tr@samadams.princeton.edu (Tom Reingold) (06/22/91)
Here is a sample program that finds the day of the week, given the
date. It works for this century only. Making it work for any century
is "left as an exercise to the reader".
#include <stdio.h>
#include <sys/types.h>
#include <time.h>
static int monlens[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
static char *daytab[] = { "Sat", "Sun", "Mon", "Tue", "Wed", "Thu", "Fri" };
static int keys[12];
void initkeys();
main(argc, argv)
int argc;
char *argv[];
{
int day;
time_t t;
struct tm *tp;
if (argc != 3 && argc != 4) {
yuck:
fprintf(stderr, "usage: %s month date [year]\n", argv[0]);
exit(1);
}
t = time(&t);
tp = localtime(&t);
tp->tm_mon = atoi(argv[1]) - 1;
tp->tm_mday = atoi(argv[2]);
if (argc == 4)
tp->tm_year = atoi(argv[3]);
initkeys(tp->tm_year);
if (tp->tm_mon == -1 || tp->tm_mday == 0 || tp->tm_year == 0)
goto yuck;
if (tp->tm_mday > monlens[tp->tm_mon]) {
fprintf(stderr, "%s: invalid date\n", argv[0]);
exit(2);
}
day = dateof(tp);
printf("%02d/%02d/%02d is a %s\n", tp->tm_mon + 1, tp->tm_mday,
tp->tm_year, daytab[day]);
exit(0);
}
dateof(tp) /* return day of week: Saturday=0, ..., Friday=6 */
struct tm *tp;
{
int crap;
crap = tp->tm_year + tp->tm_mday + keys[tp->tm_mon] +
((int) tp->tm_year / 4);
return(crap % 7);
}
isleap(year)
int year;
{
if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
return(1);
return(0);
}
void initkeys(n)
int n;
{
int i;
/* This generates a table. I could hard code it, but I wanted
to show what the table means. */
if (isleap(n))
keys[0] = 0, monlens[1] = 29;
else
keys[0] = 1;
for (i = 1; i < 12; i++)
keys[i] = (monlens[i-1] + keys[i-1]) % 7;
}
--
Tom Reingold
tr@samadams.princeton.edu OR ...!princeton!samadams!tr
"Warning: Do not drive with Auto-Shade in place. Remove
from windshield before starting ignition."gideon@cs.utexas.edu (Timothy Tin-Wai Chan) (06/22/91)
In article <tr.677526990@samadams> tr@samadams.princeton.edu (Tom Reingold) writes: >Here is a sample program that finds the day of the week, given the >date. It works for this century only. Making it work for any century >is "left as an exercise to the reader". [...] Can you tell the day of the week by using DOS interrupts? When you use the DOS command DATE, it will say something like: Current date is Sat 6-22-1991 Enter new date (mm-dd-yy): So apparently DOS finds the day of the week itself. The question is, how can I use this facility in DOS? -- "I am immersed in sadness and joy | Timothy T. Chan and your touch brings me pain | gideon@cs.utexas.edu but your tears, Lord | Dept. of CS wash all the shame away" -- Sean Colletta (1991) | U of Texas at Austin
pshuang@athena.mit.edu (Ping-Shun Huang) (06/24/91)
In article <1468@ai.cs.utexas.edu> gideon@cs.utexas.edu (Timothy Tin-Wai Chan) writes: > So apparently DOS finds the day of the week itself. The question is, > how can I use this facility in DOS? Have your program query DOS for the current date. Save it. Set the DOS date to the date you want to know about. Read the day-of-week (see HELPPC or the commonly available interrupt list -- it's probably in the BIOS data area if DOS does not provide an service which explicitly returns it). Set the DOS date back to the current date. End. Disadvantages: there are sharp limits to how early you can set the DOS date (1-1-80 may well be the earliest date you can set it to, not positive). You're also taking a chance that Microsoft's code to determine the day of week may be buggy. -- Above text where applicable is (c) Copyleft 1991, all rights deserved by: UNIX:/etc/ping instantiated (Ping Huang) [INTERNET: pshuang@athena.mit.edu]
mmccorm@d.cs.okstate.edu (McCormick Martin) (06/24/91)
I don't have the list of DOS function calls in front of me, right now, but there definitely is a call which returns the current weekday in one of the registers. 0 = Sunday and 6 = Saturday. I've written a couple of small applications using the function and it works very well.There are four DOS functions grouped together. They are called get date, set date, get time, and set time. I believe the one you want for the weekday is get date. Martin McCormick Amateur Radio WB5AGZ Oklahoma State University Computer Center Data Communication sGroup Stillwater, OK