Originální popis anglicky:
strftime - convert date and time to a string
Návod, kniha: POSIX Programmer's Manual
#include <time.h>
size_t strftime(char *restrict
s, size_t
maxsize ,
const char *restrict
format, const struct tm *restrict
timeptr);
The
strftime() function shall place bytes into the array pointed to by
s as controlled by the string pointed to by
format. The format
is a character string, beginning and ending in its initial shift state, if
any. The
format string consists of zero or more conversion
specifications and ordinary characters. A conversion specification consists of
a
'%' character, possibly followed by an
E or
O 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
maxsize 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
LC_TIME category of the
current locale and by the values of zero or more members of the broken-down
time structure pointed to by
timeptr, as specified in brackets in the
description. If any of the specified values are outside the normal range, the
characters stored are unspecified.
Local timezone information is used as though
strftime() called
tzset().
The following conversion specifications are supported:
- %a
- Replaced by the locale's abbreviated weekday name. [
tm_wday]
- %A
- Replaced by the locale's full weekday name. [
tm_wday]
- %b
- Replaced by the locale's abbreviated month name. [
tm_mon]
- %B
- Replaced by the locale's full month name. [
tm_mon]
- %c
- Replaced by the locale's appropriate date and time
representation. (See the Base Definitions volume of
IEEE Std 1003.1-2001, <time.h>.)
- %C
- Replaced by the year divided by 100 and truncated to an
integer, as a decimal number [00,99]. [ tm_year]
- %d
- Replaced by the day of the month as a decimal number
[01,31]. [ tm_mday]
- %D
- Equivalent to %m / %d / %y . [
tm_mon, tm_mday, tm_year]
- %e
- Replaced by the day of the month as a decimal number
[1,31]; a single digit is preceded by a space. [ tm_mday]
- %F
- Equivalent to %Y - %m - %d (the
ISO 8601:2000 standard date format). [ tm_year,
tm_mon, tm_mday]
- %g
- Replaced by the last 2 digits of the week-based year (see
below) as a decimal number [00,99]. [ tm_year, tm_wday,
tm_yday]
- %G
- Replaced by the week-based year (see below) as a decimal
number (for example, 1977). [ tm_year, tm_wday,
tm_yday]
- %h
- Equivalent to %b . [ tm_mon]
- %H
- Replaced by the hour (24-hour clock) as a decimal number
[00,23]. [ tm_hour]
- %I
- Replaced by the hour (12-hour clock) as a decimal number
[01,12]. [ tm_hour]
- %j
- Replaced by the day of the year as a decimal number
[001,366]. [ tm_yday]
- %m
- Replaced by the month as a decimal number [01,12]. [
tm_mon]
- %M
- Replaced by the minute as a decimal number [00,59]. [
tm_min]
- %n
- Replaced by a <newline>.
- %p
- Replaced by the locale's equivalent of either a.m. or p.m.
[ tm_hour]
- %r
- Replaced by the time in a.m. and p.m. notation; in
the POSIX locale this shall be equivalent to %I : %M :
%S %p . [ tm_hour, tm_min, tm_sec]
- %R
- Replaced by the time in 24-hour notation ( %H :
%M ). [ tm_hour, tm_min]
- %S
- Replaced by the second as a decimal number [00,60]. [
tm_sec]
- %t
- Replaced by a <tab>.
- %T
- Replaced by the time ( %H : %M : %S ).
[ tm_hour, tm_min, tm_sec]
- %u
- Replaced by the weekday as a decimal number [1,7], with 1
representing Monday. [ tm_wday]
- %U
- 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. [ tm_year, tm_wday,
tm_yday]
- %V
- 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. [ tm_year, tm_wday, tm_yday]
- %w
- Replaced by the weekday as a decimal number [0,6], with 0
representing Sunday. [ tm_wday]
- %W
- 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. [ tm_year, tm_wday,
tm_yday]
- %x
- Replaced by the locale's appropriate date representation.
(See the Base Definitions volume of IEEE Std 1003.1-2001,
<time.h>.)
- %X
- Replaced by the locale's appropriate time representation.
(See the Base Definitions volume of IEEE Std 1003.1-2001,
<time.h>.)
- %y
- Replaced by the last two digits of the year as a decimal
number [00,99]. [ tm_year]
- %Y
- Replaced by the year as a decimal number (for example,
1997). [ tm_year]
- %z
- Replaced by the offset from UTC in the ISO 8601:2000
standard format ( +hhmm or -hhmm ), or by no characters if
no timezone is determinable. For example, "-0430" means 4
hours 30 minutes behind UTC (west of Greenwich). If
tm_isdst is zero, the standard time offset is used. If
tm_isdst is greater than zero, the daylight savings time offset is
used. If tm_isdst is negative, no characters are returned. [
tm_isdst]
- %Z
- Replaced by the timezone name or abbreviation, or by no
bytes if no timezone information exists. [ tm_isdst]
- %%
- Replaced by % .
