General ⇒ How to check for existence of a cross-reference?

[knaldgas]

I'm trying to achieve something along these lines:

Code: Select all

\newcommand{\checkref}[1]{%
  Label #1 is \ifthenelse{\defined{#1}}{defined}{not defined}%
}

\label{mylabel}
\checkref{mylabel}\\
\checkref{undefinedlabel}

Which should give (without warnings):
---
Label mylabel is defined
Label undefinedlabel is not defined
---
In short: How can I check if a label has previously been defined?

[nlct]

You can check for the existence of \r@label where label is the name of the label:

Code: Select all

\documentclass{article}

\makeatletter
\newcommand{\checkref}[1]{%
  Label #1 is \@ifundefined{r@#1}{not defined}{defined}%
}
\makeatother

\begin{document}

\label{mylabel}
\checkref{mylabel}\\
\checkref{undefinedlabel}

\end{document}

You need a second run to ensure 'mylabel' is defined.

Regards
Nicola Talbot

[knaldgas]

Great, that will work for me!
Thank you very much