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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "STRFTIME" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" strftime 

.SH NAME

strftime \- convert date and time to a string

.SH SYNOPSIS

.LP

\fB#include <time.h>

.br

.sp

size_t strftime(char *restrict\fP \fIs\fP\fB, size_t\fP \fImaxsize\fP\fB,

.br

\ \ \ \ \ \  const char *restrict\fP \fIformat\fP\fB, const struct

tm *restrict\fP

\fItimeptr\fP\fB);

.br

\fP

.SH DESCRIPTION

.LP

The \fIstrftime\fP() function shall place bytes into the array pointed

to by \fIs\fP as controlled by the string pointed to by

\fIformat\fP. The format is a character string, beginning and ending

in its initial shift state, if any. The \fIformat\fP string

consists of zero or more conversion specifications and ordinary characters.

A conversion specification consists of a \fB'%'\fP

character, possibly followed by an \fBE\fP or \fBO\fP modifier, and

a terminating conversion specifier character that

determines the conversion specification's behavior. All ordinary characters

(including the terminating null byte) are copied

unchanged into the array. If copying takes place between objects that

overlap, the behavior is undefined. No more than

\fImaxsize\fP bytes are placed into the array. Each conversion specifier

is replaced by appropriate characters as described in the

following list. The appropriate characters are determined using the

\fILC_TIME\fP category of the current locale and by the values

of zero or more members of the broken-down time structure pointed

to by \fItimeptr\fP, as specified in brackets in the

description. If any of the specified values are outside the normal

range, the characters stored are unspecified.

.LP

Local timezone information is used as though \fIstrftime\fP() called

\fItzset\fP(). 

.LP

The following conversion specifications are supported:

.TP 7

\fB%a\fP

Replaced by the locale's abbreviated weekday name. [ \fItm_wday\fP]

.TP 7

\fB%A\fP

Replaced by the locale's full weekday name. [ \fItm_wday\fP]

.TP 7

\fB%b\fP

Replaced by the locale's abbreviated month name. [ \fItm_mon\fP]

.TP 7

\fB%B\fP

Replaced by the locale's full month name. [ \fItm_mon\fP]

.TP 7

\fB%c\fP

Replaced by the locale's appropriate date and time representation.

(See the Base Definitions volume of

IEEE\ Std\ 1003.1-2001, \fI<time.h>\fP.)

.TP 7

\fB%C\fP

Replaced by the year divided by 100 and truncated to an integer, as

a decimal number [00,99]. [ \fItm_year\fP]

.TP 7

\fB%d\fP

Replaced by the day of the month as a decimal number [01,31]. [ \fItm_mday\fP]

.TP 7

\fB%D\fP

Equivalent to \fB%m\fP / \fB%d\fP / \fB%y\fP . [ \fItm_mon\fP, \fItm_mday\fP,

\fItm_year\fP]

.TP 7

\fB%e\fP

Replaced by the day of the month as a decimal number [1,31]; a single

digit is preceded by a space. [ \fItm_mday\fP]

.TP 7

\fB%F\fP

Equivalent to \fB%Y\fP - \fB%m\fP - \fB%d\fP (the ISO\ 8601:2000 standard

date format). [ \fItm_year\fP,

\fItm_mon\fP, \fItm_mday\fP]

.TP 7

\fB%g\fP

Replaced by the last 2 digits of the week-based year (see below) as

a decimal number [00,99]. [ \fItm_year\fP, \fItm_wday\fP,

\fItm_yday\fP]

.TP 7

\fB%G\fP

Replaced by the week-based year (see below) as a decimal number (for

example, 1977). [ \fItm_year\fP, \fItm_wday\fP,

\fItm_yday\fP]

.TP 7

\fB%h\fP

Equivalent to \fB%b\fP . [ \fItm_mon\fP]

.TP 7

\fB%H\fP

Replaced by the hour (24-hour clock) as a decimal number [00,23].

[ \fItm_hour\fP]

.TP 7

\fB%I\fP

Replaced by the hour (12-hour clock) as a decimal number [01,12].

