1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" Permission is granted to make and distribute verbatim copies of this
4 .\" manual provided the copyright notice and this permission notice are
5 .\" preserved on all copies.
7 .\" Permission is granted to copy and distribute modified versions of this
8 .\" manual under the conditions for verbatim copying, provided that the
9 .\" entire resulting derived work is distributed under the terms of a
10 .\" permission notice identical to this one.
12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
14 .\" responsibility for errors or omissions, or for damages resulting from
15 .\" the use of the information contained herein. The author(s) may not
16 .\" have taken the same level of care in the production of this manual,
17 .\" which is licensed free of charge, as they might when working
20 .\" Formatted or processed versions of this manual, if unaccompanied by
21 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" References consulted:
24 .\" Linux libc source code
25 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
27 .\" Modified Sat Jul 24 19:49:27 1993 by Rik Faith (faith@cs.unc.edu)
28 .\" Modified Fri Apr 26 12:38:55 MET DST 1996 by Martin Schulze (joey@linux.de)
29 .\" Modified 2001-11-13, aeb
30 .\" Modified 2001-12-13, joey, aeb
31 .\" Modified 2004-11-16, mtk
33 .TH CTIME 3 2004-11-16 "" "Linux Programmer's Manual"
35 asctime, ctime, gmtime, localtime, mktime, asctime_r, ctime_r, gmtime_r,
36 localtime_r \- transform date and time to broken-down time or ASCII
41 .BI "char *asctime(const struct tm *" tm );
43 .BI "char *asctime_r(const struct tm *" tm ", char *" buf );
45 .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 );
51 .BI "struct tm *gmtime_r(const time_t *" timep ", struct tm *" result );
53 .BI "struct tm *localtime(const time_t *" timep );
55 .BI "struct tm *localtime_r(const time_t *" timep ", struct tm *" result );
57 .BI "time_t mktime(struct tm *" tm );
66 an argument of data type \fItime_t\fP which represents calendar time.
67 When interpreted as an absolute time value, it represents the number of
68 seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal
75 functions both take an argument
76 representing broken-down time which is a representation
77 separated into year, month, day, etc.
79 Broken-down time is stored
80 in the structure \fItm\fP which is defined in \fI<time.h>\fP as follows:
85 int tm_sec; /* seconds */
86 int tm_min; /* minutes */
87 int tm_hour; /* hours */
88 int tm_mday; /* day of the month */
89 int tm_mon; /* month */
90 int tm_year; /* year */
91 int tm_wday; /* day of the week */
92 int tm_yday; /* day in the year */
93 int tm_isdst; /* daylight saving time */
98 The members of the \fItm\fP structure are:
101 The number of seconds after the minute, normally in the range 0 to 59,
102 but can be up to 60 to allow for leap seconds.
105 The number of minutes after the hour, in the range 0 to 59.
108 The number of hours past midnight, in the range 0 to 23.
111 The day of the month, in the range 1 to 31.
114 The number of months since January, in the range 0 to 11.
117 The number of years since 1900.
120 The number of days since Sunday, in the range 0 to 6.
123 The number of days since January 1, in the range 0 to 365.
126 A flag that indicates whether daylight saving time is in effect at the
128 The value is positive if daylight saving time is in
129 effect, zero if it is not, and negative if the information is not
135 .BI asctime(localtime( t )) \fR.
136 It converts the calendar time \fIt\fP into a string of the form
139 "Wed Jun 30 21:49:08 1993\\n"
142 The abbreviations for the days of the week are `Sun', `Mon', `Tue', `Wed',
143 `Thu', `Fri', and `Sat'.
144 The abbreviations for the months are `Jan',
145 `Feb', `Mar', `Apr', `May', `Jun', `Jul', `Aug', `Sep', `Oct', `Nov', and
147 The return value points to a statically allocated string which
148 might be overwritten by subsequent calls to any of the date and time
150 The function also sets the external variable \fItzname\fP (see
152 with information about the current time zone.
153 The re-entrant version
155 does the same, but stores the
156 string in a user-supplied buffer of length at least 26.
162 function converts the calendar time \fItimep\fP to
163 broken-down time representation, expressed in Coordinated Universal Time
165 It may return NULL when the year does not fit into an integer.
166 The return value points to a statically allocated struct which might be
167 overwritten by subsequent calls to any of the date and time functions.
170 function does the same, but stores the data in a
171 user-supplied struct.
175 function converts the calendar time \fItimep\fP to
176 broken-time representation, expressed relative to the user's specified
178 The function acts as if it called
180 and sets the external variables \fItzname\fP with
181 information about the current time zone, \fItimezone\fP with the difference
182 between Coordinated Universal Time (UTC) and local standard time in
183 seconds, and \fIdaylight\fP to a non-zero value if daylight savings
184 time rules apply during some part of the year.
185 The return value points to a statically allocated struct which might be
186 overwritten by subsequent calls to any of the date and time functions.
189 function does the same, but stores the data in a
190 user-supplied struct.
191 It need not set \fItzname\fP.
195 function converts the broken-down time value
196 \fItm\fP into a string with the same format as
198 The return value points to a statically allocated string which might be
199 overwritten by subsequent calls to any of the date and time functions.
202 function does the same, but stores the string in
203 a user-supplied buffer of length at least 26.
207 function converts a broken-down time structure, expressed
208 as local time, to calendar time representation.
210 the specified contents of the structure members \fItm_wday\fP and \fItm_yday\fP
211 and recomputes them from the other information in the broken-down time
213 If structure members are outside their legal interval, they will be
214 normalized (so that, e.g., 40 October is changed into 9 November).
217 also sets the external variable \fItzname\fP with
218 information about the current time zone.
219 If the specified broken-down
220 time cannot be represented as calendar time (seconds since the epoch),
222 returns a value of (time_t)(\-1) and does not alter the
223 \fItm_wday\fP and \fItm_yday\fP members of the broken-down time structure.
225 Each of these functions returns the value described, or NULL
228 in case an error was detected.
236 return a pointer to static data and hence are not thread-safe.
243 are specified by SUSv2, and available since libc 5.2.5.
245 In many implementations, including
249 is interpreted as meaning the last day of the preceding month.
251 The glibc version of struct tm has additional fields
255 long tm_gmtoff; /* Seconds east of UTC */
256 const char *tm_zone; /* Timezone abbreviation */
260 defined when _BSD_SOURCE was set before including
262 This is a BSD extension, present in 4.3BSD-Reno.
274 .BR gettimeofday (2),