b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
457 lines
10 KiB
Groff
457 lines
10 KiB
Groff
.\" $NetBSD: ctime.3,v 1.37 2010/12/17 01:30:50 wiz Exp $
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.Dd December 14, 2010
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.Dt CTIME 3
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.Os
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.Sh NAME
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.Nm asctime ,
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.Nm asctime_r ,
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.Nm ctime ,
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.Nm ctime_r ,
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.Nm ctime_rz ,
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.Nm difftime ,
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.Nm gmtime ,
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.Nm gmtime_r ,
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.Nm localtime ,
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.Nm localtime_r ,
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.Nm localtime_rz ,
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.Nm mktime ,
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.Nm mktime_z ,
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.Nm tzalloc ,
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.Nm tzgetname ,
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.Nm tzfree ,
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.Nd convert date and time to ASCII
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In time.h
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.Dv extern char *tzname[2];
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.Ft char *
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.Fn ctime "const time_t *clock"
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.Ft char *
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.Fn ctime_r "const time_t *clock" "char *buf"
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.Ft char *
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.Fn ctime_rz "const timezone_t tz" "const time_t *clock" "char *buf"
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.Ft double
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.Fn difftime "time_t time1" "time_t time0"
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.Ft char *
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.Fn asctime "const struct tm *tm"
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.Ft char *
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.Fn asctime_r "const struct tm restrict tm" "char * restrict buf"
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.Ft struct tm *
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.Fn localtime "const time_t *clock"
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.Ft struct tm *
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.Fn localtime_r "const time_t * restrict clock" "struct tm * restrict result"
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.Ft struct tm *
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.Fn localtime_rz "const timezone_t tz" "const time_t * restrict clock" "struct tm * restrict result"
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.Ft struct tm *
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.Fn gmtime "const time_t *clock"
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.Ft struct tm *
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.Fn gmtime_r "const time_t * restrict clock" "struct tm * restrict result"
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.Ft time_t
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.Fn mktime "struct tm *tm"
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.Ft time_t
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.Fn mktime_z "const timezone_t tz" "struct tm *tm"
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.Ft timezone_t
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.Fn tzalloc "const char *zone"
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.Ft const char *
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.Fn tzgetname "const timezone_t tz" "int isdst"
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.Ft void
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.Fn tzfree "const timezone_t tz"
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.Sh DESCRIPTION
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.Fn ctime
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converts a
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.Tp time_t ,
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pointed to by
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.Fa clock ,
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representing the time in seconds since
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00:00:00 UTC, 1970-01-01,
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and returns a pointer to a
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string of the form
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.D1 Thu Nov 24 18:22:48 1986\en\e0
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Years requiring fewer than four characters are padded with leading zeroes.
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For years longer than four characters, the string is of the form
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.D1 Thu Nov 24 18:22:48 81986\en\e0
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with five spaces before the year.
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These unusual formats are designed to make it less likely that older
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software that expects exactly 26 bytes of output will mistakenly output
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misleading values for out-of-range years.
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.Pp
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.Fn ctime_r
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is similar to
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.Fn ctime ,
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except it places the result of the conversion on the
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.Fa buf
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argument which should be 26 or more bytes long, instead of using a global
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static buffer.
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.Pp
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.Fn ctime_rz
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is similar to
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.Fn ctime_r ,
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but it also takes a
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.Ft "const timezone_t"
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argument, returned by a previous call to
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.Fn tzalloc .
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.Pp
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.Fn localtime
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and
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.Fn gmtime
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return pointers to
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.Va tm
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structures, described below.
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.Fn localtime
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corrects for the time zone and any time zone adjustments
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(such as Daylight Saving Time in the U.S.A.).
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After filling in the
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.Va tm
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structure,
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.Fn localtime
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sets the
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.Fa tm_isdst Ns 'th
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element of
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.Fa tzname
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to a pointer to an
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ASCII string that's the time zone abbreviation to be used with
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.Fn localtime Ns 's
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return value.
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.Pp
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.Fn gmtime
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converts to Coordinated Universal Time.
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.Pp
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The
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.Fn gmtime_r
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and
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.Fn localtime_r
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functions provide the same functionality as
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.Fn gmtime
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and
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.Fn localtime
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differing in that the caller must supply a buffer area
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.Fa result
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in which the result is stored; also,
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.Fn localtime_r
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does not imply initialization of the local time conversion information;
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the application may need to do so by calling
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.Xr tzset 3 .
