"Fossies" - the Fresh Open Source Software Archive

Member "newctime.3.txt" (25 Nov 2022, 8419 Bytes) of package /linux/misc/tzcode2022g.tar.gz:

As a special service "Fossies" has tried to format the requested text file into HTML format (style: standard) with prefixed line numbers. Alternatively you can here view or download the uninterpreted source code file. See also the last Fossies "Diffs" side-by-side code changes report for "newctime.3.txt": 2021e_vs_2022e.

    1 NEWCTIME(3)                Library Functions Manual                NEWCTIME(3)
    3 NAME
    4        asctime, ctime, difftime, gmtime, localtime, mktime - convert date and
    5        time
    8        #include <time.h>
   10        extern char *tzname[]; /* (optional) */
   12        char *ctime(time_t const *clock);
   14        char *ctime_r(time_t const *clock, char *buf);
   16        double difftime(time_t time1, time_t time0);
   18        char *asctime(struct tm const *tm);
   20        char *asctime_r(struct tm const *restrict tm,
   21            char *restrict result);
   23        struct tm *localtime(time_t const *clock);
   25        struct tm *localtime_r(time_t const *restrict clock,
   26            struct tm *restrict result);
   28        struct tm *localtime_rz(timezone_t restrict zone,
   29            time_t const *restrict clock,
   30            struct tm *restrict result);
   32        struct tm *gmtime(time_t const *clock);
   34        struct tm *gmtime_r(time_t const *restrict clock,
   35            struct tm *restrict result);
   37        time_t mktime(struct tm *tm);
   39        time_t mktime_z(timezone_t restrict zone,
   40            struct tm *restrict tm);
   42        cc ... -ltz
   45        The ctime function converts a long integer, pointed to by clock, and
   46        returns a pointer to a string of the form
   47                             Thu Nov 24 18:22:48 1986\n\0
   48        Years requiring fewer than four characters are padded with leading
   49        zeroes.  For years longer than four characters, the string is of the
   50        form
   51                           Thu Nov 24 18:22:48     81986\n\0
   52        with five spaces before the year.  These unusual formats are designed
   53        to make it less likely that older software that expects exactly 26
   54        bytes of output will mistakenly output misleading values for out-of-
   55        range years.
   57        The *clock timestamp represents the time in seconds since 1970-01-01
   58        00:00:00 Coordinated Universal Time (UTC).  The POSIX standard says
   59        that timestamps must be nonnegative and must ignore leap seconds.  Many
   60        implementations extend POSIX by allowing negative timestamps, and can
   61        therefore represent timestamps that predate the introduction of UTC and
   62        are some other flavor of Universal Time (UT).  Some implementations
   63        support leap seconds, in contradiction to POSIX.
   65        The localtime and gmtime functions return pointers to "tm" structures,
   66        described below.  The localtime function corrects for the time zone and
   67        any time zone adjustments (such as Daylight Saving Time in the United
   68        States).  After filling in the "tm" structure, localtime sets the
   69        tm_isdst'th element of tzname to a pointer to a string that's the time
   70        zone abbreviation to be used with localtime's return value.
   72        The gmtime function converts to Coordinated Universal Time.
   74        The asctime function converts a time value contained in a "tm"
   75        structure to a string, as shown in the above example, and returns a
   76        pointer to the string.
   78        The mktime function converts the broken-down time, expressed as local
   79        time, in the structure pointed to by tm into a calendar time value with
   80        the same encoding as that of the values returned by the time function.
   81        The original values of the tm_wday and tm_yday components of the
   82        structure are ignored, and the original values of the other components
   83        are not restricted to their normal ranges.  (A positive or zero value
   84        for tm_isdst causes mktime to presume initially that daylight saving
   85        time respectively, is or is not in effect for the specified time.  A
   86        negative value for tm_isdst causes the mktime function to attempt to
   87        divine whether daylight saving time is in effect for the specified
   88        time; in this case it does not use a consistent rule and may give a
   89        different answer when later presented with the same argument.)  On
   90        successful completion, the values of the tm_wday and tm_yday components
