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在表格中，如何確定上一行已經結束？

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在表格中，如何確定上一行已經結束？

如果一個人在一個tabular環境中，如何確定前一行已經結束（以\\）？

\hline人們可能只想在新行的開頭添加或執行一些其他操作。

如果在之前添加\\，可能會添加一個不需要的額外空白行。

所以問題是，與\clearpagevs.相比， vs.\newpage是否有類似的指令？tabular \???\\

答案1

下面介紹一個tabular new line 宏\tnl，它檢查後面是否\tnl使用了\@ifnextchar.由於\@ifnextchar在輸入流中留下了“peeked token”，所以連接的呼叫\tnl都被忽略，除了最後一個：

在此輸入影像描述

\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}

這確實刪除了伴隨的可選參數規範\\。不確定是否需要。

答案2

只是為了說明我提出的建議一則評論:

% 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}

編輯：飾演 大衛卡萊爾已評論，\ifvmode如果使用 -type 列，則測試不起作用p，因為 TeX 在這些列中也處於垂直模式。請注意，更準確地說，TeX 是內部的垂直模式在p類型列內部和對齊線之間（教材，p。 282），因此補充\ifinner測試也無濟於事。確實有效的區別在簡單的情況下基於目前群組級別，可以透過 e-TeX 原語查詢\currentgrouplevel。

以下程式碼只是概念證明：除非您知道將要使用它的精確上下文，否則對其進行改進沒有什麼意義。

% 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}

您可以取消註釋診斷命令以獲取有關正在發生的情況的更多資訊。

答案3

大多數情況下，您可以使用 TeX 原語\crcr來實現此目的。除非前面的命令是\crcr這樣的，否則它什麼都不做。\cr\cr

\\這就是 Latex 可以忽略最後一行末尾的a 的核心原因。

唯一的問題是，如果你用 then 結束前一行，就好像它是以而不是\crcr結束的，但在大多數情況下，這會導致相同的事情。\cr\\

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