Re: [boost] warning C4275 with VC++ (non dll-interface class...) (again)

From: Luke Elliott (luke_elliott_at_[hidden])
Date: 2005-08-23 05:11:45

Vladimir Prus wrote:
> Luke Elliott wrote:
> 
> 
>>I was wondering why boost libraries don't do something like:
>>
>>class positional_options_description {
>>     public:
>>         BOOST_PROGRAM_OPTIONS_DECL positional_options_description();
>>         BOOST_PROGRAM_OPTIONS_DECL void add(const char* name, int
>>max_count);
>>...
>>};
>>
>>instead of:
>>
>>class BOOST_PROGRAM_OPTIONS_DECL positional_options_description {
>>     public:
>>max_count);
>>...
>>};
>>
>>in order to remove the irritating C4275 warning? i.e. only declspec
>>public, protected members (and any private members invoked from inline
>>methods).
> 
> 
> Well, I did what I considered to be the standard thing. I have no idea
> what's C4275 warning is, and why adding declspecs to each method is a good
> idea. Can you explain?
> 

(BTW - I just used program_options as an example as that's what I was 
looking at at the time...)

I don't have access to VC++ right now so this is from memory, but there 
are (at least) 2 cases where it raises a warning:

class MY_LIB_DECL my_class : public some_base
{
     my_class();
};

if some_base isn't a declspeced class then you get "warning non 
dll-interface class used as based for dll-interface class".

class MY_LIB_DECL my_class
{
     my_class();

     std::string  m_string;
};

Which gives "m_string must have dll-interface to be used by clients of 
my_class".

Both warnings a pretty harmless hence the usual recommendation to 
disable the warning, I guess.

However, the warnings can be removed by exporting only members which 
truly need to be exported - I was just curious as to why it isn't done 
in boost (possibly GCC issues?).

Thanks

Luke.