Re: [Boost-users] [serialization] problem using BOOST_CLASS_EXPORT macro in a static library

Subject: Re: [Boost-users] [serialization] problem using BOOST_CLASS_EXPORT macro in a static library
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2009-02-10 15:38:29

BOOST_CLASS_EXPORT relies on global objects' constructors to register
the necessary types, however the C++ standard allows a compiler to
strip away such objects unless they are actually used.

The C++ standard guarantees that all global objects contained in a
compilation unit (a CPP file) are initialized by the time execution
enters a function from that compilation unit. So, if execution never
enters a function from that compilation unit, the compiler is allowed
to deadstrip it.

You have 2 options:

1) tinker with your code to trick the compiler into leaving in (not
deadstripping) the automatic BOOST_CLASS_EXPORT registration (which is
usually possible), or

2) register the classes explicitly (not automatic, but guaranteed to work)

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode

On Tue, Feb 10, 2009 at 9:19 AM, Renaud Lepere <Renaud.Lepere_at_[hidden]> wrote:
> I have some problems with BOOST_CLASS_EXPORT macro, it
> seems that this macro have no effect if i put it in
> a separate .cpp file of a static library.
>
> I have a simple class Element that contains a pointer to a
> curve that can be of different types (geom2d.hpp).
>
> struct Curve
> {
>    Curve() {};
>    virtual ~Curve() {};
> };
> struct Line : public Curve
> {
>    Line(int y = 0): m_y(y) {};
>    int m_y;
> };
>
> typedef boost::shared_ptr< Curve > CurvePtr;
> struct Element
> {
>    Element(const CurvePtr & curve):
>        m_curve(curve) {}
>    boost::shared_ptr< Curve > m_curve;
> };
>
> I would like to be able to serialize Element, so i
> wrote a serialize.hpp file (attached) containing code for
> serializing those structures.
>
> I also wrote export.cpp using
>
> #include "geom2d.hpp"
> #include <boost/archive/text_oarchive.hpp>
> #include <boost/archive/text_iarchive.hpp>
> #include "serialize.hpp"
> #include <boost/serialization/export.hpp>
> #include <iostream>
>
> BOOST_CLASS_EXPORT(Curve);
> BOOST_CLASS_EXPORT(Line);
>
> I put the export.cpp file in a library named geom2d,
> but when trying to serialize my structures using something
> (attached main.cpp).
>
>        CurvePtr c(new Line(10));
>        const Element e(c);
>        std::ofstream ofs("filename");
>        {
>            boost::archive::text_oarchive oa(ofs);
>            oa << e;
>        }
> I received an exception "unregistered class". If i dont
> put export.cpp in a library but in the same compilation unit
> as main.cpp, the error disappear (visual studio 8.0 and 9.0).
>
> What is the good way of doing this, should i wrote an export.hpp file
> containing the macros and include this file in a .cpp of the main
> compilation unit ?
>
> Thanks,
>
> Renaud
>
>
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