4.4BSD/usr/share/man/cat3/tzsetwall.0
TZSET(3) BSD Programmer's Manual TZSET(3)
NNAAMMEE
ttzzsseett, ttzzsseettwwaallll - initialize time conversion information
SSYYNNOOPPSSIISS
##iinncclluuddee <<ttiimmee..hh>>
_v_o_i_d
ttzzsseett(_v_o_i_d);
_v_o_i_d
ttzzsseettwwaallll(_v_o_i_d);
DDEESSCCRRIIPPTTIIOONN
The ttzzsseett() function initializes time conversion information used by the
library routine localtime(3). The environment variable TZ specifies how
this is done.
If TZ does not appear in the environment, the best available approxima-
tion to local wall clock time, as specified by the tzfile(5)-format file
_/_e_t_c_/_l_o_c_a_l_t_i_m_e is used.
If TZ appears in the environment but its value is a null string, Coordi-
nated Universal Time (UTC) is used (without leap second correction).
If TZ appears in the environment and its value begins with a colon (`'):,
the rest of its value is used as a pathname of a tzfile(5)-format file
from which to read the time conversion information. If the first charac-
ter of the pathname is a slash (`/') it is used as an absolute pathname;
otherwise, it is used as a pathname relative to the system time conver-
sion information directory.
If its value does not begin with a colon, it is first used as the path-
name of a file (as described above) from which to read the time conver-
sion information. If that file cannot be read, the value is then inter-
preted as a direct specification (the format is described below) of the
time conversion information.
If the TZ environment variable does not specify a tzfile(5)-format file
and cannot be interpreted as a direct specification, UTC is used.
The ttzzsseettwwaallll() function sets things up so that localtime returns the
best available approximation of local wall clock time.
SSPPEECCIIFFIICCAATTIIOONN FFOORRMMAATT
When TZ is used directly as a specification of the time conversion infor-
mation, it must have the following syntax (spaces inserted for clarity):
_s_t_d _o_f_f_s_e_t [_d_s_t [_o_f_f_s_e_t] [ , _r_u_l_e]]
Where:
_s_t_d and _d_s_t Three or more bytes that are the designation for the
standard (_s_t_d) or summer (_d_s_t) time zone. Only _s_t_d is
required; if _d_s_t 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.
_o_f_f_s_e_t Indicates the value one must add to the local time to
arrive at Coordinated Universal Time. The _o_f_f_s_e_t has
the form:
_h_h [:_m_m[ : _s_s]]
The minutes (_m_m) and seconds (_s_s) are optional. The
hour (_h_h) is required and may be a single digit. The
_o_f_f_s_e_t following _s_t_d is required. If no _o_f_f_s_e_t fol-
lows _d_s_t, 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 (`+')).
_r_u_l_e Indicates when to change to and back from summer time.
The _r_u_l_e has the form:
_d_a_t_e_/_t_i_m_e_,_d_a_t_e_/_t_i_m_e
where the first _d_a_t_e describes when the change from
standard to summer time occurs and the second _d_a_t_e de-
scribes when the change back happens. Each _t_i_m_e field
describes when, in current local time, the change to
the other time is made.
The format of _d_a_t_e is one of the following:
JJ _n The Julian day _n (1 <= _n <= 365). Leap days
are not counted; that is, in all years -- in-
cluding 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 _m_._n_._d The _d'th 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'th day occurs. Day
zero is Sunday.
The _t_i_m_e has the same format as _o_f_f_s_e_t except
that no leading sign (`-') or (`+') is al-
lowed. The default, if _t_i_m_e is not given, is
0022::0000::0000.
If no _r_u_l_e is present in the TZ specification, the
rules specified by the tzfile(5)-format file
_p_o_s_i_x_r_u_l_e_s in the system time conversion information
directory are used, with the standard and summer time
offsets from UTC replaced by those specified by the
_o_f_f_s_e_t values in TZ.
For compatibility with System V Release 3.1, a semicolon (`'); may be
used to separate the _r_u_l_e from the rest of the specification.
FFIILLEESS
/etc/localtime local time zone file
/usr/share/zoneinfo time zone directory
/usr/share/zoneinfo/posixrules rules for POSIX-style TZ's
/usr/share/zoneinfo/GMT for UTC leap seconds
If the file _/_u_s_r_/_s_h_a_r_e_/_z_o_n_e_i_n_f_o_/_G_M_T does not exist, UTC leap seconds are
loaded from _/_u_s_r_/_s_h_a_r_e_/_z_o_n_e_i_n_f_o_/_p_o_s_i_x_r_u_l_e_s.
SSEEEE AALLSSOO
date(1), gettimeofday(2), ctime(3), getenv(3), time(3), tzfile(5)
HHIISSTTOORRYY
The ttzzsseett and ttzzsseettwwaallll functions first appeared in 4.4BSD.
4.4BSD June 9, 1993 3