CTIME(2) System Calls Manual CTIME(2)NAME
ctime, localtime, gmtime, asctime, timezone - convert date and time to ASCII
SYNOPSIS
#include <u.h>
#include <libc.h>
char* ctime(long clock)
Tm* localtime(long clock)
Tm* gmtime(long clock)
char* asctime(Tm *tm)
/env/timezone
DESCRIPTION
Ctime converts a time clock such as returned by time(2) into ASCII (sic) and returns a pointer to a 30-byte string in the following form.
All the fields have constant width.
Wed Aug 5 01:07:47 EST 1973
Localtime and gmtime return pointers to structures containing the broken-down time. Localtime corrects for the time zone and possible day-
light savings time; gmtime converts directly to GMT. Asctime converts a broken-down time to ASCII and returns a pointer to a 30-byte
string.
typedef
struct {
int sec; /* seconds (range 0..59) */
int min; /* minutes (0..59) */
int hour; /* hours (0..23) */
int mday; /* day of the month (1..31) */
int mon; /* month of the year (0..11) */
int year; /* year A.D. - 1900 */
int wday; /* day of week (0..6, Sunday = 0) */
int yday; /* day of year (0..365) */
char zone[4]; /* time zone name */
} Tm;
When local time is first requested, the program consults the timezone environment variable to determine the time zone and converts accord-
ingly. (This variable is set at system boot time by init(8).) The timezone variable contains the normal time zone name and its difference
from GMT in seconds followed by an alternate (daylight) time zone name and its difference followed by a newline. The remainder is a list
of pairs of times (seconds past the start of 1970, in the first time zone) when the alternate time zone applies. For example:
EST -18000 EDT -14400
9943200 25664400 41392800 57718800 ...
Greenwich Mean Time is represented by
GMT 0
SOURCE
/sys/src/libc/9sys
SEE ALSO date(1), time(2), init(8)BUGS
The return values point to static data whose content is overwritten by each call.
Daylight Savings Time is ``normal'' in the Southern hemisphere.
These routines are not equipped to handle non-ASCII text, and are provincial anyway.
CTIME(2)
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CTIME(3) Library Functions Manual CTIME(3)NAME
ctime, localtime, gmtime, asctime, timezone, tzset - convert date and time to ASCII
SYNOPSIS
void tzset()
char *ctime(clock)
time_t *clock;
#include <time.h>
char *asctime(tm)
struct tm *tm;
struct tm *localtime(clock)
time_t *clock;
struct tm *gmtime(clock)
time_t *clock;
char *timezone(zone, dst)
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 relative to the system time conversion information directory, defined as TZDIR
in the include file tzfile.h. If this file fails for any reason, GMT is used.
Programs that always wish to use local wall clock time should explicitly remove the environmental variable TZ with unsetenv(3).
Ctime converts a long integer, 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
Localtime and gmtime return pointers to structures containing the broken-down time. Localtime corrects for the time zone and possible day-
light savings time; gmtime converts directly to GMT, which is the time UNIX uses. Asctime converts 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 */
char **tm_zone; /* abbreviation of timezone name */
long tm_gmtoff; /* offset from GMT in seconds */
};
Tm_isdst is non-zero if a time zone adjustment such as Daylight Savings time is in effect.
Tm_gmtoff is the offset (in seconds) of the time represented from GMT, with positive values indicating East of Greenwich.
Timezone remains for compatibility reasons only; it's impossible to reliably map timezone's arguments (zone, a "minutes west of GMT" value
and dst, a "daylight saving time in effect" flag) to a time zone abbreviation.
If the environmental string TZNAME exists, timezone returns its value, unless it consists of two comma separated strings, in which case the
second string is returned if dst is non-zero, else the first string. If TZNAME doesn't exist, zone is checked for equality with a built-in
table of values, in which case timezone returns the time zone or daylight time zone abbreviation associated with that value. If the
requested zone does not appear in the table, the difference from GMT is returned; e.g. in Afghanistan, timezone(-(60*4+30), 0) is appropri-
ate because it is 4:30 ahead of GMT, and the string GMT+4:30 is returned. Programs that in the past used the timezone function should
return the zone name as set by localtime to assure correctness.
FILES
/usr/share/zoneinfotime zone information directory
/etc/localtime local time zone file
SEE ALSO gettimeofday(2), getenv(3), time(3), tzfile(5), environ(7)NOTE
The return values point to static data whose content 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).
4th Berkeley Distribution November 27, 1996 CTIME(3)