path: root/man3/strptime.3

.\" Copyright 1993 Mitchum DSouza <m.dsouza@mrc-apu.cam.ac.uk>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified, jmv@lucifer.dorms.spbu.ru, 1999-11-08
.\" Modified, aeb, 2000-04-07
.\" Updated from glibc docs, C. Scott Ananian, 2001-08-25
.\" Modified, aeb, 2001-08-31
.\" Modified, wharms 2001-11-12, remark on white space and example
.\"
.TH STRPTIME 3 2021-03-22 "Linux man-pages (unreleased)"
.SH NAME
strptime \- convert a string representation of time to a time tm structure
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#define _XOPEN_SOURCE" "       /* See feature_test_macros(7) */"
.B #include <time.h>
.PP
.BI "char *strptime(const char *restrict " s ", const char *restrict " format ,
.BI "               struct tm *restrict " tm );
.fi
.SH DESCRIPTION
The
.BR strptime ()
function is the converse of
.BR strftime (3);
it converts the character string pointed to by
.I s
to values which are stored in the
"broken-down time"
structure pointed to by
.IR tm ,
using the format specified by
.IR format .
.PP
The broken-down time structure
.I tm
is described in
.BR tm (3type).
.PP
The
.I format
argument
is a character string that consists of field descriptors and text characters,
reminiscent of
.BR scanf (3).
Each field descriptor consists of a
.B %
character followed by another character that specifies the replacement
for the field descriptor.
All other characters in the
.I format
string must have a matching character in the input string,
except for whitespace, which matches zero or more
whitespace characters in the input string.
There should be white\%space or other alphanumeric characters
between any two field descriptors.
.PP
The
.BR strptime ()
function processes the input string from left
to right.
Each of the three possible input elements (whitespace,
literal, or format) are handled one after the other.
If the input cannot be matched to the format string, the function stops.
The remainder of the format and input strings are not processed.
.PP
The supported input field descriptors are listed below.
In case a text string (such as the name of a day of the week or a month name)
is to be matched, the comparison is case insensitive.
In case a number is to be matched, leading zeros are
permitted but not required.
.TP
.B %%
The
.B %
character.
.TP
.BR %a " or " %A
The name of the day of the week according to the current locale,
in abbreviated form or the full name.
.TP
.BR %b " or " %B " or " %h
The month name according to the current locale,
in abbreviated form or the full name.
.TP
.B %c
The date and time representation for the current locale.
.TP
.B %C
The century number (0\(en99).
.TP
.BR %d " or " %e
The day of month (1\(en31).
.TP
.B %D
Equivalent to
.BR %m/%d/%y .
(This is the American style date, very confusing
to non-Americans, especially since
.B %d/%m/%y
is widely used in Europe.
The ISO 8601 standard format is
.BR %Y\-%m\-%d .)
.TP
.B %H
The hour (0\(en23).
.TP
.B %I
The hour on a 12-hour clock (1\(en12).
.TP
.B %j
The day number in the year (1\(en366).
.TP
.B %m
The month number (1\(en12).
.TP
.B %M
The minute (0\(en59).
.TP
.B %n
Arbitrary whitespace.
.TP
.B %p
The locale's equivalent of AM or PM.
(Note: there may be none.)
.TP
.B %r
The 12-hour clock time (using the locale's AM or PM).
In the POSIX locale equivalent to
.BR "%I:%M:%S %p" .
If
.I t_fmt_ampm
is empty in the
.B LC_TIME
part of the current locale,
then the behavior is undefined.
.TP
.B %R
Equivalent to
.BR %H:%M .
.TP
.B %S
The second (0\(en60; 60 may occur for leap seconds;
earlier also 61 was allowed).
.TP
.B %t
Arbitrary whitespace.
.TP
.B %T
Equivalent to
.BR %H:%M:%S .
.TP
.B %U
The week number with Sunday the first day of the week (0\(en53).
The first Sunday of January is the first day of week 1.
.TP
.B %w
The ordinal number of the day of the week (0\(en6), with Sunday = 0.
.TP
.B %W
The week number with Monday the first day of the week (0\(en53).
The first Monday of January is the first day of week 1.
.TP
.B %x
The date, using the locale's date format.
.TP
.B %X
The time, using the locale's time format.
.TP
.B %y
The year within century (0\(en99).
When a century is not otherwise specified, values in the range 69\(en99 refer
to years in the twentieth century (1969\(en1999); values in the
range 00\(en68 refer to years in the twenty-first century (2000\(en2068).
.TP
.B %Y
The year, including century (for example, 1991).
.PP
Some field descriptors can be modified by the E or O modifier characters
to indicate that an alternative format or specification should be used.
If the
alternative format or specification does not exist in the current locale, the
unmodified field descriptor is used.
.PP
The E modifier specifies that the input string may contain
alternative locale-dependent versions of the date and time representation:
.TP
.B %Ec
The locale's alternative date and time representation.
.TP
.B %EC
The name of the base year (period) in the locale's alternative representation.
.TP
.B %Ex
The locale's alternative date representation.
.TP
.B %EX
The locale's alternative time representation.
