CXX opcodes provide a means for Csound users to embed C++ source code in Csound orchestra code, and for Csound then to compile, load, link, and run C++ during the course of the Csound performance.
This could of course be done outside of Csound, e.g. by writing plugin opcodes. However, experience shows that bringing the C++ code and build commands into Csound provides a considerably more efficient composing environment.
cxx_compile opcode compiles C++ source, embedded in a Csound orchestra, into a dynamic link library, and executes its entry point at init time.