How to force inclusion of an object file in a static library when linking into executable?

Question

I have a C++ project that due to its directory structure is set up as a static library A, which is linked into shared library B, which is linked in

Answer 1

It turns out my original attempt was mostly there. The following works:

extern "C" void Af(void);
void (*Af_fp)(void) = &Af;

For those that want a self-contained preprocessor macro to encapsulate this:

#if defined(_WIN32)
# if defined(_WIN64)
#  define FORCE_UNDEFINED_SYMBOL(x) __pragma(comment (linker, "/export:" #x))
# else
#  define FORCE_UNDEFINED_SYMBOL(x) __pragma(comment (linker, "/export:_" #x))
# endif
#else
# define FORCE_UNDEFINED_SYMBOL(x) extern "C" void x(void); void (*__ ## x ## _fp)(void)=&x;
#endif

Which is used thusly:

FORCE_UNDEFINED_SYMBOL(Af)