我正在尝试使用用户命令将图形可选参数定义为默认值，但我无法在 中使用它。当我用替换[ ]时，下一个示例会引发异常。trim=0 0 0 0trim=\trim
\usepackage[demo]{graphicx}
\newcommand{\trim}{0 0 0 0}
\begin{document}
\begin{figure}[htbp]
\centering
\includegraphics[width=\linewidth,trim=0 0 0 0,clip]{Figure}
\caption{blablabla.}
\end{figure}
\end{document}
此外，我的目标是定义一个命令，例如我可以用它替换width=\linewidth,trim=0 0 0 0,clip里面的整个句子。[ ]
答案1
2020 年 8 月 20 日编辑
我（Ulrich Diez）又一次让自己陷入了尴尬的境地：
在编写下面的内容时，我（Ulrich Diez）没有考虑到方括号[和]（与花括号不同）不是类别代码 1 和 2，而是类别代码 12 的普通字符，因此方括号可以出现在宏参数中。比下面的代码更简单、更短的代码是：
\documentclass{article}
\usepackage[demo]{graphicx}
\newcommand\exchange[2]{#2#1}
\newcommand{\trim}{0 0 0 0}
\begin{document}
\begin{figure}[htbp]
\centering
\expandafter\exchange\expandafter{\trim}{%
\includegraphics[width=\linewidth,trim=%
},clip]{/path/to/graphics/file.jpg}%%%%%
% Why two captions?
\caption{Testing of the Y-axis.}%%%%%
\caption{blablabla.}%%%%%
\end{figure}
\end{document}
序列
\expandafter\exchange\expandafter{\trim}{%
\includegraphics[width=\linewidth,trim=%
},clip]{/path/to/graphics/file.jpg}%%%%%
触发以下操作：
-chain\expandafter导致扩展\trim：
\exchange{0 0 0 0}{%
\includegraphics[width=\linewidth,trim=%
},clip]{/path/to/graphics/file.jpg}%%%%%
扩大\exchange收益率：
\includegraphics[width=\linewidth,trim=%
0 0 0 0,clip]{/path/to/graphics/file.jpg}%%%%%
2020 年 8 月 20 日编辑结束
如果 -command 的定义\trim可以在各个图中改变，那么您可以使用 -expansion-\romannumeral0和参数交换技术 - -expansion 的要点\romannumeral0是：
- TeX 在收集属于⟨数字⟩- 用罗马数字表示的数量。
- 如果 TeX 在收集⟨数字⟩-数量是一个数字，例如，
0然后收集属于的代币的过程⟨数字⟩-quantity 变成了收集更多数字或非数字的过程，因此终止了收集过程。可扩展标记在收集数字时会进行扩展。终止数字序列的空格标记会终止收集更多数字的过程并被默默丢弃。 - 如果收集到的数字不为正数，TeX 将会默默地吞掉构成⟨数字⟩-数量，但不提供任何代币作为回报。
这意味着\romannumeral可以用来欺骗 TeX 做大量的扩展和参数交换工作，只要确保最终找到一个非正数。
\documentclass{article}
\usepackage[demo]{graphicx}
\newcommand\exchange[2]{#2#1}
\newcommand{\trim}{0 0 0 0}
\begin{document}
\begin{figure}[htbp]
\centering
\expandafter\includegraphics\expandafter[%
\romannumeral0%
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
% Why two captions?
