Extract year from parameter containing date [duplicate]

Question

Possible Duplicate:
How do I split a date?

Does anyone know how to extract year from date in parameter of own macro?

Namely,

\themacro#1{...}

where #1 contain either date already in format yyyy or in format dd.mm.yyyy, which \themacro would convert to plain yyyy...

I hope I made myself clear, well, simply speaking, I just need to extract the year from date (if extraction is necessary).

Answer 1

user1189687 already proposed a solution that I think is better, but since I already begun to write this, here is if you want a plain tex solution :

The point here is to recognize that you are in the first case or in the other. As @Kurt pointed out, it is trivial to do if you know the format of your input. But here, apparently you don't.

So what I would do would be :

\makeatletter

\def\@themacro #1.#2\end@themacro{%
  \def\@tempyr{#1}%
  \def\@temprem{#2}%
}%
%
\def\themacro #1 {%
  \let\day\relax%
  \let\month\relax%
  \let\year\relax%
  \let\@tempyr\relax%
  \let\@temprem\relax%
  \@themacro#1.\relax\end@themacro% get day or year
  \if\relax\@temprem\relax%
    \if\relax\@tempyr\relax%
      \GenericError{}{Wrong date format}{}{}% Manage the error
    \else%
      \edef\year{\expandafter\noexpand\@tempyr}%
    \fi%
  \else%
    \edef\day{\expandafter\noexpand\@tempyr}%
    \expandafter\@themacro\@temprem\end@themacro% get month
    \if\relax\@temprem\relax%
      \GenericError{}{Wrong date format}{}{}% Manage the Error
    \else%
      \edef\month{\expandafter\noexpand\@tempyr}%
      \expandafter\@themacro\@temprem\end@themacro% get year
      \if\relax\@temprem\relax%
        \edef\year{\expandafter\noexpand\@tempyr}%
      \else%
        \GenericError{}{Wrong date format}{}{}% Manage the Error
      \fi%
    \fi%
  \fi%
}%
\makeatother%

The advantage of this solution is that you detect incorect syntax and can have a fallback or throw an error, as you wish.

Oh, I almost forgot ... You of course get the year as the replacement text of \year.

In case they exist, you also can get \day and \month.

Answer 2

Try \StrRight in the xstring package:

\documentclass{article}

\usepackage{xstring}
\def\getYear#1{\StrRight{#1}{4}}

\begin{document}

\noindent\getYear{12.12.2012}\\
\getYear{2012}

\end{document}

with result: