Hello,

I tried your programme on my system (other linux distribution), and got the same result;
even on windows the same results;

but this is interesting

# date --date="Dec 1 00:00:00 2019" +"%s"
1575154800

# date --date="Nov 30 23:59:59 2019" +"%s"
1575154799

there you have this 1 second difference;

I'd say mktime seens to be buggy ...

Walter

On 18.12.2019 15:17, Jouk Jansen wrote:

Hi All,

I'm strugling with the C-function mktime. According to the man-pages it
returns "seconds  since  the Epoch". I tried to use this functions to get
differnces from two date-times , but was could not interpret the result.
When trying to get the diffrence between 30 Nov 2019 23:59:59 and 1 Dec 2019
00:00:00 (see code below) I expected to find 1 second difference but I find:
    1577746799 1577833200 -86401
As output of the sample program. (and not 1577833199 1577833200 -1)

How should I read "seconds  since  the Epoch"????
Is the output of mktime correct?
      (I also tried 31 Nov and got the expected 1 second)
      (should mktime not give an error for 31 Nov??)



          Regards
         Jouk






Code :


#include<stdio.h>
#include<time.h>

main()
{
    struct tm time_str , time_str2;

    time_str.tm_sec = 59; //30 Nov 2019 23:59:59
    time_str.tm_min = 59;
    time_str.tm_hour = 23;
    time_str.tm_mday = 30;
    time_str.tm_mon = 11;
    time_str.tm_year = 119;
    time_str.tm_isdst = 0;

    time_str2.tm_sec = 0; // 1 Dec 2019 00:00:00
    time_str2.tm_min = 0;
    time_str2.tm_hour = 0;
    time_str2.tm_mday = 1;
    time_str2.tm_mon = 12;
    time_str2.tm_year = 119;
    time_str2.tm_isdst = 0;

    printf( "%d %d %d\n" , mktime(&time_str ) , mktime(&time_str2 ) ,
       mktime(&time_str ) - mktime(&time_str2 ) );

}

remember that the month values (tm_mon) go from 0 to 11.

change tm_mon for November to 10 and for December to 11 and you get the expected result.

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