If a conversion specification does not correspond to any of the above, the
behavior is undefined.
If a
struct tm broken-down time structure is created by
localtime() or
localtime_r(), or modified by
mktime(),
and the value of
TZ is subsequently modified, the results of the
%Z and
%z strftime() conversion specifiers are undefined,
when
strftime() is called with such a broken-down time structure.
If a
struct tm broken-down time structure is created or modified by
gmtime() or
gmtime_r(), it is unspecified whether the result of
the
%Z and
%z conversion specifiers shall refer to UTC or the
current local timezone, when
strftime() is called with such a
broken-down time structure.
Some conversion specifiers can be modified by the
E or
O 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.
- %Ec
- Replaced by the locale's alternative appropriate date and
time representation.
- %EC
- Replaced by the name of the base year (period) in the
locale's alternative representation.
- %Ex
- Replaced by the locale's alternative date
representation.
- %EX
- Replaced by the locale's alternative time
representation.
- %Ey
- Replaced by the offset from %EC (year only) in the
locale's alternative representation.
- %EY
- Replaced by the full alternative year representation.
- %Od
- 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.
- %Oe
- Replaced by the day of the month, using the locale's
alternative numeric symbols, filled as needed with leading spaces.
- %OH
- Replaced by the hour (24-hour clock) using the locale's
alternative numeric symbols.
- %OI
- Replaced by the hour (12-hour clock) using the locale's
alternative numeric symbols.
- %Om
- Replaced by the month using the locale's alternative
numeric symbols.
- %OM
- Replaced by the minutes using the locale's alternative
numeric symbols.
- %OS
- Replaced by the seconds using the locale's alternative
numeric symbols.
- %Ou
- Replaced by the weekday as a number in the locale's
alternative representation (Monday=1).
- %OU
- Replaced by the week number of the year (Sunday as the
first day of the week, rules corresponding to %U ) using the
locale's alternative numeric symbols.
- %OV
- Replaced by the week number of the year (Monday as the
first day of the week, rules corresponding to %V ) using the
locale's alternative numeric symbols.
- %Ow
- Replaced by the number of the weekday (Sunday=0) using the
locale's alternative numeric symbols.
- %OW
- Replaced by the week number of the year (Monday as the
first day of the week) using the locale's alternative numeric
symbols.
- %Oy
- Replaced by the year (offset from %C ) using the
locale's alternative numeric symbols.
%g ,
%G , and
%V 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,
%G is
replaced by 1998 and
%V 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,
%G is replaced by
1998 and
%V is replaced by 01.
If a conversion specifier is not one of the above, the behavior is undefined.
If the total number of resulting bytes including the terminating null byte is
not more than
maxsize,
strftime() shall return the number of
bytes placed into the array pointed to by
s, not including the
terminating null byte. Otherwise, 0 shall be returned and the contents of the
array are unspecified.
No errors are defined.
The following sections are informative.
The following example first sets the locale to the user's default. The locale
information will be used in the
nl_langinfo() and
strftime()
functions. The
nl_langinfo() function returns the localized date string
which specifies how the date is laid out. The
strftime() function takes
this information and, using the
tm structure for values, places the
date and time information into
datestring.
#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);
...
The range of values for
%S is [00,60] rather than [00,59] to allow for
the occasional leap second.
Some of the conversion specifications are duplicates of others. They are
included for compatibility with
nl_cxtime() and
nl_ascxtime(),
which were published in Issue 2.
Applications should use
%Y (4-digit years) in preference to
%y
(2-digit years).
In the C locale, the
E and
O modifiers are ignored and the
replacement strings for the following specifiers are:
- %a
- The first three characters of %A .
- %A
- One of Sunday, Monday, ..., Saturday.
- %b
- The first three characters of %B .
- %B
- One of January, February, ..., December.
- %c
- Equivalent to %a %b %e %T
%Y .
- %p
- One of AM or PM.
- %r
- Equivalent to %I : %M : %S %p
.
- %x
- Equivalent to %m / %d / %y .
- %X
- Equivalent to %T .
- %Z
- Implementation-defined.
None.
None.
asctime() ,
clock() ,
ctime() ,
difftime() ,
getdate() ,
gmtime() ,
localtime() ,
mktime() ,
strptime() ,
time() ,
tzset() ,
utime() , Base
Definitions volume of IEEE Std 1003.1-2001, Section 7.3.5,
LC_TIME,
<time.h>
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
.
