newctime
Hurricane Electric Internet Services
NAME
asctime, ctime, difftime, gmtime, localtime, mktime - con-
vert 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, repre-
senting 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.). Before doing so, localtime calls tzset (if
tzset has not been called in the current process). 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'' struc-
ture to a 26-character string, as shown in the above exam-
ple, 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 com-
pletion, the values of the tm_wday and tm_yday components
of the structure are set appropriately, and the other com-
ponents 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:
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 guar-
antee 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 repre-
sented from UTC, with positive values indicating east of
the Prime Meridian.
FILES
/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
getenv(3), newtzset(3), time(2), tzfile(5)
NOTES
The return values point to static data; the data is over-
written 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.
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.