Standard C Library Functions mktime(3C)
NAME
mktime - converts a tm structure to a calendar time
SYNOPSIS
#include
time_t mktime(struct tm *timeptr);
DESCRIPTION
The mktime() function converts the time represented 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() normal-
izes the supplied tm structure. The original values of thetm_wday and tm_yday components of the structure are ignored,
and the original values of the other components are not res-
tricted to the ranges indicated in the definition of the structure. On successful completion, the values of thetm_wday and tm_yday components are set appropriately, and
the other components are set to represent the specified calendar time, but with their values forced to be within theappropriate ranges. The final value of tm_mday is not set
until tm_mon and tm_year are determined.
The tm_year member must be for year 1901 or later. Calendar
times before 20:45:52 UTC, December 13, 1901 or after03:14:07 UTC, January 19, 2038 cannot be represented. Port-
able applications should not try to create dates before 00:00:00 UTC, January 1, 1970 or after 00:00:00 UTC, January 1, 2038. The original values of the components may be either greater than or less than the specified range. For example, aSunOS 5.11 Last change: 1 Nov 2003 1
Standard C Library Functions mktime(3C)
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, the original values are assumed to
be in the alternate timezone. If it turns out that the alternate timezone is not valid for the computed calendar time, then the components are adjusted to the main timezone.Likewise, if tm_isdst is zero, the original values are
assumed to be in the main timezone and are converted to the alternate timezone if the main timezone is not valid. Iftm_isdst is negative, mktime() attempts to determine whether
the alternate timezone is in effect for the specified time.Local timezone information is used as if mktime() had called
tzset(). See ctime(3C).RETURN VALUES
If the calendar time can be represented in an object of typetime_t, mktime() returns the specified calendar time without
changing errno. If the calendar time cannot be represented,the function returns the value (time_t)-1 and sets errno to
indicate the error.ERRORS
The mktime() function will fail if:
EOVERFLOW The date represented by the input tm structcannot be represented in a time_t. Note that
the errno setting may change if future revi-
sions to the standards specify a different value.USAGE
The mktime() function is MT-Safe in multithreaded applica-
tions, as long as no user-defined function directly modifies
one of the following variables: timezone, altzone, daylight, and tzname. See ctime(3C).Note that -1 can be a valid return value for the time that
is one second before the Epoch. The user should clear errnobefore calling mktime(). If mktime() then returns -1, the
user should check errno to determine whether or not an error actually occurred.The mktime() function assumes Gregorian dates. Times before
the adoption of the Gregorian calendar will not matchSunOS 5.11 Last change: 1 Nov 2003 2
Standard C Library Functions mktime(3C)
historial records.EXAMPLES
Example 1 Sample code using mktime().
What day of the week is July 4, 2001?#include
#include
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]);
BUGS
The zoneinfo timezone data files do not transition past TueJan 19 03:14:07 2038 UTC. Therefore for 64-bit applications
using zoneinfo timezones, calculations beyond this date may not use the correct offset from standard time, and couldreturn incorrect values. This affects the 64-bit version of
mktime().
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:SunOS 5.11 Last change: 1 Nov 2003 3
Standard C Library Functions mktime(3C)
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe with exceptions |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
SEE ALSO
ctime(3C), getenv(3C), TIMEZONE(4), attributes(5), stan-
dards(5)SunOS 5.11 Last change: 1 Nov 2003 4