mktime(3C) 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.
Copyright 1994 Novell, Inc. Page 1
mktime(3C) mktime(3C)
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.
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.
USAGE
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]);
REFERENCES
ctime(3C), getenv(3C), timezone(4)
NOTICES
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
Copyright 1994 Novell, Inc. Page 2
mktime(3C) mktime(3C)
03:14:07 UTC, January 19, 2038 cannot be represented.
Copyright 1994 Novell, Inc. Page 3