tm(3type) — Linux manual page

tm(3type)                                                      tm(3type)

NAME

       tm - broken-down time

LIBRARY

       Standard C library (libc)

SYNOPSIS

       #include <time.h>

       struct tm {
           int         tm_sec;    /* Seconds          [0, 60] */
           int         tm_min;    /* Minutes          [0, 59] */
           int         tm_hour;   /* Hour             [0, 23] */
           int         tm_mday;   /* Day of the month [1, 31] */
           int         tm_mon;    /* Month            [0, 11]  (January = 0) */
           int         tm_year;   /* Year minus 1900 */
           int         tm_wday;   /* Day of the week  [0, 6]   (Sunday = 0) */
           int         tm_yday;   /* Day of the year  [0, 365] (Jan/01 = 0) */
           int         tm_isdst;  /* Daylight savings flag */

           long        tm_gmtoff; /* Seconds East of UTC */
           const char *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

DESCRIPTION

       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.

VERSIONS

       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).

STANDARDS

       C23, POSIX.1-2024.

HISTORY

       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.

NOTES

       tm_sec can represent a leap second with the value 60.

SEE ALSO

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

COLOPHON

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

Pages that refer to this page: ctime(3), strptime(3), tzset(3), time(7)

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