GCC or anyone else's C compiler doesn't really count as far as this convention goes. GCC's flag parsing is aiming to be compatible with conventions that precede

GCC or anyone else's C compiler doesn't really count as far as this convention goes. GCC's flag parsing is aiming to be compatible with conventions that preceded GNU, other vendor's compilers break their own conventions to be compatible with GCC or whatever else cc(1) is etc. GNU's conventions are generally complimentary, but not incompatible with POSIX. And POSIX specifies the behavior of the sort of flags cc(1) should understand[1]. There are many POSIX and other traditional *nix tools that are a convention unto themselves for historical reasons. E.g. notice how GNU "dd" doesn't follow normal GNU command-line conventions either. 1. https://pubs.opengroup.org/onlinepubs/7908799/xcu/cc.html https://pubs.opengroup.org/onlinepubs/7908799/xcu/cc.html