NAME
gettimeofday — get the date and time
SYNOPSIS
#include <sys/time.h>
int gettimeofday(struct timeval *tp, void *tzp);
DESCRIPTION
The
gettimeofday()
function obtains the current time, expressed as seconds and
microseconds since 00:00 Coordinated Universal Time (UTC),
January 1, 1970, and stores it in the
timeval
structure pointed to by
tp.
The resolution of the system clock is unspecified.
If
tzp
is not a null pointer, the behaviour is unspecified.
RETURN VALUE
The
gettimeofday()
function returns 0 and no value is reserved to indicate an error.
ERRORS
No errors are defined.
CHANGE HISTORY
First released in Issue 4, Version 2.
gettimeofday HP-UX EXTENSIONS
SYNOPSIS (HP-UX)
#include <time.h>
int gettimeofday(struct timeval *tp,
struct timezone *tzp);
DESCRIPTION
The structures pointed to by
tp
and
tzp
are defined in
<time.h>
as:
struct timeval {
unsigned long tv_sec; /* seconds since Jan. 1, 1970 */
long tv_usec; /* and microseconds */
};
struct timezone {
int tz_minuteswest; /* of UTC */
int tz_dsttime; /* type of DST correction to apply */
};
The
timezone
structure indicates the local time zone
(measured in minutes of time westward from UTC),
and a flag that, if nonzero, indicates that Daylight Savings Time
applies locally during the appropriate part of the year.
Programs should use this time zone information
only in the absence of the TZ environment variable.
Security Restrictions
Only a user with appropriate privileges
can set the time of day.
RETURN VALUE
gettimeofday()
return the following values:
- 0
Successful completion.
- -1
Failure.
errno
is set to indicate the error.
ERRORS
gettimeofday()
fails,
errno
is set to the following value.
- [EFAULT]
An argument address referenced invalid memory.
The reliable detection of this error is implementation dependent.
EXAMPLES
The following example calls
gettimeofday()
twice.
It then computes the lapsed time between the calls in seconds and
microseconds and stores the result in a timeval structure:
struct timeval first,
second,
lapsed;
struct timezone tzp;
gettimeofday (&first, &tzp);
/* lapsed time */
gettimeofday (&second, &tzp);
if (first.tv_usec > second.tv_usec) {
second.tv_usec += 1000000;
second.tv_sec--;
}
lapsed.tv_usec = second.tv_usec - first.tv_usec;
lapsed.tv_sec = second.tv_sec - first.tv_sec;
WARNINGS
The microsecond value usually has a granularity much greater than one
due to the resolution of the system clock.
Relying on any granularity
(particularly of one) will render code nonportable.
AUTHOR
gettimeofday()
was developed by the University of California,
Berkeley, and SecureWare Inc.
