This example shows how to set the clock one hour ahead.

 #define INCL_DOSDATETIME   /* Date and time values */
 #define INCL_DOSERRORS     /* DOS error values     */
 #include <os2.h>
 #include <stdio.h>

int main(VOID) {

   DATETIME   DateTime = {0};       /* Structure to hold date/time info.   */
   APIRET     rc       = NO_ERROR;  /* Return code                         */

   rc = DosGetDateTime(&DateTime);  /* Retrieve the current date and time  */
   if (rc != NO_ERROR) {
      printf ("DosGetDateTime error : return code = %u\n", rc);
      return 1;
   }

   DateTime.hours = (UCHAR) ((BYTE) DateTime.hours + 1);    /* Set clock ahead
                                                 for Daylight Savings Time  */

   rc = DosSetDateTime(&DateTime);  /* Update the date and time            */

   if (rc!= NO_ERROR) {
      printf ("DosSetDateTime error : return code = %u\n", rc);
      return 1;
   }

   rc = DosGetDateTime(&DateTime);  /* Retrieve the date and time          */

   if (rc!= NO_ERROR) {
      printf ("DosGetDateTime error : return code = %u\n", rc);
      return 1;
   } else {
      printf("Today is %d-%d-%d; the time is now %d:%2.2d\n", DateTime.month,
              DateTime.day, DateTime.year, DateTime.hours, DateTime.minutes);
   }
   return NO_ERROR;
}