Changing the catcode of _ in one command?

Question

In the following code, I would like _ to be a simple letter. How can I achieve this ?

% Source : http://forum.mathematex.net/latex-f6/forcer-le-retour-a-la-ligne-dans-texttt-t13246.html#p127511

\documentclass{article}
    \makeatletter
        \newcommand\breakabletexttt[1]{\texttt{\breakable@texttt#1\@nil}}
        \def\@gobble@fi#1\fi{\fi#1}
        \def\breakable@texttt#1#2\@nil{%
            #1\hspace{0pt plus 0.1pt minus 0.1pt}%
            \ifx\relax#2\relax
            %
            \else
            \@gobble@fi\breakable@texttt#2\@nil
            \fi
        }
    \makeatother


\begin{document}

\breakabletexttt{rangerangerangerange_rangerangerange_rangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerange}

\end{document}

Answer 1

It is a general trick in @unbonpetit's solution:

% start a group and change the catcodes
\def\foo{%
  \begingroup
  \catcode`\_=12\relax
  \foowitharg}
% do the work and ends the group
\def\foowitharg#1{%
  \bfseries
  #1%
  \endgroup}

But if you are not want to split the macro into two, you can use eTeX's extension \scantokens:

\def\foo#1{%
  \textbf{\scantokens{\catcode`\_=12\relax#1}}}

Either is OK.

---

That is to say, you can modify the definition as:

\documentclass{article}
\makeatletter
\newcommand\breakabletexttt[1]{\begingroup\ttfamily
  \scantokens{\catcode`\_12\makeatletter\breakable@texttt#1\@nil}%
  \endgroup}
\def\@gobble@fi#1\fi{\fi#1}
\def\breakable@texttt#1#2\@nil{%
    #1\hspace{0pt plus 0.1pt minus 0.1pt}%
    \ifx\relax#2\relax
    %
    \else
    \@gobble@fi\breakable@texttt#2\@nil
    \fi
}
\makeatother
\begin{document}
\breakabletexttt{rangerangerangerange_rangerangerange_rangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerange}
\end{document}

Answer 2

You must change the catcode of _ before you read the argument of your macro (please, read carefuly the document I sent you).

\documentclass{article}
\makeatletter
\newcommand\breakabletexttt{\begingroup\catcode`\_12 \breakabletexttt@i}
\newcommand\breakabletexttt@i[1]{\texttt{\breakable@texttt#1\@nil}\endgroup}
\def\@gobble@fi#1\fi{\fi#1}
\def\breakable@texttt#1#2\@nil{%
    #1\hspace{0pt plus 0.1pt minus 0.1pt}%
    \ifx\relax#2\relax
    %
    \else
    \@gobble@fi\breakable@texttt#2\@nil
    \fi
}
\makeatother
\begin{document}
\breakabletexttt{rangerangerangerange_rangerangerange_rangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerangerange}
\end{document}

Answer 3

You can change the catcode of a character by using

\catcode`_=11

In this case 11 is there because that is the category code of letters. Normally _ is catcode 8 (which is the category for subscript). You can change it back with

\catcode`_=8

You can read more about this in TeX by Topic