237 lines
5.6 KiB
Groff
237 lines
5.6 KiB
Groff
.TH NEWCTIME 3
|
|
.SH NAME
|
|
asctime, ctime, difftime, gmtime, localtime, mktime \- convert date and time to ASCII
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.B extern char *tzname[2];
|
|
.PP
|
|
.B void tzset()
|
|
.PP
|
|
.B #include <sys/types.h>
|
|
.PP
|
|
.B char *ctime(clock)
|
|
.B const time_t *clock;
|
|
.PP
|
|
.B double difftime(time1, time0)
|
|
.B time_t time1;
|
|
.B time_t time0;
|
|
.PP
|
|
.B #include <time.h>
|
|
.PP
|
|
.B char *asctime(tm)
|
|
.B const struct tm *tm;
|
|
.PP
|
|
.B struct tm *localtime(clock)
|
|
.B const time_t *clock;
|
|
.PP
|
|
.B struct tm *gmtime(clock)
|
|
.B const time_t *clock;
|
|
.PP
|
|
.B time_t mktime(tm)
|
|
.B struct tm *tm;
|
|
.PP
|
|
.B cc ... -ltz
|
|
.fi
|
|
.SH DESCRIPTION
|
|
.I Ctime\^
|
|
converts a long integer, pointed to by
|
|
.IR clock ,
|
|
representing the time in seconds since
|
|
00:00:00 UTC, 1970-01-01,
|
|
and returns a pointer to a
|
|
string of the form
|
|
.br
|
|
.ce
|
|
.eo
|
|
Thu Nov 24 18:22:48 1986\n\0
|
|
.br
|
|
.ec
|
|
Years requiring fewer than four characters are padded with leading zeroes.
|
|
For years longer than four characters, the string is of the form
|
|
.br
|
|
.ce
|
|
.eo
|
|
Thu Nov 24 18:22:48 81986\n\0
|
|
.ec
|
|
.br
|
|
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.
|
|
.PP
|
|
.I Localtime\^
|
|
and
|
|
.I gmtime\^
|
|
return pointers to ``tm'' structures, described below.
|
|
.I 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,
|
|
.I localtime
|
|
sets the
|
|
.BR tm_isdst 'th
|
|
element of
|
|
.B tzname
|
|
to a pointer to an
|
|
ASCII string that's the time zone abbreviation to be used with
|
|
.IR localtime 's
|
|
return value.
|
|
.PP
|
|
.I Gmtime\^
|
|
converts to Coordinated Universal Time.
|
|
.PP
|
|
.I 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.
|
|
.PP
|
|
.I Mktime\^
|
|
converts the broken-down time,
|
|
expressed as local time,
|
|
in the structure pointed to by
|
|
.I tm
|
|
into a calendar time value with the same encoding as that of the values
|
|
returned by the
|
|
.I time
|
|
function.
|
|
The original values of the
|
|
.B tm_wday
|
|
and
|
|
.B 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
|
|
.B tm_isdst
|
|
causes
|
|
.I 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
|
|
.B tm_isdst
|
|
causes the
|
|
.I mktime
|
|
function to attempt to divine whether summer time is in effect
|
|
for the specified time.)
|
|
On successful completion, the values of the
|
|
.B tm_wday
|
|
and
|
|
.B 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
|
|
.B tm_mday
|
|
is not set until
|
|
.B tm_mon
|
|
and
|
|
.B tm_year
|
|
are determined.
|
|
.I Mktime\^
|
|
returns the specified calendar time;
|
|
If the calendar time cannot be represented,
|
|
it returns
|
|
.BR -1 .
|
|
.PP
|
|
.I Difftime\^
|
|
returns the difference between two calendar times,
|
|
.RI ( time1
|
|
-
|
|
.IR time0 ),
|
|
expressed in seconds.
|
|
.PP
|
|
Declarations of all the functions and externals, and the ``tm'' structure,
|
|
are in the
|
|
.B <time.h>\^
|
|
header file.
|
|
The structure (of type)
|
|
.B struct tm
|
|
includes the following fields:
|
|
.RS
|
|
.PP
|
|
.nf
|
|
.ta .5i +\w'long tm_gmtoff;\0\0'u
|
|
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? \(**/
|
|
char \(**tm_zone; /\(** abbreviation of timezone name \(**/
|
|
long tm_gmtoff; /\(** offset from UTC in seconds \(**/
|
|
.fi
|
|
.RE
|
|
.PP
|
|
The
|
|
.I tm_zone
|
|
and
|
|
.I tm_gmtoff
|
|
fields exist, and are filled in, only if arrangements to do
|
|
so were made when the library containing these functions was
|
|
created.
|
|
There is no guarantee that these fields will continue to exist
|
|
in this form in future releases of this code.
|
|
.PP
|
|
.I Tm_isdst\^
|
|
is non-zero if summer time is in effect.
|
|
.PP
|
|
.I Tm_gmtoff
|
|
is the offset (in seconds) of the time represented
|
|
from UTC, with positive values indicating east
|
|
of the Prime Meridian.
|
|
.SH FILES
|
|
.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
|
|
/usr/share/zoneinfo time zone information directory
|
|
.br
|
|
/usr/share/zoneinfo/localtime local time zone file
|
|
.br
|
|
/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
|
|
.br
|
|
/usr/share/zoneinfo/GMT for UTC leap seconds
|
|
.sp
|
|
If
|
|
.B /usr/share/zoneinfo/GMT
|
|
is absent,
|
|
UTC leap seconds are loaded from
|
|
.BR /usr/share/zoneinfo/posixrules .
|
|
.SH SEE ALSO
|
|
getenv(3),
|
|
newstrftime(3),
|
|
newtzset(3),
|
|
time(2),
|
|
tzfile(5)
|
|
.SH NOTES
|
|
The return values point to static data;
|
|
the data is overwritten by each call.
|
|
The
|
|
.B tm_zone
|
|
field of a returned
|
|
.B "struct tm"
|
|
points to a static array of characters, which
|
|
will also be overwritten at the next call
|
|
(and by calls to
|
|
.IR tzset ).
|
|
.PP
|
|
.I Asctime\^
|
|
and
|
|
.I 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
|
|
.I strftime\^
|
|
instead.
|
|
.PP
|
|
Avoid using out-of-range values with
|
|
.I mktime
|
|
when setting up lunch with promptness sticklers in Riyadh.
|
|
.\" @(#)newctime.3 7.17
|