RE: [Log4cpp-devel] Warning: win32 dll can't export containerclasses

[Bastiaan B. <bas...@li...>]

Hi David,

I've changed getAllAppenders() to return a std::vector, could you check
whether this solves the DLL problem.
And yes, it would be nice to know if this restriction still applies to
newer MSVC versions. I'd rather recommend people to upgrade than to have
different APIs for DLL vs non-DLL builds. 

Regards,

Bastiaan
 

On Thu, 2002-06-27 at 09:01, David Resnick wrote:
> Yeah, it sucks pretty bad. I don't know if it is still true with the
> latest version of MSVC (MSVC.NET? MSVC7?). 
> 
> The problem also applies to Category::getAllAppenders().
> 
> I'm not sure that the problem is so significant. It is only relevant to
> the win32 dll build: maybe the problem methods can be made private for
> that build? Or just put warnings in the documentation?
> 
> Your solution to change the container returned to std::vector would be
> nice though... At least with getAllAppenders() it wouldn't break any
> production release APIs.
> 
> Regards,
> 
> David Resnick
> MobileSpear Inc.
>  
> 
> -----Original Message-----
> From: Bastiaan Bakker [mailto:Bas...@li...] 
> Sent: Tuesday, June 25, 2002 10:35
> To: David Resnick
> Cc: log...@li...
> Subject: Re: [Log4cpp-devel] Warning: win32 dll can't export
> containerclasses
> 
> 
> Hmm, that sucks. Any chance of MS fixing this problem soon? Being
> limited to only use std::vector in your APIs is ridiculous. However
> currrently only getCurrentCategories() is affected. It uses std::set
> now, but changing that to std::vector wouldn't hurt very much, 
> and may be more efficient as std::vector is the simplest container in
> most STL implementations. Yes, it's an incompatible API change, but
> 0.3.x is a development branch anyway. 
> 
> Regards,
> 
> Bastiaan
> 
> PS. The above is not a commitment to keep the log4cpp API MSVC DLL
> export clean.
> 
>   
> On Sun, 2002-06-23 at 10:08, David Resnick wrote:
> > I found this out when trying to use Category::getCurrentCategories(), 
> > which returns std::set<Category*>*. The set I got had 1 good pointer; 
> > the rest were invalid.
> > 
> > The problem is detailed by MS in Q168958 "HOWTO: Exporting STL 
> > Components Inside & Outside of a Class". Here is the key paragraph:
> > 
> > "Some STL classes contain nested classes. These classes can not be 
> > exported. For instance, deque contains a nested class deque::iterator.
> 
> > If you export deque, you will get a warning that you must export 
> > deque::iterator. If you export deque::iterator, you get a warning that
> 
> > you must export deque. This is caused by a designed limitation that 
> > once a template class is instantiated, it can not be re-instantiated 
> > and exported. The only STL container that can currently be exported is
> 
> > vector. The other containers (that is, map, set, queue, list, deque) 
> > all contain nested classes and cannot be exported."
> > 
> > So if you want to use methods such as 
> > Category::getCurrentCategories(), do them in a helper class that is 
> > linked as part of the DLL. I added what I needed to the 
> > SimpleConfigurator (what I needed to do was delete previously defined 
> > appenders from all categories before reloading a config file, so it 
> > made sense in any case to put it there.)
> > 
> > Regards,
> > 
> > David Resnick
> > MobileSpear Inc. 
> > 
> > 
> > 
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> 
>