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Possible Duplicate:
Changing catcode for commercial at (@) inside a macro to get it matched in pattern.

I want to test whether a string contains the @ sign. I came up with the following piece of code:

\makeatletter
\def\@testat#1@#2\@nil{%
  \def\@cdr{#2}
  \ifx\@cdr\@empty #1#2: does not have at\else #1#2: has at\fi}
\def\hasat#1{\@testat#1@\@nil}
\makeatother

Now this works fine if the document is written with \makeatletter:

\makeatletter
\newcommand\test[1]{#1}
\test{\hasat{linear@ set@}}
\hasat{linear@ set@}
\hasat{linear set}

all work fine. But without the \makeatletter, this fails miserably. If instead I define:

\def\@hasat#1{\@testat#1@\@nil\makeatother}
\def\hasat{\makeatletter\@hasat}

then only the \hasat which is not in a \test works for some reason.

Any help welcome!

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  • 1
Michaël
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  • Dammit. Stackexchange now pops up the relevant related question: http://tex.stackexchange.com/questions/17393/changing-catcode-for-commercial-at-inside-a-macro-to-get-it-matched-in-patte . Feel free to close this question as a duplicate. – Michaël Nov 04 '12 at 23:03
  • Don't define \@cdr as part of your macro; it's already a macro used in the kernel and redefining it can lead to obscure errors. – egreg Nov 04 '12 at 23:09
  • Strange, I would not consider this as a duplicate of the other one. If we really think they're "identical", I would say that this one is better and provides a better answer. – yo' Nov 05 '12 at 09:59

1 Answers1

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You can detect if the given string contains a character with the xstring package:

Code:

\documentclass{article}
\usepackage{xstring}

\newcommand*{\HasAt}[3]{%
    \StrPosition{#1}{@}[\Position]
    #1 \IfEq{\Position}{0}{#3}{#2}%
}


\begin{document}


\HasAt{ancd@foo.bar}{does}{does not} contains the @ symbol.


\HasAt{ancdfoo.bar}{does}{does not} contains the @ symbol.


\end{document}
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Peter Grill
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