OFFTIME(3) | Library Functions Manual | OFFTIME(3)

# 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”).

April 20, 2025 | NetBSD 11.0