* Reply to message originally in area NET_DEV

16 Oct 96 08:30, Paul Edwards wrote to Rowan_Crowe:

 R>> I have a couple of routines in BASIC, and the above in C, but all 3 
 R>> return different results!

 > The one that returns the same value as a commercial DOS compiler will 
 > probably be fine.  Including Pacific C.  BFN.  Paul. 

The following code returns different values with Borland, Microsoft and
Watcom's compilers:

#include 
#include 
#include 

int main(void)
{
    time_t now;
    struct tm my_tm;

    /* Set my_tm to Saturday, October 19, 1996 at 18:00:00 */
    my_tm.tm_sec = 0;
    my_tm.tm_min = 0;
    my_tm.tm_hour = 18;
    my_tm.tm_mday = 19;
    my_tm.tm_mon = 9;
    my_tm.tm_year = 96;
    my_tm.tm_isdst = 0;

    now = mktime(&my_tm);

    if (now == (time_t) -1)
    {
        printf("Data contained in structure my_tm is invalid!\n");
        return EXIT_FAILURE;
    }

    printf("asctime(&my_tm): %s", asctime(&my_tm));
    printf("(unsigned long) now == %lu\n", (unsigned long) now);

    return EXIT_SUCCESS;
}

Results:

Borland C++ for DOS 3.1      : 845762400
DJGPP 2.0                    : 845712000
EMX                          : 845748000
Microsoft QuickC for DOS 2.5 : 845748000
Watcom C/C++ for DOS 10.0    : 845712000


Here was my reply to Rowan's request in C_ECHO:

* Forwarded from C_ECHO by andrew clarke (3:635/728.4{at}fidonet).
* Originally by: andrew clarke (3:635/728.4{at}fidonet), 16 Oct 96 03:48.
* Originally to: Rowan_Crowe (0/0).

{at}MSGID: 3:635/728.4{at}fidonet 323ccec8
{at}REPLY: 3:635/728.1{at}fidonet 214f477f
15 Oct 96 08:51, Rowan_Crowe wrote to All:

 > Does anyone have a unix timestamp function?

Here's what I came up with.

/*
 *  UNIXTIME.C
 *
 *  Returns the number of seconds since midnight on January 1, 1970.
 *  Written in October 1996 by Andrew Clarke.
 *  Released to the public domain.
 */

#include 
#include 

int isleap(int year)
{
    return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
}

#define UNIX_EPOCH 1970

unsigned long unixtime(const struct tm *tm)
{
    int year, i;
    unsigned long result;

    result = 0UL;
    year = tm->tm_year + 1900;

    /* Traverse through each year */
    for (i = UNIX_EPOCH; i < year; i++)
    {
        result += 31536000UL;  /* 60s * 60m * 24h * 365d = 31536000s */
        if (isleap(i))
        {
            /* It was a leap year; add a day's worth of seconds */
            result += 86400UL;  /* 60s * 60m * 24h = 86400s */
        }
    }

    /* Traverse through each day of the year, adding a day's worth
     * of seconds each time. */
    for (i = 0; i tm_yday; i++)
    {
        result += 86400UL;  /* 60s * 60m * 24h = 86400s */
    }

    /* Now add the number of seconds remaining */
    result += 3600UL * tm->tm_hour;
    result += 60UL * tm->tm_min;
    result += (unsigned long) tm->tm_sec;

    return result;
}

#ifdef TEST

int main(void)
{
    time_t now;
    struct tm *tm;
    unsigned long unix_tm;

    now = time(NULL);
    tm = localtime(&now);
    unix_tm = unixtime(tm);
    printf("UNIX timestamp: %lu (0x%08lx), Local time: %s", unix_tm,
      unix_tm, asctime(tm));

    return 0;
}

#endif

Andrew Clarke, VidMgr author
Zone 3 moderator of the C_Echo
Melbourne, Victoria, Australia
randy{at}zws.com

-+- Msged/2 4.00
 + Origin: Blizzard of Ozz, Melbourne, Australia (3:635/728.4{at}fidonet)

--- Msged/2 4.00