table of contents
TZSET(3) | Linux Programmer's Manual | TZSET(3) |
NAME¶
tzset - initialize time conversion informationSYNOPSIS¶
#include <time.h>void tzset (void);extern char *tzname[2]
DESCRIPTION¶
The tzset() function initializes the tzname variable from the TZ environment variable. This function is automatically called by the other time conversion functions that depend on the time zone. If the TZ variable does not appear in the environment, the tzname variable is initialized with the best approximation of local wall clock time, as specified by the tzfile(5)-format file localtime found in the system timezone directory (see below). (One also often sees /etc/localtime used here, a symlink to the right file in the system timezone directory.) If the TZ variable does appear in the environment but its value is NULL or its value cannot be interpreted using any of the formats specified below, Coordinated Universal Time (UTC) is used. The value of TZ can be one of three formats. The first format is used when there is no daylight saving time in the local time zone:std offset
std offset dst
[offset],start[/time],end[/time]
- Jn
- This specifies the Julian day with n between 1 and 365. February 29 is never counted even in leap years.
- n
- This specifies the Julian day with n between 1 and 365. February 29 is counted in leap years.
- Mm.w.d
- This specifies day d (0 <= d <= 6) of week w (1 <= w <= 5) of month m (1 <= m <= 12). Week 1 is the first week in which day d occurs and week 5 is the last week in which day d occurs. Day 0 is a Sunday.
:[filespec]
FILES¶
The system time zone directory used depends on the (g)libc version. Libc4 and libc5 use /usr/lib/zoneinfo, and, since libc-5.4.6, when this doesn't work, will try /usr/share/zoneinfo. Glibc2 will use the environment variable TZDIR, when that exists. Its default depends on how it was installed, but normally is /usr/share/zoneinfo. This timezone directory contains the fileslocaltime local time zone file posixrules rules for POSIX-style TZ'sOften /etc/localtime is a symlink to the file localtime or to the correct time zone file in the system time zone directory.
CONFORMING TO¶
SVID 3, POSIX, BSD 4.3SEE ALSO¶
date(1), gettimeofday(2), time(2), ctime(3), getenv(3), tzfile(5)July 2, 1993 | BSD |