Boost Users :
From: Robert Ramey (ramey_at_[hidden])
Date: 2005-01-07 13:58:13
Bill Lear wrote:
> I am having some trouble understanding just where I am supposed to
> put BOOST_CLASS_EXPORT macros for classes I write --- in class
> headers (.h), in class implementation files (.cc), in applications
> that plan to save/load through base pointers?
The whole concept behind BOOST_CLASS_EXPORT has been problematic for me for
a couple of reasons. As a result, the confusion you cite is a real one.
My intention was that:
a) BOOST_CLASS_EXPORT be part of the header file for a particular class.
b) A typical program would look like:
// other archives used.
// other classes from my library. many of which will use EXPORT
// the BOOST_CLASS_EXPORT will guarentee that code required for
serialization for derived classes is
// included in the program even though it is not explicitly referred to
by name. Without
// BOOST_CLASS_EXPORT, a smart compiler/linker will conclude this code
is never called
// and throw it away on linking.
c) BOOST_CLASS_EXPORT emits code for each archive template for the class
specified. This could contribute to code bloat
d) This system requires that the #include for archives preceed those for
serialization implemenations. A violation of this requirement should result
in a compile time failure with and error message and point to code with a
comment explaining the problem.
I've toyed with re-implementing this to get around problems created by
two-phase lookup but managed to address these in another way so I don't
expect this explanation to change in the near future.
> I have base class B, from which I derive lots of classes. I tried
> putting the BOOST_CLASS_EXPORT in the header files of each class, but
> soon found that this resulted in link-time errors due to multiple
I'll look into this. It might be fixable. It was my intention to permit
Note that including BOOST_CLASS_EXPORT to programs which don't in fact
serialize through a base class pointer may instanciate code that is in fact
never called. I'll look into this as well.
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