Re: [boost] [serialization][trunk] mingw non-wide char regressions

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2007-11-24 16:47:21

----- Mensaje original -----
De: John Maddock <john_at_[hidden]>
Fecha: Sábado, Noviembre 24, 2007 5:48 pm
Asunto: Re: [boost] [serialization][trunk] mingw non-wide char 
regressions
Para: boost_at_[hidden]

> "JOAQUIN LOPEZ MU?Z" wrote:
> > Why do you assume moving codecvt_null.cpp from SOURCES to
> > WSOURCES would break MSVC tests? If your concern is related
> > to the possibility that codecvt_null<wchar_t> member functions
> > aren't properly exported, take into account that exportability
> > is not controled by the library the .cpp is bundled into,
> > but only by the macros BOOST_[W]ARCHIVE_DECL and
> > BOOST_[W]ARCHIVE_SOURCE: having the narrow version or the wide
> > version of the macros in place make no difference, the
> > end result is that the member functions are imported/exported
> > as they should. Of course if we switch codecvt_null.cpp from
> > SOURCES to WSOURCES having the wide macros rather than the
> > narrow is the aesthetically consistent choice, but it makes
> > no difference from a practical point of view, AFAICS.
> 
> Hmm, as it stands:
> 
> 1) When building the boost_serialization sources then the 
> codecvt_null members are declared as exported, but aren't
> actually in the dll: in the past I've been hit by linker
> errors if you don't actually export everything you claim to,
> but strangely not in this case?

No, I've just double checked it. To make surer I've conducted
the following experiment: I created a toy DLL with the following
source:

  #include <iostream>

  void __declspec(dllexport) f();
  void __declspec(dllexport) g()
  {
    std::cout<<"hello"<<std::endl;
  }

and a minimal program using it:

  void __declspec(dllimport) g();

  int main()
  {
    g();
  };

and everything works fine if I link the latter with the
import lib of the former. If I change g() to f() in the
program above there's an unresolved linking error for
f(). Building the lib generates no error or warning, so
my conclusion is that a __declspec(dllexport) *declaration*
has no effect on the object code and hence generates
no exported symbols. This is MSVC++ 8.0, maybe it was
different with other compilers of the family.

> 2) When building boost_wserialization sources other than 
> codecvt_null.cpp then the codecvt_null are declared as
> imported, even though they are actually exported: that's
> normally a linker warning.

Yep, what you say is very sensible, but the fact is that
I observe no warnings whatsoever.

Anyway, to be on the safe side is better to use the W
macro variants for codecvt_null.{hpp|cpp} as I see you're
proposing at another post of yours.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo