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