我正在尝试调试一堆程序生成的表的布局（有些longtable由于历史原因使用，有些使用tabular，有些使用xtab）。我真的很想\hline在这些表的每一行之后使用以查看发生了什么，然后\hline在不再需要它进行调试时抑制它。（我想对表格描述中由“|”产生的垂直线做同样的事情，但这似乎不太可能。）
我曾经ifthen定义过\hhline，即\hline如果设置了某个标志，则为，否则不为，但由于此处其他问题中描述的一些特殊情况，此方法失败。为了记录，我写道：
\newcommand{\lineflag}{true}
\newcommand{\hhline}{\ifthenelse{\equal{\lineflag}{true}}{\hline}{}}%
然后在我的桌子上，我有这样的东西
\begin{xtabular}{|p{\indexPageWidth}|p{\indexNameWidth}|}\hhline
}
一开始就在表格顶部画一条线，当然，LaTeX 反对。
正如我所说，我从阅读其他问答中了解到，这样做行不通，因为我已经这样做了。有没有办法得到相同的结果，即“当某个标志为真时显示所有表格单元格的轮廓形状，否则不显示”？
一个最小（ish）损坏的示例：
\documentclass[11pt,twoside]{article}
\usepackage{xtab}
\usepackage{ifthen}
\begin{document}
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\
third item & fourth item
\end{xtabular}
\vspace{0.3in}
Now with hlines:
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\hline
third item & fourth item \\\hline
\end{xtabular}
\newcommand{\lineflag}{false}
\newcommand{\oline}{\ifthenelse{\equal{\lineflag}{true}}{\hline}{}}%
\vspace{0.3in}
Now with optional hlines; notice that the middle divider hangs down because
of the macro (even though it expands to nothing at all).
I also wish I could get an hline at the top as well, but I haven't figured that out either.
Changing ``lineflag'' to ``true'' above will generate an error.
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\oline%
third item & fourth item \\\oline%
\end{xtabular}
\end{document}
根据@DavidCarlisle的建议，我修改了该文件的最后三分之一
\newif\iflineflag
\lineflagtrue
% \lineflagfalse
\iflineflag\hline\fi
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\iflineflag\hline\fi
%
third item & fourth item \\\iflineflag\hline\fi
%
...一旦我摆脱了一些愚蠢的麻烦，它就完美地工作了。我宁愿只放一个命令行，\oline而不是\iflineflag\hline\fi，但我可以用这个。
答案1
你需要一个可扩展的测试，因为之前不能有不可扩展的标记\hline
\documentclass[11pt,twoside]{article}
\usepackage{xtab}
\newif\iflineflag
\newcommand{\oline}{\iflineflag\hline\fi}%
\begin{document}
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\
third item & fourth item
\end{xtabular}
\vspace{0.3in}
Now with hlines:
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\hline
third item & fourth item \\\hline
\end{xtabular}
\vspace{0.3in}
Now with optional hlines; notice that the middle divider hangs down because
of the macro (even though it expands to nothing at all).
I also wish I could get an hline at the top as well, but I haven't figured that out either.
Changing ``lineflag'' to ``true'' above will generate an error.
\bigskip
TRUE
\lineflagtrue
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\oline%
third item & fourth item \\\oline%
\end{xtabular}
\bigskip
FALSE
\lineflagfalse
\begin{xtabular}
{p{1.0in}|p{2.0in}}
first item & second item\\\oline%
third item & fourth item \\\oline%
\end{xtabular}
\end{document}