（这个问题源于这一。）
我在主 tex 文件中生成了两个代码片段\input{}。这两个片段看起来非常相似，但它只对其中一个片段有效，我不明白为什么。
可重现的示例
主 tex 文件：
\documentclass[11pt, a4paper]{article}
\usepackage{booktabs}
\usepackage[flushleft]{threeparttable}
\begin{document}
\begin{table}[!t]
\begin{small}
\begin{threeparttable}
{
\def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}
\begin{tabular}{lllll}
\toprule
& \multicolumn{4}{c}{\textit{Dep. var: } price in dollars} \\
\cline{2-5}
& (1) & (2) & (3) & (4)\\
\midrule
\input{test.tex}
\bottomrule
\end{tabular}
}
\end{threeparttable}
\begin{tablenotes}
\item\textit{Note:} Here I'm putting many great comments about my regression setup. *** p$<$0.01, ** p$<$0.05, * p$<$0.1.
\end{tablenotes}
\end{small}
\end{table}
\end{document}
片段 1（适用于此）：
&\multicolumn{1}{c}{price}&\multicolumn{1}{c}{price}&\multicolumn{1}{c}{price}&\multicolumn{1}{c}{price}\\
\midrule
weight & 2.04\sym{***}& 1.75\sym{**} & 2.06\sym{**} & 4.36\sym{***}\\
& (5.42) & (2.72) & (3.13) & (3.74) \\
\addlinespace
mpg & & -49.5 & -56.2 & -86.8 \\
& & (-0.57) & (-0.66) & (-1.03) \\
\addlinespace
headroom & & & -675.6 & \\
& & & (-1.72) & \\
\addlinespace
length & & & & -104.9\sym{*} \\
& & & & (-2.64) \\
\midrule
Obs. & 74 & 74 & 74 & 74 \\
R$^2$ & 0.29 & 0.29 & 0.32 & 0.36 \\
这作品并产生：
片段 2（无效）：
\midrule
weight & 2.04\sym{***}& 1.75\sym{**} & 2.06\sym{**} & 4.36\sym{***}\\
& (5.42) & (2.72) & (3.13) & (3.74) \\
\addlinespace
mpg & & -49.5 & -56.2 & -86.8 \\
& & (-0.57) & (-0.66) & (-1.03) \\
\addlinespace
headroom & & & -675.6 & \\
& & & (-1.72) & \\
\addlinespace
length & & & & -104.9\sym{*} \\
& & & & (-2.64) \\
\midrule
Obs. & 74 & 74 & 74 & 74 \\
R$^2$ & 0.29 & 0.29 & 0.32 & 0.36 \\
我收到以下错误信息：
D:\test\test.tex:1: Misplaced \noalign. [\midrule]
D:\test\test.tex:2: Missing } inserted. [w]
D:\test\test.tex:2: Missing } inserted. [w]
D:\test\test.tex:2: Missing } inserted. [w]
D:\test\test.tex:2: Missing \cr inserted. [w]
D:\test\test.tex:2: Missing { inserted. [w]
D:\test\test.tex:2: Misplaced alignment tab character &. [weight &]
D:\test\test.tex:2: Misplaced alignment tab character &. [weight & 2.04\sym{***}&]
D:\test\test.tex:2: Misplaced alignment tab character &. [... 2.04\sym{***}& 1.75\sym{**} &]
D:\test\test.tex:2: Misplaced alignment tab character &. [... 1.75\sym{**} & 2.06\sym{**} &]
D:\test\test.tex:3: Misplaced \cr. [ &]
D:\test\test.tex:3: Misplaced alignment tab character &. [ &]
D:\test\test.tex:3: Misplaced alignment tab character &. [ & (5.42) &]
D:\test\test.tex:3: Misplaced alignment tab character &. [... (5.42) & (2.72) &]
D:\test\test.tex:3: Misplaced alignment tab character &. [... (2.72) & (3.13) &]
D:\test\test.tex:4: Misplaced \cr. [\addlinespace]
D:\test\test.tex:4: Misplaced \noalign. [\addlinespace]
D:\test\test.tex:5: Missing $ inserted. [m]
D:\test\test.tex:5: Missing } inserted. [m]
D:\test\test.tex:5: Missing } inserted. [m]
D:\test\test.tex:5: Missing } inserted. [m]
D:\test\test.tex:5: Extra }, or forgotten \endgroup. [m]
