NAME

gettimeofday - get time

SYNOPSIS

#include <sys/time.h> #include <time.h> int gettimeofday(struct timeval *tv, struct timezone *tz);

DESCRIPTION

gettimeofday can get the time as well as a timezone. tv is a timeval struct, as specified in /usr/include/sys/time.h

struct timeval {

long tv_sec; /* seconds / long tv_usec; / microseconds */

};

The tv_sec member of the struct is the number of seconds since the Epoch (see time(2)), and tv_usec is the amount of microseconds past the current tv_sec value.

The tz argument is a timezone

struct timezone {

int tz_minuteswest; /* minutes W of Greenwich / int tz_dsttime; / type of dst correction */

};

The use of the timezone struct is obsolete; the tz_dsttime field has never been used under Linux - it has not been and will not be supported by libc or glibc. Each and every occurrence of this field in the kernel source (other than the declaration) is a bug. Thus, the following is purely of historic interest.

The field tz_dsttime contains a symbolic constant (values are given below) that indicates in which part of the year Daylight Saving Time is in force. (Note: its value is constant throughout the year - it does not indicate that DST is in force, it just selects an algorithm.) The daylight saving time algorithms defined are as follows

DST_NONE /* not on dst / DST_USA / USA style dst / DST_AUST / Australian style dst / DST_WET / Western European dst / DST_MET / Middle European dst / DST_EET / Eastern European dst / DST_CAN / Canada / DST_GB / Great Britain and Eire / DST_RUM / Rumania / DST_TUR / Turkey / DST_AUSTALT / Australian style with shift in 1986 */

Of course it turned out that the period in which Daylight Saving Time is in force cannot be given by a simple algorithm, one per country; indeed, this period is determined by unpredictable political decisions. So this method of representing time zones has been abandoned.

The following macros are defined to operate on a struct timeval

1. define timerisset(tvp)\

   ((tvp)->tv_sec || (tvp)->tv_usec)

2. define timercmp(tvp, uvp, cmp)\

   ((tvp)->tv_sec cmp (uvp)->tv_sec ||\ (tvp)->tv_sec == (uvp)->tv_sec &&\ (tvp)->tv_usec cmp (uvp)->tv_usec)

3. define timerclear(tvp)\

   ((tvp)->tv_sec = (tvp)->tv_usec = 0)

If either tv or tz is null, the corresponding structure is not set or returned.

RETURN VALUE

gettimeofday(2) return 0 for success, or -1 for failure (in which case errno is set appropriately).

ERRORS

EINVAL

Timezone (or something else) is invalid.

EFAULT

One of tv or tz pointed outside your accessible address space.

NOTE

The defines for timercmp, timerisset, timerclear, timeradd, timersub are (since glibc2.2.2) only available if _BSD_SOURCE is defined (either explicitly, or implicitly, by not defining _POSIX_SOURCE or compiling with the -ansi flag).

CONFORMING TO

SVr4, BSD 4.3

SEE ALSO

date(1), adjtimex(2), time(2), ctime(3), ftime(3)