Implementation status: to be implemented

Synopsis

#include <time.h>

struct tm *getdate(const char *string);

Description

The getdate() function converts user format date and time.

Arguments:

string - a string representation of a date or time,

The getdate() function converts a string representation of a date or time into a broken-down time.

The external variable getdate_err, which has type int, is used by getdate() to return error values.

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 indicates 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 are 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 is 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 .
  • %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] refers to years 1969 to 1999 inclusive, and values in the range [00,68] 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 results. 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() is 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).

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 are 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() initializes the broken-down time to be the current time in the scanned timezone. Otherwise, it initializes 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 is 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 is 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 is 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.

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.

Errors

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).

Implementation tasks

  • Implement the DATEMSK environment variable.
  • Implement the getdate() function.