int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *restrict value,
struct itimerval *restrict ovalue);
The getitimer() function shall store the current value of the timer specified by which into the structure pointed to by value. The setitimer() function shall set the timer specified by which to the value specified in the structure pointed to by value, and if ovalue is not a null pointer, store the previous value of the timer in the structure pointed to by ovalue.
A timer value is defined by the itimerval structure, specified in <sys/time.h>. If it_value is non-zero, it shall indicate the time to the next timer expiration. If it_interval is non-zero, it shall specify a value to be used in reloading it_value when the timer expires. Setting it_value to 0 shall disable a timer, regardless of the value of it_interval. Setting it_interval to 0 shall disable a timer after its next expiration (assuming it_value is non-zero).
Implementations may place limitations on the granularity of timer values. For each interval timer, if the requested timer value requires a finer granularity than the implementation supports, the actual timer value shall be rounded up to the next supported value.
An XSI-conforming implementation provides each process with at least three interval timers, which are indicated by the which argument:
The interaction between setitimer() and any of alarm(), sleep(), or usleep() is unspecified.
Upon successful completion, getitimer() or setitimer() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.
The setitimer() function shall fail if:
The getitimer() and setitimer() functions may fail if:
The following sections are informative.
alarm() , sleep() , timer_getoverrun() , ualarm() , usleep() , the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>, <sys/time.h>