Updated: 2021/Apr/14


STRFTIME(3)                Library Functions Manual                STRFTIME(3)

NAME
     strftime, strftime_z - format date and time

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <time.h>

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

     size_t
     strftime_z(const timezone_t tz, char * restrict buf, size_t maxsize,
         const char * restrict format, const struct tm * restrict timeptr);

DESCRIPTION
     The strftime() function formats the information from timeptr into the
     array pointed to by buf according to the string pointed to by format.

     The format string consists of zero or more conversion specifications and
     ordinary characters.  All ordinary characters are copied directly into
     the array.  A conversion specification consists of a percent sign `%' and
     one other character.

     No more than maxsize bytes will be placed into the array.  Otherwise,
     zero is returned.

     Each conversion specification is replaced by the characters as follows
     which are then copied into the array.

     %A    is replaced by the locale's full weekday name.

     %a    is replaced by the locale's abbreviated weekday name.

     %B    is replaced by the locale's full month name.

     %b or %h
           is replaced by the locale's abbreviated month name.

     %C    is replaced by the century (a year divided by 100 and truncated to
           an integer) as a decimal number [00,99].

     %c    is replaced by the locale's appropriate date and time
           representation.

     %D    is replaced by the date in the format "%m/%d/%y".

     %d    is replaced by the day of the month as a decimal number [01,31].

     %e    is replaced by the day of month as a decimal number [1,31]; single
           digits are preceded by a blank.

     %F    is equivalent to "%Y-%m-%d" (the ISO 8601 date format).

     %G    is replaced by the ISO 8601 year with century as a decimal number.
           See also the %V conversion specification

     %g    is replaced by the ISO 8601 year without century as a decimal
           number [00-99].  This is the year that includes the greater part of
           the week.  (Monday as the first day of a week).  See also the `%V'
           conversion specification.

     %H    is replaced by the hour (24-hour clock) as a decimal number
           [00,23].

     %I    is replaced by the hour (12-hour clock) as a decimal number
           [01,12].

     %j    is replaced by the day of the year as a decimal number [001,366].

     %k    is replaced by the hour (24-hour clock) as a decimal number [0,23];
           single digits are preceded by a blank.

     %l    is replaced by the hour (12-hour clock) as a decimal number [1,12];
           single digits are preceded by a blank.

     %M    is replaced by the minute as a decimal number [00,59].

     %m    is replaced by the month as a decimal number [01,12].

     %n    is replaced by a newline.

     %p    is replaced by the locale's equivalent of either "AM" or "PM".

     %R    is replaced by the time in the format "%H:%M".

     %r    is replaced by the locale's representation of 12-hour clock time
           using AM/PM notation.

     %S    is replaced by the second as a decimal number [00,60].  The range
           of seconds is [00-60] instead of [00-59] to allow for the periodic
           occurrence of leap seconds.

     %s    is replaced by the number of seconds since the Epoch (see
           ctime(3)).

     %T    is replaced by the time in the format "%H:%M:%S".

     %t    is replaced by a tab.

     %U    is replaced by the week number of the year (Sunday as the first day
           of the week) as a decimal number [00,53].

     %u    is replaced by the weekday (Monday as the first day of the week) as
           a decimal number [1,7].

     %V    is replaced by the week number of the year (Monday as the first day
           of the week) as a decimal number [01,53]. According to ISO 8601 the
           week containing January 1 is week 1 if it has four or more days in
           the new year, otherwise it is week 53 of the previous year, and the
           next week is week 1.  The year is given by the `%G' conversion
           specification.

     %v    is replaced by the date in the format "%e-%b-%Y".

     %W    is replaced by the week number of the year (Monday as the first day
           of the week) as a decimal number [00,53].

     %w    is replaced by the weekday (Sunday as the first day of the week) as
           a decimal number [0,6].

     %X    is replaced by the locale's appropriate time representation.

     %x    is replaced by the locale's appropriate date representation.

     %Y    is replaced by the year with century as a decimal number.

     %y    is replaced by the year without century as a decimal number
           [00,99].

     %Z    is replaced by the time zone abbreviation, or the empty string if
           this is not determinable.

     %z    is replaced by the offset from the Prime Meridian in the format
           +HHMM or -HHMM (ISO 8601) as appropriate, with positive values
           representing locations east of Greenwich, or by the empty string if
           this is not determinable.  The numeric time zone abbreviation -0000
           is used when the time is Universal Time but local time is
           indeterminate; by convention this is used for locations while
           uninhabited, and corresponds to a zero offset when the time zone
           abbreviation begins with "[-]".

     %+    is replaced by locale's date and time in date(1) format.  On NetBSD
           currently this only works for the C locale.

     %-*   GNU libc extension.  Do not do any padding when performing
           numerical outputs.

     %_*   GNU libc extension.  Explicitly specify space for padding.

     %0*   GNU libc extension.  Explicitly specify zero for padding.

     %%    is replaced by `%'.

     The strftime_z() function is similar to strftime(), but it also takes a
     const timezone_t tz argument.

RETURN VALUES
     If the conversion is successful, strftime returns the number of bytes
     placed into the array, not counting the terminating NUL; errno is
     unchanged if the returned value is zero.  Otherwise, errno is set to
     indicate the error, zero is returned, and the array contents are
     unspecified.

ERRORS
     This function fails if:

     [ERANGE]           The specified file offset is invalid.  The total
                        number of resulting bytes, including the terminating
                        NUL character, is more than maxsize.

     [EOVERFLOW]        The format includes an %s conversion and the number of
                        seconds since the Epoch cannot be represented in a
                        time_t.

SEE ALSO
     date(1), printf(1), ctime(3), printf(3), strptime(3), tm(3)

STANDARDS
     The There is no conversion specification for the phase of the moon.
     strftime() function conforms to ISO/IEC 9899:1999 ("ISO C99").  The `%C',
     `%D', `%e', `%g', `%G', `%h', `%k', `%l', `%n', `%r', `%R', `%s', `%t',
     `%T', `%u', `%V', and `%v' conversion specifications are extensions.

     Use of the ISO 8601 conversions may produce non-intuitive results.  Week
     01 of a year is per definition the first week which has the Thursday in
     this year, which is equivalent to the week which contains the fourth day
     of January.  In other words, the first week of a new year is the week
     which has the majority of its days in the new year.  Week 01 might also
     contain days from the previous year and the week before week 01 of a year
     is the last week (52 or 53) of the previous year even if it contains days
     from the new year.  A week starts with Monday (day 1) and ends with
     Sunday (day 7).  For example, the first week of the year 1997 lasts from
     1996-12-30 to 1997-01-05.

BUGS
     There is no conversion specification for the phase of the moon.

     A return value of zero does not necessarily indicate an error.  If the
     resulting string is an empty string, the result value is zero and it is
     not possible to distinguish between success and error.  For example, in
     many locales %p yields an empty string.  This problem can be avoided by
     inserting an extra space at the beginning of the format string and then
     skipping over it or removing it from the result.

NetBSD 9.99                     October 9, 2020                    NetBSD 9.99