extern
char
*tzname[2];
char
*
ctime(
const time_t *clock
)
char
*
ctime_r(
const time_t *clock
, char *buf
)
double
difftime(
time_t time1
, time_t time0
)
char
*
asctime(
const struct tm *tm
)
char
*
asctime_r(
const struct tm restrict tm
, char * restrict buf
)
struct
tm
*
localtime(
const time_t *clock
)
struct
tm
*
localtime_r(
const time_t * restrict clock
, struct tm * restrict result
)
struct
tm
*
gmtime(
const time_t *clock
)
struct
tm
*
gmtime_r(
const time_t * restrict clock
, struct tm * restrict result
)
time_t
mktime(
struct tm *tm
)
)
converts a long integer, pointed to by
clock
,
representing the time in seconds since 00:00:00 UTC, 1970-01-01,
and returns a pointer to a 26-character string of the form
Thu
Nov
24
18:22:48
1986\n\0
The
ctime_r()
function provides the same functionality as
ctime(
)
differing in that the caller must supply a buffer area
buf
with a size of at least 26 bytes, in which the result is stored.
localtime()
and
gmtime(
)
return pointers to
tm
structures, described below.
localtime(
)
corrects for the time zone and any time zone adjustments
(such as Daylight Saving Time in the U.S.A.).
After filling in the
tm
structure,
localtime(
)
sets the
tm_isdst
'th
element of
tzname
to a pointer to an
ASCII string that's the time zone abbreviation to be used with
localtime('s)
return value.
gmtime()
converts to Coordinated Universal Time.
The
gmtime_r()
and
localtime_r(
)
functions provide the same functionality as
gmtime(
)
and
localtime(
)
differing in that the caller must supply a buffer area
result
in which the result is stored; also,
localtime_r()
does not imply initialization of the local time conversion information;
the application may need to do so by calling
tzset(3).
asctime()
converts a time value contained in a
tm
structure to a 26-character string, as shown in the above example,
and returns a pointer to the string.
The
asctime_r()
function provides the same functionality as
asctime(
)
differing in that the caller must supply a buffer area
buf
with a size of at least 26 bytes, in which the result is stored.
mktime()
converts the broken-down time, expressed as local time,
in the structure pointed to by
tm
into a calendar time value with the same encoding as that of the values
returned by the
time(3)
function.
The original values of the
tm_wday
and
tm_yday
components of the structure are ignored,
and the original values of the other components are not restricted
to their normal ranges.
(A positive or zero value for
tm_isdst
causes
mktime()
to presume initially that summer time (for example, Daylight Saving Time
in the U.S.A.) respectively,
is or is not in effect for the specified time.
A negative value for
tm_isdst
causes the
mktime()
function to attempt to divine whether summer time is in effect
for the specified time.)
On successful completion, the values of the
tm_wday
and
tm_yday
components of the structure are set appropriately,
and the other components are set to represent the specified calendar time,
but with their values forced to their normal ranges; the final value of
tm_mday
is not set until
tm_mon
and
tm_year
are determined.
mktime()
returns the specified calendar time; if the calendar time cannot be
represented, it returns -1.
difftime()
returns the difference between two calendar times,
(
time1
- time0
),
expressed in seconds.
The structure (of type) struct tm includes the following fields:
int tm_sec; /* seconds after the minute [0,61] */
int tm_min; /* minutes after the hour [0,59] */
int tm_hour; /* hours since midnight [0,23] */
int tm_mday; /* day of the month [1,31] */
int tm_mon; /* months since January [0,11] */
int tm_year; /* years since 1900 */
int tm_wday; /* day of week [0,6] (Sunday = 0) */
int tm_yday; /* day of year [0,365] (Jan 1 = 0) */
int tm_isdst; /* daylight savings flag */
long tm_gmtoff; /* offset from UTC in seconds */
char *tm_zone; /* abbreviation of timezone name */
The
tm_zone
and
tm_gmtoff
fields exist, and are filled in, only if arrangements to do
so were made when the library containing these functions was
created.
There is no guarantee that these fields will continue to exist
in this form in future releases of this code.
tm_isdst
is non-zero if summer time is in effect.
tm_gmtoff
is the offset (in seconds) of the time represented
from UTC, with positive values indicating east
of the Prime Meridian.
/etc/localtime
/usr/share/zoneinfo
/usr/share/zoneinfo/posixrules
/usr/share/zoneinfo/GMT
If
/usr/share/zoneinfo/GMT
is absent, UTC leap seconds are loaded from
/usr/share/zoneinfo/posixrules
.
),
difftime(
),
asctime(
),
localtime(
),
gmtime(
)
and
mktime(
)
functions conform to
ANSI X3.159-1989 (``ANSI C89'')
The
ctime_r(
),
asctime_r(
),
localtime_r(
)
and
gmtime_r(
)
functions conform to
IEEE Std 1003.1c-1995 (``POSIX.1'') .
tm_zone
field of a returned
struct tm
points to a static array of characters, which will also be overwritten
at the next call (and by calls to
tzset(3)).
Avoid using out-of-range values with
mktime()
when setting up lunch with promptness sticklers in Riyadh.