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? 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 definitions. So, I moved the macro to an implementation (.cc) file, creating it if necessary, with the form: #include "Derived.h" BOOST_CLASS_EXPORT(Derived); The problem with this is that I have an application that does this: #include "Base.h" #include "Derived.h" // fails with or without this void foo() { Base* b = load("file.xml"); } Now, since no instance of Derived is appearing in my application, the linker apparently does not pull in the (expanded) macro, and when I run the application, I get an unregistered class exception. So, I removed all of the macros from the implementation files and put them in a header (again), that is designed for applications that may want to serialize (any) of my derived classes: #include "Base.h" #include "Derived.h" #include "BoostExports.h" void foo() { Base* b = load("file.xml"); } and this works fine. So my question is this: is this what other people do, or are there other solutions that people prefer? The problem with the above is that if I have 20 derived classes and put all the macro exports in BoostExports.h, even if my application may only be interested in a smaller subset, I have to pull in 20 header files each time, and I had hoped to avoid that. This is not a terrible thing, I just wondered what other approaches there might be. Bill