1. Error message:
Incomplete \iffalse; all text was ignored after line 20.
<inserted text>
\fi
l.103 ^^I\tableofcontents
2. Cause Analysis
When writing a thesis, the above error occurred because you wrote text between the section and subsection, that is, written text between the first-level title and the second-level title, for example
\section{
XXXXXXXXXXXXXXXXXX}
XXXXXXXXXXX错误出现的文字XXXXXXXXXXXXXXX
\subsection{
引言}
3. Solutions
1) Delete the text added between the two, and then save
\section{
XXXXXXXXXXXXXXXXXX}
\subsection{
引言}
2) Then delete all the generated auxiliary files (from the first picture to the second picture)
-------------------------------------------------- ------------------------------------------
3) Re-run the latex file