Where does \label write to?

Question

Sorry this is a basic question. I do not know where does \label write the data to?

In my previous installation of MikTex 2.9 I can use \CJKnumber{\ref{X}} to reference a previously defined number X and \CJKnumber will change this number into Chinese character. But the present installation cannot. It said the number \ref{X} is undefined. Therefore I want to check whether does \ref{X} really exists.

Provide a MWE please, otherwise we can't guess what's wrong with your code. — Stephen, Dec 09 '23 at 03:26
I don't suppose you just need to compile a second time so that \ref{X} is defined? (And \label is written to the aux file, but this hasn't changed for a long time, so changing to MikTeX 2.9 wouldn't have broken it.) — Teepeemm, Dec 09 '23 at 03:32
You should look at refcount. Possible duplicate: How to use \pageref{foo} as a number? — Werner, Dec 09 '23 at 04:12
\label write into the aux file. The should be a \newlabel entry. If the aux file is not there, check if you have some clean option in your compilation. — Ulrike Fischer, Dec 09 '23 at 07:51

Mico · Accepted Answer · 2023-12-09T11:16:38.550

The reason why \CJKnumber{\ref{X}} cannot work is as follows. While \CJKnumber expects its argument to be a number, the \ref macro isn't expandable; therefore, \CJKnumber is not receiving a number to work on. (Jargon-Alert: "expandability" and "expansion" of macros is at the very core of the TeX programming language.)

What's the remedy? I suggest you employ the refcount package and its \getrefnumber macro; in contrast to \ref{<some_label>}, \getrefnumber{<some_label>} is expandable. The upshot is that \CJKnumber{\getrefnumber{<some_label>}} works as expected.

% !TEX TS-program = xelatex
\documentclass{article} % or some other suitable document class
\usepackage{xeCJK,CJKnumb}
\setCJKmainfont{SimSun}
\usepackage{refcount} % for \getrefnumber macro
\begin{document}
\addtocounter{equation}{554} % just for this example
\refstepcounter{equation}\label{eq:something}
\ref{eq:something}
\CJKnumber{\getrefnumber{eq:something}}
\end{document}

Mico your method indeed work. But why could the same file be successful in previous installation? — nana, Dec 09 '23 at 13:38
@nana - Regarding your follow-up question: Not having any connections to the maintainer of the CJKnumb package, I'm afraid I have no answer. I do know that the non-expandability of the\ref macro has been a constant feature for many years (and, more likely, decades). — Mico, Dec 09 '23 at 13:55

Where does \label write to?

1 Answers1