NAME

     ctime, localtime, gmtime, asctime, tzset -  convert date and
     time to ASCII


SYNOPSIS

     #include <sys/types.h>
     #include <time.h>

     void tzset(void)
     char *ctime(const time_t *clock)
     char *asctime(const struct tm *tm)
     struct tm *localtime(const time_t *clock)
     struct tm *gmtime(const time_t *clock)


DESCRIPTION

     Tzset uses the value of the environment variable TZ  to  set
     up the time conversion information used by localtime.

     If TZ does not appear in the environment, the TZDEFAULT file
     (as  defined  in  <tzfile.h>) is used by localtime.  If this
     file fails for any reason, the GMT offset as provided by the
     kernel  is used.  In this case, DST is ignored, resulting in
     the time being incorrect by some amount if DST is  currently
     in effect.  If this fails for any reason, GMT is used.

     If TZ appears in the environment but its  value  is  a  null
     string,  Greenwich  Mean  Time  is  used;  if TZ appears and
     begins with a slash, it is used as the absolute pathname  of
     the  tzfile(5)-format  file  from  which  to  read  the time
     conversion information; if TZ  appears  and  begins  with  a
     character  other than a slash, it's used as a pathname rela-
     tive to the system time  conversion  information  directory,
     defined as TZDIR in the include file tzfile.h.  If this file
     fails for any reason, the GMT offset as provided by the ker-
     nel is used, as described above.  If this fails for any rea-
     son, GMT is used.  See TZ(5) for a proper description of the
     TZ variable.

     Ctime converts a time value, pointed to by  clock,  such  as
     returned  by  time(2)  into ASCII and returns a pointer to a
     26-character string in the following form.  All  the  fields
     have constant width.

          Sun Sep 16 01:03:52 1973\n\0

     Localtime and gmtime return pointers to structures  contain-
     ing  the  broken-down time.  Localtime corrects for the time
     zone and possible daylight  savings  time;  gmtime  converts
     directly  to GMT, which is the time UNIX uses.  Asctime con-
     verts a broken-down time to ASCII and returns a pointer to a
     26-character string.

     The structure declaration from the include file is:

          struct tm {
               int tm_sec;    /* 0-59  seconds */
               int tm_min;    /* 0-59  minutes */
               int tm_hour;   /* 0-23  hour */
               int tm_mday;   /* 1-31  day of month */
               int tm_mon;    /* 0-11  month */
               int tm_year;   /* 0-    year - 1900 */
               int tm_wday;   /* 0-6   day of week (Sunday = 0) */
               int tm_yday;   /* 0-365 day of year */
               int tm_isdst;  /* flag: daylight savings time in effect */
          };

     Tm_isdst is non-zero if a time zone adjustment such as  Day-
     light Savings time is in effect.


FILES

     /usr/lib/zoneinfo  time zone information directory
     /etc/localtime     local time zone file


SEE ALSO

     time(2), getenv(3), tzfile(5), TZ(5), environ(7), zic(8).


NOTE

     The return values point to  static  data  whose  content  is
     overwritten by each call.