[Tex/LaTex] How to test if a label exists

cross-referencingmacros

I have tried to follow another question but I cannot get it to work. My question is: How do print a text based on if a reference exists or not?

I have tried the following:

\usepackage{etoolbox}
\usepackage{xparse} 

...

\NewDocumentCommand\calledName{m}{%
    \ifcsundef{r@KN:#1}{\ref{FN:#1}}{\ref{KN:#1}}%
}

Best Answer

Here's a way with \@ifundefined and using latex.ltx core features.

If the label KN:#1 is undefined, a reference to FN:#1 is used (or at least tried to do so.

Another way would use \getrefnumber etc. by refcount package. 

\documentclass{article}


\makeatletter
\newcommand\calledName[1]{%
  \@ifundefined{r@KN:#1}{%
    \ref{FN:#1}%
  }{%
    \ref{KN:#1}%
  }%
}
\makeatother


\begin{document}

\section{Foo} \label{KN:foostuffwrong}

\section{OtherFoo} \label{FN:foostuff}


\calledName{foostuff}
\calledName{stuff}

\calledName{foostuff}


\end{document}
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