[cs631apue] Confusing with header files

[kwang9]

Dear all,

I solved this issue by using macros:

S_ISFIFO
S_ISDIR
...

Thanks all!
But there is another strange thing on linux-lab when using strmode, even 
if I include <bsd/string.h>, BOMB!:

undefined reference to `strmode'

...

Sincerely,
Kai