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strftime(3)
NAME
strftime, wcsftime - Converts a date and time to a string or wide-character
string
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <time.h>
size_t strftime(
char *s,
size_t maxsize,
const char *format,
const struct tm *timeptr);
#include <wchar.h>
size_t wcsftime(
wchar_t *wcs,
size_t maxsize,
const wchar_t *format,
const struct tm *timeptr);
For the wcsftime() function, the XPG4 standard specifies the format
parameter as type const char * rather than const wchar_t *, as specified by
the latest version of the ISO C standard. Both type declarations are
supported.
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
strftime(), wcsftime(): ISO C, XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
s Points to the array containing the output date and time string.
maxsize Specifies the maximum number of bytes or wide characters to be
written to the array pointed to by the s or wcs parameter.
format Points to a sequence of format codes that specify the format of
the date and time to be written to the output string or wide-
character string. See the DESCRIPTION section for more
information.
timeptr Points to a type tm structure that contains broken-down time
information.
wcs Points to the wide-character array containing the output date and
time string.
DESCRIPTION
The strftime() function places characters into the array pointed to by the
s parameter as controlled by the string pointed to by the format parameter.
The string pointed to by the format parameter is a sequence of characters.
Depending on the locale setting, the characters may be single-byte or
multibyte characters.
Local time zone information is used as though the strftime() function
called the tzset() function. Time information used in this subroutine is
fetched from space containing type tm structure data, which is defined in
the time.h include file. The type tm structure must contain the time
information used by this subroutine to construct the time and date string.
The format string consists of characters that represent zero or more
conversion specifications and ordinary characters that represent the date
and time values and null string terminator. A conversion specification
consists of a % (percent sign) character followed by a character that
determines how the conversion specification constructs the formatted
string.
All ordinary characters (including the terminating null character) are
copied unchanged into the s array. When copying between objects that
overlap, behavior of this function is undefined. No more than the number of
bytes specified by the maxsize parameter are written to the array
(including the terminating null byte). Each conversion specification is
replaced by the appropriate characters as described in the following list.
The appropriate characters are determined by the LC_TIME category of the
current locale and by values specified by the type tm structure pointed to
by the timeptr parameter.
The wcsftime() function formats the data in the timeptr parameter according
to the specification contained in the format parameter and places the
resulting wide-character string into the wcs parameter. No more than the
number of wide characters specified by the maxsize parameter are written to
the array (including the terminating null wide character).
The wcsftime() function behaves as if the character string generated by the
strftime() function is passed to the mbstowcs() function as the character-
string parameter and the mbstowcs function places the result in the wcs
parameter of the wcsftime() function, up to the limit of wide-character
codes specified by the maxsize parameter. Only the wchar.h include file
needs to be specified for the wcsftime() function.
These functions use the local timezone information.
The format parameter consists of a series of zero or more conversion
specifiers and ordinary characters. Each conversion specification starts
with a % (percent sign) and ends with a conversion-code character that
specifies the conversion format. The strftime() function and the version of
the wcsftime() function that conforms to XPG4 replace the conversion
specification with the appropriately formatted date or time value.
Ordinary characters are written to the output buffer unchanged.
[ISO C] For wcsftime(), each conversion specification starts with a %
(percent sign) and ends with a conversion-code wide character that
specifies the conversion format. The function replaces the conversion
specification with the appropriately formatted date or time value.
Ordinary wide characters in the format are written to the output buffer
unchanged.
The format parameter has the following syntax:
[ordinary-text] [%[[-|0]width] [.precision] format-code \
[ordinary-text]]...
ordinary-text
Text that is copied to the output parameter with no changes.
width
[Digital] A decimal digit string that specifies the minimum field
width. If the width of the item equals or exceeds the minimum field
width, the minimum is ignored. If the width of the item is less than
the minimum field width, the function justifies and pads the item. The
optional - (minus sign) or 0 (zero digit) control the justification and
padding as follows:
None
Item is right justified and spaces are added to the beginning of
the item to fill the minimum width.
Minus sign
Item is left justified and spaces are added to the end of the item
to fill the minimum width.
Zero digit
Item is right justified and zeros are added to the beginning of the
item to fill the minimum width.
precision
[Digital] A decimal string that specifies the minimum number of digits
to appear for the d, H, I, j, m, M, o, S, U, w, W, y, and Y conversion
formats and the maximum number of characters to used from the a, A, b,
B, c, D, E, h, n, N, p, r, t, T, x, X, Z, and % conversion formats.
If no field width or precision is specified for the d, H, I, m, M, S,
U, W, or y conversion character, a default precision of .2 is used. If
no field width or precision is specified for the j conversion
character, a default precision of 3 is used.
format-code
A single character that specifies the date and time conversion to
perform. The following list describes the conversion code characters:
a The short day of the week is output as a string as defined for the
current locale (Mon, for example).
A The long day of the week is output as defined for the current
locale (Monday, for example).
b (or h)
The short month is output as a string as defined for the current
locale (Jan, for example).
B The long month is output as a string as defined for the current
locale (January, for example).
c The date and time is output with the default date and time as
defined for the current locale.
