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    The following form allows you to view linux man pages.

    Command:

    ctime_r

    
           ASCII
    
    
    

    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_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
           value) to a positive value or to 0, respectively, to  indicate  whether
           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.
    
    
    

    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.   Thread-safe
           versions asctime_r(), ctime_r(), gmtime_r() and localtime_r() are spec-
           ified by SUSv2, and available since libc 5.2.5.
    
           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.
    
           In many implementations, including glibc, a 0 in tm_mday is interpreted
           as meaning the last day of the preceding month.
    
           The glibc version of struct tm has additional fields
    
                  long tm_gmtoff;           /* Seconds east of UTC */
                  const char *tm_zone;      /* Timezone abbreviation */
    
           defined when _BSD_SOURCE was set before including <time.h>.  This is  a
           BSD extension, present in 4.3BSD-Reno.
    
           According  to POSIX.1-2004, localtime() is required to behave as though
           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)
    
    
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