term% cat index.txt 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:
/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/*
* ISO C99 Standard: 7.23 Date and time <time.h>
*/
#ifndef _TIME_H
#define _TIME_H 1
#include <features.h>
#define __need_size_t
#define __need_NULL
#include <stddef.h>
/* This defines CLOCKS_PER_SEC, which is the number of processor clock
ticks per second, and possibly a number of other constants. */
#include <bits/time.h>
/* Many of the typedefs and structs whose official home is this header
may also need to be defined by other headers. */
#include <bits/types/clock_t.h>
#include <bits/types/time_t.h>
#include <bits/types/struct_tm.h>
#if defined __USE_POSIX199309 || defined __USE_ISOC11
# include <bits/types/struct_timespec.h>
#endif
#ifdef __USE_POSIX199309
# include <bits/types/clockid_t.h>
# include <bits/types/timer_t.h>
# include <bits/types/struct_itimerspec.h>
struct sigevent;
#endif
#ifdef __USE_XOPEN2K
# ifndef __pid_t_defined
typedef __pid_t pid_t;
# define __pid_t_defined
# endif
#endif
#ifdef __USE_XOPEN2K8
# include <bits/types/locale_t.h>
#endif
#ifdef __USE_ISOC11
/* Time base values for timespec_get. */
# define TIME_UTC 1
#endif
__BEGIN_DECLS
/* Time used by the program so far (user time + system time).
The result / CLOCKS_PER_SEC is program time in seconds. */
extern clock_t clock (void) __THROW;
#ifndef __USE_TIME_BITS64
/* Return the current time and put it in *TIMER if TIMER is not NULL. */
extern time_t time (time_t *__timer) __THROW;
/* Return the difference between TIME1 and TIME0. */
extern double difftime (time_t __time1, time_t __time0)
__THROW __attribute__ ((__const__));
/* Return the `time_t' representation of TP and normalize TP. */
extern time_t mktime (struct tm *__tp) __THROW;
#else
# ifdef __REDIRECT_NTH
extern time_t __REDIRECT_NTH (time, (time_t *__timer), __time64);
extern double __REDIRECT_NTH (difftime, (time_t __time1, time_t __time0),
__difftime64) __attribute__ ((__const__));
extern time_t __REDIRECT_NTH (mktime, (struct tm *__tp), __mktime64);
# else
# define time __time64
# define difftime __difftime64
# define mktime __mktime64
# endif
#endif
/* Format TP into S according to FORMAT.
Write no more than MAXSIZE characters and return the number
of characters written, or 0 if it would exceed MAXSIZE. */
extern size_t strftime (char *__restrict __s, size_t __maxsize,
const char *__restrict __format,
const struct tm *__restrict __tp) __THROW;
#ifdef __USE_XOPEN
/* Parse S according to FORMAT and store binary time information in TP.
The return value is a pointer to the first unparsed character in S. */
extern char *strptime (const char *__restrict __s,
const char *__restrict __fmt, struct tm *__tp)
__THROW;
#endif
#ifdef __USE_XOPEN2K8
/* Similar to the two functions above but take the information from
the provided locale and not the global locale. */
extern size_t strftime_l (char *__restrict __s, size_t __maxsize,
const char *__restrict __format,
const struct tm *__restrict __tp,
locale_t __loc) __THROW;
#endif
#ifdef __USE_GNU
extern char *strptime_l (const char *__restrict __s,
const char *__restrict __fmt, struct tm *__tp,
locale_t __loc) __THROW;
#endif
#ifndef __USE_TIME_BITS64
/* Return the `struct tm' representation of *TIMER
in Universal Coordinated Time (aka Greenwich Mean Time). */
extern struct tm *gmtime (const time_t *__timer) __THROW;
/* Return the `struct tm' representation
of *TIMER in the local timezone. */
extern struct tm *localtime (const time_t *__timer) __THROW;
#else
# ifdef __REDIRECT_NTH
extern struct tm*__REDIRECT_NTH (gmtime, (const time_t *__timer), __gmtime64);
extern struct tm *__REDIRECT_NTH (localtime, (const time_t *__timer),
__localtime64);
# else
# define gmtime __gmtime64
# define localtime __localtime64
# endif
#endif
#if defined __USE_POSIX || __GLIBC_USE (ISOC2X)
# ifndef __USE_TIME_BITS64
/* Return the `struct tm' representation of *TIMER in UTC,
using *TP to store the result. */
extern struct tm *gmtime_r (const time_t *__restrict __timer,
struct tm *__restrict __tp) __THROW;
/* Return the `struct tm' representation of *TIMER in local time,
using *TP to store the result. */
extern struct tm *localtime_r (const time_t *__restrict __timer,
struct tm *__restrict __tp) __THROW;
# else
# ifdef __REDIRECT_NTH
extern struct tm*__REDIRECT_NTH (gmtime_r, (const time_t *__restrict __timer,
struct tm *__restrict __tp),
