Unrecognized macros like "timerisset" "timercmp"

I'm a new guy on splint, does anyone can help me about the error of
"unrecognized ids"!

following is my simple c file "test2.c"

     1. #include <stdio.h>
     2. #include <stdlib.h>
     3. #include <sys/types.h>
     4. #include <sys/time.h>
     5. 
     6. 
     7. typedef struct timeval * p_timer;
     8. typedef struct timeval obj_timer;
     9. obj_timer now;
    10. int
    11. _timer_expire(p_timer tp)
    12. {
    13.         if (timerisset(tp) && timercmp((&now), (tp), >)) {
    14.                 timerclear(tp);
    15.                 return 1;
    16.         }
    17.         return 0;
    18. }

I use the splint cmd like this:

        splint +posixlib -skip-posix-headers test2.c

it outputs :

        Splint 3.1.1 --- 06 Jan 2006
        
        test2.c: (in function _timer_expire)
        test2.c:13:6: Unrecognized identifier: timerisset
          Identifier used in code has not been declared. (Use -unrecog
        to inhibit
          warning)
        test2.c:13:24: Unrecognized identifier: timercmp
        test2.c:13:48: Parse Error. (For help on parse errors, see
        splint -help
                          parseerrors.)
        *** Cannot continue.
        
It seems splint can not recognize the macro in <sys/time.h> like
"timerisset" & "timercmp"

Help me!!!!
Thanks a lot!!