Okay, to summarize the tools I know:
1. The latest, free (as in beer) version of MPW, available from Macintosh Garden. Should run under Classic.
Has a C compiler, and a horribly outdated C++ compiler. No C++ standard library.
2. The compilers and libraries from 1., but run from the Mac OS X command line using the MPW emulator: https://github.com/ksherlock/mpw
3. CodeWarrior Pro 4 (hard to find). The C++ compiler is surprisingly decent for its time, but still horribly outdated. A standard library exists, but I doubt it really conforms to the C++98 standard.
4. Various older compilers might run under Classic, too.
5. My own https://github.com/autc04/Retro68 does run on G4s with Tiger. The only way to get *modern* C99 and C++11 for old Macs. Also, definitely a less polished product than the other options. It works, but you may run into bugs and unfinished features at any time.
1. The latest, free (as in beer) version of MPW, available from Macintosh Garden. Should run under Classic.
Has a C compiler, and a horribly outdated C++ compiler. No C++ standard library.
2. The compilers and libraries from 1., but run from the Mac OS X command line using the MPW emulator: https://github.com/ksherlock/mpw
3. CodeWarrior Pro 4 (hard to find). The C++ compiler is surprisingly decent for its time, but still horribly outdated. A standard library exists, but I doubt it really conforms to the C++98 standard.
4. Various older compilers might run under Classic, too.
5. My own https://github.com/autc04/Retro68 does run on G4s with Tiger. The only way to get *modern* C99 and C++11 for old Macs. Also, definitely a less polished product than the other options. It works, but you may run into bugs and unfinished features at any time.