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\if 嵌套在 \ifdefined 中

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\if 嵌套在 \ifdefined 中

我有类似以下 MWE 代码的东西（见下文），\if仅当相应的if 命令已定义。否则，条件\if将被跳过。但是，当“if 命令”（即）未定义时，我会收到错误。\else\ifdefined\ifiskomascriptloaded

! 额外\其他。

l.13 \其他

这两种if嵌套有问题吗？

\documentclass[]{article}

% Defining an 'if command'
% !!! The ERROR pops up IF THIS LINE IS COMMENTED OUT
\newif\ifiskomascriptloaded \iskomascriptloadedfalse

%Checking if the 'if command' is defined
\ifdefined\ifiskomascriptloaded
    %In case defined we use the 'if command'
    \ifiskomascriptloaded 
        \newcommand{\testtext}{Package Not Loaded}
    \else
        %Note: Never to use with a komma script document
        \usepackage{scrextend} %with the nice functionality addmargin. 
        \newcommand{\testtext}{Package Loaded}
    \fi
\else
    %In case not defined we do something else
    \newcommand{\testtext}{Not defined}
\fi

\begin{document}
   The result is: \testtext    
\end{document}

答案1

看看如果没有定义会发生什么

\ifdefined\ifiskomascriptloaded % false so skip to matching \else 
   \ifiskomascriptloaded % skip over this (this is not an if remember)
   \newcommand{\testtext}{Package Not Loaded}% skip this
\else % _this_ else matches the \ifdefined
   % so do these
   \usepackage{scrextend} 
   \newcommand{\testtext}{Package Loaded}
\fi % this closes the \ifdefined
\else %oops this is an error an \else with no if
\newcommand{\testtext}{Not defined}% this is an error as the command was defined just above 
\fi % and so is this an error as no matching if.

如果你使用标准 Latex 语法

\@ifundefined{ifiskomascriptloaded}
  {undefined case}
  {defined case}

那么问题就不会出现。这是因为 latex 语法......

答案2

我找到了一篇好文章这里我发现了一个答案'清洁工'（使用ifthen包；）），无需使用@（makeatletter和 co.）

另一方面，if 条件稍微长一些，因为\isundefined它不适用于 if 命令，例如\ifiskomascriptloaded，所以我需要检查两个宏-true并-false与 if 相关联。

我相信 LaTeX 专家可以定义一个很好的宏\isifundefined，使整个表达式更加紧凑。:)

\ifthenelse{\isundefined{\iskomascriptloadedtrue} \AND \isundefined{\iskomascriptloadedfalse}}
    {\newcommand{\testtext}{Not defined}} %then code
    { \ifiskomascriptloaded 
            \newcommand{\testtext}{Package Not Loaded}
         \else
            \usepackage{scrextend} %with the nice functionality addmargin. 
            \newcommand{\testtext}{Package Loaded}
         \fi} %end ifthenelse

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