__gmtime64_r);
extern struct tm*__REDIRECT_NTH (localtime_r, (const time_t *__restrict __t,
struct tm *__restrict __tp),
__localtime64_r);
# else
# define gmtime_r __gmtime64_r
# define localtime_r __localtime_r
# endif
# endif
#endif /* POSIX || C2X */
/* Return a string of the form "Day Mon dd hh:mm:ss yyyy0
that is the representation of TP in this format. */
extern char *asctime (const struct tm *__tp) __THROW;
/* Equivalent to `asctime (localtime (timer))'. */
#ifndef __USE_TIME_BITS64
extern char *ctime (const time_t *__timer) __THROW;
#else
# ifdef __REDIRECT_NTH
extern char *__REDIRECT_NTH (ctime, (const time_t *__timer), __ctime64);
# else
# define ctime __ctime64
# endif
#endif
#ifdef __USE_POSIX
/* Reentrant versions of the above functions. */
/* Return in BUF a string of the form "Day Mon dd hh:mm:ss yyyy0
that is the representation of TP in this format. */
extern char *asctime_r (const struct tm *__restrict __tp,
char *__restrict __buf) __THROW;
/* Equivalent to `asctime_r (localtime_r (timer, *TMP*), buf)'. */
#ifndef __USE_TIME_BITS64
extern char *ctime_r (const time_t *__restrict __timer,
char *__restrict __buf) __THROW;
#else
# ifdef __REDIRECT_NTH
extern char *__REDIRECT_NTH (ctime_r, (const time_t *__restrict __timer,
char *__restrict __buf), __ctime64_r);
# else
# define ctime_r __ctime64_r
# endif
#endif
#endif /* POSIX */
/* Defined in localtime.c. */
extern char *__tzname[2]; /* Current timezone names. */
extern int __daylight; /* If daylight-saving time is ever in use. */
extern long int __timezone; /* Seconds west of UTC. */
#ifdef __USE_POSIX
/* Same as above. */
extern char *tzname[2];
/* Set time conversion information from the TZ environment variable.
If TZ is not defined, a locale-dependent default is used. */
extern void tzset (void) __THROW;
#endif
#if defined __USE_MISC || defined __USE_XOPEN
extern int daylight;
extern long int timezone;
#endif
/* Nonzero if YEAR is a leap year (every 4 years,
except every 100th isn't, and every 400th is). */
#define __isleap(year) ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
#if defined __USE_MISC || __GLIBC_USE (ISOC2X)
# ifndef __USE_TIME_BITS64
/* Like `mktime', but for TP represents Universal Time, not local time. */
extern time_t timegm (struct tm *__tp) __THROW;
# else
# ifdef __REDIRECT_NTH
extern time_t __REDIRECT_NTH (timegm, (struct tm *__tp), __timegm64);
# else
# define timegm __timegm64
# endif
# endif
#endif
#ifdef __USE_MISC
/* Miscellaneous functions many Unices inherited from the public domain
localtime package. These are included only for compatibility. */
#ifndef __USE_TIME_BITS64
/* Another name for `mktime'. */
extern time_t timelocal (struct tm *__tp) __THROW;
#else
# ifdef __REDIRECT_NTH
extern time_t __REDIRECT_NTH (timelocal, (struct tm *__tp), __mktime64);
# endif
#endif
/* Return the number of days in YEAR. */
extern int dysize (int __year) __THROW __attribute__ ((__const__));
#endif
#ifdef __USE_POSIX199309
# ifndef __USE_TIME_BITS64
/* Pause execution for a number of nanoseconds.
This function is a cancellation point and therefore not marked with
__THROW. */
extern int nanosleep (const struct timespec *__requested_time,
struct timespec *__remaining);
/* Get resolution of clock CLOCK_ID. */
extern int clock_getres (clockid_t __clock_id, struct timespec *__res) __THROW;
/* Get current value of clock CLOCK_ID and store it in TP. */
extern int clock_gettime (clockid_t __clock_id, struct timespec *__tp)
__THROW __nonnull((2));
/* Set clock CLOCK_ID to value TP. */
extern int clock_settime (clockid_t __clock_id, const struct timespec *__tp)
__THROW __nonnull((2));
# else
# ifdef __REDIRECT
extern int __REDIRECT (nanosleep, (const struct timespec *__requested_time,
struct timespec *__remaining),
__nanosleep64);
extern int __REDIRECT_NTH (clock_getres, (clockid_t __clock_id,
struct timespec *__res),
__clock_getres64);
extern int __REDIRECT_NTH (clock_gettime, (clockid_t __clock_id, struct
timespec *__tp), __clock_gettime64)
__nonnull((2));
extern int __REDIRECT_NTH (clock_settime, (clockid_t __clock_id, const struct
timespec *__tp), __clock_settime64)
__nonnull((2));
# else
# define nanosleep __nanosleep64
# define clock_getres __clock_getres64
# define clock_gettime __clock_gettime64
# define clock_settime __clock_settime64
# endif
# endif
# ifdef __USE_XOPEN2K
/* High-resolution sleep with the specified clock.