D:\test\test.tex:5: Misplaced alignment tab character &. [mpg &]
D:\test\test.tex:5: Misplaced alignment tab character &. [mpg & &]
D:\test\test.tex:5: Misplaced alignment tab character &. [... & -49.5 &]
D:\test\test.tex:5: Misplaced alignment tab character &. [... -49.5 & -56.2 &]
D:\test\test.tex:6: Misplaced alignment tab character &. [ &]
D:\test\test.tex:6: Misplaced alignment tab character &. [ & &]
D:\test\test.tex:6: Misplaced alignment tab character &. [... & (-0.57) &]
D:\test\test.tex:6: Misplaced alignment tab character &. [... (-0.57) & (-0.66) &]
D:\test\test.tex:7: Misplaced \noalign. [\addlinespace]
D:\test\test.tex:8: Misplaced alignment tab character &. [headroom &]
D:\test\test.tex:8: Misplaced alignment tab character &. [headroom & &]
D:\test\test.tex:8: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:8: Misplaced alignment tab character &. [... & -675.6 &]
D:\test\test.tex:9: Misplaced alignment tab character &. [ &]
D:\test\test.tex:9: Misplaced alignment tab character &. [ & &]
D:\test\test.tex:9: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:9: Misplaced alignment tab character &. [... & (-1.72) &]
D:\test\test.tex:10: Misplaced \noalign. [\addlinespace]
D:\test\test.tex:11: Misplaced alignment tab character &. [length &]
D:\test\test.tex:11: Misplaced alignment tab character &. [length & &]
D:\test\test.tex:11: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:11: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:12: Misplaced alignment tab character &. [ &]
D:\test\test.tex:12: Misplaced alignment tab character &. [ & &]
D:\test\test.tex:12: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:12: Misplaced alignment tab character &. [... & &]
D:\test\test.tex:13: Misplaced \noalign. [\midrule]
D:\test\test.tex:14: Misplaced alignment tab character &. [Obs. &]
D:\test\test.tex:14: Misplaced alignment tab character &. [Obs. & 74 &]
D:\test\test.tex:14: Misplaced alignment tab character &. [... 74 & 74 &]
D:\test\test.tex:14: Misplaced alignment tab character &. [... 74 & 74 &]
D:\test\test.tex:15: Misplaced alignment tab character &. [R$^2$ &]
D:\test\test.tex:15: Misplaced alignment tab character &. [R$^2$ & 0.29 &]
D:\test\test.tex:15: Misplaced alignment tab character &. [... 0.29 & 0.29 &]
D:\test\test.tex:15: Misplaced alignment tab character &. [... 0.29 & 0.32 &]
D:\test\regepr.tex:20: Misplaced \noalign. [\bottomrule]
D:\test\regepr.tex:21: Misplaced \crcr. [\end{tabular}]
D:\test\regepr.tex:21: Extra }, or forgotten \endgroup. [\end{tabular}]
D:\test\regepr.tex:21: Extra }, or forgotten \endgroup. [\end{tabular}]
D:\test\regepr.tex:21: Extra }, or forgotten $. [\end{tabular}]
D:\test\regepr.tex:21: Extra }, or forgotten $. [\end{tabular}]
D:\test\regepr.tex:21: Missing $ inserted. [\end{tabular}]
答案1
\midrule（如\hline和\multicolumn）必须是单元格中第一个不可扩展的命令，任何甚至在其之前\relax或{}之前的命令都会导致它给出该错误。LaTeX\input不可扩展，因此不能在这里使用。您可以使用
\myinput test.tex
其中\myinput定义为
\makeatletter
\let\myinput\@@input
\makeatother