C++ can be found pretty much everywhere. There is a free C++ compiler from GNU which exists on nearly every platform (even OS9). Many operating system vendors distribute C++ compilers.
Advantage of GNU is that you only need to be familiar with one command, g++. Also quite a good compiler. Works on OS9. It has been lagging behind recent developments though (notably templates).
Other manufacturers products include:
Most products include a class library. See manufacturers documentation.