strftime.3

早期freebsd实现

.TH STRFTIME 3
.SH NAME
strftime \- generate formatted time information
.SH SYNOPSIS
.ft B
.nf
#include <sys/types.h>
#include <time.h>
.sp
size_t strftime(char *s, size_t maxsize, const char *format,
	const struct tm *timeptr);
.SH DESCRIPTION
The following description is transcribed verbatim from the December 7, 1988
draft standard for ANSI C.
This draft is essentially identical in technical content
to the final version of the standard.
.LP
The
.B strftime
function places characters into the array pointed to by
.B s
as controlled by the string pointed to by
.BR format .
The format shall be a multibyte character sequence, beginning and ending in
its initial shift state.
The
.B format
string consists of zero or more conversion specifiers and ordinary
multibyte characters.  A conversion specifier consists of a
.B %
character followed by a character that determines the behavior of the
conversion specifier.
All ordinary multibyte characters (including the terminating null
character) are copied unchanged into the array.
If copying takes place between objects that overlap the behavior is undefined.
No more than
.B maxsize
characters are placed into the array.
Each conversion specifier is replaced by appropriate characters as described
in the following list.
The appropriate characters are determined by the
.B LC_TIME
category of the current locale and by the values contained in the
structure pointed to by
.BR timeptr .
.TP
.B %a
is replaced by the locale's abbreviated weekday name.
.TP
.B %A
is replaced by the locale's full weekday name.
.TP
.B %b
is replaced by the locale's abbreviated month name.
.TP
.B %B
is replaced by the locale's full month name.
.TP
.B %c
is replaced by the locale's appropriate date and time representation.
.TP
.B %d
is replaced by the day of the month as a decimal number
.RB ( 01 - 31 ).
.TP
.B %H
is replaced by the hour (24-hour clock) as a decimal number
.RB ( 00 - 23 ).
.TP
.B %I
is replaced by the hour (12-hour clock) as a decimal number
.RB ( 01 - 12 ).
.TP
.B %j
is replaced by the day of the year as a decimal number
.RB ( 001 - 366 ).
.TP
.B %m
is replaced by the month as a decimal number
.RB ( 01 - 12 ).
.TP
.B %M
is replaced by the minute as a decimal number
.RB ( 00 - 59 ).
.TP
.B %p
is replaced by the locale's equivalent of the AM/PM designations associated
with a 12-hour clock.
.TP
.B %S
is replaced by the second as a decimal number
.RB ( 00 - 61 ).
.TP
.B %U
is replaced by the week number of the year (the first Sunday as the first
day of week 1) as a decimal number
.RB ( 00 - 53 ).
.TP
.B %w
is replaced by the weekday as a decimal number
.RB [ "0 " (Sunday)- 6 ].
.TP
.B %W
is replaced by the week number of the year (the first Monday as the first
day of week 1) as a decimal number
.RB ( 00 - 53 ).
.TP
.B %x
is replaced by the locale's appropriate date representation.
.TP
.B %X
is replaced by the locale's appropriate time representation.
.TP
.B %y
is replaced by the year without century as a decimal number
.RB ( 00 - 99 ).
.TP
.B %Y
is replaced by the year with century as a decimal number.
.TP
.B %Z
is replaced by the time zone name or abbreviation, or by no characters if
no time zone is determinable.
.TP
.B %%
is replaced by
.BR % .
.LP
If a conversion specifier is not one of the above, the behavior is
undefined.
.SH RETURNS
If the total number of resulting characters including the terminating null
character is not more than
.BR maxsize ,
the
.B strftime
function returns the number of characters placed into the array pointed to
by
.B s
not including the terminating null character.
Otherwise, zero is returned and the contents of the array are indeterminate.
.SH NON-ANSI EXTENSIONS
If
.B SYSV_EXT
is defined when the routine is compiled, then the following additional
conversions will be available.
These are borrowed from the System V
.IR cftime (3)
and
.IR ascftime (3)
routines.
.TP
.B %D
is equivalent to specifying
.BR %m/%d/%y .
.TP
.B %e
is replaced by the day of the month,
padded with a blank if it is only one digit.
.TP
.B %h
is equivalent to
.BR %b ,
above.
