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34 .\" $FreeBSD: src/lib/libc/stdtime/ctime.3,v 1.11.2.7 2003/05/23 23:53:40 keramida Exp $
51 .Nd transform binary date and time values
56 .Vt extern char *tzname[2] ;
58 .Fn ctime "const time_t *clock"
60 .Fn difftime "time_t time1" "time_t time0"
62 .Fn asctime "const struct tm *tm"
64 .Fn localtime "const time_t *clock"
66 .Fn gmtime "const time_t *clock"
68 .Fn mktime "struct tm *tm"
70 .Fn timegm "struct tm *tm"
72 .Fn ctime_r "const time_t *clock" "char *buf"
74 .Fn localtime_r "const time_t *clock" "struct tm *result"
76 .Fn gmtime_r "const time_t *clock" "struct tm *result"
78 .Fn asctime_r "const struct tm *tm" "char *buf"
85 all take as an argument a time value representing the time in seconds since
93 converts the time value pointed at by
95 and returns a pointer to a
97 (described below) which contains
98 the broken-out time information for the value after adjusting for the current
99 time zone and any time zone adjustments.
100 Time zone adjustments are performed as specified by the
102 environment variable (see
105 After filling in the tm structure,
113 string that's the time zone abbreviation to be
120 similarly converts the time value, but without any time zone adjustment,
121 and returns a pointer to a tm structure (described below).
126 adjusts the time value for the current time zone in the same manner as
128 and returns a pointer to a string of the form:
129 .Bd -literal -offset indent
130 Thu Nov 24 18:22:48 1986\en\e0
133 Years requiring fewer than four characters are padded with leading zeroes.
134 For years longer than four characters, the string is of the form
135 .Bd -literal -offset indent
136 Thu Nov 24 18:22:48 81986\en\e0
139 with five spaces before the year.
140 These unusual formats are designed to make it less likely that older
141 software that expects exactly 26 bytes of output will mistakenly output
142 misleading values for out-of-range years.
147 provides the same functionality as
149 except the caller must provide the output buffer
151 to store the result, which must be at least 26 characters long.
157 provide the same functionality as
161 respectively, except the caller must provide the output buffer
167 converts the broken down time in the structure
172 shown in the example above.
177 provides the same functionality as
179 except the caller provide the output buffer
181 to store the result, which must be at least 26 characters long.
187 convert the broken-down time in the structure
188 pointed to by tm into a time value with the same encoding as that of the
189 values returned by the
191 function (that is, seconds from the Epoch,
196 interprets the input structure according to the current timezone setting
202 interprets the input structure as representing Universal Coordinated Time
205 The original values of the
209 components of the structure are ignored, and the original values of the
210 other components are not restricted to their normal ranges, and will be
211 normalized if needed.
213 October 40 is changed into November 9,
216 of \-1 means 1 hour before midnight,
218 of 0 means the day preceding the current month, and
220 of \-2 means 2 months before January of
222 (A positive or zero value for
226 to presume initially that summer time (for example, Daylight Saving Time)
227 is or is not in effect for the specified time, respectively.
232 function to attempt to divine whether summer time is in effect for the
233 specified time; in this case it does not use a consistent
234 rule and may give a different answer when later
235 presented with the same argument.
240 members are forced to zero by
243 On successful completion, the values of the
247 components of the structure are set appropriately, and the other components
248 are set to represent the specified calendar time, but with their values
249 forced to their normal ranges; the final value of
259 returns the specified calendar time; if the calendar time cannot be
260 represented, it returns \-1;
265 returns the difference between two calendar times,
269 expressed in seconds.
271 External declarations as well as the tm structure definition are in the
274 The tm structure includes at least the following fields:
275 .Bd -literal -offset indent
276 int tm_sec; /\(** seconds (0 - 60) \(**/
277 int tm_min; /\(** minutes (0 - 59) \(**/
278 int tm_hour; /\(** hours (0 - 23) \(**/
279 int tm_mday; /\(** day of month (1 - 31) \(**/
280 int tm_mon; /\(** month of year (0 - 11) \(**/
281 int tm_year; /\(** year \- 1900 \(**/
282 int tm_wday; /\(** day of week (Sunday = 0) \(**/
283 int tm_yday; /\(** day of year (0 - 365) \(**/
284 int tm_isdst; /\(** is summer time in effect? \(**/
285 char \(**tm_zone; /\(** abbreviation of timezone name \(**/
286 long tm_gmtoff; /\(** offset from UTC in seconds \(**/
292 is non-zero if summer time is in effect.
296 is the offset (in seconds) of the time represented from
299 values indicating east of the Prime Meridian.
306 behave strangely for years before 1000 or after 9999.
307 The 1989 and 1999 editions of the C Standard say
308 that years from -99 through 999 are converted without
309 extra spaces, but this conflicts with longstanding
310 tradition and with this implementation.
311 Traditional implementations of these two functions are
312 restricted to years in the range 1900 through 2099.
313 To avoid this portability mess, new programs should use
337 provided the selected local timezone does not contain a leap-second table
347 functions are expected to conform to
349 (again provided the selected local timezone does not contain a leap-second
354 function is not specified by any standard; its function cannot be
355 completely emulated using the standard functions described above.
357 This manual page is derived from
358 the time package contributed to Berkeley by
360 and which appeared in
368 variants of the other functions,
369 these functions leaves their result in an internal static object and return
370 a pointer to that object.
371 Subsequent calls to these
372 function will modify the same object.
374 The C Standard provides no mechanism for a program to modify its current
375 local timezone setting, and the
376 .Tn POSIX Ns No \&-standard
377 method is not reentrant. (However, thread-safe implementations are provided
380 threaded environment.)
386 structure points to a static array of characters,
387 which will also be overwritten by any subsequent calls (as well as by
393 Use of the external variable
397 entry in the tm structure is preferred.