CTIME(3)            Linux Programmer's Manual            CTIME(3)


NAME
       asctime,  ctime,  gmtime,  localtime,  mktime  - transform
       binary date and time to ASCII

SYNOPSIS
       #include <time.h>

       char *asctime(const struct tm *timeptr);

       char *ctime(const time_t *timep);

       struct tm *gmtime(const time_t *timep);

       struct tm *localtime(const time_t *timep);

       time_t mktime(struct tm *timeptr);

       extern char *tzname[2];
       long int timezone;
       extern int daylight;

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 rep-
       resents  the  number  of seconds elapsed since 00:00:00 on
       January 1, 1970, Coordinated Universal Time (UTC).

       The asctime() and mktime() functions both take an argument
       representing  broken-down time which is a binary represen-
       tation separated into year, month, day, etc.   Broken-down
       time  is  stored  in  the structure tm which is defined in
       <time.h> as follows:

              struct tm
              {
                      int     tm_sec;         /* seconds */
                      int     tm_min;         /* minutes */
                      int     tm_hour;        /* hours */
                      int     tm_mday;        /* day of the month */
                      int     tm_mon;         /* month */
                      int     tm_year;        /* year */
                      int     tm_wday;        /* day of the week */
                      int     tm_yday;        /* day in the year */
                      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 61 to allow for
              leap seconds.

       tm_min The number of minutes after the hour, in the  range



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CTIME(3)            Linux Programmer's Manual            CTIME(3)


              0 to 59.

       tm_hour
              The  number  of hours past midnight, in the range 0
              to 23.

       tm_mday
              The day of the month, in the range 1 to 31.

       tm_mon The number of months since January, in the range  0
              to 11.

       tm_year
              The number of years since 1900.

       tm_wday
              The  number of days since Sunday, in the range 0 to
              6.

       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 daylight saving time is in effect, zero
              if it is not, and negative if  the  information  is
              not available.

       The ctime() function converts the calendar time timep into
       a 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 abbre-
       viations 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 variable tzname with information about
       the current time zone.

       The gmtime() function converts the calendar time timep  to
       broken-down  time representation, expressed in Coordinated
       Universal Time (UTC).

       The localtime() function converts the calendar time  timep
       to  broken-time  representation, expressed relative to the
       user's specified  time  zone.     The  function  sets  the
       external  variables tzname with information about the cur-
       rent time  zone,  timezone  with  the  difference  between



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CTIME(3)            Linux Programmer's Manual            CTIME(3)


       Coordinated  Universal  Time (UTC) and local standard time
       in seconds, and daylight to a non-zero value  if  standard
       US daylight savings time rules apply.

       The asctime() function converts the broken-down time value
       timeptr into a string with the  same  format  as  ctime().
       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  mktime()  function converts a broken-down time struc-
       ture  to  calendar  time  representation.   The   function
       ignores  the  specified  contents of the structure members
       tm_wday and tm_yday and recomputes  them  from  the  other
       information  in  the  broken-down time structure.  Calling
       mktime() also  sets  the  external  variable  tzname  with
       information about the current time zone.  If the specified
       broken-down time cannot be represented as  calendar  time,
       mktime()  returns  a  value  of  (time_t)(-1) and does not
       alter the tm_wday and tm_yday members of  the  broken-down
       time structure.

CONFORMING TO
       SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO

date, gettimeofday, time, tzset, difftime, strftime,

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