UNSETENV (man3p)
unsetenv — remove an environment variable
unsetenv — remove an environment variable
printf — print formatted output
setlogmask — set the log priority mask
fesetround — set current rounding direction
creal, crealf, creall — complex real functions
pthread_mutex_getprioceiling, pthread_mutex_setprioceiling — get and set the priority ceiling of a mutex (REALTIME THREADS)
iswcntrl, iswcntrl_l — test for a control wide-character code
islessgreater — test if x is less than or greater than y
setpwent — user database function
killpg — send a signal to a process group