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NAME
     ctime, ctime_r, localtime,  localtime_r,  gmtime,  gmtime_r,
     asctime, asctime_r, tzset, tzsetwall - convert date and time
     to string

SYNOPSIS
     #include <time.h>

     char *ctime(const time_t *clock);

     struct tm *localtime(const time_t *clock);

     struct tm *gmtime(const time_t *clock);

     char *asctime(const struct tm *tm);

     extern time_t timezone, altzone;
     extern int daylight;
     extern char *tzname[2];

     void tzset(void);

     void tzsetwall(void);

     char *ctime_r(const time_t *clock, char *buf, int buflen);

     struct tm *localtime_r(const time_t *clock, struct tm *res);

     struct tm *gmtime_r(const time_t *clock, struct tm *res);

     char *asctime_r(const struct tm *tm, char *buf, int buflen);

  POSIX
     cc [ flag... ] file... -D_POSIX_PTHREAD_SEMANTICS [ library... ]

     char *ctime_r(const time_t *clock, char *buf);

     char *asctime_r(const struct tm *tm, char *buf);

DESCRIPTION
     The ctime() function converts the time pointed to by  clock,
     representing  the  time in seconds since the Epoch (00:00:00
     UTC, January 1, 1970), to local time in the form  of  a  26-
     character string as shown below. Time zone and daylight sav-
     ings corrections are  made  before  string  generation.  The
     fields are constant width:

          Fri Sep 13 00:00:00 1986\n\0


     The ctime() function is equivalent to:

          asctime(localtime(clock))


     The ctime(), asctime(), gmtime(), and localtime()  functions
     return  values  in  one of two static objects: a broken-down
     time structure and an array of char. Execution of any of the
     functions  may  overwrite the information returned in either
     of these objects by any of the other functions.

     The ctime_r() function has the same functionality as ctime()
     except  that the caller must supply a buffer buf with length
     buflen to store the result; buf must be at least  26  bytes.
     The  POSIX ctime_r() function does not take a buflen parame-
     ter.

     The localtime() and gmtime() functions return pointers to tm
     structures  (see  below).  The localtime() function corrects
     for the main time zone  and  possible  alternate  ("daylight
     savings") time zone; the gmtime() function converts directly
     to Coordinated Universal Time (UTC), which is what the  UNIX
     system uses internally.

     The localtime_r() and gmtime_r()  functions  have  the  same
     functionality  as  localtime()  and  gmtime()  respectively,
     except that the caller must supply a buffer res to store the
     result.

     The asctime() function converts a  tm  structure  to  a  26-
     character string, as shown in the above example, and returns
     a pointer to the string.

     The asctime_r() function has the same functionality as  asc-
     time()  except that the caller must supply a buffer buf with
     length buflen for the result to be stored.  The buf argument
     must  be  at  least 26 bytes. The POSIX asctime_r() function
     does not take a buflen parameter.  The asctime_r()  function
     returns  a pointer to buf upon success.  In case of failure,
     NULL is returned and errno is set.

     Declarations of all the functions and externals, and the  tm
     structure, are in the <time.h> header. The members of the tm
     structure are:

     int   tm_sec;    /* seconds after the minute - [0, 61] */
                      /* for leap seconds */
     int   tm_min;    /* minutes after the hour - [0, 59] */
     int   tm_hour;   /* hour 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;  /* flag for alternate daylight savings time */

      The value of tm_isdst is positive if daylight savings  time
     is  in  effect,  zero  if  daylight  savings  time is not in
     effect, and negative if the information  is  not  available.
     Previously, the value of tm_isdst was defined as non-zero if
     daylight savings was in effect.

     The external time_t variable altzone  contains  the  differ-
     ence, in seconds, between Coordinated Universal Time and the
     alternate time zone. The external variable timezone contains
     the  difference,  in seconds, between UTC and local standard
     time. The external variable daylight indicates whether  time
     should  reflect  daylight  savings  time.  Both timezone and
     altzone default to 0 (UTC). The external  variable  daylight
     is  non-zero if an alternate time zone exists. The time zone
     names are contained in the external variable  tzname,  which
     by default is set to:

          char *tzname[2] = { "GMT", "" };


     These functions know about the peculiarities of this conver-
     sion  for  various  time periods for the U.S. (specifically,
     the years 1974, 1975, and 1987). They will  handle  the  new
     daylight  savings  time  starting  with  the first Sunday in
     April, 1987.

     The tzset() function uses the contents  of  the  environment
     variable  TZ to override the value of the different external
     variables. It is called by asctime() and may also be  called
     by  the  user.  See  environ(5)  for a description of the TZ
     environment variable.

     Starting and ending times are relative to the current  local
     time  zone.  If  the alternate time zone start and end dates
     and the time are not  provided,  the  days  for  the  United
     States  that year will be used and the time will be 2 AM. If
     the start and end dates are provided but  the  time  is  not
     provided,  the  time  will  be  2 AM. The effects of tzset()
     change  the  values  of  the  external  variables  timezone,
     altzone, daylight, and tzname.

