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OS/2 Shareware BBS: 10 Tools
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ISDST.C
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1997-07-05
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/* +++Date last modified: 05-Jul-1997 */
/*
** ISDST.C - Determine is a date falls within Daylight Savings Time.
**
** The rule is that DST starts at 2:00 AM on the first Sunday of April
** and ends at 2:00 AM on the last Sunday of October.
**
** Original Copyright 1995 by Bob Stout as part of
** the MicroFirm Function Library (MFL)
**
** The user is granted a free limited license to use this source file
** to create royalty-free programs, subject to the terms of the
** license restrictions specified in the LICENSE.MFL file.
*/
#include "sniptype.h"
#include "scaldate.h"
/*
** Encode DST rules here - defaults to standard U.S. rules.
*/
unsigned DST_start_mo = 4; /* Month when DST starts */
unsigned DST_start_dt = 1; /* Date when it can start */
enum DOW_T DST_start_dy = SUNDAY; /* Day of week, or DOW_IGNORE */
unsigned DST_stop_mo = 10; /* Month when DST stops */
unsigned DST_stop_dt = 31; /* Date when it can stop */
enum DOW_T DST_stop_dy = SUNDAY; /* Day of week, or DOW_IGNORE */
/*
** isDST()
**
** Parameters: 1 - Year of interest.
** 2 - Month to check.
** 3 - Day to check.
** 4 - Pointer to storage for scalar date representation of
** the year's DST start date.
** 5 - Pointer to storage for scalar date representation of
** the year's DST stop date.
**
** Returns: True_ if date is in DST range
** False_ if date is not in DST range
** Error_ if date is invalid,
*/
Boolean_T isDST(unsigned yr,
unsigned mo,
unsigned dy,
long *Start,
long *Stop)
{
long date;
if (!valiDate(yr, mo, dy))
return Error_;
else date = ymd_to_scalar(yr, mo, dy);
*Start = ymd_to_scalar(yr, DST_start_mo, DST_start_dt);
*Stop = ymd_to_scalar(yr, DST_stop_mo, DST_stop_dt);
if (DST_start_dy != DOW_IGNORE)
{
while (DST_start_dy != (*Start % 7L))
++*Start;
}
if (DST_stop_dy != DOW_IGNORE)
{
while (DST_stop_dy != (*Stop % 7L))
--*Stop;
}
return (date >= *Start && date < *Stop);
}
#ifdef TEST
#include <stdio.h>
#include <stdlib.h>
#include "datetime.h"
main(int argc, char *argv[])
{
long Start, Stop;
unsigned yr, mo, dy;
Boolean_T retval;
if (2 > argc)
{
puts("Usage: ISDST \"date_string\"");
return EXIT_FAILURE;
}
if (Success_ != parse_date(argv[1], &yr, &mo, &dy, USA))
{
printf("Error parsing date \"%s\"\n", argv[1]);
return EXIT_FAILURE;
}
if (Error_ == (retval = isDST(yr, mo, dy, &Start, &Stop)))
printf("%d/%d,%d is invalid!\n", mo, dy, yr);
else
{
printf("%d/%d/%d is%s within DST range\n\n", mo, dy, yr,
retval ? "" : " not");
scalar_to_ymd(Start, &yr, &mo, &dy);
printf("In %d, DST starts on %d/%d\n", yr, mo, dy);
scalar_to_ymd(Stop, &yr, &mo, &dy);
printf("In %d, DST stops on %d/%d\n", yr, mo, dy);
}
return EXIT_SUCCESS;
}
#endif /* TEST */