![在表格中,如何确定上一行已经结束?](https://linux22.com/image/357993/%E5%9C%A8%E8%A1%A8%E6%A0%BC%E4%B8%AD%EF%BC%8C%E5%A6%82%E4%BD%95%E7%A1%AE%E5%AE%9A%E4%B8%8A%E4%B8%80%E8%A1%8C%E5%B7%B2%E7%BB%8F%E7%BB%93%E6%9D%9F%EF%BC%9F.png)
如果一个人在一个tabular
环境中,他如何能确定上一行已经结束(以\\
)?
\hline
人们可能只想在新行的开头添加或做一些其他的事情。
如果之前添加\\
,则可能会添加不必要的额外空行。
所以问题是,与\clearpage
vs.相比\newpage
,是否有类似的tabular
\???
命令\\
?
答案1
下面引入了一个t
abular n
ew l
ine 宏\tnl
,它检查后面是否使用\tnl
。\@ifnextchar
由于\@ifnextchar
在输入流中留下了“偷看的标记”,因此\tnl
除了最后一个之外,连接的 调用 都将被忽略:
\documentclass{article}
\makeatletter
\newcommand{\tnl}{\@ifnextchar\tnl{}{\\}}
\makeatother
\begin{document}
\begin{tabular}{ l }
one \\ two
\end{tabular}\quad
\begin{tabular}{ l }
one \tnl two
\end{tabular}
\bigskip
\begin{tabular}[t]{ l }
one \\ \\ two
\end{tabular}\quad
\begin{tabular}[t]{ l }
one \tnl \tnl two
\end{tabular}
\bigskip
\begin{tabular}[t]{ l }
one \\ \\ \\ two
\end{tabular}\quad
\begin{tabular}[t]{ l }
one \tnl \tnl \tnl two
\end{tabular}
\end{document}
这确实删除了随附的可选参数规范\\
。不确定是否需要。
答案2
只是为了说明我提出的建议一条评论:
% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly
% declare the paper format.
\usepackage[T1]{fontenc} % Not always necessary, but recommended.
% End of standard header. What follows pertains to the problem at hand.
\newcommand*{\ensureLineHasEnded}{\ifvmode \else \expandafter \\\fi}
\newcommand*{\NLhline}{\ensureLineHasEnded\hline}
\begin{document}
\noindent
\begin{tabular}{|l|}
\hline
A one-column \texttt{tabular}, just for demo purposes. \\
\NLhline
It uses both vertical and horizontal rules (arrggh\ldots!). \\
\NLhline
But some of the \verb|\\|~commands are missing\ldots
\NLhline
\ldots yet the horizontal rules are typeset normally. \\*[6pt]
\NLhline
The \verb|\ensureLineHasEnded| can take the same optional arguments\ldots
\ensureLineHasEnded*[6pt]\hline
\ldots as the \verb|\\|~command.
\NLhline
Moreover, it works as expected when used at the end of the \texttt{tabular}.
\ensureLineHasEnded[9pt]
\end{tabular}\par
\end{document}
编辑:大卫·卡莱尔曾指出,\ifvmode
如果使用 -type 列,则测试不起作用p
,因为 TeX 在这些列中也处于垂直模式。注意,更准确地说,TeX 是内部的垂直模式既包括p
类型列内模式,也包括对齐线之间的模式(TeXbook,第 282 页),因此补充\ifinner
测试也无济于事。在简单的情况下基于当前的组级别,可以通过 e-TeX 原语进行查询\currentgrouplevel
。
以下代码仅仅是一个概念证明:除非您知道它将被使用的精确环境,否则改进它就没有什么意义。
% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly
% declare the paper format.
\usepackage[T1]{fontenc} % Not always necessary, but recommended.
% End of standard header. What follows pertains to the problem at hand.
\makeatletter
\@ifdefinable\@tabular@group@level{\newcount\@tabular@group@level}
\newcommand*\ensureLineHasEnded{%
\ifnum \currentgrouplevel>\@tabular@group@level
% % Diagnostics:
% \count@ \currentgrouplevel
% \typeout{Inserting \protect\\ at line \number\inputlineno,
% since \number\count@\space > \number\@tabular@group@level}%
\expandafter \\%
\fi
}
\newcommand*\saltAwayLevel{%
\noalign{%
\global \@tabular@group@level
\numexpr \currentgrouplevel -\@ne \relax
% % Diagnostics:
% \typeout{\number\@tabular@group@level}
}%
}
\makeatother
\newcommand*{\NLhline}{\ensureLineHasEnded\hline}
\begin{document}
With \texttt{l}~columns:
\begin{center}
\begin{tabular}{|l|}
\saltAwayLevel
\hline
A one-column \texttt{tabular}, just for demo purposes. \\%
\NLhline
It uses both vertical and horizontal rules (arrggh\ldots!). \\
\NLhline
But some of the \verb|\\|~commands are missing\ldots
% \typeout{\number\currentgrouplevel}%
\NLhline
\ldots yet the horizontal rules are typeset normally. \\*[6pt]
\NLhline
The \verb|\ensureLineHasEnded| can take the same optional arguments\ldots
\ensureLineHasEnded*[6pt]\hline
\ldots as the \verb|\\|~command. \\
\NLhline
Moreover, it works as expected when used at the end of the \texttt{tabular}.
\ensureLineHasEnded[9pt]
\end{tabular}\par
\end{center}
\bigbreak
With \texttt{p}~columns:
\begin{center}
\begin{tabular}{|p{.9\linewidth}|}
\saltAwayLevel
\hline
A one-column \texttt{tabular}, just for demo purposes. \\%
\NLhline
It uses both vertical and horizontal rules (arrggh\ldots!). \\
\NLhline
But some of the \verb|\\|~commands are missing\ldots
% \typeout{\number\currentgrouplevel}%
\NLhline
\ldots yet the horizontal rules are typeset normally. \\*[6pt]
\NLhline
The \verb|\ensureLineHasEnded| can take the same optional arguments\ldots
\ensureLineHasEnded*[6pt]\hline
\ldots as the \verb|\\|~command. \\
\NLhline
Moreover, it works as expected when used at the end of the \texttt{tabular}.
\ensureLineHasEnded[9pt]
\end{tabular}\par
\end{center}
\end{document}
您可以取消注释诊断命令以获取有关正在发生的事情的更多信息。
答案3
大多数情况下,您可以使用 TeX 原语\crcr
来实现这一点。\crcr
除非\cr
前一个命令是,\cr
否则它什么也不做。
\\
这就是 Latex 可以忽略最后一行末尾的a 的原因的核心。
唯一的问题是,如果您以 结束上一行,\crcr
那么它就好像以 结束一样,\cr
而不是\\
,但在大多数情况下,结果是相同的。