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ctime(3)							      ctime(3)

NAME
       asctime, asctime_r, ctime, ctime_r, gmtime, gmtime_r, localtime, local‐
       time_r, mktime, ctime64, ctime64_r, gmtime64, gmtime64_r,  localtime64,
       localtime64_r, mktime64 - converts time units

SYNOPSIS
       #include <time.h>

       char *asctime(
	       const struct tm *timeptr ); char *asctime_r(
	       const struct tm *timeptr,
	       char *buffer ); char *ctime(
	       const time_t *timer ); char *ctime_r(
	       const time_t *timer,
	       char *buffer ); struct tm *gmtime(
	       const time_t *timer ); struct tm *gmtime_r(
	       const time_t *timer,
	       struct tm *result ); struct tm *localtime(
	       const time_t *timer ); struct tm *localtime_r(
	       const time_t *timer,
	       struct tm *result ); time_t mktime(
	       struct tm *timeptr );

       [Tru64  UNIX]  The  following functions are supported in order to main‐
       tain backward compatibility with previous  versions  of	the  operating
       system. You should not use them in new designs.

       int asctime_r(
	       const struct tm *timeptr,
	       char *buffer,
	       int len ); int ctime_r(
	       const time_t *timer,
	       char *buffer,
	       int len ); int gmtime_r(
	       const time_t *timer,
	       struct tm *result ); int localtime_r(
	       const time_t *timer,
	       struct tm *result );

       The  following  function	 declarations are Tru64 UNIX extensions and do
       not conform to current standards. These functions are provided to  sup‐
       port  the time64_t data type and are accessible only when the _TIME64_T
       feature macro is defined during compilation.

       #include <time.h>

       char *ctime64(
	       const time64_t *timer64 ); char *ctime64_r(
	       const time64_t *timer64,
	       char *buffer ); struct tm *gmtime64(
	       const time64_t *timer64 ); struct tm *gmtime64_r(
	       const time64_t *timer64,
	       struct tm *result ); struct tm *localtime64(
	       const time64_t *timer64 ); struct tm *localtime64_r(
	       const time64_t **timer64,
	       struct tm *result ); time64_t mktime64(
	       struct tm *timeptr );

LIBRARY
       Standard C Library (libc.so, libc.a)

STANDARDS
       Interfaces documented on this reference page conform to industry	 stan‐
       dards as follows:

       asctime_r(), ctime_r(), gmtime_r(), localtime_r(): POSIX.1c

       asctime(), ctime(), gmtime(), localtime(), mktime(): XPG4, XPG4-UNIX

       Refer  to  the  standards(5)  reference page for more information about
       industry standards and associated tags.

PARAMETERS
       Points to a type tm structure that defines space for a broken-down time
       value.  Points to a variable of type time_t that specifies a time value
       in seconds since the Epoch.  Points to a variable of type time64_t that
       specifies a time value in seconds since the Epoch.  Points to a charac‐
       ter array that is at least 26 bytes long. This array is used  to	 store
       the  generated date and time string.  Specifies an integer that defines
       the length of the character array.

DESCRIPTION
       The asctime(), ctime(), gmtime(), localtime(),  mktime(),  and  tzset()
       functions  convert time values between tm structures, time_t type vari‐
       ables, and strings.

       [POSIX]	The  asctime_r(),  ctime_r(),  gmtime_r(),  and	 localtime_r()
       functions  in libc_r.a are threadsafe because they do not return point‐
       ers to static data.

       The tm structure, which is defined in the <time.h>  header  file,  con‐
       tains the following elements:

       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 Saving Time option:
			  tm_isdst = 0 for Standard Time
			  tm_isdst = 1 for Daylight Time
       long tm_gmtoff	Seconds	 east of Greenwich. (Negative values indi‐
			cate
			seconds west of Greenwich.)
       char *tm_zone	Timezone string, for example, GMT

       A time_t variable, also defined in <time.h>,  contains  the  number  of
       seconds since the Epoch, 00:00:00 UTC 1 Jan 1970.

       A  time64_t  variable, also defined in <time.h>, contains the number of
       seconds since the Epoch, 00:00:00 UTC 1	Jan  1970,  but	 is  a	64-bit
       signed value capable of storing a wider range of values than those of a
       32-bit time_t. This data type is only available when the _TIME64_T fea‐
       ture  macro  is	defined	 during compilation. See the time(3) reference
       page for additional details.

       A string used to represent a time value has a  five-field  format.  For
       example:

       Tue Nov 9 15:37:29 1993\n\0

       The  asctime()  function	 converts  the	tm structure pointed to by the
       timeptr parameter to a string with this five-field format. The function
       uses the following members of the tm structure:

       tm_wday tm_mon tm_mday tm_hour tm_min tm_sec tm_year

       The  ctime()  function  converts	 the time_t variable pointed to by the
       timer parameter to a string with the five-field format. Local  timezone
       information  is	set  as	 though	 the tzset() function had been called.
       This function is equivalent to asctime(localtime(timer)).

       The gmtime() function converts the time_t variable pointed  to  by  the
       timer  parameter	 to  a	tm structure, expressed as GMT (Greenwich Mean
       Time).

       The localtime() function converts the time_t variable pointed to by the
       timer  parameter to a tm structure, expressed as local time. This func‐
       tion corrects for the local timezone and any seasonal time adjustments.
       Local  timezone	information is set as if the tzset() function had been
       called.

       The mktime() function converts the  tm  structure  pointed  to  by  the
       timeptr parameter to a time_t variable. The function uses the following
       members of the tm structure:

       tm_year tm_mon tm_mday tm_hour tm_min tm_sec tm_isdst

       The values of these members are not restricted to the ranges defined in
       <time.h>.  The  range for tm_sec is increased to [0-61] to allow for an
       occasional leap second or double leap second.

