at_[hidden]>
To: boost-users_at_[hidden]
Sent: Tuesday, 29 July, 2008 6:09:37 AM
Subject: Re: [Boost-users] dll-interface problems

Andrej van der Zee <mavdzee <at> yahoo.co.uk> writes:

> #include <boost/exception/exception.hpp>
> 
> namespace speedo {
> 
>     typedef boost::error_info<struct tag_error, unsigned> error_info;
> 
>     class __declspec(dllexport) exception : public boost::exception
>     {
>     };
> 
> }
> 
> When I try to compile this, I get the following warning:
> 
> c:\cygwin\home\andrej\speedo\trunk\util\exception.h(14) : warning C4275: non 
dll-interface class
> 'boost::exception' used as base for dll-interface class 'speedo::exception'
>         C:\cygwin\home\Andrej\speedo\trunk\boost/exception/exception.hpp
(47) : see declaration of 'boost::exception'
>         c:\cygwin\home\andrej\speedo\trunk\util\exception.h(13) : see 
declaration of 'speedo::exception'
> 
> Is this a problem, and, how do I get rid of this without changing the boost-
exception lib itself?

The exported attribute indicates that all functions from the class are 
exported. The warning is that you can potentially call a non exported function 
from the base class, e.g.:

struct public Base
{
   void Foo1();  //impl. in cpp
};

struct __declspec(dllexport) Derived : public Base
{
   void Foo2();  //impl. in cpp
};

void Foo()
{
   Derived d;
   d.Foo1();   //error, but at least a linker error
   d.Foo2(); 
}

wkr,
me

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