PROLOG¶

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME¶

strftime - convert date and time to a string

SYNOPSIS¶

#include <time.h>

size_t strftime(char *restrict s, size_t maxsize,
       const char *restrict format, const struct tm *restrict timeptr);

DESCRIPTION¶

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.

RETURN VALUE¶

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.

ERRORS¶

No errors are defined.

The following sections are informative.

EXAMPLES¶

#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);
...

APPLICATION USAGE¶

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.

RATIONALE¶

None.

FUTURE DIRECTIONS¶

None.

SEE ALSO¶

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>

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 .