General ⇒ Defining a new counter conditional on it being undefined

[leo simon]

I have a counter that has been defined in two packages. One is a general
purpose package that I input into all my files, the other is a special purpose
one used just for one document. I want to be able to check in the latter
package to see if the counter has been defined. That is, I'd like to do
something like

Code: Select all

\ifx\mycounter\undefined
    \newcounter{mycounter}
\fi

But this syntax doesn't work for counters

Any advice would be most appreciated

[sommerfee]

But this syntax doesn't work for counters

A counter defined with \newcounter will be defined with the prefix c@ internally. Doing so one can define counters and environments resp. commands with the same name, e.g. "section" (there is a \section command and a "section" counter related to it), "figure" (there is a "figure" environment and a counter related to it) etc.

So try

Code: Select all

\ifx\c@mycounter\undefined
 \newcounter{mycounter}
\fi

instead.

[leo simon]

Thanks very much for this. have only just login in again and seen your response after many months!

[talion]

I run into a problem using this solution, but could fix it using a proposal shown on StackOverflow. Before using @ in the label name, it's necessary (at least in my setup) to use \makeatletter before and \makeatother afterwards. With this additional step, the solution works for me.

[cgnieder]

... before using it in the label name, it's necessary (at least in my setup) to use \makeatletter before and \makeatother afterwards.

That's correct if used in the preamble of a document. In a package file such as stated in the question the use of \makeatletter and \makeatother is not needed and in fact even wrong

Regards