\@abspage@last fails to typeset number in header

Question

I tried to typeset the total pages number in right header by \@abspage@last under pagestyle fancy. Instead of number, the text abspage@last is printed. Why? And how to deal with it?

MWE:

\documentclass[a4paper]{article}
\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhf{}
\rhead{Page \thepage\ of \makeatletter\@abspage@last\makeatother}
\begin{document}
First page:\\
total pages are: \@abspage@last\\ % typeset abspage@last. Why not give error message?
total pages are: \makeatletter\@abspage@last\makeatother % typeset the right number
\clearpage
Second page
\clearpage
Third page
\end{document}

egreg · Accepted Answer · 2022-05-07T10:32:55.493

2

You need \makeatletter around \rhead{...}, not inside it, but you can do better.

There is no “official” interface for using \@abspage@last in the document, mainly because it's not meant to save the last page number, but the total number of pages, including those with different numbering scheme.

If you don't change numbering scheme, you can use it by first defining your own interface

\documentclass[a4paper]{article}
\usepackage{fancyhdr}
\makeatletter
\newcommand{\lastpagenumber}{@abspage@last}
\makeatother
\pagestyle{fancy}
\fancyhf{}
\rhead{Page \thepage\ of \lastpagenumber}
\begin{document}
First page:
\clearpage
Second page
\clearpage
Third page
\end{document}

The default value is 1073741823, which you will obtain when the .aux file doesn't yet exist.

If you want to be warned that a rerun is necessary, you can check whether \@abspage@last equals \maxdimen:

\documentclass[a4paper]{article}
\usepackage{fancyhdr}
\makeatletter
\newcommand{\lastpagenumber}{%
  \ifnum@abspage@last=\maxdimen
    @lastpagewarning
  \else
    @abspage@last
  \fi
}
\newcommand{@lastpagewarning}{%
   @latex@warning@no@line{Could not determine last page number, rerun LaTeX}%
   ??\gdef@lastpagewarning{??}%
}
\makeatother
\pagestyle{fancy}
\fancyhf{}
\rhead{Page \thepage\ of \lastpagenumber}
\begin{document}
First page:
\clearpage
Second page
\clearpage
Third page
\end{document}

If the .aux file is missing or, for some reason, \@abspage@last isn't yet defined, you will get

LaTeX Warning: Could not determine last page number, rerun LaTeX.

Of course this would fail if your document has 1073741823 pages, but…

edited May 07 '22 at 10:32

answered May 07 '22 at 09:18

egreg

1,121,712

Why does dirct use of \@abspage@last just gobble \@ and typeset abspage@last? – lyl May 07 '22 at 15:26
1

@lyl Because the text stored has @ of category code 12, so TeX just executes \@ and prints abspage@last. That's why you should use \makeatletter and \makeatother *around* \rhead{...}, not *inside* it, where it has no useful effect. Another possibility is to do \csname @abspage@last\endcsname inside \rhead; you can remove \makeatletter and \makeatother that do nothing. – egreg May 07 '22 at 15:30
\@ typeset nothing and does not give any error message, so in TeX, what does @ mean? – lyl May 07 '22 at 15:36
@lyl You can use it after a period following an abbreviation, which should not be sentence ending (but in this case .~ is more frequent; or before a period to tell TeX to consider it as a sentence ending period, when it follows a capital letter. – egreg May 07 '22 at 15:39
Thank you so much! I lean a lot from this question. – lyl May 07 '22 at 15:43
quote: The default value is 1073741823, which you will obtain when the .aux file doesn't yet exist. How to make sure .aux file does exist when I use \@abspage@last? I don't want 1073741823, the number of total pages is I desire. – lyl Sep 23 '22 at 01:09
@lyl You just compile again. – egreg Sep 23 '22 at 07:39
But each time the first try fails to complete comilation and causes error. For example, \makeatletter\foreach \i in {1,...,\@abspage@last} {(\i)}\makeatother – lyl Sep 23 '22 at 07:53
@lyl The code in my answer doesn't produce errors when the .aux file doesn't exist. If yours does, then the changes you made are the cause. – egreg Sep 23 '22 at 07:56
For example, the document only contain this: \makeatletter\foreach \i in {1,...,\@abspage@last} {(\i)}\makeatother . The first running causes ERROR: Dimension too large. I think this is because no .aux file exists as you mentioned. – lyl Sep 23 '22 at 07:59
@lyl That's obvious. You can add \def\@abspage@last{-1} in the code, after \@lastpagewarning – egreg Sep 23 '22 at 08:23
Would you kindly provide more details about why dircet use of @abspage@last in the above sample is wrong? And why does \def\@abspage@last{-1} solve the problem? – lyl Sep 25 '22 at 06:54

\@abspage@last fails to typeset number in header

1 Answers1