Ubuntu Manpage: strptime - convert a string representation of time to a time tm structure

NAME

       strptime - convert a string representation of time to a time tm structure

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
       #include <time.h>

       char *strptime(const char *restrict s, const char *restrict format,
                      struct tm *restrict tm);

DESCRIPTION

The strptime() function is the converse of strftime(3); it converts the character string
pointed to by s to values which are stored in the "broken-down time" structure pointed to
by tm, using the format specified by format.

The broken-down time structure tm is described in tm(3type).

The format argument is a character string that consists of field descriptors and text
characters, reminiscent of scanf(3). Each field descriptor consists of a % character
followed by another character that specifies the replacement for the field descriptor.
All other characters in the 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 whitespace or other alphanumeric characters between any two
field descriptors.

The 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.

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.

%% The % character.

%a or %A
The name of the day of the week according to the current locale, in abbreviated
form or the full name.

%b or %B or %h
The month name according to the current locale, in abbreviated form or the full
name.

%c The date and time representation for the current locale.

%C The century number (0–99).

%d or %e
The day of month (1–31).

%D Equivalent to %m/%d/%y. (This is the American style date, very confusing to non-
Americans, especially since %d/%m/%y is widely used in Europe. The ISO 8601
standard format is %Y-%m-%d.)

%H The hour (0–23).

%I The hour on a 12-hour clock (1–12).

%j The day number in the year (1–366).

%m The month number (1–12).

%M The minute (0–59).

%n Arbitrary whitespace.

%p The locale's equivalent of AM or PM. (Note: there may be none.)

%r The 12-hour clock time (using the locale's AM or PM). In the POSIX locale
equivalent to %I:%M:%S %p. If t_fmt_ampm is empty in the LC_TIME part of the
current locale, then the behavior is undefined.

%R Equivalent to %H:%M.

%S The second (0–60; 60 may occur for leap seconds; earlier also 61 was allowed).

%t Arbitrary whitespace.

%T Equivalent to %H:%M:%S.

%U The week number with Sunday the first day of the week (0–53). The first Sunday of
January is the first day of week 1.

%w The ordinal number of the day of the week (0–6), with Sunday = 0.

%W The week number with Monday the first day of the week (0–53). The first Monday of
January is the first day of week 1.

%x The date, using the locale's date format.

%X The time, using the locale's time format.

%y The year within century (0–99). When a century is not otherwise specified, values
in the range 69–99 refer to years in the twentieth century (1969–1999); values in
the range 00–68 refer to years in the twenty-first century (2000–2068).

%Y The year, including century (for example, 1991).

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.

The E modifier specifies that the input string may contain alternative locale-dependent
versions of the date and time representation:

%Ec The locale's alternative date and time representation.

%EC The name of the base year (period) in the locale's alternative representation.

%Ex The locale's alternative date representation.

%EX The locale's alternative time representation.

%Ey The offset from %EC (year only) in the locale's alternative representation.

%EY The full alternative year representation.

The O modifier specifies that the numerical input may be in an alternative locale-
dependent format:

%Od or %Oe
The day of the month using the locale's alternative numeric symbols; leading zeros
are permitted but not required.

%OH The hour (24-hour clock) using the locale's alternative numeric symbols.

%OI The hour (12-hour clock) using the locale's alternative numeric symbols.

%Om The month using the locale's alternative numeric symbols.

%OM The minutes using the locale's alternative numeric symbols.

%OS The seconds using the locale's alternative numeric symbols.

%OU The week number of the year (Sunday as the first day of the week) using the
locale's alternative numeric symbols.

%Ow The ordinal number of the day of the week (Sunday=0), using the locale's
alternative numeric symbols.

%OW The week number of the year (Monday as the first day of the week) using the
locale's alternative numeric symbols.

%Oy The year (offset from %C) using the locale's alternative numeric symbols.

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 strptime() fails to match all of the format string and therefore an
       error occurred, the function returns NULL.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────────────────────────┬───────────────┬────────────────────┐
       │Interface                                           │ Attribute     │ Value              │
       ├────────────────────────────────────────────────────┼───────────────┼────────────────────┤
       │strptime()                                          │ Thread safety │ MT-Safe env locale │
       └────────────────────────────────────────────────────┴───────────────┴────────────────────┘

STANDARDS

       POSIX.1-2001, POSIX.1-2008, SUSv2.

NOTES

In principle, this function does not initialize tm but stores only the values specified.
This means that 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 tm_wday and tm_yday field if any
of the year, month, or day elements changed.

The 'y' (year in century) specification is taken to specify a year in the range 1950–2049
by glibc 2.0. It is taken to be a year in 1969–2068 since glibc 2.1.

glibc notes
For reasons of symmetry, glibc tries to support for strptime() the same format characters
as for strftime(3). (In most cases, the corresponding fields are parsed, but no field in
tm is changed.) This leads to

%F Equivalent to %Y-%m-%d, the ISO 8601 date format.

%g The year corresponding to the ISO week number, but without the century (0–99).

%G The year corresponding to the ISO week number. (For example, 1991.)

%u The day of the week as a decimal number (1–7, where Monday = 1).

%V The ISO 8601:1988 week number as a decimal number (1–53). 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.

%z An RFC-822/ISO 8601 standard timezone specification.

%Z The timezone name.

Similarly, because of GNU extensions to strftime(3), %k is accepted as a synonym for %H,
and %l should be accepted as a synonym for %I, and %P is accepted as a synonym for %p.
Finally

%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.

The glibc implementation does not require whitespace between two field descriptors.

EXAMPLES

       The following example demonstrates the use of strptime() and strftime(3).

       #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);
       }