为什么文本模式下的空间比数学模式下的空间大

Question

我定义了一个命令，在文本周围画一个框，并可选择在这个框内放置另一个字符。

命令如下（与 MWE 一起）：

\documentclass{minimal}

\newlength{\xboxh} % Sets a macro for the height
\newlength{\xboxw} % and for the width

\newcommand{\putbox}[2][]{
\settoheight{\xboxh}{#2}% Gets the height
\settowidth{\xboxw}{#2}% and width of the input
\frame{\phantom{\rule{\xboxw}{\xboxh}}}% And draws a frame around it
\setbox0=\hbox{#1\unskip}\ifdim\wd0=0pt% And if the optional argument is not empty
  \relax
\else
  \hspace{-\xboxw}#1% Prints it too
\fi\relax
}

\begin{document}
  Some text to \putbox{Z} fill up space \par

  Some text to \putbox[Z]{Z} fill up space \par

  Some text to \(\putbox{Z}\) fill up space

  Some text to \(\putbox[Z]{Z}\) fill up space
\end{document}

该命令在文本和数学模式下的行为应该相同。但事实并非如此。在文本模式下使用时，该命令会在框前后输出不需要的空格，并且还会错放框的内容（如果有）：

如何修复命令的间距问题？

Answer 1

您的定义中有一个虚假的空间\putbox：

\documentclass{article}

\newlength{\xboxh} % Sets a macro for the height
\newlength{\xboxw} % and for the width

\newcommand{\putbox}[2][]{% <------------------- spurious space
  \settoheight{\xboxh}{#2}% Gets the height
  \settowidth{\xboxw}{#2}% and width of the input
  \frame{\phantom{\rule{\xboxw}{\xboxh}}}% And draws a frame around it
  \setbox0=\hbox{#1\unskip}\ifdim\wd0=0pt% And if the optional argument is not empty
    \relax
  \else
    \hspace{-\xboxw}#1% Prints it too
  \fi\relax
}

\begin{document}

Some text to \putbox{Z} fill up space

Some text to \putbox[Z]{Z} fill up space

Some text to \(\putbox{Z}\) fill up space

Some text to \(\putbox[Z]{Z}\) fill up space

Width of Z: \setbox0=\hbox{Z}\the\wd0

Width of $Z$: \setbox0=\hbox{$Z$}\the\wd0

\end{document}

注意\hbox以文本模式设置其内容。

Answer 2

您不需要测量；此外，您忘记了深度。

\documentclass{article}
\usepackage{amsmath}
\usepackage{xparse}

\makeatletter
\NewDocumentCommand{\putbox}{sm}{%
  \begingroup
  \ifmmode\@tempswatrue\else\@tempswafalse\fi
  \setlength{\fboxsep}{-\fboxrule}%
  \fbox{\IfBooleanTF{#1}{\po@math{#2}}{\po@math{\phantom{#2}}}}%
  \endgroup
}
\newcommand{\po@math}[1]{\if@tempswa\ensuremath{#1}\else#1\fi}
\makeatother

\begin{document}

Some text to \putbox{Z} fill up space

Some text to \putbox*{Z} fill up space

Some text to \putbox*{g} fill up space

Some text to \(\putbox{Z}\) fill up space

Some text to \(\putbox*{Z}\) fill up space

Some text to \(\putbox*{g}\) fill up space

\end{document}

如您所见，如果在数学模式下调用宏，则参数也会在数学模式下排版。*-variant 打印符号。