Misra-c compliance: some call the system function, 2012 regulations need to be forewarned, when using FD_SET, static censorship demands require advance declaration, check found FD_SET is a macro definition of a function, how do the declaration,
# define FD_SET (fd, fdsetp) __FD_SET (fd, fdsetp) (sys/select. H)
# define __FD_SET (d, set) \
((void) (__FDS_BITS (set) [__FD_ELT (d)] |=__FD_MASK (d))) (bits/select. H)