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34 .\" From: @(#)ctime.3 8.1 (Berkeley) 6/4/93
35 .\" $FreeBSD: src/lib/libc/stdtime/ctime.3,v 1.11.2.7 2003/05/23 23:53:40 keramida Exp $
36 .\" $DragonFly: src/lib/libc/stdtime/ctime.3,v 1.2 2003/06/17 04:26:46 dillon Exp $
53 .Nd transform binary date and time values
58 .Vt extern char *tzname[2] ;
60 .Fn ctime "const time_t *clock"
62 .Fn difftime "time_t time1" "time_t time0"
64 .Fn asctime "const struct tm *tm"
66 .Fn localtime "const time_t *clock"
68 .Fn gmtime "const time_t *clock"
70 .Fn mktime "struct tm *tm"
72 .Fn timegm "struct tm *tm"
74 .Fn ctime_r "const time_t *clock" "char *buf"
76 .Fn localtime_r "const time_t *clock" "struct tm *result"
78 .Fn gmtime_r "const time_t *clock" "struct tm *result"
80 .Fn asctime_r "const struct tm *tm" "char *buf"
87 all take as an argument a time value representing the time in seconds since
95 converts the time value pointed at by
97 and returns a pointer to a
99 (described below) which contains
100 the broken-out time information for the value after adjusting for the current
101 time zone (and any other factors such as Daylight Saving Time).
102 Time zone adjustments are performed as specified by the
104 environment variable (see
110 to initialize time conversion information if
112 has not already been called by the process.
114 After filling in the tm structure,
122 string that's the time zone abbreviation to be
129 similarly converts the time value, but without any time zone adjustment,
130 and returns a pointer to a tm structure (described below).
135 adjusts the time value for the current time zone in the same manner as
137 and returns a pointer to a 26-character string of the form:
138 .Bd -literal -offset indent
139 Thu Nov 24 18:22:48 1986\en\e0
142 All the fields have constant width.
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
238 members are forced to zero by
241 On successful completion, the values of the
245 components of the structure are set appropriately, and the other components
246 are set to represent the specified calendar time, but with their values
247 forced to their normal ranges; the final value of
257 returns the specified calendar time; if the calendar time cannot be
258 represented, it returns \-1;
263 returns the difference between two calendar times,
267 expressed in seconds.
269 External declarations as well as the tm structure definition are in the
272 The tm structure includes at least the following fields:
273 .Bd -literal -offset indent
274 int tm_sec; /\(** seconds (0 - 60) \(**/
275 int tm_min; /\(** minutes (0 - 59) \(**/
276 int tm_hour; /\(** hours (0 - 23) \(**/
277 int tm_mday; /\(** day of month (1 - 31) \(**/
278 int tm_mon; /\(** month of year (0 - 11) \(**/
279 int tm_year; /\(** year \- 1900 \(**/
280 int tm_wday; /\(** day of week (Sunday = 0) \(**/
281 int tm_yday; /\(** day of year (0 - 365) \(**/
282 int tm_isdst; /\(** is summer time in effect? \(**/
283 char \(**tm_zone; /\(** abbreviation of timezone name \(**/
284 long tm_gmtoff; /\(** offset from UTC in seconds \(**/
290 is non-zero if summer time is in effect.
294 is the offset (in seconds) of the time represented from
297 values indicating east of the Prime Meridian.
318 provided the selected local timezone does not contain a leap-second table
328 functions are expected to conform to
330 (again provided the selected local timezone does not contain a leap-second
335 function is not specified by any standard; its function cannot be
336 completely emulated using the standard functions described above.
338 This manual page is derived from
339 the time package contributed to Berkeley by
341 and which appeared in
349 variants of the other functions,
350 these functions leaves their result in an internal static object and return
351 a pointer to that object.
352 Subsequent calls to these
353 function will modify the same object.
355 The C Standard provides no mechanism for a program to modify its current
356 local timezone setting, and the
357 .Tn POSIX Ns No \&-standard
358 method is not reentrant. (However, thread-safe implementations are provided
361 threaded environment.)
367 structure points to a static array of characters,
368 which will also be overwritten by any subsequent calls (as well as by
374 Use of the external variable
378 entry in the tm structure is preferred.