NAME

offtime, offtime_r, timeoff, timegm, timelocal — convert date and time

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <time.h>

struct tm *
offtime(const time_t * clock, long int offset);

struct tm *
offtime_r(const time_t * clock, long int offset, struct tm *ret);

time_t
timeoff(struct tm * tm, long int offset);

time_t
timegm(struct tm * tm);

time_t
timelocal(struct tm * tm);

DESCRIPTION

These functions are inspired by C standard interfaces named similarly.

offtime() converts the calendar time clock, offset by offset seconds, into broken-down time, expressed as Coordinated Universal Time (UTC).

offtime_r() is similar to offtime() but it places the returned struct tm * in the user supplied ret argument.

timeoff() converts the broken-down time tm, expressed as UTC, offset by offset seconds, into a calendar time value.

timegm() converts the broken-down time tm into a calendar time value, effectively being the inverse of gmtime(3). It is equivalent to the C standard function mktime(3) operating in UTC.

timelocal() converts the broken down time tm, expressed as local time, into a calendar time value. It is equivalent to the C standard function mktime(3), and is provided for symmetry only.

SEE ALSO

ctime(3), tm(3), tzset(3)

STANDARDS

The timegm() function conforms to ISO/IEC 9899:2024 (“ISO C23”).