This function is a cancellation point and therefore not marked with
__THROW. */
# ifndef __USE_TIME_BITS64
extern int clock_nanosleep (clockid_t __clock_id, int __flags,
const struct timespec *__req,
struct timespec *__rem);
# else
# ifdef __REDIRECT
extern int __REDIRECT (clock_nanosleep, (clockid_t __clock_id, int __flags,
const struct timespec *__req,
struct timespec *__rem),
__clock_nanosleep_time64);
# else
# define clock_nanosleep __clock_nanosleep_time64
# endif
# endif
/* Return clock ID for CPU-time clock. */
extern int clock_getcpuclockid (pid_t __pid, clockid_t *__clock_id) __THROW;
# endif
/* Create new per-process timer using CLOCK_ID. */
extern int timer_create (clockid_t __clock_id,
struct sigevent *__restrict __evp,
timer_t *__restrict __timerid) __THROW;
/* Delete timer TIMERID. */
extern int timer_delete (timer_t __timerid) __THROW;
/* Set timer TIMERID to VALUE, returning old value in OVALUE. */
# ifndef __USE_TIME_BITS64
extern int timer_settime (timer_t __timerid, int __flags,
const struct itimerspec *__restrict __value,
struct itimerspec *__restrict __ovalue) __THROW;
/* Get current value of timer TIMERID and store it in VALUE. */
extern int timer_gettime (timer_t __timerid, struct itimerspec *__value)
__THROW;
# else
# ifdef __REDIRECT_NTH
extern int __REDIRECT_NTH (timer_settime, (timer_t __timerid, int __flags,
const struct itimerspec *__restrict __value,
struct itimerspec *__restrict __ovalue),
__timer_settime64);
extern int __REDIRECT_NTH (timer_gettime, (timer_t __timerid,
struct itimerspec *__value),
__timer_gettime64);
# else
# define timer_settime __timer_settime64
# define timer_gettime __timer_gettime64
# endif
# endif
/* Get expiration overrun for timer TIMERID. */
extern int timer_getoverrun (timer_t __timerid) __THROW;
#endif
#ifdef __USE_ISOC11
# ifndef __USE_TIME_BITS64
/* Set TS to calendar time based in time base BASE. */
extern int timespec_get (struct timespec *__ts, int __base)
__THROW __nonnull ((1));
# else
# ifdef __REDIRECT_NTH
extern int __REDIRECT_NTH (timespec_get, (struct timespec *__ts, int __base),
__timespec_get64) __nonnull ((1));
# else
# define timespec_get __timespec_get64
# endif
# endif
#endif
#if __GLIBC_USE (ISOC2X)
# ifndef __USE_TIME_BITS64
/* Set TS to resolution of time base BASE. */
extern int timespec_getres (struct timespec *__ts, int __base)
__THROW;
# else
# ifdef __REDIRECT_NTH
extern int __REDIRECT_NTH (timespec_getres, (struct timespec *__ts,
int __base),
__timespec_getres64);
# else
# define timespec_getres __timespec_getres64
# endif
# endif
#endif
#ifdef __USE_XOPEN_EXTENDED
/* Set to one of the following values to indicate an error.
1 the DATEMSK environment variable is null or undefined,
2 the template file cannot be opened for reading,
3 failed to get file status information,
4 the template file is not a regular file,
5 an error is encountered while reading the template file,
6 memory allication failed (not enough memory available),
7 there is no line in the template that matches the input,
8 invalid input specification Example: February 31 or a time is
specified that can not be represented in a time_t (representing
the time in seconds since 00:00:00 UTC, January 1, 1970) */
extern int getdate_err;
/* Parse the given string as a date specification and return a value
representing the value. The templates from the file identified by
the environment variable DATEMSK are used. In case of an error
`getdate_err' is set.
This function is a possible cancellation point and therefore not
marked with __THROW. */
extern struct tm *getdate (const char *__string);
#endif
#ifdef __USE_GNU
/* Since `getdate' is not reentrant because of the use of `getdate_err'
and the static buffer to return the result in, we provide a thread-safe
variant. The functionality is the same. The result is returned in
the buffer pointed to by RESBUFP and in case of an error the return
value is != 0 with the same values as given above for `getdate_err'.
This function is not part of POSIX and therefore no official
cancellation point. But due to similarity with an POSIX interface
or due to the implementation it is a cancellation point and
therefore not marked with __THROW. */
extern int getdate_r (const char *__restrict __string,
struct tm *__restrict __resbufp);
#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)