For synthesizable SystemC, there is a standard, but even so it is VERY vendor/software dependent. So the answers for using SystemC in a synthesizable context depend on which synthesis software you intend to use. Several companies often software for this (including, but no limited to, Cadence, Xilinx, Mentor (now Siemens)). In general, my experience is that most C/C++ is synthesizable subject to some simple restrictions (e.g. may not use the heap (i.e. new/delete/malloc/free), which also often means you will not be able to use very much of the STL, which is heavily dynamic. Polymorphism is restricted if not forbidden by most of the tools as well. That said, I have successfully synthesized huge designs fairly easily and with decent results.