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.Pp
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.Fn localtime_rz
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is similar to
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.Fn localtime_r ,
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but it also takes a
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.Ft "const timezone_t"
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argument, returned by a previous call to
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.Fn tzalloc .
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.Pp
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.Fn asctime
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converts a time value contained in a
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.Dq tm
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structure to a string,
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as shown in the above example,
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and returns a pointer to the string.
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.Pp
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.Fn mktime
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converts the broken-down time,
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expressed as local time,
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in the structure pointed to by
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.Fa tm
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into a calendar time value with the same encoding as that of the values
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returned by the
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.Xr time 3
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function.
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The original values of the
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.Fa tm_wday
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and
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.Fa tm_yday
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components of the structure are ignored,
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and the original values of the other components are not restricted
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to their normal ranges.
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(A positive or zero value for
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.Fa tm_isdst
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causes
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.Fn mktime
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to presume initially that summer time (for example, Daylight Saving Time
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in the U.S.A.) respectively,
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is or is not in effect for the specified time.
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A negative value for
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.Fa tm_isdst
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causes the
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.Fn mktime
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function to attempt to divine whether summer time is in effect
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for the specified time; in this case it does not use a consistent
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rule and may give a different answer when later
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presented with the same argument.)
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On successful completion, the values of the
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.Fa tm_wday
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and
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.Fa tm_yday
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components of the structure are set appropriately,
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and the other components are set to represent the specified calendar time,
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but with their values forced to their normal ranges; the final value of
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.Fa tm_mday
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is not set until
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.Fa tm_mon
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and
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.Fa tm_year
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are determined.
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.Fn mktime
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returns the specified calendar time; if the calendar time cannot be
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represented, it returns
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.Va "(time_t)-1" .
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.Pp
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.Fn mktime_z
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is similar to
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.Fn mktime
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but it also takes a
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.Ft "const timezone_t"
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argument, returned by a previous call to
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.Fn tzalloc .
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.Pp
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.Fn difftime
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returns the difference between two calendar times,
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.Fa ( time1 No - Fa time0 ) ,
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expressed in seconds.
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.Pp
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.Fn tzalloc
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takes as an argument a timezone name and returns a
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.Ft timezone_t
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object suitable to be used in
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.Fn ctime_rz ,
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.Fn localtime_rz ,
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and
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.Fn mktime_z .
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Instead of setting the environment variable
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.Va TZ ,
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and globally changing the behavior of the calling program, one can use
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multiple timezones at the same time by using separate
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.Ft timezone_t
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objects allocated by
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.Fn tzalloc
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and calling the
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.Dq z
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variants of the functions.
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.Pp
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.Fn tzgetname
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returns the name for the given
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.Fa tz .
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If
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.Fa isdst
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is
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.Va 0 ,
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the call is equivalent to
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.Va tzname[0] .
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If
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.Fa isdst
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is set to
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.Va 1
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the call is equivalent to
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.Va tzname[1] .
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.Pp
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.Fn tzfree
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frees the
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.Fa tz
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argument previously returned by
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.Fa tzalloc .
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.Pp
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The structure (of type)
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.Va "struct tm"
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includes the following fields:
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.Bd -literal -offset indent
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int tm_sec; /* seconds after the minute [0,61] */
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int tm_min; /* minutes after the hour [0,59] */
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int tm_hour; /* hours since midnight [0,23] */
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int tm_mday; /* day of the month [1,31] */
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int tm_mon; /* months since January [0,11] */
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int tm_year; /* years since 1900 */
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int tm_wday; /* day of week [0,6] (Sunday = 0) */
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int tm_yday; /* day of year [0,365] (Jan 1 = 0) */
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int tm_isdst; /* daylight savings flag */
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long tm_gmtoff; /* offset from UTC in seconds */
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char *tm_zone; /* abbreviation of timezone name */
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.Ed
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.Pp
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The
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.Fa tm_zone
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and
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.Fa tm_gmtoff
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fields exist, and are filled in, only if arrangements to do
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so were made when the library containing these functions was
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created.
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There is no guarantee that these fields will continue to exist
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in this form in future releases of this code.
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The
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.Fa tm_zone
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field will become invalid and point to freed storage if the corresponding
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.Va "struct tm"
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was returned by
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.Fn localtime_rz
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and the
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.Ft "const timezone_t"
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.Fa tz
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argument has been freed by
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.Fn tzfree .
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.Pp
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.Fa tm_isdst
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is non-zero if summer time is in effect.
