| CTIME(3) |
AerieBSD 1.0 Refernce Manual |
CTIME(3) |
NAME
asctime —
asctime_r,
ctime,
ctime_r,
difftime,
gmtime,
gmtime_r,
localtime,
localtime_r,
mktime,
timegm,
timelocal
convert date and time to ASCII
SYNOPSIS
#include <sys/types.h>
#include <time.h>
extern char *tzname[2];
"char*"
ctime(const time_t *clock);
"char*"
ctime_r(const time_t *clock, char *buf);
double
difftime(time_t time1, time_t time0);
"char*"
asctime(const struct tm *tm);
"char*"
asctime_r(const struct tm *tm, char *buf);
"structtm *"
localtime(const time_t *clock);
"structtm *"
localtime_r(const time_t *clock, struct tm *result);
"structtm *"
gmtime(const time_t *clock);
"structtm *"
gmtime_r(const time_t *clock, struct tm *result);
time_t
mktime(struct tm *tm);
time_t
timegm(struct tm *tm);
time_t
timelocal(struct tm *tm);
DESCRIPTION
The
ctime();
function converts a
time_t,
pointed to by
clock,
representing the time in seconds since
00:00:00 UTC, 1970-01-01,
and returns a pointer to a
string of the form
Thu Nov 24 18:22:48 1986\en
Years requiring fewer than four characters are padded with leading zeroes.
For years longer than four characters, the string is of the form
Thu Nov 24 18:22:48\ \ \ \ \ 81986\en
with five spaces before the year.
These unusual formats are designed to make it less likely that older
software that expects exactly 26 bytes of output will mistakenly output
misleading values for out-of-range years.
The
ctime_r();
function converts the calendar time pointed to by
clock
to local time in exactly the same way as
ctime();
and puts the string into the array pointed to by
buf
(which contains at least 26 bytes) and returns
buf.
Unlike
ctime();,
the thread-safe version
ctime_r();
is not required to set
tzname.
The
localtime();
and
gmtime();
functions return pointers to
tm
structures, described below.
localtime();
corrects for the time zone and any time zone adjustments
(such as Daylight Saving Time in the United States).
After filling in the
tm
structure,
localtime();
sets the
tm_isdst
element of
tzname
to a pointer to an
ASCII string that's the time zone abbreviation to be used with
the return value of
localtime();.
gmtime();
converts to Coordinated Universal Time.
The
localtime_r();
and
gmtime_r();
functions convert the calendar time pointed to by
clock
into a broken-down time in exactly the same way as their non-reentrant
counterparts,
localtime();
and
gmtime();,
but instead store the result directly into the structure pointed to by
result.
Unlike
localtime();,
the reentrant version is not required to set
tzname.
asctime();
converts a time value contained in a
tm
structure to a string,
as shown in the above example,
and returns a pointer to the string.
asctime_r();
uses the buffer pointed to by
buf
(which should contain at least 26 bytes) and then
returns
buf.
mktime();
converts the broken-down time,
expressed as local time,
in the structure pointed to by
tm
into a calendar time value with the same encoding as that of the values
returned by the
time();
function.
The original values of the
tm_wday
and
tm_yday
components of the structure are ignored,
and the original values of the other components are not restricted
to their normal ranges.
(A positive or zero value for
tm_isdst
causes
mktime();
to presume initially that summer time (for example, Daylight Saving Time
in the U.S.A.)\&
respectively,
is or is not in effect for the specified time.
A negative value for
tm_isdst
causes the
mktime();
function to attempt to divine whether summer time is in effect
for the specified time; in this case it does not use a consistent
rule and may give a different answer when later
presented with the same argument.)
On successful completion, the values of the
tm_wday
and
tm_yday
components of the structure are set appropriately,
and the other components are set to represent the specified calendar time,
but with their values forced to their normal ranges; the final value of
tm_mday
is not set until
tm_mon
and
tm_year
are determined.
mktime();
returns the specified calendar time;
if the calendar time cannot be represented,
it returns \-1.
timelocal();
is a deprecated interface that is equivalent to calling
mktime();
with a negative value for
tm_isdst.
timegm();
is a deprecated interface that converts the broken-down time, as returned by
gmtime();,
into a calendar time value with the same encoding as that of the values
returned by the
time();
function.
difftime();
returns the difference between two calendar times,
.Pf ( Fa time1 No \- Fa time0 ) ,
expressed in seconds.
Declarations of all the functions and externals, and the
tm
structure, are in the
‹time.h›
header file.
The structure (of type)
struct tm
includes the following fields:
int tm_sec; /* seconds (0 \- 60) */
int tm_min; /* minutes (0 \- 59) */
int tm_hour; /* hours (0 \- 23) */
int tm_mday; /* day of month (1 \- 31) */
int tm_mon; /* month of year (0 \- 11) */
int tm_year; /* year \- 1900 */
int tm_wday; /* day of week (Sunday = 0) */
int tm_yday; /* day of year (0 \- 365) */
int tm_isdst; /* is summer time in effect? */
long tm_gmtoff; /* offset from UTC in seconds */
char *tm_zone; /* abbreviation of timezone name */
The
tm_zone
and
tm_gmtoff
fields exist, and are filled in by
mktime();,
localtime();,
timegm();,
and
gmtime();,
but are not standardized.
There is no guarantee that these fields will continue to exist
in this form and they may be altered or removed in a future release.
tm_isdst
is non-zero if summer time is in effect.
tm_gmtoff
is the offset (in seconds) of the time represented
from UTC, with positive values indicating east
of the Prime Meridian.
FILES
- /usr/share/zoneinfo
-
time zone information directory
- /etc/localtime
-
local time zone file
- /usr/share/zoneinfo/posixrules
-
used with POSIX-style TZ's
- /usr/share/zoneinfo/GMT
-
for UTC leap seconds
If
/usr/share/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
/usr/share/zoneinfo/posixrules.
SEE ALSO
getenv(3),
strftime(3),
time(3),
tzset(3),
tzfile(5),
zic(8)
NOTES
The return values
of the non re-entrant functions
point to static data;
the data is overwritten by each call.
The
tm_zone
field of a returned
struct tm
points to a static array of characters, which
will also be overwritten at the next call
(and by calls to
tzset(3/)).
asctime();
and
ctime();
behave strangely for years before 1000 or after 9999.
The 1989 and 1999 editions of the C Standard say
that years from \-99 through 999 are converted without
extra spaces, but this conflicts with longstanding
tradition and with this implementation.
Traditional implementations of these two functions are
restricted to years in the range 1900 through 2099.
To avoid this portability mess, new programs should use
strftime();
instead.
The default system time zone may be set by running
“zic -l timezone”
as the superuser.
Avoid using out-of-range values with
mktime();
when setting up lunch with promptness sticklers in Riyadh.
| AerieBSD 1.0 Reference Manual |
May 26 2009 |
CTIME(3) |