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mktime(3c)

Standard C Library Functions                                        mktime(3C)



NAME
       mktime, timegm, timelocal - converts a tm structure to a calendar time

SYNOPSIS
       #include <time.h>


       time_t mktime(struct tm *timeptr);


       time_t timegm(struct tm *timeptr);


       time_t timelocal(struct tm *timeptr);

DESCRIPTION
       The mktime(), timegm(), and timelocal() functions convert the time rep‐
       resented by the tm structure pointed to by timeptr into a calendar time
       (the number of seconds since 00:00:00 UTC, January 1, 1970).


       The tm structure contains the following members:

         int  tm_sec;     /* seconds after the minute [0, 60]  */
         int  tm_min;     /* minutes after the hour [0, 59] */
         int  tm_hour;    /* hour since midnight [0, 23] */
         int  tm_mday;    /* day of the month [1, 31] */
         int  tm_mon;     /* months since January [0, 11] */
         int  tm_year;    /* years since 1900 */
         int  tm_wday;    /* days since Sunday [0, 6] */
         int  tm_yday;    /* days since January 1 [0, 365] */
         int  tm_isdst;   /* flag for daylight savings time */



       In  addition  to  computing  the calendar time, mktime(), timegm(), and
       timelocal() normalize the supplied tm structure. The original values of
       the  tm_wday  and  tm_yday components of the structure are ignored, and
       the original values of the other components are not restricted  to  the
       ranges indicated in the definition of the structure. On successful com‐
       pletion, the values of the  tm_wday  and  tm_yday  components  are  set
       appropriately, and the other components are set to represent the speci‐
       fied calendar time, but with their  values  forced  to  be  within  the
       appropriate  ranges. The final value of tm_mday is not set until tm_mon
       and tm_year are determined.


       Calendar time in a 32-bit application cannot  represent  values  before
       20:45:52  UTC,  December  13,  1901  or after 03:14:07 UTC, January 19,
       2038. As the tm_year member is a signed integer,  calendar  time  in  a
       64-bit application cannot represent years before 2147483649 BC or after
       2147485546 AD. Portable applications should not  try  to  create  dates
       before  00:00:00 UTC, January 1, 1970 or after 00:00:00 UTC, January 1,
       2038. Where practical 64-bit applications should  limit  themselves  to
       dates  in  the  range  00:00:00  UTC,  January 1, 1970 to 00:00:00 UTC,
       December 31, 9999.


       The original values of the components may be  either  greater  than  or
       less  than  the  specified  range. For example, a tm_hour of −1 means 1
       hour before midnight, tm_mday of 0 means the day preceding the  current
       month, and tm_mon of −2 means 2 months before January of tm_year.


       If  tm_isdst is positive, mktime() assumes the original values to be in
       the alternate time zone. If it turns out that the alternate  time  zone
       is  not  valid  for the computed calendar time, then the components are
       adjusted to the main time zone. Likewise,  if  tm_isdst  is  zero,  the
       original  values  are  assumed to be in the main time zone and are con‐
       verted to the alternate time zone if the main time zone is  not  valid.
       If  tm_isdst  is  negative,  mktime() attempts to determine whether the
       alternate time zone is in effect for the specified time. timelocal() is
       equivalent to mktime() with a negative tm_isdst value.


       Local  time  zone information is used as if mktime() or timelocal() had
       called tzset(). See ctime(3C).


       The function timegm() performs the inverse conversion to  gmtime()  and
       ignores  the  local  time  zone  information.  The  original values are
       assumed to be in the UTC time zone. See ctime(3C).

RETURN VALUES
       If the calendar time can be represented in an object  of  type  time_t,
       then  mktime(), timegm(), and timelocal() return the specified calendar
       time without changing errno. If the  calendar  time  cannot  be  repre‐
       sented,  the functions return the value (time_t)\(mi1) and set errno to
       indicate the error.

ERRORS
       The mktime(), timegm(), and timelocal() functions will fail if:

       EOVERFLOW    The date represented by the input tm struct cannot be rep‐
                    resented  in  a  time_t.  Note  that the errno setting may
                    change if future revisions to the standards specify a dif‐
                    ferent value.


USAGE
       The  mktime()  and  timelocal()  functions are MT-Safe in multithreaded
       applications, as long as no user-defined function directly modifies one
       of  the  following  variables: timezone, altzone, daylight, and tzname.
       See ctime(3C). The timegm() function is MT-Safe in multithreaded appli‐
       cations.


       Note  that −1 can be a valid return value for the time that is one sec‐
       ond before the Epoch.  The  user  should  clear  errno  before  calling
       mktime().  If  mktime() then returns −1, the user should check errno to
       determine whether or not an error actually occurred.


       The mktime(), timegm(),  and  timelocal()  functions  assume  Gregorian
       dates.  Times  before  the  adoption of the Gregorian calendar will not
       match historical records.

EXAMPLES
       Example 1 Sample code using mktime().




       What day of the week is July 4, 2001?


         #include <stdio.h>
         #include <time.h>
         static char *const wday[] = {
                 "Sunday", "Monday", "Tuesday", "Wednesday",
                 "Thursday", "Friday", "Saturday", "-unknown-"
         };
         struct tm time_str;
         /*...*/
         time_str.tm_year    = 2001 - 1900;
         time_str.tm_mon = 7 - 1;
         time_str.tm_mday = 4;
         time_str.tm_hour = 0;
         time_str.tm_min = 0;
         time_str.tm_sec = 1;
         time_str.tm_isdst = −1;
         if (mktime(&time_str)== −1)
                 time_str.tm_wday=7;
         printf("%s\n", wday[time_str.tm_wday]);



ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE  TYPEAT‐
       TRIBUTE  VALUE  _  Interface  StabilityCommitted _ MT-LevelMT-Safe with
       exceptions _ StandardSee standards(7).


SEE ALSO
       ctime(3C), getenv(3C), attributes(7), standards(7)



Oracle Solaris 11.4               11 May 2021                       mktime(3C)
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