使用 \input 的环境在 \tabular 中失败

Question

我想\input{...}在新环境中使用该命令，然后在表格环境中使用该命令。我想包含的文件包含&并\\格式化表格。如果我使用单个命令或\<EnvironmentName>\end<EnvironmentName>makros，一切都会正常工作。但\begin{...}\end{...}结果却出现错误...

怎么办？为什么？我不明白 :(

\documentclass{article}
\usepackage{filecontents}
%
%
\begin{filecontents}{in0.tex}
a
\end{filecontents}
%
\begin{filecontents}{in1.tex}
a\\
b
\end{filecontents}
%
\begin{filecontents}{in2.tex}
a & b
\end{filecontents}
%
%
\newcommand{\myinputcmd}[1]{\input{in#1}}
\newenvironment{myinputenv}[1]{\input{in#1}}{}
%
%
%
\begin{document}
%
% use command
\begin{tabular}{c}
    \myinputcmd{0} % works
\end{tabular}
\begin{tabular}{c}
    \myinputcmd{1} % works
\end{tabular}
\begin{tabular}{cc}
    \myinputcmd{2} % works
\end{tabular}
%
% use \environmen\endenvironment
\begin{tabular}{c}
    \myinputenv0\endmyinputenv  % works
\end{tabular}
\begin{tabular}{c}
    \myinputenv1\endmyinputenv  % works
\end{tabular}
\begin{tabular}{cc}
    \myinputenv2\endmyinputenv  % works
\end{tabular}
%
% use \begin{environmen}\end{environment}
\begin{tabular}{c}
    \begin{myinputenv}{0}\end{myinputenv}  % works
\end{tabular}
\begin{tabular}{c}
    \begin{myinputenv}{1}\end{myinputenv}  % error: \begin{tabular} ended by \end{myinputenv} (and others)
\end{tabular}
\begin{tabular}{cc}
    \begin{myinputenv}{2}\end{myinputenv}  % error: \begin{tabular} ended by \end{myinputenv} (and others)
\end{tabular}
%
\end{document}