STRFTIME(3) | Library Functions Manual | STRFTIME(3)

# NAME

`strftime`, `strftime_l` — format date and time

# SYNOPSIS

`#include <time.h>`

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

size_t
`strftime_l`(char *buf, size_t maxsize, const char *format, const struct tm *timeptr, locale_t locale);

# DESCRIPTION

These functions format the information from timeptr (as described in mktime(3)) into the buffer 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 buffer. A conversion specification consists of a percent sign ‘`%`’ and one other character.

No more than maxsize characters will be placed into the array.

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

`%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 replaced by the date in the format “`%Y-%m-%d`”.
`%G`
  is replaced by the ISO 8601 week-numbering year with century as a decimal number. See also the `%V` conversion specification and the STANDARDS section for more details.
`%g`
  is replaced by the ISO 8601 week-numbering year without century as a decimal number (00-99). See also the `%V` conversion specification and the STANDARDS section for more details.
`%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). If the week containing January 1 has four or more days in the new year, then it is week 1; 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. See the STANDARDS section for more details.
`%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 name, or by the empty string if this is not determinable.
`%z`
  is replaced by the offset from the Prime Meridian in the format “`+HHMM`” or “`-HHMM`” as appropriate, with positive values representing locations east of Greenwich, or by the empty string if this is not determinable.
`%%`
  is replaced by ‘`%`’.
`%+`
  is replaced by the date and time in date(1) format.

The OpenBSD implementation always uses the C locale and ignores the global locale, the thread-specific locale, and the locale argument.

# RETURN VALUES

If the total number of resulting characters, including the terminating NUL character, is not more than maxsize, `strftime`() returns the number of characters placed in the array, not counting the terminating NUL. Otherwise, zero is returned.

# SEE ALSO

date(1), printf(1), ctime(3), getenv(3), printf(3), strptime(3), time(3), tzset(3), tzfile(5)

# STANDARDS

The `strftime`() function conforms to ISO/IEC 9899:1999 (“ISO C99”), and `strftime_l`() to IEEE Std 1003.1-2008 (“POSIX.1”), except that the ‘`E`’ and ‘`O`’ conversion modifiers are ignored by this implementation.

The ‘`%k`’, ‘`%l`’, ‘`%s`’, ‘`%v`’, and ‘`%+`’ 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.

# HISTORY

A predecessor to `strftime`(), `ptime`(), first appeared in Version 1 AT&T UNIX. The `strftime`() function has been available since 4.3BSD-Reno, and `strftime_l`() since OpenBSD 6.2.

# AUTHORS

Keith Bostic implemented the BSD version of `strftime`() in 1989.

# CAVEATS

On systems other than OpenBSD, the `LC_TIME` locale(1) category can cause erratic output; see CAVEATS in setlocale(3) for details.

# BUGS

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

Note that while this implementation of `strftime`() will always NUL terminate buf, other implementations may not do so when maxsize is not large enough to store the entire time string. The contents of buf are implementation specific in this case.

June 23, 2025 | Debian