     Note that in most installations, TZ is set  to  the  correct
     value  by  default  when  the  user logs on, using the local
     /etc/default/init file (see TIMEZONE(4)).

     The tzsetwall() function sets things up so that  localtime()
     returns the best available approximation of local wall clock
     time.


ERRORS
     The ctime_r() and asctime_r() functions will fail if:

     ERANGE
           The length of the buffer supplied by the caller is not
           large enough to store the result.

USAGE
     These functions do not support localized date and time  for-
     mats.  The  strftime(3C) function can be used when localiza-
     tion is required.

     The  localtime(),   localtime_r(),   gmtime(),   gmtime_r(),
     ctime(),  and  ctime_r()  functions  assume Gregorian dates.
     Times before the adoption of the  Gregorian  calendard  will
     not match historial records.

EXAMPLES
     Example 1: Examples of the tzset() function.

     The tzset() function scans the contents of  the  environment
     variable  and assigns the different fields to the respective
     variable. For example, the most  complete  setting  for  New
     Jersey in 1986 could be

     EST5EDT4,116/2:00:00,298/2:00:00

     or simply

     EST5EDT

     An example of a southern hemisphere setting such as the Cook
     Islands could be

     KDT9:30KST10:00,63/5:00,302/20:00

     In the longer version of  the  New  Jersey  example  of  TZ,
     tzname[0] is EST, timezone will be set to 5*60*60, tzname[1]
     is EDT, altzone will be set to 4*60*60, the starting date of
     the alternate time zone is the 117th day at 2 AM, the ending
     date of the alternate time zone is the 299th  day  at  2  AM
     (using  zero-based  Julian  days),  and daylight will be set
     positive. Starting and ending  times  are  relative  to  the
     current  local  time  zone. If the alternate time zone start
     and end dates and the time are not provided,  the  days  for
     the  United  States that year will be used and the time will
     be 2 AM. If the start and end dates  are  provided  but  the
     time  is not provided, the time will be 2 AM. The effects of
     tzset() are thus to change the values of the external  vari-
     ables timezone, altzone, daylight, and tzname.  The ctime(),
     localtime(), mktime(), and strftime()  functions  will  also
     update  these  external  variables  as  if  they  had called
     tzset() at the time specified by the  time_t  or  struct  tm
     value that they are converting.

BUGS
     The zoneinfo timezone data files do not transition past  Tue
     Jan 19 03:14:07 2038 UTC.  Therefore for 64-bit applications
     using zoneinfo timezones, calculations beyond this date  may
     not  use  the  correct  offset from standard time, and could
     return incorrect values.  This affects the 64-bit version of
     localtime(), localtime_r(), ctime(), and ctime_r().

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe with exceptions     |
    |_____________________________|_____________________________|
    | CSI                         | Enabled                     |
    |_____________________________|_____________________________|


SEE ALSO
     time(2),  Intro(3),  getenv(3C),   mktime(3C),   printf(3C),
     putenv(3C), setlocale(3C), strftime(3C), TIMEZONE(4), attri-
     butes(5), environ(5)

NOTES
     When compiling multithreaded programs, see  Intro(3),  Notes
     On Multithreaded Applications.

     The return values for  ctime(),  localtime(),  and  gmtime()
     point  to  static  data whose content is overwritten by each
     call.

     Setting the time during the interval of change from timezone
     to  altzone or vice versa can produce unpredictable results.
     The system administrator must change the  Julian  start  and
     end days annually.

     The asctime(), ctime(), gmtime(), and localtime()  functions
     are unsafe in multithread applications.  The asctime_r() and
     gmtime_r()   functions   are   MT-Safe.    The    ctime_r(),
     localtime_r(),  tzset(),  and  tzsetwall() functions are MT-
     Safe in multithread applications, as long as no user-defined
     function  directly  modifies one of the following variables:
     timezone, altzone, daylight, and tzname.  These  four  vari-
     ables  are  not  MT-Safe to access. They are modified by the
     tzset() function  in  an  MT-Safe  manner.   The   mktime(),
     localtime_r(), and ctime_r() functions call tzset().
     Solaris 2.4 and earlier releases provided definitions of the
     ctime_r(),  localtime_r(), gmtime_r(), and asctime_r() func-
     tions as specified in POSIX.1c Draft 6. The  final  POSIX.1c
     standard   changed   the   interface   for   ctime_r()   and
     asctime_r(). Support for the Draft 6 interface  is  provided
     for  compatibility  only  and may not be supported in future
     releases. New applications  and  libraries  should  use  the
     POSIX standard interface.

     For       POSIX.1c-compliant        applications,        the
     _POSIX_PTHREAD_SEMANTICS  and _REENTRANT flags are automati-
     cally turned on by defining the _POSIX_C_SOURCE flag with  a
     value >= 199506L.

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