proc.5: Note kernel version for /proc/PID/smaps VmFlags "wf" flag

[thirdparty/man-pages.git] / man3 / strftime.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\"     GNU texinfo documentation on glibc date/time functions.
.\" Modified Sat Jul 24 18:03:44 1993 by Rik Faith (faith@cs.unc.edu)
.\" Applied fix by Wolfgang Franke, aeb, 961011
.\" Corrected return value, aeb, 970307
.\" Added Single UNIX Spec conversions and %z, aeb/esr, 990329.
.\" 2005-11-22 mtk, added Glibc Notes covering optional 'flag' and
.\"           'width' components of conversion specifications.
.\"
.TH STRFTIME 3  2020-04-11 "GNU" "Linux Programmer's Manual"
.SH NAME
strftime \- format date and time
.SH SYNOPSIS
.nf
.B #include <time.h>
.PP
.BI "size_t strftime(char *" s ", size_t " max ", const char *" format ,
.BI "                const struct tm *" tm );
.fi
.SH DESCRIPTION
The
.BR strftime ()
function formats the broken-down time
.I tm
according to the format specification
.I format
and places the
result in the character array
.I s
of size
.IR max .
The broken-down time structure
.I tm
is defined in
.IR <time.h> .
See also
.BR ctime (3).
.\" FIXME . POSIX says: Local timezone information is used as though
.\" strftime() called tzset().  But this doesn't appear to be the case
.PP
The format specification is a null-terminated string and may contain
special character sequences called
.IR "conversion specifications",
each of which is introduced by a \(aq%\(aq character and terminated by
some other character known as a
.IR "conversion specifier character".
All other character sequences are
.IR "ordinary character sequences".
.PP
The characters of ordinary character sequences (including the null byte)
are copied verbatim from
.I format
to
.IR s .
However, the characters
of conversion specifications are replaced as shown in the list below.
In this list, the field(s) employed from the
.I tm
structure are also shown.
.TP
.B %a
The abbreviated name of the day of the week according to the current locale.
(Calculated from
.IR tm_wday .)
(The specific names used in the current locale can be obtained by calling
.BR nl_langinfo (3)
with
.BR ABDAY_ { 1 \(en 7 }
as an argument.)
.TP
.B %A
The full name of the day of the week according to the current locale.
(Calculated from
.IR tm_wday .)
(The specific names used in the current locale can be obtained by calling
.BR nl_langinfo (3)
with
.BR DAY_ { 1 \(en 7 }
as an argument.)
.TP
.B %b
The abbreviated month name according to the current locale.
(Calculated from
.IR tm_mon .)
(The specific names used in the current locale can be obtained by calling
.BR nl_langinfo (3)
with
.BR ABMON_ { 1 \(en 12 }
as an argument.)
.TP
.B %B
The full month name according to the current locale.
(Calculated from
.IR tm_mon .)
(The specific names used in the current locale can be obtained by calling
.BR nl_langinfo (3)
with
.BR MON_ { 1 \(en 12 }
as an argument.)
.TP
.B %c
The preferred date and time representation for the current locale.
(The specific format used in the current locale can be obtained by calling
.BR nl_langinfo (3)
with
.B D_T_FMT
as an argument for the
.B %c
conversion specification, and with
.B ERA_D_T_FMT
for the
.B %Ec
conversion specification.)
(In the POSIX locale this is equivalent to
.BR "%a %b %e %H:%M:%S %Y" .)
.TP
.B %C
The century number (year/100) as a 2-digit integer. (SU)
(The
.B %EC
conversion specification corresponds to the name of the era.)
(Calculated from
.IR tm_year .)
.TP
.B %d
The day of the month as a decimal number (range 01 to 31).
(Calculated from
.IR tm_mday .)
.TP
.B %D
Equivalent to
.BR %m/%d/%y .
(Yecch\(emfor Americans only.
Americans should note that in other countries
.B %d/%m/%y
is rather common.
This means that in international context this format is
ambiguous and should not be used.) (SU)
.TP
.B %e
Like
.BR %d ,
the day of the month as a decimal number, but a leading
zero is replaced by a space. (SU)
(Calculated from
.IR tm_mday .)
.TP
.B %E
Modifier: use alternative ("era-based") format, see below. (SU)
.TP
.B %F
Equivalent to
.B %Y-%m-%d
(the ISO\ 8601 date format). (C99)
.TP
.B %G
The ISO\ 8601 week-based year (see NOTES) with century as a decimal number.
The 4-digit year corresponding to the ISO week number (see
.BR %V ).
This has the same format and value as
.BR %Y ,
except that if the ISO week number belongs to the previous or next year,
that year is used instead. (TZ)
(Calculated from
.IR tm_year ,
.IR tm_yday ,
and
.IR tm_wday .)
.TP
.B %g
Like
.BR %G ,
but without century, that is, with a 2-digit year (00\(en99). (TZ)
(Calculated from
.IR tm_year ,
.IR tm_yday ,
and
.IR tm_wday .)
.TP
.B %h
Equivalent to
.BR %b .
(SU)
.TP
.B %H
The hour as a decimal number using a 24-hour clock (range 00 to 23).
(Calculated from
.IR tm_hour .)
.TP
.B %I
The hour as a decimal number using a 12-hour clock (range 01 to 12).
(Calculated from
.IR tm_hour .)
.TP
.B %j
The day of the year as a decimal number (range 001 to 366).
(Calculated from
.IR tm_yday .)
.TP
.B %k
The hour (24-hour clock) as a decimal number (range 0 to 23);
single digits are preceded by a blank.
(See also
.BR %H .)
(Calculated from
.IR tm_hour .)
(TZ)
.TP
.B %l
The hour (12-hour clock) as a decimal number (range 1 to 12);
single digits are preceded by a blank.
(See also
.BR %I .)
(Calculated from
.IR tm_hour .)
(TZ)
.TP
.B %m
The month as a decimal number (range 01 to 12).
(Calculated from
.IR tm_mon .)
.TP
.B %M
The minute as a decimal number (range 00 to 59).
(Calculated from
.IR tm_min .)
.TP
.B %n
A newline character. (SU)
.TP
.B %O
Modifier: use alternative numeric symbols, see below. (SU)
.TP
.B %p
Either "AM" or "PM" according to the given time value, or the
corresponding strings for the current locale.