NAME
tzfile - 时区信息
SYNOPSIS
#include <tzfile.h>
DESCRIPTION
时区信息文件被 tzset(3) 使用, 其开头为特征字符"TZif", 以此标示该文件为时区信息文件, 随后六个字节保留未用. 接下来是六个"标准"字节顺序(高位在前)的四字节 long 类型值, 按顺序描述如下:
- tzh_ttisgmtcnt
- 保存在文件中的UTC/local指示器数目.
- tzh_ttisstdcnt
- 保存在文件中的standard/wall指示器数目.
- tzh_leapcnt
- 其值保存在文件中的leap second的数目
- tzh_timecnt
- 其值保存在文件中的"变化时间"数目
- tzh_typecnt
- 其值保存在文件中的"本地时间类型"数目(非零!)
- tzh_charcnt
- 保存在文件中的"时区简写符"数目
跟在上面这些头部后的是 tzh_timecnt 个"标准"字节顺序的四字节 long 类型值, 以升序排序. 每个值均作为一个变化时间(就像 time(2) 的返回), 系统依赖这些值来计算本地时间变化. 而在此之后的是 tzh_timecnt 个 unsigned char 类型的一字节值, 这些值指出了文件中描述的多种"本地时间"类型中哪一个与具有相同索引的变化时间相关. 这些值可作为 ttinfo 结构数组的索引. 而 ttinfo 结构在文件中随后就有定义, 描述如下:
struct ttinfo { long tt_gmtoff; int tt_isdst; unsigned int tt_abbrind; };
结构包括一个"标准"字节顺序的四字节 long 类型值 tt_gmtoff, 以及一个一字节的 tt_isdst 和一个一字节的 tt_abbrind. 在每个结构里, tt_gmtoff 给出了要被加到UTC的时间, 以秒为单位, tt_isdst 表明 tm_isdst 是否可通过 localtime (3) 设置, 而 tt_abbrind 可作为时区简写符的数组索引, 该数组在文件中跟在 ttinfo 结构后面.
这样就有 tzh_leapcnt 个标准字节顺序的四字节对, 每个四字节对的***个值给出一个leap second发生的时间, 就如 time(2) 的返回; 每个四字节对的第二个值给出给定时间之后所实现的总的 leap second数. 四字节对按时间的升序排序.
同样有 tzh_ttisstdcnt 个standard/wall指示器, 每个保存了一个一字节值; 这些指示器指出了变化时间(与本地时间类型相关)是否被说明为standard time或者wall clock time, 以及当一个时区文件被用于处理POSIX 格式时区环境变量时是否使用变化时间.
***, 有 tzh_ttisgmtcnt 个UTC/local指示器, 每个保存了一个一字节值; 这些指示器指出了变化时间(与本地时间类型相关)是否被说明为UTC 或者local time, 以及当一个时区文件被用于处理 POSIX格式时区环境变量时是否使用变化时间.
如果 tzh_timecnt 等于零或者时间参数比文件记录的***个变化时间小的话, Localtime 就使用文件中的***个标准时间 ttinfo, 或者在没有标准时间结构是就直接使用***个 ttinfo 结构.
SEE ALSO
newctime(3)
#p#
NAME
tzfile - time zone information
SYNOPSIS
#include <tzfile.h>
DESCRIPTION
The time zone information files used by tzset(3) begin with the magic characters "TZif" to identify then as time zone information files, followed by sixteen bytes reserved for future use, followed by six 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:
- tzh_ttisgmtcnt
- The number of UTC/local indicators stored in the file.
- tzh_ttisstdcnt
- The number of standard/wall indicators stored in the file.
- tzh_leapcnt
- The number of leap seconds for which data is stored in the file.
- tzh_timecnt
- The number of "transition times" for which data is stored in the file.
- tzh_typecnt
- The number of "local time types" for which data is stored in the file (must not be zero).
- tzh_charcnt
- The number of characters of "time zone abbreviation strings" stored in the file.
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 UTC, 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.
Then there are 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.
Then there are 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.
Finally, there are tzh_ttisgmtcnt UTC/local indicators, each stored as a one-byte value; they tell whether the transition times associated with local time types were specified as UTC or local time, and are used when a time zone file is used in handling POSIX-style time zone environment variables.
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.