.TP
.B %n
is replaced with a newline character (\s-1ASCII LF\s+1).
.TP
.B %r
is equivalent to specifying
.BR "%I:%M:%S %p" .
.TP
.B %R
is equivalent to specifying
.BR %H:%M .
.TP
.B %T
is equivalent to specifying
.BR %H:%M:%S .
.TP
.B %t
is replaced with a \s-1TAB\s+1 character.
.PP
If
.B SUNOS_EXT
is defined when the routine is compiled, then the following additional
conversions will be available.
These are borrowed from the SunOS version of
.IR strftime .
.TP
.B %k
is replaced by the hour (24-hour clock) as a decimal number
.RB ( 0 - 23 ).
Single digit numbers are padded with a blank.
.TP
.B %l
is replaced by the hour (12-hour clock) as a decimal number
.RB ( 1 - 12 ).
Single digit numbers are padded with a blank.
.SH POSIX 1003.2 EXTENSIONS
If
.B POSIX2_DATE
is defined, then all of the conversions available with
.B SYSV_EXT
and
.B SUNOS_EXT
are available, as well as the
following additional conversions:
.TP
.B %C
The century, as a number between 00 and 99.
.TP
.B %u
is replaced by the weekday as a decimal number
.RB [ "1 " (Monday)- 7 ].
.TP
.B %V
is replaced by the week number of the year (the first Monday as the first
day of week 1) as a decimal number
.RB ( 01 - 53 ).
The method for determining the week number is as specified by ISO 8601
(to wit: if the week containing January 1 has four or more days in the
new year, then it is week 1, otherwise it is week 53 of the previous year
and the next week is week 1).
.LP
The text of the POSIX standard for the
.I date
utility describes
.B %U
and
.B %W
this way:
.TP
.B %U
is replaced by the week number of the year (the first Sunday as the first
day of week 1) as a decimal number
.RB ( 00 - 53 ).
All days in a new year preceding the first Sunday are considered to be
in week 0.
.TP
.B %W
is replaced by the week number of the year (the first Monday as the first
day of week 1) as a decimal number
.RB ( 00 - 53 ).
All days in a new year preceding the first Sunday are considered to be
in week 0.
(Note: this last statement is quoted verbatim from the POSIX standard.
It probably means to say ``all days in a new year preceding the first
.I Monday
are considered to be in week 0.'')
.LP
In addition, the alternate representations
.BR %Ec ,
.BR %EC ,
.BR %Ex ,
.BR %Ey ,
.BR %EY ,
.BR %Od ,
.BR %Oe ,
.BR %OH ,
.BR %OI ,
.BR %Om ,
.BR %OM ,
.BR %OS ,
.BR %Ou ,
.BR %OU ,
.BR %OV ,
.BR %Ow ,
.BR %OW ,
and
.B %Oy
are recognized, but their normal representations are used.
.SH VMS EXTENSIONS
If
.B VMS_EXT
is defined, then the following additional conversion is available:
.TP
.B %v
The date in VMS format (e.g. 20-JUN-1991).
.SH SEE ALSO
.IR time (2),
.IR ctime (3),
.IR localtime (3),
.IR tzset (3)
.SH BUGS
This version does not handle multibyte characters or pay attention to the
setting of the
.B LC_TIME
environment variable.
.LP
It is not clear what is ``appropriate'' for the C locale; the values
returned are a best guess on the author's part.
.SH CAVEATS
The pre-processor symbol
.B POSIX_SEMANTICS
is automatically defined, which forces the code to call
.IR tzset (3)
whenever the
.B TZ
environment variable has changed.
If this routine will be used in an application that will not be changing
.BR TZ ,
then there may be some performance improvements by not defining
.BR POSIX_SEMANTICS .
.SH AUTHOR
.nf
Arnold Robbins
.sp
INTERNET: [e-mail]
UUCP:     emory!skeeve!arnold
Phone:    [phone]
.fi
.SH ACKNOWLEDGEMENTS
Thanks to Geoff Clare <[e-mail]> for helping debug earlier
versions of this routine, and for advice about POSIX semantics.
Additional thanks to Arthur David Olsen <[e-mail]>
for some code improvements.