tm - broken-down time

       Describes time, broken down into distinct components.

       tm_isdst  describes  whether  daylight  saving  time  is  in  effect at the time described.  The value is
       positive if daylight saving time is in effect, zero if it is not, and negative if the information is  not
       available.

       tm_gmtoff  is  the  difference,  in seconds, of the timezone represented by this broken-down time and UTC
       (this is the additive inverse of timezone(3)).

       tm_zone is the equivalent of tzname(3) for the timezone represented by this broken-down time.

       C89, POSIX.1-1988.

       tm_gmtoff  and  tm_zone  originate  from  4.3BSD-Tahoe  (where  tm_zone  is  a  char*),  and were first
       standardized in POSIX.1-2024.

       Standard C library (libc)

       tm - broken-down time

tm_sec can represent a leap second with the value 60.

ctime(3), strftime(3), strptime(3), time(7)

Linux man-pages 6.9.1                              2024-06-12                                          tm(3type)

       C23, POSIX.1-2024.

#include<time.h>structtm{inttm_sec;    /* Seconds          [0, 60] */
           inttm_min;    /* Minutes          [0, 59] */
           inttm_hour;   /* Hour             [0, 23] */
           inttm_mday;   /* Day of the month [1, 31] */
           inttm_mon;    /* Month            [0, 11]  (January = 0) */
           inttm_year;   /* Year minus 1900 */
           inttm_wday;   /* Day of the week  [0, 6]   (Sunday = 0) */
           inttm_yday;   /* Day of the year  [0, 365] (Jan/01 = 0) */
           inttm_isdst;  /* Daylight savings flag */

           longtm_gmtoff; /* Seconds East of UTC */
           constchar*tm_zone;   /* Timezone abbreviation */
       };

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       tm_gmtoff, tm_zone:
           Since glibc 2.20:
               _DEFAULT_SOURCE
           glibc 2.20 and earlier:
               _BSD_SOURCE

       In C90, tm_sec could represent values in the range [0, 61], which could represent a double  leap  second.
       UTC doesn't permit double leap seconds, so it was limited to 60 in C99.

       timezone(3),  as  a  variable,  is  an  XSI extension: some systems provide the V7-compatible timezone(3)
       function.  The tm_gmtoff field provides an alternative (with the opposite sign) for those systems.

       tm_zone points to static storage and may be overridden on subsequent calls to  localtime(3)  and  similar
       functions (however, this never happens under glibc).