[ \fItm_hour\fP]

.TP 7

\fB%j\fP

Replaced by the day of the year as a decimal number [001,366]. [ \fItm_yday\fP]

.TP 7

\fB%m\fP

Replaced by the month as a decimal number [01,12]. [ \fItm_mon\fP]

.TP 7

\fB%M\fP

Replaced by the minute as a decimal number [00,59]. [ \fItm_min\fP]

.TP 7

\fB%n\fP

Replaced by a <newline>.

.TP 7

\fB%p\fP

Replaced by the locale's equivalent of either a.m. or p.m. [ \fItm_hour\fP]

.TP 7

\fB%r\fP

Replaced by the time in a.m. and p.m. notation;   \ in the POSIX locale

this shall be equivalent to \fB%I\fP :

\fB%M\fP : \fB%S\fP \fB%p\fP .  [ \fItm_hour\fP,

\fItm_min\fP, \fItm_sec\fP]

.TP 7

\fB%R\fP

Replaced by the time in 24-hour notation ( \fB%H\fP : \fB%M\fP ).

[ \fItm_hour\fP, \fItm_min\fP]

.TP 7

\fB%S\fP

Replaced by the second as a decimal number [00,60]. [ \fItm_sec\fP]

.TP 7

\fB%t\fP

Replaced by a <tab>.

.TP 7

\fB%T\fP

Replaced by the time ( \fB%H\fP : \fB%M\fP : \fB%S\fP ). [ \fItm_hour\fP,

\fItm_min\fP, \fItm_sec\fP]

.TP 7

\fB%u\fP

Replaced by the weekday as a decimal number [1,7], with 1 representing

Monday. [ \fItm_wday\fP]

.TP 7

\fB%U\fP

Replaced by the week number of the year as a decimal number [00,53].

The first Sunday of January is the first day of week 1;

days in the new year before this are in week 0. [ \fItm_year\fP, \fItm_wday\fP,

\fItm_yday\fP]

.TP 7

\fB%V\fP

Replaced by the week number of the year (Monday as the first day of

the week) as a decimal number [01,53]. If the week

containing 1 January has four or more days in the new year, then it

is considered week 1. Otherwise, it is the last week of the

previous year, and the next week is week 1. Both January 4th and the

first Thursday of January are always in week 1. [

\fItm_year\fP, \fItm_wday\fP, \fItm_yday\fP]

.TP 7

\fB%w\fP

Replaced by the weekday as a decimal number [0,6], with 0 representing

Sunday. [ \fItm_wday\fP]

.TP 7

\fB%W\fP

Replaced by the week number of the year as a decimal number [00,53].

The first Monday of January is the first day of week 1;

days in the new year before this are in week 0. [ \fItm_year\fP, \fItm_wday\fP,

\fItm_yday\fP]

.TP 7

\fB%x\fP

Replaced by the locale's appropriate date representation. (See the

Base Definitions volume of IEEE\ Std\ 1003.1-2001,

\fI<time.h>\fP.)

.TP 7

\fB%X\fP

Replaced by the locale's appropriate time representation. (See the

Base Definitions volume of IEEE\ Std\ 1003.1-2001,

\fI<time.h>\fP.)

.TP 7

\fB%y\fP

Replaced by the last two digits of the year as a decimal number [00,99].

[ \fItm_year\fP]

.TP 7

\fB%Y\fP

Replaced by the year as a decimal number (for example, 1997). [ \fItm_year\fP]

.TP 7

\fB%z\fP

Replaced by the offset from UTC in the ISO\ 8601:2000 standard format

( \fB+hhmm\fP or \fB-hhmm\fP ), or by no

characters if no timezone is determinable. For example, \fB"-0430"\fP

means 4 hours 30 minutes behind UTC (west of Greenwich).

\ If \fItm_isdst\fP is zero, the standard time offset is used. If

\fItm_isdst\fP is greater than zero, the daylight savings

time offset is used. If \fItm_isdst\fP is negative, no characters

are returned.  [ \fItm_isdst\fP]

.TP 7

\fB%Z\fP

Replaced by the timezone name or abbreviation, or by no bytes if no

timezone information exists. [ \fItm_isdst\fP]

.TP 7

\fB%%\fP

Replaced by \fB%\fP .

