localtime


SYNOPSIS
       #include <time.h>

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

       char *ctime(const time_t *timep);
       char *ctime_r(const time_t *timep, char *buf);

       struct tm *gmtime(const time_t *timep);
       struct tm *gmtime_r(const time_t *timep, struct tm *result);

       struct tm *localtime(const time_t *timep);
       struct tm *localtime_r(const time_t *timep, struct tm *result);

       time_t mktime(struct tm *tm);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       asctime_r(), ctime_r(), gmtime_r(), localtime_r():
              _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
              _SVID_SOURCE || _POSIX_SOURCE

DESCRIPTION
       The ctime(), gmtime() and localtime() functions all take an argument of
       data  type time_t, which represents calendar time.  When interpreted as
       an absolute time value, it represents the  number  of  seconds  elapsed
       since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

       The asctime() and mktime() functions both take an argument representing
       broken-down time, which is a representation separated into year, month,
       day, and so on.

       Broken-down  time  is  stored  in the structure tm, which is defined in
       <time.h> as follows:

           struct tm {
               int tm_sec;    /* Seconds (0-60) */
               int tm_min;    /* Minutes (0-59) */
               int tm_hour;   /* Hours (0-23) */
               int tm_mday;   /* Day of the month (1-31) */
               int tm_mon;    /* Month (0-11) */
               int tm_year;   /* Year - 1900 */
               int tm_wday;   /* Day of the week (0-6, Sunday = 0) */
               int tm_yday;   /* Day in the year (0-365, 1 Jan = 0) */
               int tm_isdst;  /* Daylight saving time */
           };

       The members of the tm structure are:

       tm_sec    The number of seconds after the minute, normally in the range
                 0 to 59, but can be up to 60 to allow for leap seconds.

       tm_yday   The number of days since January 1, in the range 0 to 365.

       tm_isdst  A  flag  that  indicates  whether  daylight saving time is in
                 effect at the time described.  The value is positive if  day-
                 light  saving time is in effect, zero if it is not, and nega-
                 tive if the information is not available.

       The call ctime(t) is equivalent to asctime(localtime(t)).  It  converts
       the calendar time t into a null-terminated string of the form

              "Wed Jun 30 21:49:08 1993\n"

       The  abbreviations  for  the  days of the week are "Sun", "Mon", "Tue",
       "Wed", "Thu", "Fri", and "Sat".  The abbreviations for the  months  are
       "Jan",  "Feb",  "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct",
       "Nov", and "Dec".  The return value points to  a  statically  allocated
       string  which  might  be  overwritten by subsequent calls to any of the
       date and time functions.  The function also sets the external variables
       tzname,  timezone,  and  daylight (see tzset(3)) with information about
       the current timezone.  The reentrant version ctime_r() does  the  same,
       but  stores the string in a user-supplied buffer which should have room
       for at least 26 bytes.  It need not set tzname, timezone, and daylight.

       The gmtime() function converts the calendar time timep  to  broken-down
       time representation, expressed in Coordinated Universal Time (UTC).  It
       may return NULL when the year does not fit into an integer.  The return
       value  points to a statically allocated struct which might be overwrit-
       ten by subsequent calls to any of the date  and  time  functions.   The
       gmtime_r()  function  does the same, but stores the data in a user-sup-
       plied struct.

       The localtime() function converts the calendar time  timep  to  broken-
       down  time  representation,  expressed relative to the user's specified
       timezone.  The function acts as if it  called  tzset(3)  and  sets  the
       external  variables tzname with information about the current timezone,
       timezone with the difference between Coordinated Universal  Time  (UTC)
       and  local standard time in seconds, and daylight to a nonzero value if
       daylight savings time rules apply during some part of  the  year.   The
       return  value  points  to  a statically allocated struct which might be
       overwritten by subsequent calls to any of the date and time  functions.
       The  localtime_r()  function  does  the  same, but stores the data in a
       user-supplied struct.  It need not set tzname, timezone, and daylight.

       The asctime() function converts the broken-down time value  tm  into  a
       null-terminated  string  with  the  same format as ctime().  The return
       value points to a statically allocated string which might be  overwrit-
       ten  by  subsequent  calls  to any of the date and time functions.  The
       asctime_r() function does the same, but stores the string  in  a  user-
       supplied buffer which should have room for at least 26 bytes.

       The  mktime() function converts a broken-down time structure, expressed
       as local time, to calendar time representation.  The  function  ignores
       the  values  supplied  by the caller in the tm_wday and tm_yday fields.
       The value specified in the tm_isdst field informs mktime()  whether  or
       DST  is  or  is  not in effect at the specified time.  Calling mktime()
       also sets the external variable tzname with information about the  cur-
       rent timezone.

       If  the  specified  broken-down  time cannot be represented as calendar
       time (seconds since the Epoch), mktime() returns (time_t) -1  and  does
       not alter the members of the broken-down time structure.

RETURN VALUE
       Each  of  these  functions  returns the value described, or NULL (-1 in
       case of mktime()) in case an error was detected.

ATTRIBUTES
       For  an  explanation  of  the  terms  used   in   this   section,   see
       attributes(7).

       +---------------+---------------+---------------------------------+
       |Interface      | Attribute     | Value                           |
       +---------------+---------------+---------------------------------+
       |asctime()      | Thread safety | MT-Unsafe race:asctime locale   |
       +---------------+---------------+---------------------------------+
       |asctime_r()    | Thread safety | MT-Safe locale                  |
       +---------------+---------------+---------------------------------+
       |ctime()        | Thread safety | MT-Unsafe race:tmbuf            |
       |               |               | race:asctime env locale         |
       +---------------+---------------+---------------------------------+
       |ctime_r(),     | Thread safety | MT-Safe env locale              |
       |gmtime_r(),    |               |                                 |
       |localtime_r(), |               |                                 |
       |mktime()       |               |                                 |
       +---------------+---------------+---------------------------------+
       |gmtime(),      | Thread safety | MT-Unsafe race:tmbuf env locale |
       |localtime()    |               |                                 |
       +---------------+---------------+---------------------------------+

CONFORMING TO
       POSIX.1-2001.  C89 and C99 specify asctime(), ctime(), gmtime(), local-
       time(),  and  mktime().   POSIX.1-2008  marks  asctime(),  asctime_r(),
       ctime(), and ctime_r() as obsolete, recommending the use of strftime(3)
       instead.

NOTES
       The four functions asctime(), ctime(), gmtime() and localtime()  return
       a  pointer  to  static data and hence are not thread-safe.  The thread-
       safe versions, asctime_r(), ctime_r(),  gmtime_r()  and  localtime_r(),
       are specified by SUSv2.

       POSIX.1-2001  says:  "The asctime(), ctime(), gmtime(), and localtime()
       functions shall return values in one of two static objects:  a  broken-
       down time structure and an array of type char.  Execution of any of the
       functions may overwrite the information returned  in  either  of  these
       objects  by  any  of the other functions."  This can occur in the glibc
       implementation.

       tzset(3)  was  called,  while localtime_r() does not have this require-
       ment.  For portable code,  tzset(3)  should  be  called  before  local-
       time_r().

SEE ALSO
       date(1),  gettimeofday(2),  time(2),  utime(2),  clock(3), difftime(3),
       strftime(3), strptime(3), timegm(3), tzset(3), time(7)

COLOPHON
       This page is part of release 4.04 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       http://www.kernel.org/doc/man-pages/.

                                  2015-04-19                          CTIME(3)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2019 Hurricane Electric. All Rights Reserved.