Re: subtracting days from localtime problem

From: ALeine (aleine_at_austrosearch.net)
Date: 03/31/05

  • Next message: Nexohrion (JeanPaul) (Webmaster AT Shizukana.net): "FreeBSD 5.3-CURRENT" 
    Date: Thu, 31 Mar 2005 05:55:06 -0800 (PST)
To: ganbold@micom.mng.net

    ganbold@micom.mng.net wrote:

    > I have problem subtracting days from current date using test
    > program. We have daylight saving occured on 2AM of March 26, 2005.
    > As you can see below, there is missing March 26th line from
    > program output.
    >
    > And all lines after 27th March are wrong.
    > Instead of 25th March it should be 26th March, 24th March should
    > be 25th March and so on.
    >
    > Can somebody tell me why is this happening? How can I correct
    > this problem?

    You should set the tm_isdst to -1 before making the call to
    mktime(3) in order to make mktime(3) try to figure out whether
    Daylight Savings Time is in effect or not. See man 3 mktime for
    details.

    So, your getDate() function should look something like this:

    char *
    getDate(int day)
    {
            struct tm *t;
            time_t now;
            char date[12];
            char *localdate;
            time_t p;

            now = time(NULL);
            t = localtime(&now);
     
            t->tm_mday -= day;
            t->tm_hour = t->tm_min = t->tm_sec = 0;

            /* make mktime(3) figure out whether DST is in effect */
            t->tm_isdst = -1;
     
            p = mktime(t);
            if (p == (time_t)-1)
                    printf ("mktime failed\n");
     
            snprintf(date,11,"%d-%.2d-%.2d", t->tm_year + 1900,
                                             t->tm_mon + 1,
                                             t->tm_mday);
     
            if ((localdate=my_alloc(date)) == NULL) {
                    fprintf(stderr, "Allocation error!\n");
                    exit(2);
            }
            printf("Date: %s\n",localdate);
            return localdate;
    }

    ALeine
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