I want to have a base class which dictates the alignment of the objects which inherit from it. This works fine for the heap because I can control how that gets allocated, and how arrays of it get allocated in a custom array template. However, the actual size of the class as far as C++ is concerned doesn’t change at all. Which is to say if I perform pointer arithmetic on a pointer of the derived class then it will skip to the wrong location. That’s issue one.
Issue two is stack alignment. There doesn’t seem to be a way to directly force the entire stack to be 16 byte aligned pointers.
The only thing I can see to affect these at all is the vc++ and g++ compiler specific settings, but the problem here is I don’t want to have to manually fix the alignment all the time. That would be bound to be error prone, not to mention a pain.
I could also maybe make some kind of smart pointer but that would introduce more issues, too.
If I just align the base class, will the child classes be aligned, as well? If so, that would solve most of my problems but that seems doubtful to be the case (though I will try this).
If a base class has a particular alignment requirement, then any derived classes will have at least that alignment (they could get a stricter alignment requirement due to their own members). Otherwise the compiler couldn’t guarantee that accessing the base members would meet the requirements they have.
However, there’s really nothing you can portably do for stack alignment – that’s handled entirely by the compiler and the compiler’s platform ABI requirements. As you indicate, a compiler option or maybe a pragma might let you exert some control, but nothing portable.