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.Pp
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.Fa tm_gmtoff
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is the offset (in seconds) of the time represented
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from UTC, with positive values indicating east
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of the Prime Meridian.
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.Sh RETURN VALUES
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On success the
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.Fn asctime
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and
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.Fn ctime
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functions return a pointer to a static character buffer, and the
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.Fn asctime_r ,
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.Fn ctime_r ,
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and
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.Fn ctime_rz
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function return a pointer to the user-supplied buffer.
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On failure they all return
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.Dv NULL
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and no errors are defined for them.
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On success the
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.Fn gmtime ,
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and
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.Fn localtime
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functions return a pointer to a statically allocated
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.Va "struct tm"
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whereas the
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.Fn gmtime_r ,
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.Fn localtime_r ,
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and
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.Fn localtime_rz ,
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functions return a pointer to the user-supplied
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.Va "struct tm" .
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On failure they all return
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.Dv NULL
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and the global variable
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.Va errno
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is set to indicate the error.
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The
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.Fn mktime
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and
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.Fn mktime_z
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function returns the specified time since the Epoch as a
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.Va time_t
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type value.
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If the time cannot be represented, then
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.Fn mktime
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and
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.Fn mktime_z
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return
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.Va "(time_t)-1"
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setting the global variable
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.Va errno
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to indicate the error.
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The
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.Fn tzalloc
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function returns a pointer to a
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.Ft timezone_t
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object or
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.Dv NULL
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on failure, setting
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.Va errno
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to indicate the error.
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.Fn tzgetzone
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function returns string containing the name of the timezone given in
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.Fa tz .
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.Sh FILES
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.Bl -tag -width /usr/share/zoneinfo/posixrules -compact
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.It Pa /etc/localtime
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local time zone file
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.It Pa /usr/share/zoneinfo
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time zone information directory
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.It Pa /usr/share/zoneinfo/posixrules
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used with POSIX-style TZ's
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.It Pa /usr/share/zoneinfo/GMT
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for UTC leap seconds
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.El
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.Pp
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If
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.Pa /usr/share/zoneinfo/GMT
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is absent, UTC leap seconds are loaded from
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.Pa /usr/share/zoneinfo/posixrules .
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.Sh ERRORS
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The
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.Fn gmtime_r ,
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.Fn localtime_r ,
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.Fn localtime_rz ,
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.Fn gmtime ,
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.Fn localtime ,
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and
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.Fn mktime ,
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and
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.Fn mktime_z
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will fail when:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The result cannot be represented.
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.It Bq Er EOVERFLOW
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The result cannot be represented.
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.El
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.Pp
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All functions that return values except their
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.Dq z
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variants, can also return the same errors as
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.Xr open 2
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and
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.Xr malloc 3 .
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.Sh SEE ALSO
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.Xr getenv 3 ,
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.Xr strftime 3 ,
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.Xr time 3 ,
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.Xr tzset 3 ,
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.Xr tzfile 5
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.Sh STANDARDS
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The
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.Fn ctime ,
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.Fn difftime ,
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.Fn asctime ,
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.Fn localtime ,
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.Fn gmtime
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and
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.Fn mktime
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functions conform to
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.St -ansiC
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The
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.Fn ctime_r ,
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.Fn asctime_r ,
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.Fn localtime_r
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and
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.Fn gmtime_r
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functions conform to
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.St -p1003.1c-95 .
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.Sh NOTES
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The return values point to static data; the data is overwritten by
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each call.
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The
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.Fa tm_zone
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field of a returned
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.Va "struct tm"
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points to a static array of characters, which
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will also be overwritten at the next call
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(and by calls to
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.Xr tzset 3 ) .
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.Pp
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.Fn asctime
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and
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.Fn ctime
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behave strangely for years before 1000 or after 9999.
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The 1989 and 1999 editions of the C Standard say
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that years from \-99 through 999 are converted without
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extra spaces, but this conflicts with longstanding
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tradition and with this implementation.
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Traditional implementations of these two functions are
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restricted to years in the range 1900 through 2099.
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To avoid this portability mess, new programs should use
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.Fn strftime
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instead.
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.Pp
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Avoid using out-of-range values with
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.Fn mktime
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when setting up lunch with promptness sticklers in Riyadh.
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.\" @(#)newctime.3 8.3
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.\" This file is in the public domain, so clarified as of
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.\" 2009-05-17 by Arthur David Olson.
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