\caption{Testing of the Y-axis.}%%%%%
\caption{blablabla.}%%%%%
\end{figure}
\end{document}
序列
\expandafter\includegraphics\expandafter[%
\romannumeral0%
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
触发以下操作：
获取（顶级）扩展的过程\expandafter触发传递下一个第二个标记的顶级扩展的过程，并在获取下一个第二个标记的顶级扩展的过程终止时终止。因此：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggers the process of obtaining the top-level-
% expansion of the next but one token:
\includegraphics\expandafter[%
\romannumeral0%
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
从第一个传出的倒数第二个标记\expandafter也是一个\expandafter，因此：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggers the process of obtaining the top-level-
% expansion of the next but one token:
[%
\romannumeral0%
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
从第二个传出的下一个标记\expandafter是\romannumeral，因此：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering tokens of a <number>-
% quantity in progress:
0%
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
TeX 找到数字0，因此\romannumeral的子过程收集了⟨数字⟩-quantity 变成了收集更多数字或终止数字序列的过程：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress; digit "0" found so far:
\expandafter\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
在搜索属于⟨数字⟩-quantity，TeX 遇到第三个\expandafter：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress; digit "0" found so far:
% Process of obtaining the top-level-expansion of the third \expandafter
% in progress, this process triggers the process of obtaining the top-
% level-expansion of the next but one token:
\exchange
\expandafter{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
从第三个传出的下一个标记\expandafter是\expandafter，因此：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress; digit "0" found so far:
% Process of obtaining the top-level-expansion of the third \expandafter
% in progress, this process triggerd the process of obtaining the top-
% level-expansion of the fourth \expandafter:
\exchange
% Process of obtaining the top-level-expansion of the fourth \expandafter
% in progress, this process triggers the process of obtaining the top-
% level-expansion of the next but one token:
{\trim}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
从第四个传出的倒数第二个标记\expandafter是\trim，因此当获取 的顶级扩展的过程\expandafter终止时，获取第四个的顶级扩展的过程也将终止\trim：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress, digit "0" found so far:
% Process of obtaining the top-level-expansion of the third \expandafter
% in progress, this process triggerd the process of obtaining the top-
% level-expansion of the fourth \expandafter:
\exchange
% Process of obtaining the top-level-expansion of the fourth \expandafter
% terminated.
{0 0 0 0}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
随着获取第四个顶层展开的过程\expandafter终止，获取第三个顶层展开的过程\expandafter也终止：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress, digit "0" found so far:
% Process of obtaining the top-level-expansion of the third \expandafter
% terminated.
\exchange
{0 0 0 0}{ width=\linewidth,trim=},clip%
]{/path/to/graphics/file.jpg}%%%%%
随着获取第三个顶层扩展的过程\expandafter终止，\romannumeral-扩展继续，从而产生扩展\exchange：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity in progress; digit "0" found so far:
<space-token>width=\linewidth,trim=0 0 0 0,clip%
]{/path/to/graphics/file.jpg}%%%%%
TeX 找到一个空格标记。该空格标记终止收集更多数字的子过程⟨数字⟩-数量并被默默丢弃。
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral in progress;
% Sub-process of \romannumeral-expansion for gathering more digits of a
% <number>-quantity terminated; number "0" found.
width=\linewidth,trim=0 0 0 0,clip%
]{/path/to/graphics/file.jpg}%%%%%
TeX 发现⟨数字⟩-quantity 的值为0，而0不是正值，则获取 顶层扩展 的过程会\romannumeral通过默默吞掉形成 的 token 而终止⟨数字⟩-quantity，而 TeX 不会返回任何标记。
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of \romannumeral:
[%
% Process of obtaining the top-level-expansion of \romannumeral terminated.
width=\linewidth,trim=0 0 0 0,clip%
]{/path/to/graphics/file.jpg}%%%%%
随着获取顶层展开的过程\romannumeral终止，获取第二个顶层展开的过程\expandafter也终止：
% Process of obtaining the top-level-expansion of the first \expandafter in
% progress, this process triggerd the process of obtaining the top-level-
% expansion of the second \expandafter:
\includegraphics
% Process of obtaining the top-level-expansion of the second \expandafter
% terminated.
[%
width=\linewidth,trim=0 0 0 0,clip%
]{/path/to/graphics/file.jpg}%%%%%
随着获取第二个顶层展开的过程\expandafter终止，获取第一个顶层展开的过程\expandafter也终止：
% Process of obtaining the top-level-expansion of the first \expandafter
% terminated.
\includegraphics
[%
width=\linewidth,trim=0 0 0 0,clip%
]{/path/to/graphics/file.jpg}%%%%%