此脚本
\documentclass{article}
%\usepackage{fontspec} %requires XeLatex
\usepackage{graphicx}
\begin{document}
\listoffigures
\begin{figure}[hbtp]
\includegraphics[width=0.4\textwidth]{example-image-a}
\caption{Histogram of results listed in Table \ref{tab:list}.}
\label{fig:results}
\end{figure}
\begin{table}
\begin{tabular}{l l}
A & B
\end{tabular}
\caption{table caption}
\label{tab:list}
\end{table}
\end{document}
我运行三次，编译成功xelatex。当我取消注释以下行时，会出现问题
\usepackage{fontspec}
然后第二次编译因错误而停止：
(./xe.lof
! Missing $ inserted.
<inserted text>
$
l.1 ...rence `tab:list' on page 1 undefined}.}}{1}
What is the problem and how to solve it?
文件内容.log：
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entering extended mode
restricted \write18 enabled.
%&-line parsing enabled.
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(./xetest.tex
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Babel <3.18> and hyphenation patterns for 84 language(s) loaded.
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(./xetest.lof
! Missing $ inserted.
<inserted text>
$
l.1 ...rence `tab:list' on page 1 undefined}.}}{1}
? x
Here is how much of TeX's memory you used:
10656 strings out of 493007
244068 string characters out of 6136718
309782 words of memory out of 5000000
14653 multiletter control sequences out of 15000+600000
530312 words of font info for 27 fonts, out of 8000000 for 9000
1348 hyphenation exceptions out of 8191
39i,1n,33p,10410b,233s stack positions out of 5000i,500n,10000p,200000b,80000s
No pages of output.
文件.aux：
\relax
该文件的内容.lof如下：
\contentsline {figure}{\numberline {1}{\ignorespaces Histogram of results listed in Table \G@refundefinedtrue {\unhbox \voidb@x \hbox {\normalfont \int _zero:N \l __fontspec_em_int \int _zero:N \l __fontspec_strong_int \bfseries ??}}\GenericWarning { }{LaTeX Warning: Reference `tab:list' on page 1 undefined}.}}{1}
答案1
该\ref命令很脆弱，请使用\protect。
\caption{Histogram of results listed in Table \protect\ref{tab:list}.}
修复后，删除.aux和.lof文件。此类删除仅限首次进行。