rt-thread-official/components/libc/compilers/common/extension/fcntl/README.md

Because of the history issue, flags in fcntl.h, such as O_CREAT, have difference types of value. Some OS use hex flags and others use octal flags.

In terms of RT-Thread, Keil, IAR and MSVC use octal flags, which is located in the tcntl/octal folder; newlib uses hex flags; musl uses octal flags.