конвертировать дату и время в пользовательском формате (convert user format date and time)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
getdate — convert user format date and time
Синопсис (Synopsis)
#include <time.h>
struct tm *getdate(const char *string);
Описание (Description)
The getdate() function shall convert a string representation of a
date or time into a broken-down time.
The external variable or macro getdate_err, which has type int,
is used by getdate() to return error values. It is unspecified
whether getdate_err is a macro or an identifier declared with
external linkage, and whether or not it is a modifiable lvalue.
If a macro definition is suppressed in order to access an actual
object, or a program defines an identifier with the name
getdate_err, the behavior is undefined.
Templates are used to parse and interpret the input string. The
templates are contained in a text file identified by the
environment variable DATEMSK. The DATEMSK variable should be set
to indicate the full pathname of the file that contains the
templates. The first line in the template that matches the input
specification is used for interpretation and conversion into the
internal time format.
The following conversion specifications shall be supported:
%% Equivalent to %.
%a Abbreviated weekday name.
%A Full weekday name.
%b Abbreviated month name.
%B Full month name.
%c Locale's appropriate date and time representation.
%C Century number [00,99]; leading zeros are permitted but
not required.
%d Day of month [01,31]; the leading 0 is optional.
%D Date as %m/%d/%y.
%e Equivalent to %d.
%h Abbreviated month name.
%H Hour [00,23].
%I Hour [01,12].
%m Month number [01,12].
%M Minute [00,59].
%n Equivalent to <newline>.
%p Locale's equivalent of either AM or PM.
%r The locale's appropriate representation of time in AM and
PM notation. In the POSIX locale, this shall be
equivalent to %I:%M:%S %p.
%R Time as %H:%M.
%S Seconds [00,60]. The range goes to 60 (rather than
stopping at 59) to allow positive leap seconds to be
expressed. Since leap seconds cannot be predicted by any
algorithm, leap second data must come from some external
source.
%t Equivalent to <tab>.
%T Time as %H:%M:%S.
%w Weekday number (Sunday = [0,6]).
%x Locale's appropriate date representation.
%X Locale's appropriate time representation.
%y Year within century. When a century is not otherwise
specified, values in the range [69,99] shall refer to
years 1969 to 1999 inclusive, and values in the range
[00,68] shall refer to years 2000 to 2068 inclusive.
Note: It is expected that in a future version of this
standard the default century inferred from a
2-digit year will change. (This would apply to all
commands accepting a 2-digit year as input.)
%Y Year as "ccyy" (for example, 2001).
%Z Timezone name or no characters if no timezone exists. If
the timezone supplied by %Z is not the timezone that
getdate() expects, an invalid input specification error
shall result. The getdate() function calculates an
expected timezone based on information supplied to the
function (such as the hour, day, and month).
The match between the template and input specification performed
by getdate() shall be case-insensitive.
The month and weekday names can consist of any combination of
upper and lowercase letters. The process can request that the
input date or time specification be in a specific language by
setting the LC_TIME category (see setlocale(3p)).
Leading zeros are not necessary for the descriptors that allow
leading zeros. However, at most two digits are allowed for those
descriptors, including leading zeros. Extra white space in either
the template file or in string shall be ignored.
The results are undefined if the conversion specifications %c,
%x, and %X include unsupported conversion specifications.
The following rules apply for converting the input specification
into the internal format:
* If %Z is being scanned, then getdate() shall initialize the
broken-down time to be the current time in the scanned
timezone. Otherwise, it shall initialize the broken-down time
based on the current local time as if localtime() had been
called.
* If only the weekday is given, the day chosen shall be the
day, starting with today and moving into the future, which
first matches the named day.
* If only the month (and no year) is given, the month chosen
shall be the month, starting with the current month and
moving into the future, which first matches the named month.
The first day of the month shall be assumed if no day is
given.
* If no hour, minute, and second are given, the current hour,
minute, and second shall be assumed.
* If no date is given, the hour chosen shall be the hour,
starting with the current hour and moving into the future,
which first matches the named hour.
If a conversion specification in the DATEMSK file does not
correspond to one of the conversion specifications above, the
behavior is unspecified.
The getdate() function need not be thread-safe.
Возвращаемое значение (Return value)
Upon successful completion, getdate() shall return a pointer to a
struct tm. Otherwise, it shall return a null pointer and set
getdate_err to indicate the error.
