strftime - format date and time
size_t strftime(char *s, size_t max, const char *format
const struct tm *tm));
The strftime() function formats the broken-down time tm
according to the format specification format and places the
result in the character array s of size max.
Ordinary characters placed in the format string are copied
to s without conversion. Conversion specifiers are intro-
duced by a `%' character, and are replaced in s as follows:
%a The abbreviated weekday name according to the current
%A The full weekday name according to the current locale.
%b The abbreviated month name according to the current
%B The full month name according to the current locale.
%c The preferred date and time representation for the
%d The day of the month as a decimal number (range 01 to
%H The hour as a decimal number using a 24-hour clock
(range 00 to 23).
%I The hour as a decimal number using a 12-hour clock
(range 01 to 12).
%j The day of the year as a decimal number (range 001 to
%m The month as a decimal number (range 01 to 12).
%M The minute as a decimal number.
%p Either `am' or `pm' according to the given time value,
or the corresponding strings for the current locale.
%S The second as a decimal number.
%U The week number of the current year as a decimal
number, starting with the first Sunday as the first day
of the first week.
%W The week number of the current year as a decimal
number, starting with the first Monday as the first day
of the first week.
%w The day of the week as a decimal, Sunday being 0.
%x The preferred date representation for the current
locale without the time.
%X The preferred time representation for the current
locale without the date.
%y The year as a decimal number without a century (range
00 to 99).
%Y The year as a decimal number including the century.
%Z The time zone or name or abbreviation.
%% A literal `%' character.
The broken-down time structure tm is defined in <time.h> as
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
The members of the tm structure are:
The number of seconds after the minute, normally in the
range 0 to 59, but can be up to 61 to allow for leap
The number of minutes after the hour, in the range 0 to
The number of hours past midnight, in the range 0 to
The day of the month, in the range 1 to 31.
The number of months since January, in the range 0 to
The number of years since 1900.
The number of days since Sunday, in the range 0 to 6.
The number of days since January 1, in the range 0 to
A flag that indicates whether daylight saving time is
in effect at the time described. The value is positive
if daylight saving time is in effect, zero if it is
not, and negative if the information is not available.
The strftime() function returns the number of characters
placed in the array s, not including the terminating NULL
character, provided the string, including the terminating
NULL, fits. Otherwise, it returns 0, and the contents of
the array is undefined. (Thus at least since libc 4.4.4;
very old versions of libc, such as libc 4.4.1, would return
max if the array was too small.)
Note that the return value 0 does not necessarily indicate
an error; for example, in many locales %p yields an empty
ANSI C, SVID 3, POSIX, BSD 4.3, ISO 9899
date(1), time(2), ctime(3),