NAME
ctime, localtime, gmtime, asctime, tzset - convert date and
time to ASCII
SYNOPSIS
#include <sys/types.h>
#include <time.h>
void tzset(void)
char *ctime(const time_t *clock)
char *asctime(const struct tm *tm)
struct tm *localtime(const time_t *clock)
struct tm *gmtime(const time_t *clock)
DESCRIPTION
Tzset uses the value of the environment variable TZ to set
up the time conversion information used by localtime.
If TZ does not appear in the environment, the TZDEFAULT file
(as defined in <tzfile.h>) is used by localtime. If this
file fails for any reason, the GMT offset as provided by the
kernel is used. In this case, DST is ignored, resulting in
the time being incorrect by some amount if DST is currently
in effect. If this fails for any reason, GMT is used.
If TZ appears in the environment but its value is a null
string, Greenwich Mean Time is used; if TZ appears and
begins with a slash, it is used as the absolute pathname of
the tzfile(5)-format file from which to read the time
conversion information; if TZ appears and begins with a
character other than a slash, it's used as a pathname rela-
tive to the system time conversion information directory,
defined as TZDIR in the include file tzfile.h. If this file
fails for any reason, the GMT offset as provided by the ker-
nel is used, as described above. If this fails for any rea-
son, GMT is used. See TZ(5) for a proper description of the
TZ variable.
Ctime converts a time value, pointed to by clock, such as
returned by time(2) into ASCII and returns a pointer to a
26-character string in the following form. All the fields
have constant width.
Sun Sep 16 01:03:52 1973\n\0
Localtime and gmtime return pointers to structures contain-
ing the broken-down time. Localtime corrects for the time
zone and possible daylight savings time; gmtime converts
directly to GMT, which is the time UNIX uses. Asctime con-
verts a broken-down time to ASCII and returns a pointer to a
26-character string.
The structure declaration from the include file is:
struct tm {
int tm_sec; /* 0-59 seconds */
int tm_min; /* 0-59 minutes */
int tm_hour; /* 0-23 hour */
int tm_mday; /* 1-31 day of month */
int tm_mon; /* 0-11 month */
int tm_year; /* 0- year - 1900 */
int tm_wday; /* 0-6 day of week (Sunday = 0) */
int tm_yday; /* 0-365 day of year */
int tm_isdst; /* flag: daylight savings time in effect */
};
Tm_isdst is non-zero if a time zone adjustment such as Day-
light Savings time is in effect.
FILES
/usr/lib/zoneinfo time zone information directory
/etc/localtime local time zone file
SEE ALSO
time(2), getenv(3), tzfile(5), TZ(5), environ(7), zic(8).
NOTE
The return values point to static data whose content is
overwritten by each call.