1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
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8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Modified Sat Jul 24 19:49:27 1993 by Rik Faith (faith@cs.unc.edu)
30 .\" Modified Fri Apr 26 12:38:55 MET DST 1996 by Martin Schulze (joey@linux.de)
31 .\" Modified 2001-11-13, aeb
32 .\" Modified 2001-12-13, joey, aeb
33 .\" Modified 2004-11-16, mtk
35 .TH CTIME 3 2019-03-06 "" "Linux Programmer's Manual"
37 asctime, ctime, gmtime, localtime, mktime, asctime_r, ctime_r, gmtime_r,
38 localtime_r \- transform date and time to broken-down time or ASCII
43 .BI "char *asctime(const struct tm *" tm );
44 .BI "char *asctime_r(const struct tm *" tm ", char *" buf );
46 .BI "char *ctime(const time_t *" timep );
47 .BI "char *ctime_r(const time_t *" timep ", char *" buf );
49 .BI "struct tm *gmtime(const time_t *" timep );
50 .BI "struct tm *gmtime_r(const time_t *" timep ", struct tm *" result );
52 .BI "struct tm *localtime(const time_t *" timep );
53 .BI "struct tm *localtime_r(const time_t *" timep ", struct tm *" result );
55 .BI "time_t mktime(struct tm *" tm );
59 Feature Test Macro Requirements for glibc (see
60 .BR feature_test_macros (7)):
70 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
80 an argument of data type \fItime_t\fP, which represents calendar time.
81 When interpreted as an absolute time value, it represents the number of
82 seconds elapsed since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
88 functions both take an argument
89 representing broken-down time, which is a representation
90 separated into year, month, day, and so on.
92 Broken-down time is stored
93 in the structure \fItm\fP, which is defined in \fI<time.h>\fP as follows:
98 int tm_sec; /* Seconds (0\-60) */
99 int tm_min; /* Minutes (0\-59) */
100 int tm_hour; /* Hours (0\-23) */
101 int tm_mday; /* Day of the month (1\-31) */
102 int tm_mon; /* Month (0\-11) */
103 int tm_year; /* Year \- 1900 */
104 int tm_wday; /* Day of the week (0\-6, Sunday = 0) */
105 int tm_yday; /* Day in the year (0\-365, 1 Jan = 0) */
106 int tm_isdst; /* Daylight saving time */
111 The members of the \fItm\fP structure are:
114 The number of seconds after the minute, normally in the range 0 to 59,
115 but can be up to 60 to allow for leap seconds.
118 The number of minutes after the hour, in the range 0 to 59.
121 The number of hours past midnight, in the range 0 to 23.
124 The day of the month, in the range 1 to 31.
127 The number of months since January, in the range 0 to 11.
130 The number of years since 1900.
133 The number of days since Sunday, in the range 0 to 6.
136 The number of days since January 1, in the range 0 to 365.
139 A flag that indicates whether daylight saving time is in effect at the
141 The value is positive if daylight saving time is in
142 effect, zero if it is not, and negative if the information is not
148 .BI asctime(localtime( t )) \fR.
149 It converts the calendar time \fIt\fP into a
150 null-terminated string of the form
154 "Wed Jun 30 21:49:08 1993\en"
158 The abbreviations for the days of the week are "Sun", "Mon", "Tue", "Wed",
159 "Thu", "Fri", and "Sat".
160 The abbreviations for the months are "Jan",
161 "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", and
163 The return value points to a statically allocated string which
164 might be overwritten by subsequent calls to any of the date and time
166 The function also sets the external
167 variables \fItzname\fP, \fItimezone\fP, and \fIdaylight\fP (see
169 with information about the current timezone.
170 The reentrant version
172 does the same, but stores the
173 string in a user-supplied buffer
174 which should have room for at least 26 bytes.
176 set \fItzname\fP, \fItimezone\fP, and \fIdaylight\fP.
