POSIX not only defines how to read and write a file from a POSIX-compliant operating system, it also defines where files should be located on the filesystem. In Chapter 8, Learning to Program File Input/Output, we will go into great detail about how to read and write to a filesystem using C, C++, and POSIX.
With respect to the layout of the filesystem, POSIX defines where files should be located, including common folders such as the following:
/bin: for binaries used by all users
/boot: for files needed to boot the operating system
/dev: for physical and virtual devices
/etc: for configuration files needed by the operating system
/home: for user-specific files
/lib: for libraries needed by executables
/mnt and /media: used as temporary mount points
/sbin: for system-specific binaries
/tmp: for files that are deleted on reboot
/usr: for user-specific versions of the preceding folders