Unfortunately there are no official examples on how to use SPP on C++. As you mentioned only SPP-loopback.py is the only official example. So my best suggestion for this case would be for you to look for generic C/C++ code for Linux. I will leave you a couple of links where you may be able to start:
Also, I believe the BlueZ may have a more appropriate answer for your question, so why don't you submit your question to BlueZ » Contact?