180 function converts the calendar time \fItimep\fP to
181 broken-down time representation, expressed in Coordinated Universal Time
183 It may return NULL when the year does not fit into an integer.
184 The return value points to a statically allocated struct which might be
185 overwritten by subsequent calls to any of the date and time functions.
188 function does the same, but stores the data in a
189 user-supplied struct.
193 function converts the calendar time \fItimep\fP to
194 broken-down time representation,
195 expressed relative to the user's specified timezone.
196 The function acts as if it called
198 and sets the external variables \fItzname\fP with
199 information about the current timezone, \fItimezone\fP with the difference
200 between Coordinated Universal Time (UTC) and local standard time in
201 seconds, and \fIdaylight\fP to a nonzero value if daylight savings
202 time rules apply during some part of the year.
203 The return value points to a statically allocated struct which might be
204 overwritten by subsequent calls to any of the date and time functions.
207 function does the same, but stores the data in a
208 user-supplied struct.
209 It need not set \fItzname\fP, \fItimezone\fP, and \fIdaylight\fP.
213 function converts the broken-down time value
214 \fItm\fP into a null-terminated string with the same format as
216 The return value points to a statically allocated string which might be
217 overwritten by subsequent calls to any of the date and time functions.
220 function does the same, but stores the string in
221 a user-supplied buffer which should have room for at least 26 bytes.
225 function converts a broken-down time structure, expressed
226 as local time, to calendar time representation.
228 the values supplied by the caller in the
233 The value specified in the
237 whether or not daylight saving time (DST)
238 is in effect for the time supplied in the
241 a positive value means DST is in effect;
242 zero means that DST is not in effect;
243 and a negative value means that
245 should (use timezone information and system databases to)
246 attempt to determine whether DST is in effect at the specified time.
250 function modifies the fields of the
252 structure as follows:
256 are set to values determined from the contents of the other fields;
257 if structure members are outside their valid interval, they will be
258 normalized (so that, for example, 40 October is changed into 9 November);
260 is set (regardless of its initial value)
261 to a positive value or to 0, respectively,
262 to indicate whether DST is or is not in effect at the specified time.
265 also sets the external variable \fItzname\fP with
266 information about the current timezone.
268 If the specified broken-down
269 time cannot be represented as calendar time (seconds since the Epoch),
273 and does not alter the
274 members of the broken-down time structure.
280 return a pointer to a
287 return the address of the structure pointed to by
294 return a pointer to a string.
300 return a pointer to the string pointed to by
305 returns the calendar time (seconds since the Epoch),
306 expressed as a value of type
313 The remaining functions return NULL on error.
316 is set to indicate the cause of the error.
320 The result cannot be represented.
322 For an explanation of the terms used in this section, see
329 Interface Attribute Value
332 T} Thread safety MT-Unsafe race:asctime locale
335 T} Thread safety MT-Safe locale
341 race:asctime env locale
348 T} Thread safety MT-Safe env locale
352 T} Thread safety MT-Unsafe race:tmbuf env locale
371 recommending the use of
381 return a pointer to static data and hence are not thread-safe.
382 The thread-safe versions,
388 are specified by SUSv2.
397 functions shall return values in one of two static objects:
398 a broken-down time structure and an array of type
400 Execution of any of the functions may overwrite the information returned
401 in either of these objects by any of the other functions."
402 This can occur in the glibc implementation.
404 In many implementations, including glibc, a 0 in
406 is interpreted as meaning the last day of the preceding month.
408 The glibc version of \fIstruct tm\fP has additional fields
412 const char *tm_zone; /* Timezone abbreviation */
418 was set before including
420 This is a BSD extension, present in 4.3BSD-Reno.
422 According to POSIX.1-2004,
424 is required to behave as though
428 does not have this requirement.
429 .\" See http://thread.gmane.org/gmane.comp.time.tz/2034/
432 should be called before
436 .BR gettimeofday (2),
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