问一下 \newif 这个命令的用法

[Lingtao Pan]

Hi, all:

发现 texbook 这本书还是不容易看懂的。下面这一段我看了好几篇还是没弄清楚 \newif 的用法。

To facilitate \if... constructions, plain TEX has a \newif
macro, such that
after you say '\newif\ifabc' three control sequences will be
defined: \ifabc
(for testing the switch), \abctrue (for making the switch true), and
\abcfalse (for
making it false). The \phantom problem is now solved in Appendix B by writing

\newif\ifhph \newif\ifvph
\def\hphantom{\hphtrue\vphfalse\phant}

and with similar definitions of \vphantom and \phantom. There is no
longer any need
for a \ph macro; again \phant tests \ifhph and \ifvph. Appendix E contains other
examples of conditionals created by \newif. New conditionals are
initially false.

另外，ThuThesis 中是这样使用 \newif 的 (当然我也没看懂)。

\newif\ifthu@bachelor\thu@bachelorfalse
\DeclareOption{bachelor}{\thu@bachelortrue}
\ifthu@bachelor\relax\else

Best regards.

[Ruini Xue]

On Nov 15, 2007 4:49 PM, Lingtao Pan <free...@gmail.com> wrote:

Hi, all:

发现 texbook 这本书还是不容易看懂的。下面这一段我看了好几篇还是没弄清楚 \newif 的用法。

         To facilitate \if... constructions, plain TEX has a \newif
macro, such that
         after you say '\newif\ifabc' three control sequences will be
defined: \ifabc
(for testing the switch), \abctrue (for making the switch true), and
\abcfalse (for
making it false).

用c++对比可以这样理解：

\newif\ifabc            bool abc;
\abctrue                abc = true;
\abcfalse               abc = false;
\ifabc                    if (abc) {
  abc is true             cout << "abc is true";
\else                     } else {
  abc is false            cout << "abc is false";
\fi                         }
 
也就是说\newif\ifabc看起来定义一个宏，实际上它定义了三个宏：\ifabc, \abctrue, \abcfalse。
\ifabc用来判断abc是否为真，而后两个分别用来设置abc的值为真或假.

The \phantom problem is now solved in Appendix B by writing

         \newif\ifhph \newif\ifvph
         \def\hphantom{\hphtrue\vphfalse\phant}

and with similar definitions of \vphantom and \phantom. There is no
longer any need
for a \ph macro; again \phant tests \ifhph and \ifvph. Appendix E contains other
examples of conditionals created by \newif. New conditionals are
initially false.

另外，ThuThesis 中是这样使用 \newif 的 (当然我也没看懂)。

    \newif\ifthu@bachelor\thu@bachelorfalse

这跟上面一样，定义一个"布尔变量"thu@bachelor，并给它赋初值为false
 

    \DeclareOption{bachelor}{\thu@bachelortrue}

\DeclareOption是LaTeX的命令，表示如果文档类有bachelor选项，那么执行后面的命令，即将thu@bachelor设置为真。
 

      \ifthu@bachelor\relax\else

 
翻译成c++就是
if (thu@bachelor == true) {
     // do nothing. \relax means 'do nothing' in TeX
     // 当然这里的\relax可以忽略，TeX会将\ifXXX和\else之间的东西作为条件判断为真时执行的部分。
} else {
   ....
}


Best

Ruini

Best regards.

[Lingtao Pan]

在 07-11-15，Ruini Xue<xuer...@gmail.com> 写道：

>
>
> On Nov 15, 2007 4:49 PM, Lingtao Pan <free...@gmail.com> wrote:
> > Hi, all:
> >
> > 发现 texbook 这本书还是不容易看懂的。下面这一段我看了好几篇还是没弄清楚 \newif 的用法。
> >
> > To facilitate \if... constructions, plain TEX has a \newif
> > macro, such that
> > after you say '\newif\ifabc' three control sequences will be
> > defined: \ifabc
> > (for testing the switch), \abctrue (for making the switch true), and
> > \abcfalse (for
> > making it false).
>
> 用c++对比可以这样理解：
>
> \newif\ifabc bool abc;
> \abctrue abc = true;
> \abcfalse abc = false;
> \ifabc if (abc) {
> abc is true cout << "abc is true";
> \else } else {
> abc is false cout << "abc is false";
> \fi }
>
> 也就是说\newif\ifabc看起来定义一个宏，实际上它定义了三个宏：\ifabc, \abctrue,
> \abcfalse。
> \ifabc用来判断abc是否为真，而后两个分别用来设置abc的值为真或假.
>

多谢, 解释地很清楚，我明白了。

我原来主要是没理解这句话：
three control sequences will be defined.

[moz]

谢谢 4年后还教会了我 ^_^

在 2007年11月15日星期四UTC+8下午4时49分15秒，Lingtao Pan写道：