MKTIME

Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
 

PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.  

NAME

mktime --- convert broken-down time into time since the Epoch  

SYNOPSIS

#include <time.h>

time_t mktime(struct tm *timeptr);
 

DESCRIPTION

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

The mktime() function shall convert the broken-down time, expressed as local time, in the structure pointed to by timeptr, into a time since the Epoch value with the same encoding as that of the values returned by time(). The original values of the tm_wday and tm_yday components of the structure shall be ignored, and the original values of the other components shall not be restricted to the ranges described in <time.h>.

A positive or 0 value for tm_isdst shall cause mktime() to presume initially that Daylight Savings Time, respectively, is or is not in effect for the specified time. A negative value for tm_isdst shall cause mktime() to attempt to determine whether Daylight Savings Time is in effect for the specified time.

Local timezone information shall be set as though mktime() called tzset().

The relationship between the tm structure (defined in the <time.h> header) and the time in seconds since the Epoch is that the result shall be as specified in the expression given in the definition of seconds since the Epoch (see the Base Definitions volume of POSIX.1-2017, Section 4.16, Seconds Since the Epoch) corrected for timezone and any seasonal time adjustments, where the names other than tm_yday in the structure and in the expression correspond, and the tm_yday value used in the expression is the day of the year from 0 to 365 inclusive, calculated from the other tm structure members specified in <time.h> (excluding tm_wday).

Upon successful completion, the values of the tm_wday and tm_yday components of the structure shall be set appropriately, and the other components shall be set to represent the specified time since the Epoch, but with their values forced to the ranges indicated in the <time.h> entry; the final value of tm_mday shall not be set until tm_mon and tm_year are determined.  

RETURN VALUE

The mktime() function shall return the specified time since the Epoch encoded as a value of type time_t. If the time since the Epoch cannot be represented, the function shall return the value (time_t)-1 and set errno to indicate the error.  

ERRORS

The mktime() function shall fail if:
EOVERFLOW
The result cannot be represented.

The following sections are informative.  

EXAMPLES

What day of the week is July 4, 2001? 


#include <stdio.h>
#include <time.h>

struct tm time_str;

char daybuf[20];

int main(void)
{
    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)
        (void)puts("-unknown-");
    else {
        (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
        (void)puts(daybuf);
    }
    return 0;
}

 

APPLICATION USAGE

None.  

RATIONALE

None.  

FUTURE DIRECTIONS

None.  

SEE ALSO

asctime(), clock(), ctime(), difftime(), gmtime(), localtime(), strftime(), strptime(), time(), tzset(), utime()

The Base Definitions volume of POSIX.1-2017, Section 4.16, Seconds Since the Epoch, <time.h>  

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

 

Index

PROLOG
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
EXAMPLES
APPLICATION USAGE
RATIONALE
FUTURE DIRECTIONS
SEE ALSO
COPYRIGHT