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如何提前获得后一页的逻辑编号

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如何提前获得后一页的逻辑编号

我需要通过某个页面的绝对页码获取该页面的逻辑编号。

例如在一个有 9 页的文档中，其逻辑页码如下：I II 1 2 3 4 A B C，在第五页的部分，使用\getlogicalpn{7}将获得第七页的逻辑页码—— A。

我的解决方案是：先构造一个所有页面的keyval list（\pagelist代码中），key表示绝对页码，value表示对应的逻辑页码，然后\pagelist通过key查询得到value。

我的尝试失败了。请参见以下代码中的注释。对此还有更好的想法吗？

代碼：

\documentclass{article}
\usepackage{geometry,fancyhdr}
\pagestyle{fancy}\fancyhf{}

\ExplSyntaxOn
% obtain the page-list
\prop_new:N \pagelist
\AddToHook{shipout/after}{
  \prop_gput:Nxx \pagelist {\the\ReadonlyShipoutCounter} {\thepage}
}

% defination of \getlogicalpn
\NewExpandableDocumentCommand{\getlogicalpn}{m}{
  \prop_get:NnN \pagelist {#1} \_temp
  \_temp
}
\ExplSyntaxOff

\lhead{absPage: \the\numexpr\ReadonlyShipoutCounter+1\relax}
\chead{Logical Page: \thepage}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
\begin{document}
\tableofcontents
\pagenumbering{Roman}%-----------------
\section{S1}
first page\par
\clearpage
\section{S2}
sencond page\par
\clearpage
\pagenumbering{arabic}%----------------
\section{S3}
third page\par
\clearpage
\section{S4}
fourth page\par
\clearpage
\section{S5}
fifth page\par

% Test if the logical page number can be aquired in advance.
\ExplSyntaxOn
pagelist~is:~|\meaning\pagelist|\par
\prop_get:NnNTF \pagelist{7} \_temp {\_temp}{no~such~key}\par
\ExplSyntaxOff

%Typeset of "A" is wanted, but this causes codes fail to compile.
\getlogicalpn{7}

% Test if the macro is expandable.
% Typeset of \rule{1in}{5pt} is wanted.
% It fails. How to make it work?
\rule{\getlogicalpn{3} in}{5pt}
\clearpage
\section{S6}
sixth page\par 
\clearpage
\pagenumbering{Alph}%------------------
\section{S7}
seventh page\par
\clearpage
\section{S8}
eighth page\par
\clearpage
\section{S9}
nineth page\par
\end{document}

答案1

如果你坚持的话，它就在这儿。

关键是直到发货时才知道这些信息，因此您需要将信息写入辅助文件，然后在下一次编译过程中读取它。

%! TEX program = lualatex
\documentclass{article}
\usepackage{geometry,fancyhdr}
\errorcontextlines=100
\pagestyle{fancy}\fancyhf{}

\ExplSyntaxOn
\makeatletter
\prop_new:N \pagelist
\cs_new_protected:Npn\addpagelist  #1 #2
{
    \prop_gput:Nnn\pagelist        {#1}{#2}
}
% we could also write this which is actually slightly faster but I put explicit argument for clarity
%\cs_new_protected:Npn\addpagelist  
%{
%   \prop_gput:Nnn\pagelist        
%}
\write\@mainaux{\unexpanded{\providecommand\addpagelist[2]{}}}  % later if you remove this block of code you don't get error, it just silently do nothing
\AddToHook{shipout/after}{
    % https://tex.stackexchange.com/questions/10919/what-is-the-basic-mechanism-for-writing-something-to-an-aux-file
    \write\@mainaux{\addpagelist{\the\ReadonlyShipoutCounter}{\thepage}}
}

% defination of \getlogicalpn
\NewExpandableDocumentCommand{\getlogicalpn}{m}{
  \prop_item:Nn \pagelist {#1}
}
\makeatother
\ExplSyntaxOff

\lhead{absPage: \the\numexpr\ReadonlyShipoutCounter+1\relax}
\chead{Logical Page: \thepage}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
\begin{document}
\tableofcontents
\pagenumbering{Roman}%-----------------
\section{S1}
first page\par
\clearpage
\section{S2}
sencond page\par
\clearpage
\pagenumbering{arabic}%----------------
\section{S3}
third page\par
\clearpage
\section{S4}
fourth page\par
\clearpage
\section{S5}
fifth page\par

% Test if the logical page number can be aquired in advance.
\ExplSyntaxOn
pagelist~is:~|\meaning\pagelist|\par
\prop_get:NnNTF \pagelist{7} \_temp {\_temp}{no~such~key}\par
\ExplSyntaxOff

%Typeset of "A" is wanted, but this causes codes fail to compile.
\getlogicalpn{7}

% Test if the macro is expandable.
% Typeset of \rule{1in}{5pt} is wanted.
% It fails. How to make it work?
\rule{\getlogicalpn{3} in}{5pt}

\rule{1 in}{5pt}
\clearpage
\section{S6}
sixth page\par 
\clearpage
\pagenumbering{Alph}%------------------
\section{S7}
seventh page\par
\clearpage
\section{S8}
eighth page\par
\clearpage
\section{S9}
nineth page\par
\end{document}

也许使用zref会更容易。例如https://tex.stackexchange.com/a/4258/250119

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