.TP
.B %Ey
The offset from
.B %EC
(year only) in the locale's alternative representation.
.TP
.B %EY
The full alternative year representation.
.PP
The O modifier specifies that the numerical input may be in an
alternative locale-dependent format:
.TP
.BR %Od " or " %Oe
The day of the month using the locale's alternative numeric symbols;
leading zeros are permitted but not required.
.TP
.B %OH
The hour (24-hour clock) using the locale's alternative numeric symbols.
.TP
.B %OI
The hour (12-hour clock) using the locale's alternative numeric symbols.
.TP
.B %Om
The month using the locale's alternative numeric symbols.
.TP
.B %OM
The minutes using the locale's alternative numeric symbols.
.TP
.B %OS
The seconds using the locale's alternative numeric symbols.
.TP
.B %OU
The week number of the year (Sunday as the first day of the week)
using the locale's alternative numeric symbols.
.TP
.B %Ow
The ordinal number of the day of the week (Sunday=0),
using the locale's alternative numeric symbols.
.TP
.B %OW
The week number of the year (Monday as the first day of the week)
using the locale's alternative numeric symbols.
.TP
.B %Oy
The year (offset from
.BR %C )
using the locale's alternative numeric symbols.
.SH RETURN VALUE
The return value of the function is a pointer to the first character
not processed in this function call.
In case the input string
contains more characters than required by the format string, the return
value points right after the last consumed input character.
In case the whole input string is consumed,
the return value points to the null byte at the end of the string.
If
.BR strptime ()
fails to match all
of the format string and therefore an error occurred, the function
returns NULL.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR strptime ()
T}	Thread safety	MT-Safe env locale
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2001, POSIX.1-2008, SUSv2.
.SH NOTES
In principle, this function does not initialize
.I tm
but
stores only the values specified.
This means that
.I tm
should be initialized before the call.
Details differ a bit between different UNIX systems.
The glibc implementation does not touch those fields which are not
explicitly specified, except that it recomputes the
.I tm_wday
and
.I tm_yday
field if any of the year, month, or day elements changed.
.\" .PP
.\" This function is available since libc 4.6.8.
.\" Linux libc4 and libc5 includes define the prototype unconditionally;
.\" glibc2 includes provide a prototype only when
.\" .B _XOPEN_SOURCE
.\" or
.\" .B _GNU_SOURCE
.\" are defined.
.\" .PP
.\" Before libc 5.4.13 whitespace
.\" (and the \(aqn\(aq and \(aqt\(aq specifications) was not handled,
.\" no \(aqE\(aq and \(aqO\(aq locale modifier characters were accepted,
.\" and the \(aqC\(aq specification was a synonym for the \(aqc\(aq specification.
.PP
The \(aqy\(aq (year in century) specification is taken to specify a year
.\" in the 20th century by libc4 and libc5.
.\" It is taken to be a year
in the range 1950\(en2049 by glibc 2.0.
It is taken to be a year in
1969\(en2068 since glibc 2.1.
.\" In libc4 and libc5 the code for %I is broken (fixed in glibc;
.\" %OI was fixed in glibc 2.2.4).
.SS Glibc notes
For reasons of symmetry, glibc tries to support for
.BR strptime ()
the same format characters as for
.BR strftime (3).
(In most cases, the corresponding fields are parsed, but no field in
.I tm
is changed.)
This leads to
.TP
.B %F
Equivalent to
.BR %Y\-%m\-%d ,
the ISO 8601 date format.
.TP
.B %g
The year corresponding to the ISO week number, but without the century
(0\(en99).
.TP
.B %G
The year corresponding to the ISO week number.
(For example, 1991.)
.TP
.B %u
The day of the week as a decimal number (1\(en7, where Monday = 1).
.TP
.B %V
The ISO 8601:1988 week number as a decimal number (1\(en53).
If the week (starting on Monday) containing 1 January has four or more days
in the new year, then it is considered week 1.
Otherwise, it is the last week
of the previous year, and the next week is week 1.
.TP
.B %z
An RFC-822/ISO 8601 standard timezone specification.
.TP
.B %Z
The timezone name.
.PP
Similarly, because of GNU extensions to
.BR strftime (3),
.B %k
is accepted as a synonym for
.BR %H ,
and
.B %l
should be accepted
as a synonym for
.BR %I ,
and
.B %P
is accepted as a synonym for
.BR %p .
Finally
.TP
.B %s
The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
Leap seconds are not counted unless leap second support is available.
.PP
The glibc implementation does not require whitespace between
two field descriptors.
.SH EXAMPLES
The following example demonstrates the use of
.BR strptime ()
and
.BR strftime (3).
.PP
.EX
#define _XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int
main(void)
{
    struct tm tm;
    char buf[255];

    memset(&tm, 0, sizeof(tm));
    strptime("2001\-11\-12 18:31:01", "%Y\-%m\-%d %H:%M:%S", &tm);
    strftime(buf, sizeof(buf), "%d %b %Y %H:%M", &tm);
    puts(buf);
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR time (2),
.BR getdate (3),
.BR scanf (3),
.BR setlocale (3),
.BR strftime (3)