open \*- open for reading or writing
is 1) or for both reading and writing
is the address of a string of ASCII characters representing
a path name, terminated by a null character.
The returned file descriptor should be saved for subsequent calls
creat(II), read(II), write(II), close(II)
(c-bit) is set if the file does not exist,
if one of the necessary directories
does not exist or is unreadable, if the file is not
readable (resp. writable), or if 10 files are open.
From C, a \*-1 value is returned on an error.