How to define two labels inside an environment to compute the number of pages the environment spans?

Question

I would like to count the number of pages that a certain environment (named myenv) spans. In principle, I set two labels, one in the beginning and one in the end of the environment. These labels should be unique for every call of the environment, which is the part that still fails (.tex:19: Missing \endcsname inserted):

\documentclass{scrartcl}
\usepackage{blindtext}

% adapted from https://tex.stackexchange.com/questions/38139/how-can-i-calculate-the-difference-of-2-counters-pageref
\usepackage{refcount}
\newcommand{\pageRange}[2]{%
  \number\numexpr\getpagerefnumber{#2}-\getpagerefnumber{#1}+1\relax}

\newcounter{howOftenCalled}% counts how often the environment 'myenv' was called (to create unique labels)
\setcounter{howOftenCalled}{0}
\newenvironment{myenv}[1]{
  \stepcounter{howOftenCalled}% increase counter
  \label{startPage:\ref{howOftenCalled}}% define the first label
  {\LARGE The following text covers \pageRange{startPage:\ref{howOftenCalled}}{endPage:\ref{howOftenCalled}} pages:}\\% compute the number of pages between the first and the second label
  \blindtext[#1]
}{\label{endPage:\ref{howOftenCalled}}\clearpage}% defined the second label

\begin{document}
\begin{myenv}{8}
\end{myenv}
\clearpage
\begin{myenv}{15}
\end{myenv}
\end{document}

score 3 · Accepted Answer · 2018-11-23T11:19:42.397

Your code works except that you cannot retrieve the value of your counter with \ref{howOftenCalled}. If you use \number\value{howOftenCalled} instead, everything works as expected.

\documentclass{scrartcl}
\usepackage{blindtext}

% adapted from https://tex.stackexchange.com/questions/38139/how-can-i-calculate-the-difference-of-2-counters-pageref
\usepackage{refcount}
\newcommand\NumberOfPages[1]{\edef\tmp{\number\numexpr\getpagerefnumber{endPage:#1}-\getpagerefnumber{startPage:#1}+1\relax}%
\ifnum\tmp=1\relax%
1 page%
\else%
\tmp\space pages%
\fi}

\newcounter{howOftenCalled}% counts how often the environment 'myenv' was called (to create unique labels)
\setcounter{howOftenCalled}{0}
\newenvironment{myenv}[1]{%
   \stepcounter{howOftenCalled}% increase counter
   \label{startPage:\number\value{howOftenCalled}}% define the first label
  {\LARGE The following text covers
  \NumberOfPages{\number\value{howOftenCalled}}:}\\% compute the number of pages between the first and the second label
  \blindtext[#1]
}{\label{endPage:\number\value{howOftenCalled}}\clearpage}% defined the second label

\begin{document}
\begin{myenv}{8}
\end{myenv}
\clearpage
\begin{myenv}{15}
\end{myenv}
\clearpage
\begin{myenv}{1}
\end{myenv}
\end{document}

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ACKNOWLEDGEMENTS: Big thanks to @Andrew and @UlrikeFischer, who made suggestions how to make the code more elegant and secure!

Note that you may have to remove the aux file if you just copy this code into your old file that caused the problem. — , Nov 23 '18 at 04:32
+1 I would use \newcommand\NumberOfPages[1]{\number\numexpr\getpagerefnumber{endPage:#1}-\getpagerefnumber{startPage:#1}+1\relax}, which would be used as \NumberOfPages{thehowOftenCalled}. Perhaps this macro should should print page or pages X depending on whether or not the environment spans multiple pages (since 1 pages is grammatically incorrect). — , Nov 23 '18 at 05:21
I wouldn't use \thecounter in contexts like labels where you actually actually want something "simple". The \the-commands are meant for typesetting, the default definition uses internally@arabic` and if some package, e.g. for arabic or hebrew, redefines this, your code will explode. Use e.g. \number\value{howOftenCalled} instead. — Ulrike Fischer, Nov 23 '18 at 08:36

How to define two labels inside an environment to compute the number of pages the environment spans?

1 Answers1