       A positive value for tm_isdst tells the mktime() function that Daylight
       Saving Time is in effect. A zero (0) value indicates that Standard Time
       is in effect. A negative values directs the mktime() function to deter‐
       mine  whether Daylight Saving Time is in effect for the specified time.
       Local timezone information is set as if the tzset() function  had  been
       called.

       On  successful  completion of the call, values for the timeptr->tm_wday
       and timeptr->tm_yday members of the structure are set. The  other  mem‐
       bers  are  set  to specified times, but have their values forced to the
       ranges indicated previously. The	 final	timeptr->tm_mday  is  not  set
       until  the  values  of the members timeptr->tm_mon and timeptr->tm_year
       are determined. If member tm_isdst is given as a negative number, it is
       set to 0 or 1 by mktime(), depending on whether Daylight Saving Time is
       in effect at the specified time.

       The ctime64(),  gmtime64(),  localtime64(),  and	 mktime64()  functions
       behave  as  their ctime(), gmtime(), localtime(), and mktime() counter‐
       parts, but they accept or return values of  type	 time64_t  instead  of
       time_t,	providing  the	ability	 to handle times beyond the range of a
       32-bit time_t. These function declarations are only available when  the
       _TIME64_T feature macro is defined during compilation.  See the time(3)
       reference page for additional details.

NOTES
       The asctime(), ctime(), gmtime(), and  localtime()  functions  are  not
       supported for multithreaded applications.

       [POSIX]	  Instead,   their   reentrant	 equivalents  --  asctime_r(),
       ctime_r(), gmtime_r(), and localtime_r() -- should be used with	multi‐
       ple threads.

       As  with	 their counterpart functions above, the ctime64(), gmtime64(),
       and localtime64() functions are not supported for multithreaded	appli‐
       cations.	  Instead,   their   reentrant	 equivalents  --  ctime64_r(),
       gmtime64_r(), and localtime64_r()  --  should  be  used	with  multiple
       threads.	 These	function  declarations	are  only  available  when the
       _TIME64_T feature macro is defined during compilation. See the  time(3)
       reference page for additional details.

RETURN VALUES
       When  any of the asctime(), ctime(), gmtime(), or localtime() functions
       complete successfully, the return value may point  to  static  storage,
       which  may  be  overwritten  by subsequent calls to these functions. On
       error, these functions return a null pointer and	 errno	is  set	 to  a
       value indicating the error.

       Upon  successful	 completion,  the asctime(), asctime_r(), ctime(), and
       ctime_r() functions  return  a  pointer	to  a  character  string  that
       expresses the time in a fixed format.

       Upon  successful	 completion,  the  gmtime()  and  gmtime_r() functions
       return a pointer to a tm structure containing converted GMT time infor‐
       mation.

       Upon successful completion, the localtime() and localtime_r() functions
       return a pointer to a tm structure containing converted local time.

       Upon successful completion, the mktime() function returns the specified
       time  since  the Epoch as a value of type time_t. If the time since the
       Epoch cannot be represented, mktime() returns the value	(time_t)-1  to
       indicate the error.

       [Tru64  UNIX]  In  addition to returning (time_t)-1 when the time since
       the Epoch cannot be represented, the mktime() function also sets	 errno
       to the value ERANGE.  This extension is provided to support times prior
       to the Epoch (that is, negative time_t  values);	 in  which  case,  the
       value (time_t)-1 may also correspond to the time 23:59:59 UTC 31 Decem‐
       ber 1969 (one second before the	Epoch).	 For  applications  supporting
       pre-Epoch  times,  it  is  therefore necessary to check both the return
       value and the value of errno to reliably	 determine  whether  an	 error
       occurred.  Note	that  this extension is not a standard feature and may
       not be portable to other UNIX platforms.

       [Tru64 UNIX]  Upon successful completion, the obsolete versions of  the
       asctime_r(),  ctime_r(), gmtime_r(), and localtime_r() functions return
       a value of 0 (zero).  Otherwise, -1 is returned and  errno  is  set  to
       indicate the error.

       The  ctime64(),	ctime64_r(),  gmtime64(), gmtime64_r(), localtime64(),
       localtime64_r(), and mktime64() functions have  return  value  behavior
       consistent  with	 their	counterparts described above, but they use the
       time64_t data type in place of time_t.

ERRORS
       With the exception of mktime() and mktime64(), if any  of  these	 func‐
       tions fails, errno may be set to the following value: [Tru64 UNIX]  The
       buffer, timer, timer64, or timeptr parameter is null, the len parameter
       is less than 1.

       If  mktime() or mktime64() are not able to represent the time since the
       Epoch, they return the value (time_t)-1 or (time64_t)-1,	 respectively,
       and set errno to ERANGE as defined below.

       If the localtime64() or gmtime64() functions are called with a time64_t
       value that exceeds their limits, they return a  null  pointer  and  set
       errno to ERANGE as defined below. These functions are currently limited
       to 35-bit signed values, providing an effective	range  of  Thu	Aug  4
       22:06:56	 1425  GMT to Wed May 30 01:53:03 2514 GMT.  [Tru64 UNIX]  The
       time since the Epoch cannot be represented by mktime()  or  mktime64(),
       or the value passed to the localtime64() or gmtime64() functions is out
       of range.

SEE ALSO
       Functions: difftime(3), getenv(3), strftime(3), time(3), timezone(3)

       Standards: standards(5)

								      ctime(3)
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