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30 .\" $FreeBSD: src/lib/libc/stdtime/ctime.3,v 1.11.2.7 2003/05/23 23:53:40 keramida Exp $
47 .Nd transform binary date and time values
52 .Vt extern char *tzname[2] ;
54 .Fn ctime "const time_t *clock"
56 .Fn difftime "time_t time1" "time_t time0"
58 .Fn asctime "const struct tm *tm"
60 .Fn localtime "const time_t *clock"
62 .Fn gmtime "const time_t *clock"
64 .Fn mktime "struct tm *tm"
66 .Fn timegm "struct tm *tm"
68 .Fn ctime_r "const time_t *clock" "char *buf"
70 .Fn localtime_r "const time_t *clock" "struct tm *result"
72 .Fn gmtime_r "const time_t *clock" "struct tm *result"
74 .Fn asctime_r "const struct tm *tm" "char *buf"
81 all take as an argument a time value representing the time in seconds since
89 converts the time value pointed at by
91 and returns a pointer to a
93 (described below) which contains
94 the broken-out time information for the value after adjusting for the current
95 time zone and any time zone adjustments.
96 Time zone adjustments are performed as specified by the
98 environment variable (see
101 After filling in the tm structure,
109 string that's the time zone abbreviation to be
116 similarly converts the time value, but without any time zone adjustment,
117 and returns a pointer to a tm structure (described below).
122 adjusts the time value for the current time zone in the same manner as
124 and returns a pointer to a string of the form:
125 .Bd -literal -offset indent
126 Thu Nov 24 18:22:48 1986\en\e0
129 Years requiring fewer than four characters are padded with leading zeroes.
130 For years longer than four characters, the string is of the form
131 .Bd -literal -offset indent
132 Thu Nov 24 18:22:48 81986\en\e0
135 with five spaces before the year.
136 These unusual formats are designed to make it less likely that older
137 software that expects exactly 26 bytes of output will mistakenly output
138 misleading values for out-of-range years.
143 provides the same functionality as
145 except the caller must provide the output buffer
147 to store the result, which must be at least 26 characters long.
153 provide the same functionality as
157 respectively, except the caller must provide the output buffer
163 converts the broken down time in the structure
168 shown in the example above.
173 provides the same functionality as
175 except the caller provide the output buffer
177 to store the result, which must be at least 26 characters long.
183 convert the broken-down time in the structure
184 pointed to by tm into a time value with the same encoding as that of the
185 values returned by the
187 function (that is, seconds from the Epoch,
192 interprets the input structure according to the current timezone setting
198 interprets the input structure as representing Universal Coordinated Time
201 The original values of the
205 components of the structure are ignored, and the original values of the
206 other components are not restricted to their normal ranges, and will be
207 normalized if needed.
209 October 40 is changed into November 9,
212 of \-1 means 1 hour before midnight,
214 of 0 means the day preceding the current month, and
216 of \-2 means 2 months before January of
218 (A positive or zero value for
222 to presume initially that summer time (for example, Daylight Saving Time)
223 is or is not in effect for the specified time, respectively.
228 function to attempt to divine whether summer time is in effect for the
229 specified time; in this case it does not use a consistent
230 rule and may give a different answer when later
231 presented with the same argument.
236 members are forced to zero by
239 On successful completion, the values of the
243 components of the structure are set appropriately, and the other components
244 are set to represent the specified calendar time, but with their values
245 forced to their normal ranges; the final value of
255 returns the specified calendar time; if the calendar time cannot be
256 represented, it returns \-1;
261 returns the difference between two calendar times,
265 expressed in seconds.
267 External declarations as well as the tm structure definition are in the
270 The tm structure includes at least the following fields:
271 .Bd -literal -offset indent
272 int tm_sec; /\(** seconds (0 - 60) \(**/
273 int tm_min; /\(** minutes (0 - 59) \(**/
274 int tm_hour; /\(** hours (0 - 23) \(**/
275 int tm_mday; /\(** day of month (1 - 31) \(**/
276 int tm_mon; /\(** month of year (0 - 11) \(**/
277 int tm_year; /\(** year \- 1900 \(**/
278 int tm_wday; /\(** day of week (Sunday = 0) \(**/
279 int tm_yday; /\(** day of year (0 - 365) \(**/
280 int tm_isdst; /\(** is summer time in effect? \(**/
281 char \(**tm_zone; /\(** abbreviation of timezone name \(**/
282 long tm_gmtoff; /\(** offset from UTC in seconds \(**/
288 is non-zero if summer time is in effect.
292 is the offset (in seconds) of the time represented from
295 values indicating east of the Prime Meridian.
302 behave strangely for years before 1000 or after 9999.
303 The 1989 and 1999 editions of the C Standard say
304 that years from -99 through 999 are converted without
305 extra spaces, but this conflicts with longstanding
306 tradition and with this implementation.
307 Traditional implementations of these two functions are
308 restricted to years in the range 1900 through 2099.
309 To avoid this portability mess, new programs should use
333 provided the selected local timezone does not contain a leap-second table
343 functions are expected to conform to
345 (again provided the selected local timezone does not contain a leap-second
350 function is not specified by any standard; its function cannot be
351 completely emulated using the standard functions described above.
353 This manual page is derived from
354 the time package contributed to Berkeley by
356 and which appeared in
364 variants of the other functions,
365 these functions leaves their result in an internal static object and return
366 a pointer to that object.
367 Subsequent calls to these
368 function will modify the same object.
370 The C Standard provides no mechanism for a program to modify its current
371 local timezone setting, and the
372 .Tn POSIX Ns No \&-standard
373 method is not reentrant. (However, thread-safe implementations are provided
376 threaded environment.)
382 structure points to a static array of characters,
383 which will also be overwritten by any subsequent calls (as well as by
389 Use of the external variable
393 entry in the tm structure is preferred.