mktime(3C) (C Programming Language Utilities) mktime(3C)
NAME
mktime - converts a tm structure to a calendar time
SYNOPSIS
#include <time.h>
time_t mktime (struct tm *timeptr);
DESCRIPTION
mktime 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
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mktime(3C) (C Programming Language Utilities) mktime(3C)
and the components are not adjusted.
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]);
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.
SEE ALSO
ctime(3C), getenv(3C), timezone(4).
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