TZFILE

Section: File Formats (5)
Index Return to Main Contents

BSD mandoc
 

NAME

tzfile - time zone information  

SYNOPSIS

Fd #include <tzfile.h>  

DESCRIPTION

The time zone information files used by tzset(3) begin with bytes reserved for future use, followed by four four-byte values of type long written in a ``standard'' byte order (the high-order byte of the value is written first). These values are, in order:

Fa tzh_ttisstdcnt
The number of standard/wall indicators stored in the file.
Fa tzh_leapcnt
The number of leap seconds for which data is stored in the file.
Fa tzh_timecnt
The number of "transition times" for which data is stored in the file.
Fa tzh_typecnt
The number of "local time types" for which data is stored in the file (must not be zero).
Fa tzh_charcnt
The number of characters of "time zone abbreviation strings" stored in the file.

The above header is followed by Fa tzh_timecnt four-byte values of type long sorted in ascending order. These values are written in ``standard'' byte order. Each is used as a transition time (as returned by time(2)) at which the rules for computing local time change. Next come Fa tzh_timecnt one-byte values of type Fa unsigned char ; each one tells which of the different types of ``local time'' types described in the file is associated with the same-indexed transition time. These values serve as indices into an array of Fa ttinfo structures that appears next in the file; these structures are defined as follows:

struct ttinfo { 
        long    tt_gmtoff;
        int     tt_isdst;
        unsigned int    tt_abbrind;
};

Each structure is written as a four-byte value for Fa tt_gmtoff of type long in a standard byte order, followed by a one-byte value for Fa tt_isdst and a one-byte value for Fa tt_abbrind . In each structure, Fa tt_gmtoff gives the number of seconds to be added to GMT, Fa tt_isdst tells whether Fa tm_isdst should be set by localtime(3) and Fa tt_abbrind serves as an index into the array of time zone abbreviation characters that follow the Fa ttinfo structure(s) in the file.

Then there are Fa tzh_leapcnt pairs of four-byte values, written in standard byte order; the first value of each pair gives the time (as returned by time(2)) at which a leap second occurs; the second gives the total number of leap seconds to be applied after the given time. The pairs of values are sorted in ascending order by time.

Finally there are Fa tzh_ttisstdcnt standard/wall indicators, each stored as a one-byte value; they tell whether the transition times associated with local time types were specified as standard time or wall clock time, and are used when a time zone file is used in handling POSIX -style time zone environment variables.

Fa Localtime uses the first standard-time Fa ttinfo structure in the file (or simply the first Fa ttinfo structure in the absence of a standard-time structure) if either Fa tzh_timecnt is zero or the time argument is less than the first transition time recorded in the file.  

SEE ALSO

ctime(3)  

HISTORY

The tzfile file format appeared in BSD 4.3 tahoe.


 

Index

NAME
SYNOPSIS
DESCRIPTION
SEE ALSO
HISTORY

This document was created by man2html, using the manual pages.
Time: 15:41:12 GMT, August 08, 2024