What command for starting a timer to count a period of about 10 second, how should I implement the method in time.h ? 

Solution:

Setitimer Function To Set Timer Interval

You can use setitimer function on Unix to set a timer interval. After the specified timer expires it generates SIGALRM which can be captured using signal() function to call a signal handler function.

setitimer takes argument of type "struct itimerval" found int sys/time.h and has following structure:

Code:

struct itimerval {
             struct timeval it_interval; /* next value */
             struct timeval it_value;    /* current value */
};
struct timeval {
           long tv_sec;                /* seconds */
           long tv_usec;               /* microseconds */
};
 

A sample code would be:

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>

#define INTERVAL 10

void alarm_wakeup (int i)
{
   signal(SIGALRM,alarm_wakeup);
   printf("%d sec up partner, Wakeup!!!\n",INTERVAL);
   exit(0);
}

int main ()
{
  struct itimerval tout_val;

  tout_val.it_interval.tv_sec = 0;
  tout_val.it_interval.tv_usec = 0;
  tout_val.it_value.tv_sec = INTERVAL; /* set timer for "INTERVAL (10) seconds */
  tout_val.it_value.tv_usec = 0;
  setitimer(ITIMER_REAL, &tout_val,0);

  signal(SIGALRM,alarm_wakeup); /* set the Alarm signal capture */

  while (1)
  {
    ;
  }

  return 0;

}
 

Program output:

Quote:
[root@ounix1 tools]# gcc -o sample sample.c 
[root@ounix1 tools]# ./sample 
10 sec up partner, Wakeup!!!
[root@ounix1 tools]# 
 

Another example with setitimer() to implement a repetitive timer. Signal handler for SIGALRM signal, resets the timer.

Code:

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>

#define INTERVAL 5

int howmany = 0;

void alarm_wakeup (int i)
{
   struct itimerval tout_val;

   signal(SIGALRM,alarm_wakeup);

   howmany += INTERVAL;

   printf("\n%d sec up partner, Wakeup!!!\n",howmany);
   tout_val.it_interval.tv_sec = 0;
   tout_val.it_interval.tv_usec = 0;
   tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
   tout_val.it_value.tv_usec = 0;

   setitimer(ITIMER_REAL, &tout_val,0);

}

void exit_func (int i)
{
    signal(SIGINT,exit_func);
    printf("\nBye Bye!!!\n");
    exit(0);
}

int main ()
{
  struct itimerval tout_val;

  tout_val.it_interval.tv_sec = 0;
  tout_val.it_interval.tv_usec = 0;
  tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
  tout_val.it_value.tv_usec = 0;
  setitimer(ITIMER_REAL, &tout_val,0);

  signal(SIGALRM,alarm_wakeup); /* set the Alarm signal capture */
  signal(SIGINT,exit_func);

  while (1)
  {
    //printf("!");
  }

  return 0;

}

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