mktime(3C) Standard C Library Functions mktime(3C)NAMEmktime - converts a tm structure to a calendar time
SYNOPSIS
#include <time.h>
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() normalizes 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 def‐
inition of the structure. On successful completion, the values of the
tm_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 the appropriate 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 after 03:14:07 UTC, January
19, 2038 cannot be represented. 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.
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, 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 val‐
ues are assumed to be in the main timezone and are converted to the
alternate timezone if the main timezone is not valid. If tm_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 type time_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 struct cannot be
represented in a time_t. Note that the errno setting
may change if future revisions to the standards specify
a different value.
USAGE
The mktime() function is 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).
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() function assumes Gregorian dates. Times before the adop‐
tion of the Gregorian calendar will not match historial 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]);
BUGS
The zoneinfo timezone data files do not transition past Tue Jan 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 could return incorrect values.
This affects the 64-bit version of mktime().
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe with exceptions │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOctime(3C), getenv(3C), TIMEZONE(4), attributes(5), standards(5)SunOS 5.10 1 Nov 2003 mktime(3C)