.sp

.LP

If a conversion specification does not correspond to any of the above,

the behavior is undefined.

.LP

If

a \fBstruct tm\fP broken-down time structure is created by \fIlocaltime\fP()

or \fIlocaltime_r\fP(), or modified by \fImktime\fP(), and the value

of \fITZ\fP is subsequently modified, the results of the \fB%Z\fP

and \fB%z\fP \fIstrftime\fP() conversion specifiers are undefined,

when \fIstrftime\fP() is called with such a broken-down

time structure.

.LP

If a \fBstruct tm\fP broken-down time structure is created or modified

by \fIgmtime\fP() or \fIgmtime_r\fP(), it is unspecified

whether the result of the \fB%Z\fP and \fB%z\fP conversion specifiers

shall refer to UTC or the current local timezone, when

\fIstrftime\fP() is called with such a broken-down time structure.

.SS Modified Conversion Specifiers

.LP

Some conversion specifiers can be modified by the \fBE\fP or \fBO\fP

modifier characters to indicate that an alternative

format or specification should be used rather than the one normally

used by the unmodified conversion specifier. If the alternative

format or specification does not exist for the current locale (see

ERA in the Base Definitions volume of

IEEE\ Std\ 1003.1-2001, Section 7.3.5, LC_TIME), the behavior shall

be as if the unmodified conversion specification were used.

.TP 7

\fB%Ec\fP

Replaced by the locale's alternative appropriate date and time representation.

.TP 7

\fB%EC\fP

Replaced by the name of the base year (period) in the locale's alternative

representation.

.TP 7

\fB%Ex\fP

Replaced by the locale's alternative date representation.

.TP 7

\fB%EX\fP

Replaced by the locale's alternative time representation.

.TP 7

\fB%Ey\fP

Replaced by the offset from \fB%EC\fP (year only) in the locale's

alternative representation.

.TP 7

\fB%EY\fP

Replaced by the full alternative year representation.

.TP 7

\fB%Od\fP

Replaced by the day of the month, using the locale's alternative numeric

symbols, filled as needed with leading zeros if there

is any alternative symbol for zero; otherwise, with leading spaces.

.TP 7

\fB%Oe\fP

Replaced by the day of the month, using the locale's alternative numeric

symbols, filled as needed with leading spaces.

.TP 7

\fB%OH\fP

Replaced by the hour (24-hour clock) using the locale's alternative

numeric symbols.

.TP 7

\fB%OI\fP

Replaced by the hour (12-hour clock) using the locale's alternative

numeric symbols.

.TP 7

\fB%Om\fP

Replaced by the month using the locale's alternative numeric symbols.

.TP 7

\fB%OM\fP

Replaced by the minutes using the locale's alternative numeric symbols.

.TP 7

\fB%OS\fP

Replaced by the seconds using the locale's alternative numeric symbols.

.TP 7

\fB%Ou\fP

Replaced by the weekday as a number in the locale's alternative representation

(Monday=1).

.TP 7

\fB%OU\fP

Replaced by the week number of the year (Sunday as the first day of

the week, rules corresponding to \fB%U\fP ) using the

locale's alternative numeric symbols.

.TP 7

\fB%OV\fP

Replaced by the week number of the year (Monday as the first day of

the week, rules corresponding to \fB%V\fP ) using the

locale's alternative numeric symbols.

.TP 7

\fB%Ow\fP

Replaced by the number of the weekday (Sunday=0) using the locale's

alternative numeric symbols.

.TP 7

\fB%OW\fP

Replaced by the week number of the year (Monday as the first day of

the week) using the locale's alternative numeric

symbols.

.TP 7

\fB%Oy\fP

Replaced by the year (offset from \fB%C\fP ) using the locale's alternative

numeric symbols.

