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tzfile(4) Kernel Interfaces Manual tzfile(4) NAME tzfile - Time zone information SYNOPSIS #include <tzfile.h> DESCRIPTION The time zone information file used by tzset begins with bytes reserved for future use, followed by three 4-byte values written in a ``stan- dard'' byte order (that is, with the high-order byte of the value writ- ten first). These values are, in order: The number of transition times for which data is stored in the file. The number of local time types for which data is stored in the file. (This value must not be zero.) The number of characters of ``time zone abbreviation strings'' stored in the file. This header is followed by tzh_timecnt 4-byte values sorted in ascend- ing order. These values are written in ``standard'' byte order. Each is used as a transition time (as returned by the time at which the rules for computing local time change). Next come the tzh_timecnt 1-byte values of type unsigned char. Each value tells which of the different local time types described in the file is associated with the same-indexed transition time. These values serve as indexes into an array of ttinfo structures that appears next in the file. These struc- tures are defined as follows: struct ttinfo { long tt_gmtoff; int tt_isdst; unsigned int tt_abbrind; }; Each structure is written as a 4-byte value for tt_gmtoff of type long, in a standard byte order, followed by a 1-byte value for tt_isdst and a 1-byte value for tt_abbrind. In each structure, tt_gmtoff gives the number of seconds to be added to GMT, tt_isdst tells whether tm_isdst should be set by localtime, and tt_abbrind serves as an index into the array of time zone abbreviation characters that follows the ttinfo structure or structures in the file. The localtime call uses the first standard-time ttinfo structure in the file (or simply the first ttinfo structure, in the absence of a stan- dard-time structure) if either tzh_timecnt is zero or the time argument is less than the first transition time recorded in the file. RELATED INFORMATION ctime(3) delim off tzfile(4)