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mktime(3c)
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 ap‐
propriately, and the other components are set to represent the speci‐
fied calendar time, but with their values forced to be within the ap‐
propriate 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 be‐
fore 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, De‐
cember 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 al‐
ternate 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 as‐
sumed 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 ap‐
plications, 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 mk‐
time(). If mktime() then returns −1, the user should check errno to de‐
termine 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 ex‐
ceptions _ StandardSee standards(7).
SEE ALSO
ctime(3C), getenv(3C), attributes(7), standards(7)
Oracle Solaris 11.4 11 May 2021 mktime(3C)