.sp

.LP

\fB%g\fP , \fB%G\fP , and \fB%V\fP give values according to the ISO\ 8601:2000

standard week-based year. In this

system, weeks begin on a Monday and week 1 of the year is the week

that includes January 4th, which is also the week that includes

the first Thursday of the year, and is also the first week that contains

at least four days in the year. If the first Monday of

January is the 2nd, 3rd, or 4th, the preceding days are part of the

last week of the preceding year; thus, for Saturday 2nd January

1999, \fB%G\fP is replaced by 1998 and \fB%V\fP is replaced by 53.

If December 29th, 30th, or 31st is a Monday, it and any

following days are part of week 1 of the following year. Thus, for

Tuesday 30th December 1997, \fB%G\fP is replaced by 1998 and

\fB%V\fP is replaced by 01.

.LP

If a conversion specifier is not one of the above, the behavior is

undefined.

.SH RETURN VALUE

.LP

If the total number of resulting bytes including the terminating null

byte is not more than \fImaxsize\fP, \fIstrftime\fP()

shall return the number of bytes placed into the array pointed to

by \fIs\fP, not including the terminating null byte. Otherwise,

0 shall be returned and the contents of the array are unspecified.

.SH ERRORS

.LP

No errors are defined.

.LP

\fIThe following sections are informative.\fP

.SH EXAMPLES

.SS Getting a Localized Date String

.LP

The following example first sets the locale to the user's default.

The locale information will be used in the \fInl_langinfo\fP() and

\fIstrftime\fP() functions. The \fInl_langinfo\fP() function returns

the localized date string which specifies how the date is

laid out. The \fIstrftime\fP() function takes this information and,

using the \fBtm\fP structure for values, places the date and

time information into \fIdatestring\fP.

.sp

.RS

.nf

\fB#include <time.h>

#include <locale.h>

#include <langinfo.h>

\&...

struct tm *tm;

char datestring[256];

\&...

setlocale (LC_ALL, "");

\&...

strftime (datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);

\&...

\fP

.fi

.RE

.SH APPLICATION USAGE

.LP

The range of values for \fB%S\fP is [00,60] rather than [00,59] to

allow for the occasional leap second.

.LP

Some of the conversion specifications are duplicates of others. They

are included for compatibility with \fInl_cxtime\fP() and

\fInl_ascxtime\fP(), which were published in Issue 2.

.LP

Applications should use \fB%Y\fP (4-digit years) in preference to

\fB%y\fP (2-digit years).

.LP

In the C locale, the \fBE\fP and \fBO\fP modifiers are ignored and

the replacement strings for the following specifiers

are:

.TP 7

\fB%a\fP

The first three characters of \fB%A\fP .

.TP 7

\fB%A\fP

One of Sunday, Monday, ..., Saturday.

.TP 7

\fB%b\fP

The first three characters of \fB%B\fP .

.TP 7

\fB%B\fP

One of January, February, ..., December.

.TP 7

\fB%c\fP

Equivalent to \fB%a\fP \fB%b\fP \fB%e\fP \fB%T\fP \fB%Y\fP .

.TP 7

\fB%p\fP

One of AM or PM.

.TP 7

\fB%r\fP

Equivalent to \fB%I\fP : \fB%M\fP : \fB%S\fP \fB%p\fP .

.TP 7

\fB%x\fP

Equivalent to \fB%m\fP / \fB%d\fP / \fB%y\fP .

.TP 7

\fB%X\fP

Equivalent to \fB%T\fP .

.TP 7

\fB%Z\fP

Implementation-defined.

.sp

.SH RATIONALE

.LP

None.

.SH FUTURE DIRECTIONS

.LP

None.

.SH SEE ALSO

.LP

\fIasctime\fP() , \fIclock\fP() , \fIctime\fP()

, \fIdifftime\fP() , \fIgetdate\fP() , \fIgmtime\fP() , \fIlocaltime\fP()

, \fImktime\fP() ,

\fIstrptime\fP() , \fItime\fP() , \fItzset\fP() ,

\fIutime\fP() , Base Definitions volume of IEEE\ Std\ 1003.1-2001,

Section 7.3.5, LC_TIME, \fI<time.h>\fP

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group. In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.opengroup.org/unix/online.html .