C The century is output as a decimal number in the range 00 to 99.
d The day of the month is output as a number between 01 and 31.
D The format is fixed to return %m/%d/%y. (For example, 20 Jun 1990
will return 06/20/90.)
e The day of the month is output as a number between 1 and 31 in a
2-digit field with leading space fill.
Ec Specifies the locale's alternative appropriate date and time
representation.
EC Specifies the name of the base year (period) in the locale's
alternative representation.
Ex Specifies the locale's alternative date representation.
EX Specifies the locale's alternative time representation.
Ey Specifies the offset from %EC (year only) in the locale's
alternative representation.
EY Specifies the full alternative year representation.
H The hour of the day is output as a number between 00 and 23.
h Same as b.
I The hour of the day is output as a number between 01 and 12.
j The Julian day of the year is output as a number between 001 and
366.
m The month of the year is output as a number between 01 and 12.
M The minute is output as a number between 00 and 59.
n Only a newline character is output.
N The locale-dependent Emperor/Era name is output.
o The locale-dependent Emperor/Era year is output.
Od Specifies the day of the month using the locale's alternative
numeric symbols.
Oe Specifies the day of the month using the locale's alternative
numeric symbols.
OH Specifies the hour (24-hour clock) using the locale's alternative
numeric symbols.
OI Specifies the hour (12-hour clock) using the locale's alternative
numeric symbols.
Om Specifies the month using the locale's alternative numeric
symbols.
OM Specifies the minutes using the locale's alternative numeric
symbols.
OS Specifies the seconds using the locale's alternative numeric
symbols.
Ou Specifies the weekday as a number in the locale's alternative
representation (Monday=1).
OU Specifies the week number of the year (Sunday as the first day of
the week) using the locale's alternative numeric symbols.
OV Specifies 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 Specifies the week day as a number in the locale's alternative
representation (Sunday = 0).
OW Specifies the week number of the year (Monday as the first day of
the week) using the locale's alternative numeric symbols.
Oy Specifies the year (offset from %C) in alternative representation.
p The AM or PM indicator is output as a string specified for the
current locale.
r The time in AM/PM notation is output, according to British/US
conventions (%I:%M:%S [AM|PM]).
R The time in hours (24-hour clock) and minutes (%H:%M).
S The second is output as a number between 00 and 61.
t Only a tab character is output.
T The time is output as %H:%M:%S.
u Specifies the weekday as a decimal number [1,7], with 1
representing Monday.
U The week number of the year (Sunday as the first day of the week).
Output format is a decimal number between 0 and 53.
V The week number of the year (Monday as the first day of the week).
Output format is a decimal number between 1 and 53. If the week
containing January 1 has four or more days in the new year, then
it is considered week 1; otherwise, it is week 53 or the previous
year, and the next week is week 1.
w The day of the week is output as a number between 0 (Sunday) and
6.
W The week number of the year (Monday as the first day of the week).
Output format is a decimal number between 0 and 53.
x The short date is output in the format specified for the current
locale.
X The time is output in the format specified for the current locale.
y The year is output as a number (without the century) between 00
and 99.
Y The year is output as a number (with the century) between 0000 and
9999.
Z The (standard time or daylight saving time) time zone name or
abbreviation is output as a string from the environment variable
TZ (CDT, for example). If no time zone information exists, no
characters are output.
% The % (percent) character is output.
When a conversion-code character or conversion-code wide character is not
from the preceding list, the behavior of these functions is undefined.
EXAMPLES
The following example uses strftime() to display the current date:
#include <time.h>
#include <locale.h>
#include <stdio.h>
#define SLENGTH 80
main()
{
char nowstr[SLENGTH];
time_t nowbin;
const struct tm *nowstruct;
(void)setlocale(LC_ALL, "");
if (time(&nowbin) == (time_t) - 1)
printf("Could not get time of day from time()\n");
nowstruct = localtime(&nowbin);
if (strftime(nowstr, SLENGTH, "%A %x", nowstruct) == (size_t) 0)
printf("Could not get string from strftime()\n");
printf("Today's date is %s\n", nowstr);
}
NOTES
The %S seconds field can contain a value up to 61 seconds rather than up to
59 seconds to allow leap seconds that are sometimes added to years to keep
clocks in correspondence with the solar year.
RETURN VALUES
The strftime() function returns the number of bytes written into the array
pointed to by the s parameter when the total number of resulting bytes,
including the terminating null byte, is not more than the value of the
maxsize parameter. The returned value does not count the terminating null
byte in the number of bytes written into the array. Otherwise, a value of
0 cast to size_t is returned and the contents of the array are undefined.
The wcsftime() function returns the number of wide characters written into
the array pointed to by the wcs parameter when the total number of
resulting wide characters, including the terminating null wide character,
is not more than the value of the maxsize parameter. The returned value
does not count the terminating null wide character in the number of wide
characters written into the array. Otherwise, a value of 0 cast to size_t
is returned and the contents of the array are undefined.
RELATED INFORMATION
Functions: ctime(3), mbstowcs(3), setlocale(3), strptime(3)
Standards: standards(5)