NAME

mktime − 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:

inttm_sec;/∗ seconds after the minute [0, 61]  ∗/
inttm_min;/∗ minutes after the hour [0, 59] ∗/
inttm_hour;/∗ hour since midnight [0, 23] ∗/
inttm_mday;/∗ day of the month [1, 31] ∗/
inttm_mon;/∗ months since January [0, 11] ∗/
inttm_year;/∗ years since 1900 ∗/
inttm_wday;/∗ days since Sunday [0, 6] ∗/
inttm_yday;/∗ days since January 1 [0, 365] ∗/
inttm_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 tm_year member 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. 

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, 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

The mktime() function returns the specified calendar time.  If the calendar time cannot be represented, the function returns the value (time_t)−1. 

EXAMPLES

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(5) for descriptions of the following attributes:

SEE ALSO

ctime(3C), getenv(3C), TIMEZONE(4), attributes(5)

NOTES

The mktime() function is MT-Safe in multithread applications, as long as no user-defined function directly modifies one of the following variables: timezone, altzone, daylight, and tzname.  See ctime(3C)). 

SunOS 5.6  —  Last change: 29 Dec 1996