mktime(3C)mktime(3C)NAMEmktime - converts a tm structure to a calendar time
SYNOPSIS
#include <time.h>
time_t mktime (struct tm *timeptr);
DESCRIPTIONmktime 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 has the following format.
struct tm {
int tm_sec; /* seconds after the minute [0, 61] */
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
definition 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 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 values
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, the
correct timezone is determined and the components are not adjusted.
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mktime(3C)mktime(3C)
Local timezone information is used as if mktime had called tzset.
mktime returns the specified calendar time. If the calendar time cannot
be represented, the function returns the value (time_t)-1.
EXAMPLE
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]);
SEE ALSOctime(3C), getenv(3C), timezone(4).
NOTES
tm_year of the tm structure must be for year 1970 or later. Calendar
times before 00:00:00 UTC, January 1, 1970 or after 03:14:07 UTC, January
19, 2038 cannot be represented.
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