gettimeofday(2)

NAME

gettimeofday, settimeofday − get/set date and time

SYNOPSIS

#include <time.h>

int gettimeofday(

struct timeval *tp,
struct timezone *tzp

);

int settimeofday(

const struct timeval *tp,
const struct timezone *tzp

);

DESCRIPTION

gettimeofday() returns and settimeofday() sets the system’s notion of the current Coordinated Universal Time (UTC) and the system’s notion of the current time zone. Time is expressed in seconds and microseconds since midnight January 1, 1970.

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 timezone information only in the absence of the TZ environment variable.

Only users with appropriate privileges can set the time of day.

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;

RETURN VALUE

gettimeofday() and settimeofday() return 0 on success; otherwise, if an error occurs, they return −1 and set errno to indicate the error.

ERRORS

gettimeofday() and settimeofday() fail if any of the following conditions are encountered:

[EFAULT] An argument address referenced invalid memory. The reliable detection of this error will be implementation dependent.

[EPERM] A user lacking appropriate privileges attempted to set the time.

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 non-portable.

DEPENDENCIES

Series 300/400

gettimeofday() has a granularity of 4 microseconds.

Clustered Systems

In an HP Clustered Environment, setting the time of day sets the date and timezone on all systems in the cluster.

AUTHOR

gettimeofday() was developed by the University of California, Berkeley.

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