tzset()

NAME

tzset() - set time-zone and daylight-savings-time variables

SYNOPSIS

#include <time.h>
extern char *tzname[];
extern long int timezone;
extern int daylight;


void tzset (void)

DESCRIPTION

The tzset(3) function uses the value of the TZ environment variable to set the time conversion information used by the library routines localtime(3), ctime(3), strftime(3), and mktime(3). It also sets the external variables tzname, timezone, and daylight:

extern char *tzname[2] = { "std","dst"};
extern long int timezone;
extern int daylight;

The timezone variable contains the difference (in seconds) between Universal Coordinated Time (UTC) and local time. The daylight variable is non-zero when daylight savings time is in effect.

The value of TZ has the following syntax (spaces inserted for clarity):

std offset [ dst [ offset ] [ rule ] ]

Where:

std and dst

Three or more bytes that designate the standard (std or summer (dst time zone. Only std is required; if dst is missing, then summer time does not apply in this locale. Upper and lowercase letters are explicitly allowed. Any characters except a leading colon (:), digits, comma ,), minus -), plus +), and ASCII NUL are allowed.

offset

Indicates the value one must add to the local time to arrive at Coordinated Universal Time. The offset has the form:

hh [ : mm [: ss ] ]

The minutes mm and seconds ss are optional. The hour hh is required and may be a single digit. The offset following std is required. If no offset follows dst summer time is assumed to be one hour ahead of standard time. One or more digits may be used; the value is always interpreted as a decimal number. The hour must be between zero and 24, and the minutes (and seconds) if present between zero and 59. If preceded by a (-) the time zone shall be east of the Prime Meridian; otherwise it shall be west (which may be indicated by an optional preceding (+).)

rule

Indicates when to change to and back from summer time. The rule has the form:

date / time , date / time

where the first date describes when the change from standard to summer time occurs and the second date describes when the change back happens. Each time field describes when, in current local time, the change to the other time is made.

The format of date is one of the following:

Jn

The Julian day n (1 < n < 365). Leap days are not counted; that is, in all years -- including leap years -- February 28 is day 59 and March 1 is day 60. It is impossible to explicitly refer to the occasional February 29.

n

The zero-based Julian day (0 < n < 365 ) . Leap days are counted, and it is possible to refer to February 29.

Mm.n.d

The d day (0 < d < 6) of week n of month m of the year (1 < n < 5), (1 < m < 12), where week 5 means the last d day in month m which may occur in either the fourth or the fifth week). Week 1 is the first week in which the d day occurs. Day zero is Sunday.

The time has the same format as offset except that no leading sign (-) or (+) is allowed. The default, if time is not given, is 02:00:00.

For compatibility with System V Release 3.1, a semicolon (;) can be used to separate the rule from the rest of the specification.

If the TZ variable is absent from the environment, it defaults to the local Windows system's timezone settings.

SEE ALSO

date(1)

gettimeofday(3)

ctime(3)

getenv(3)

time(2)