CTIME(3C)                                               CTIME(3C)



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

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

          char *ctime (clock)
          timet *clock;

          struct tm *localtime (clock)
          timet *clock;

          struct tm *gmtime (clock)
          timet *clock;

          char *asctime (tm)
          struct tm *tm;

          extern long timezone;

          extern int daylight;

          extern char *tzname[2];

          void tzset ( )

     DESCRIPTION
          ctime converts a long integer, pointed to by clock,
          representing the time in seconds since 00:00:00 GMT, January
          1, 1970, 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 1985\n\0

          Localtime and gmtime return pointers to ``tm'' structures,
          described below.  Localtime corrects for the time zone and
          possible Daylight Savings Time; gmtime converts directly to
          Greenwich Mean Time (GMT), which is the time the UNIX system
          uses.

          Asctime converts a ``tm'' structure to a 26-character
          string, as shown in the above example, and returns a pointer
          to the string.

          Declarations of all the functions and externals, and the
          ``tm'' structure, are in the <time.h> header file.  The
          structure declaration is:

               struct tm {
                       int tm_sec;      /* seconds (0 - 59) */



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     CTIME(3C)                                               CTIME(3C)



                       int tm_min;      /* minutes (0 - 59) */
                       int tm_hour;          /* hours (0 - 23) */
                       int tm_mday;     /* day of month (1 - 31) */
                       int tm_mon;      /* month of year (0 - 11) */
                       int tm_year;          /* year - 1900 */
                       int tm_wday;     /* day of week (Sunday = 0) */
                       int tm_yday;          /* day of year (0 - 365) */
                       int tm_isdst;
               };

          Tm_isdst is non-zero if Daylight Savings Time is in effect.

          The external long variable timezone contains the difference,
          in seconds, between GMT and local standard time (in EST,
          timezone is 5*60*60); the external variable daylight is
          non-zero if and only if the standard U.S.A.  Daylight
          Savings Time conversion should be applied.  The program
          knows about the peculiarities of this conversion in 1974 and
          1975; if necessary, a table for these years can be extended.

          If an environment variable named TZ is present, asctime uses
          the contents of the variable to override the default time
          zone.  The value of TZ must be a three-letter time zone
          name, followed by a number representing the difference
          between local time and Greenwich Mean Time in hours,
          followed by an optional three-letter name for a daylight
          time zone.  For example, the setting for New Jersey would be
          EST5EDT.  The effects of setting TZ are thus to change the
          values of the external variables timezone and daylight; in
          addition, the time zone names contained in the external
          variable

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

          are set from the environment variable TZ.  The function
          tzset sets these external variables from TZ; tzset is called
          by asctime and may also be called explicitly by the user.

          Note that in most installations, TZ is set by default when
          the user logs on, to a value in the local /etc/profile file
          [see profile(4)].

     SEE ALSO
          time(2), getenv(3C), profile(4), environ(5).

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

     ORIGIN
          AT&T V.3




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