The above header is followed by 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 tzh_timecnt one-byte values of type 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 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 tt_gmtoff of type long, in a standard byte order, followed by a one-byte value for tt_isdst and a one-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 (3) and tt_abbrind serves as an index into the array of time zone abbreviation characters that follow the ttinfo structure(s) in the file.
Localtime uses the first standard-time ttinfo structure in the file (or simply the first ttinfo structure in the absence of a standard-time structure) if either tzh_timecnt is zero or the time argument is less than the first transition time recorded in the file.