Changing System Time or Date Will Temporarily Pause Clock (43331)

SUMMARY

The system clock temporarily pauses when the time or the date is set. This feature prevents cases in which the date or time may need to be updated during the actual time change. For example, an attempt to set the system date exactly at midnight using _dos_setdate() will not produce the desired effect if the system changes the date at the same time it is being set. Therefore, the system clock pauses.

The effects of such a pause can be seen in the sample program that follows. If you run this program, you will find upon exit that the system time is the same as when the program was started.

MORE INFORMATION

The following is the sample program:

/* Note - this code takes a couple of minutes to run */ 
#include <stdio.h>
#include <dos.h>
struct dosdate_t Date;
struct dostime_t Time;
unsigned long loop;
void main(void)  {
   _dos_getdate(&Date);       /* Show time when starting */ 
   _dos_gettime(&Time);
   printf ("Today's date is %d-%d-%d\n", Date.month, Date.day,
           Date.year);
   printf ("Start time = %d:%d\n", Time.hour, Time.minute);

   Date.year = 1988;
   for (loop = 1; loop <= 200000; loop++) {
      _dos_setdate(&Date);
   }

   _dos_getdate(&Date);       /* Show time after loop */ 
   _dos_gettime(&Time);
   printf ("Date is now %d-%d-%d\n", Date.month, Date.day, Date.year);
   printf ("End time = %d:%d\n", Time.hour, Time.minute);
}