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CTIME(3) Library Functions Manual CTIME(3) NAME ctime, localtime, gmtime, asctime, timezone - convert date and time to ASCII SYNOPSIS char *ctime(clock) long *clock; #include <time.h> struct tm *localtime(clock) long *clock; struct tm *gmtime(clock) long *clock; char *asctime(tm) struct tm *tm; char *timezone(zone, dst) DESCRIPTION Ctime converts a time pointed to by clock such as returned by time(2) into ASCII and returns a pointer to a 26-character string in the fol- lowing form. All the fields have constant width. Sun Sep 16 01:03:52 1973\n\0 Localtime and gmtime return pointers to structures containing the bro- ken-down time. Localtime corrects for the time zone and possible day- light savings time; gmtime converts directly to GMT, which is the time UNIX uses. Asctime converts a broken-down time to ASCII and returns a pointer to a 26-character string. The structure declaration from the include file is: /*- * SPDX-License-Identifier: BSD-3-Clause * * Copyright (c) 1989, 1993 * The Regents of the University of California. All rights reserved. * (c) UNIX System Laboratories, Inc. * All or some portions of this file are derived from material licensed * to the University of California by American Telephone and Telegraph * Co. or Unix System Laboratories, Inc. and are reproduced herein with * the permission of UNIX System Laboratories, Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)time.h 8.3 (Berkeley) 1/21/94 */ /* */ #ifndef _TIME_H_ #define _TIME_H_ #include <sys/cdefs.h> #include <sys/_null.h> #include <sys/_types.h> #include <sys/_clock_id.h> #if __POSIX_VISIBLE > 0 && __POSIX_VISIBLE < 200112 || __BSD_VISIBLE /* * Frequency of the clock ticks reported by times(). Deprecated - use * sysconf(_SC_CLK_TCK) instead. (Removed in 1003.1-2001.) */ #define CLK_TCK 128 #endif /* Frequency of the clock ticks reported by clock(). */ #define CLOCKS_PER_SEC 128 #ifndef _CLOCK_T_DECLARED typedef __clock_t clock_t; #define _CLOCK_T_DECLARED #endif #ifndef _TIME_T_DECLARED typedef __time_t time_t; #define _TIME_T_DECLARED #endif #ifndef _SIZE_T_DECLARED typedef __size_t size_t; #define _SIZE_T_DECLARED #endif #if __POSIX_VISIBLE >= 199309 /* * New in POSIX 1003.1b-1993. */ #ifndef _CLOCKID_T_DECLARED typedef __clockid_t clockid_t; #define _CLOCKID_T_DECLARED #endif #ifndef _TIMER_T_DECLARED typedef __timer_t timer_t; #define _TIMER_T_DECLARED #endif #include <sys/timespec.h> #endif /* __POSIX_VISIBLE >= 199309 */ #if __POSIX_VISIBLE >= 200112 #ifndef _PID_T_DECLARED typedef __pid_t pid_t; #define _PID_T_DECLARED #endif #endif struct tm { int tm_sec; /* seconds after the minute [0-60] */ int tm_min; /* minutes after the hour [0-59] */ int tm_hour; /* hours since midnight [0-23] */ int tm_mday; /* day of the month [1-31] */ int tm_mon; /* months since January [0-11] */ int tm_year; /* years since 1900 */ int tm_wday; /* days since Sunday [0-6] */ int tm_yday; /* days since January 1 [0-365] */ int tm_isdst; /* Daylight Savings Time flag */ long tm_gmtoff; /* offset from UTC in seconds */ char *tm_zone; /* timezone abbreviation */ }; #if __POSIX_VISIBLE extern char *tzname[]; #endif __BEGIN_DECLS char *asctime(const struct tm *); clock_t clock(void); char *ctime(const time_t *); #ifndef _STANDALONE double difftime(time_t, time_t); #endif /* XXX missing: getdate() */ struct tm *gmtime(const time_t *); struct tm *localtime(const time_t *); time_t mktime(struct tm *); size_t strftime(char * __restrict, size_t, const char * __restrict, const struct tm * __restrict); time_t time(time_t *); #if __POSIX_VISIBLE >= 200112 struct sigevent; int timer_create(clockid_t, struct sigevent *__restrict, timer_t *__restrict); int timer_delete(timer_t); int timer_gettime(timer_t, struct itimerspec *); int timer_getoverrun(timer_t); int timer_settime(timer_t, int, const struct itimerspec *__restrict, struct itimerspec *__restrict); #endif #if __POSIX_VISIBLE void tzset(void); #endif #if __POSIX_VISIBLE >= 199309 int clock_getres(clockid_t, struct timespec *); int clock_gettime(clockid_t, struct timespec *); int clock_settime(clockid_t, const struct timespec *); int nanosleep(const struct timespec *, struct timespec *); #endif /* __POSIX_VISIBLE >= 199309 */ #if __POSIX_VISIBLE >= 200112 int clock_getcpuclockid(pid_t, clockid_t *); int clock_nanosleep(clockid_t, int, const struct timespec *, struct timespec *); #endif #if __POSIX_VISIBLE >= 199506 char *asctime_r(const struct tm *, char *); char *ctime_r(const time_t *, char *); struct tm *gmtime_r(const time_t *, struct tm *); struct tm *localtime_r(const time_t *, struct tm *); #endif #if __XSI_VISIBLE char *strptime(const char * __restrict, const char * __restrict, struct tm * __restrict); #endif #if __BSD_VISIBLE char *timezone(int, int); /* XXX XSI conflict */ time_t timelocal(struct tm * const); time_t timegm(struct tm * const); int timer_oshandle_np(timer_t timerid); time_t time2posix(time_t t); time_t posix2time(time_t t); #endif /* __BSD_VISIBLE */ #if __POSIX_VISIBLE >= 200809 || defined(_XLOCALE_H_) #include <xlocale/_time.h> #endif #if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2011 || (defined(__cplusplus) && __cplusplus >= 201703) #include <sys/_timespec.h> /* ISO/IEC 9899:2011 7.27.2.5 The timespec_get function */ #define TIME_UTC 1 /* time elapsed since epoch */ int timespec_get(struct timespec *ts, int base); #if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023 /* ISO/IEC 9899:2024 7.29.1 Components of time */ #define TIME_MONOTONIC 2 /* monotonic time */ /* ISO/IEC 9899:2024 7.29.2.7 The timespec_getres function */ int timespec_getres(struct timespec *, int); #endif #endif __END_DECLS #endif /* !_TIME_H_ */ These quantities give the time on a 24-hour clock, day of month (1-31), month of year (0-11), day of week (Sunday = 0), year - 1900, day of year (0-365), and a flag that is nonzero if daylight saving time is in effect. When local time is called for, the program consults the system to de- termine the time zone and whether the standard U.S.A. daylight saving time adjustment is appropriate. The program knows about the peculiari- ties of this conversion in 1974 and 1975; if necessary, a table for these years can be extended. Timezone returns the name of the time zone associated with its first argument, which is measured in minutes westward from Greenwich. If the second argument is 0, the standard name is used, otherwise the Daylight Saving version. If the required name does not appear in a table built into the routine, the difference from GMT is produced; e.g. in Afghanistan timezone(-(60*4+30), 0) is appropriate because it is 4:30 ahead of GMT and the string GMT+4:30 is produced. SEE ALSO time(2) BUGS The return values point to static data whose content is overwritten by each call. CTIME(3)