Ошибки (Error)
The getdate() function shall fail in the following cases, setting
getdate_err to the value shown in the list below. Any changes to
errno are unspecified.
1. The DATEMSK environment variable is null or undefined.
2. The template file cannot be opened for reading.
3. Failed to get file status information.
4. The template file is not a regular file.
5. An I/O error is encountered while reading the template file.
6. Memory allocation failed (not enough memory available).
7. There is no line in the template that matches the input.
8. Invalid input specification. For example, February 31; or a
time is specified that cannot be represented in a time_t
(representing the time in seconds since the Epoch).
The following sections are informative.
Примеры (Examples)
1. The following example shows the possible contents of a
template:
%m
%A %B %d, %Y, %H:%M:%S
%A
%B
%m/%d/%y %I %p
%d,%m,%Y %H:%M
at %A the %dst of %B in %Y
run job at %I %p,%B %dnd
%A den %d. %B %Y %H.%M Uhr
2. The following are examples of valid input specifications for
the template in Example 1:
getdate("10/1/87 4 PM");
getdate("Friday");
getdate("Friday September 18, 1987, 10:30:30");
getdate("24,9,1986 10:30");
getdate("at monday the 1st of december in 1986");
getdate("run job at 3 PM, december 2nd");
If the LC_TIME category is set to a German locale that
includes freitag as a weekday name and oktober as a month
name, the following would be valid:
getdate("freitag den 10. oktober 1986 10.30 Uhr");
3. The following example shows how local date and time
specification can be defined in the template:
┌───────────────────────────┬──────────────────┐
│ Invocation │ Line in Template │
├───────────────────────────┼──────────────────┤
│getdate("11/27/86") │ %m/%d/%y │
│getdate("27.11.86") │ %d.%m.%y │
│getdate("86-11-27") │ %y-%m-%d │
│getdate("Friday 12:00:00") │ %A %H:%M:%S │
└───────────────────────────┴──────────────────┘
4. The following examples help to illustrate the above rules
assuming that the current date is Mon Sep 22 12:19:47 EDT
1986 and the LC_TIME category is set to the default C or
POSIX locale:
┌─────────────┬──────────────────┬──────────────────────────────┐
│ Input │ Line in Template │ Date │
├─────────────┼──────────────────┼──────────────────────────────┤
│Mon │ %a │ Mon Sep 22 12:19:47 EDT 1986 │
│Sun │ %a │ Sun Sep 28 12:19:47 EDT 1986 │
│Fri │ %a │ Fri Sep 26 12:19:47 EDT 1986 │
│September │ %B │ Mon Sep 1 12:19:47 EDT 1986 │
│January │ %B │ Thu Jan 1 12:19:47 EST 1987 │
│December │ %B │ Mon Dec 1 12:19:47 EST 1986 │
│Sep Mon │ %b %a │ Mon Sep 1 12:19:47 EDT 1986 │
│Jan Fri │ %b %a │ Fri Jan 2 12:19:47 EST 1987 │
│Dec Mon │ %b %a │ Mon Dec 1 12:19:47 EST 1986 │
│Jan Wed 1989 │ %b %a %Y │ Wed Jan 4 12:19:47 EST 1989 │
│Fri 9 │ %a %H │ Fri Sep 26 09:00:00 EDT 1986 │
│Feb 10:30 │ %b %H:%S │ Sun Feb 1 10:00:30 EST 1987 │
│10:30 │ %H:%M │ Tue Sep 23 10:30:00 EDT 1986 │
│13:30 │ %H:%M │ Mon Sep 22 13:30:00 EDT 1986 │
└─────────────┴──────────────────┴──────────────────────────────┘
Использование в приложениях (Application usage)
Although historical versions of getdate() did not require that
<time.h> declare the external variable getdate_err, this volume
of POSIX.1‐2017 does require it. The standard developers
encourage applications to remove declarations of getdate_err and
instead incorporate the declaration by including <time.h>.
Applications should use %Y (4-digit years) in preference to %y
(2-digit years).
Обоснование (Rationale)
In standard locales, the conversion specifications %c, %x, and %X
do not include unsupported conversion specifiers and so the text
regarding results being undefined is not a problem in that case.
Будущие направления (Future directions)
None.
Смотри также (See also)
ctime(3p), localtime(3p), setlocale(3p), strftime(3p), times(3p)
The Base Definitions volume of POSIX.1‐2017, time.h(0p)
