[Tex/LaTex] Using \newcommand with arguments inside of \newcommand

macros

I'm using the following commands inside my main TeX file right after the ToC.

\mainmatter
\pagestyle{fancy}
\renewcommand{\chaptermark}[1]{\markboth{\chaptername\ \thechapter.\ #1}{}}
\lhead[\thepage]{\leftmark}\chead[]{}\rhead[\myentitle]{\thepage}
\lfoot{}\cfoot{}\rfoot{}

I want to put it all into a new command \MainMatter. How can I do this? I have just tried to do so, however, I get the following error.

Illegal parameter number in definition of `\MainMatter`}.

How can this be done?

Best Answer

\newcommand definitions with arguments within another \renewcommand or \newcommand require a ##1, ##2 etc. for argument replacement, even if the outer command has no arguments at all.

In lack of a MWE, I just 'invented' one, defining the unknown command \myentitle.

\documentclass{book}

\usepackage{fancyhdr}%
\usepackage{blindtext}

\newcommand{\myentitle}{Some unknown text}
\newcommand{\MainMatter}{%
\mainmatter%
\pagestyle{fancy}%
\renewcommand{\chaptermark}[1]{\markboth{\chaptername\ \thechapter.\ ##1}{}}
\lhead[\thepage]{\leftmark}\chead[]{}\rhead[\myentitle]{\thepage}
\lfoot{}\cfoot{}\rfoot{}
}%

\begin{document}

\MainMatter

\chapter{The very first chapter}
\blindtext[10]

\end{document}

enter image description here

Related Solutions

[Tex/LaTex] Passing arguments to \def inside \newcommand (TikZ/PGF)

In the \draw command in your version \endpt is expanded to \pgfmathparse{#1+#2}\pgfmathresult. So you get

\draw (0,0) -- (\pgfmathparse{#1+#2}\pgfmathresult,0);

which greatly confuses TikZ.

Instead you should set \endpt to the result of the calculation, either via

\pgfmathsetmacro{\endpt}{#1+#2}

as Peter suggested or equivalently via

\pgfmathparse{#1+#2}
\edef\endpt{\pgfmathresult}

Alternatively for this MWE you can of course simply do

\newcommand{\drawmestg}[2]{
    \draw (0,0) -- ({#1+#2},0);
}

Combining Newcommand and Renewcommand with Optional Arguments

(La)TeX allows for nested (re)definition of macros, i.e. (re)definitions inside of other macros. In order to let (La)TeX distinguish between the (possible) arguments of the outer macro and the inner arguments, the number of argument specifiers # etc. has to be doubled for the inner macro, i.e. #1, #2 becomes ##1, ##2 etc.

If there is another level of nesting, the argument specifiers # has to doubled again, i.e.

First level: #1

Second level: ##1

Third level: ####1

Fourth level ########1

etc. (Both more than three levels is weird), with other words: 2^{level-of-nesting-1} occurences of the # character must be used.

I've added a version for xparse as well to get around the 'weird' \empty optional argument parameter. However, I don't suggest the redefinition a) with another wrapper and b) the wrapper having an optional argument as well.

\documentclass{article}

\usepackage{xparse}


\newcommand{\foo}[3][\empty]{%
  #1#2#3%
}

\newcommand{\renewfoo}[2][]{\renewcommand{\foo}[3][#1]{And now for something completely different: #2 and ##2##3[##1]}}

\NewDocumentCommand{\foobar}{o+m+m}{%
  \IfValueT{#1}{#1}%
  #2#3%
}

\NewDocumentCommand{\RenewFooBar}{o+m}{%
  \IfValueTF{#1}{%
    \RenewDocumentCommand{\foobar}{O{#1}+m+m}{%
      And now for something completely different with xparse: #2 and ##2##3[##1]%
    }%
  }{%
    \RenewDocumentCommand{\foobar}{+m+m}{%
      And now for something completely different with xparse: #2 and ##1##2%
    }%
  }%
}

\begin{document}

\foo[A]{B}{C}

\renewfoo{\LaTeXe}

\foo[C]{A}{B}

\foobar{E}{F}

\foobar[D]{E}{F}

\RenewFooBar{Mr. Gumby}

\foobar{E}{F}


\RenewFooBar[Brain Surgeon]{Mr. Gumby}


\foobar{E}{F}



\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Passing arguments to \def inside \newcommand (TikZ/PGF)

Combining Newcommand and Renewcommand with Optional Arguments

Related Question