NEWCTIME (3)
convert date and time to ASCII
SYNOPSIS
extern char *tzname[2];
void tzset()
#include <sys/types.h>
char *ctime(clock)
const time_t *clock;
double difftime(time1, time0)
time_t time1;
time_t time0;
#include <time.h>
char *asctime(tm)
const struct tm *tm;
struct tm *localtime(clock)
const time_t *clock;
struct tm *gmtime(clock)
const time_t *clock;
time_t mktime(tm)
struct tm *tm;
cc ... -lz
DESCRIPTION
Ctime\^
converts a long integer, pointed to by
clock ,
representing the time in seconds since
00:00:00 UTC, January 1, 1970,
and returns a pointer to a
26-character string
of the form
Thu Nov 24 18:22:48 1986\n\0
All the fields have constant width.
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.
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.
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
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.
Declarations of all the functions and externals, and the ``tm'' structure,
are in the
<time.h>\^
header file.
The structure (of type)
struct tm
includes the following fields:
.5i +\w'long tm_gmtoff;\0\0'u
int tm_sec; /\(** seconds (0 - 60) \(**/
int tm_min; /\(** minutes (0 - 59) \(**/
int tm_hour; /\(** hours (0 - 23) \(**/
int tm_mday; /\(** day of month (1 - 31) \(**/
int tm_mon; /\(** month of year (0 - 11) \(**/
int tm_year; /\(** year - 1900 \(**/
int tm_wday; /\(** day of week (Sunday = 0) \(**/
int tm_yday; /\(** day of year (0 - 365) \(**/
int tm_isdst; /\(** is summer time in effect? \(**/
char \(**tm_zone; /\(** abbreviation of timezone name \(**/
long tm_gmtoff; /\(** offset from UTC in seconds \(**/
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.
FILES
\w'/usr/local/etc/zoneinfo/posixrules\0\0'u
/usr/local/etc/zoneinfo time zone information directory
/usr/local/etc/zoneinfo/localtime local time zone file
/usr/local/etc/zoneinfo/posixrules used with POSIX-style TZ's
/usr/local/etc/zoneinfo/GMT for UTC leap seconds
If
/usr/local/etc/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
/usr/local/etc/zoneinfo/posixrules .
SEE ALSO
NOTES
The return values point to static data;
the data is overwritten by each call.
The
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 ).
Avoid using out-of-range values with
mktime
when setting up lunch with promptness sticklers in Riyadh.
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