16, 32 bit machine etc.

Anyone know how to check if a machine is 16 bit, 32 bit etc?
I need to make my C++ program portable,
but I'm not sure what macro can I use to accomplish this

>>8
HEAR HEAR

Who compiles code for 16-bit x86 these days anyhow, outside the embedded world? And in the embedded devices biz you rarely recycle code, let alone write in C++. (Can't predict what the compiler produces being the reason.)