   91        of the structure are set appropriately, and the other components are
   92        set to represent the specified calendar time, but with their values
   93        forced to their normal ranges; the final value of tm_mday is not set
   94        until tm_mon and tm_year are determined.  The mktime function returns
   95        the specified calendar time; If the calendar time cannot be
   96        represented, it returns -1.
   98        The difftime function returns the difference between two calendar
   99        times, (time1 - time0), expressed in seconds.
  101        The ctime_r, localtime_r, gmtime_r, and asctime_r functions are like
  102        their unsuffixed counterparts, except that they accept an additional
  103        argument specifying where to store the result if successful.
  105        The localtime_rz and mktime_z functions are like their unsuffixed
  106        counterparts, except that they accept an extra initial zone argument
  107        specifying the timezone to be used for conversion.  If zone is null, UT
  108        is used; otherwise, zone should be have been allocated by tzalloc and
  109        should not be freed until after all uses (e.g., by calls to strftime)
  110        of the filled-in tm_zone fields.
  112        Declarations of all the functions and externals, and the "tm"
  113        structure, are in the <time.h> header file.  The structure (of type)
  114        struct tm includes the following fields:
  116                 int tm_sec;      /* seconds (0-60) */
  117                 int tm_min;      /* minutes (0-59) */
  118                 int tm_hour;     /* hours (0-23) */
  119                 int tm_mday;     /* day of month (1-31) */
  120                 int tm_mon;      /* month of year (0-11) */
  121                 int tm_year;     /* year - 1900 */
  122                 int tm_wday;     /* day of week (Sunday = 0) */
  123                 int tm_yday;     /* day of year (0-365) */
  124                 int tm_isdst;    /* is daylight saving time in effect? */
  125                 char *tm_zone;   /* time zone abbreviation (optional) */
  126                 long tm_gmtoff;  /* offset from UT in seconds (optional) */
  128        The tm_isdst field is non-zero if daylight saving time is in effect.
  130        The tm_gmtoff field is the offset (in seconds) of the time represented
  131        from UT, with positive values indicating east of the Prime Meridian.
  132        The field's name is derived from Greenwich Mean Time, a precursor of
  133        UT.
  135        In struct tm the tm_zone and tm_gmtoff fields exist, and are filled in,
  136        only if arrangements to do so were made when the library containing
  137        these functions was created.  Similarly, the tzname variable is
  138        optional; also, there is no guarantee that tzname will continue to
  139        exist in this form in future releases of this code.
  141 FILES
  142        /usr/share/zoneinfo             timezone information directory
  143        /usr/share/zoneinfo/localtime   local timezone file
  144        /usr/share/zoneinfo/posixrules  used with POSIX-style TZ's
  145        /usr/share/zoneinfo/GMT         for UTC leap seconds
  147        If /usr/share/zoneinfo/GMT is absent, UTC leap seconds are loaded from
  148        /usr/share/zoneinfo/posixrules.
  150 SEE ALSO
  151        getenv(3), newstrftime(3), newtzset(3), time(2), tzfile(5)
  153 NOTES
  154        The return values of asctime, ctime, gmtime, and localtime point to
  155        static data overwritten by each call.  The tzname variable (once set)
  156        and the tm_zone field of a returned struct tm both point to an array of
  157        characters that can be freed or overwritten by later calls to the
  158        functions localtime, tzfree, and tzset, if these functions affect the
  159        timezone information that specifies the abbreviation in question.  The
  160        remaining functions and data are thread-safe.
  162        The asctime, asctime_r, ctime, and ctime_r functions behave strangely
  163        for years before 1000 or after 9999.  The 1989 and 1999 editions of the
  164        C Standard say that years from -99 through 999 are converted without
  165        extra spaces, but this conflicts with longstanding tradition and with
  166        this implementation.  The 2011 edition says that the behavior is
  167        undefined if the year is before 1000 or after 9999.  Traditional
  168        implementations of these two functions are restricted to years in the
  169        range 1900 through 2099.  To avoid this portability mess, new programs
  170        should use strftime instead.
  172                                                                    NEWCTIME(3)