Size of lstlisting in subfig

Question

For a paper, I have to present two code snippets that do the same thing to compare them.

I started having them in two different figures, but now, I'm trying to have them side by side, and that's where the trouble starts.

First of all, I couldn't seem to get listings to work in subfig.

\lstset{%
language=C,
frame=single,
numbers=left,
numberstyle=\footnotesize,
tabsize=2,
keepspaces=true,
columns=fullflexible,
basicstyle=\ttfamily,
keywordstyle=\color{blue}
}


\begin{figure}
\subfloat[small code]{%
\begin{lstlisting}
for(int i = 0 ; i < N ; i++)
 for(int j = 0 ; j < N ; j++)
  for(int k = 0 ; k < N ; k++)
   c[i][j] += a[i][k] * b[k][j];
\end{lstlisting}
}
\hfill
\subfloat[Larger code]{%
\begin{lstlisting}
for(int ii = 0 ; ii < N ; ii+=B) {
 for(int jj = 0 ; jj < N ; jj+=B) {
  for(int kk = 0 ; kk < N ; kk+=B) {
   for(int i = ii ; i < ii + B ; i++) {
    for(int k = kk ; k < kk + B ; k++){
     c_i = c[i];
     a_ik = a[i][k];
     b_k = b[k];
     for(int j = jj ; j < jj + B ; j+=2){
      c_i[j] += a_ik * b_k[j];
      c_i[j+1] += a_ik * b_k[j+1];
     }
    }
   }
  }
 }
}
\end{lstlisting}
}
\end{figure}

This, generates a score of errors that I can't make sense of. After browsing the web, I found that a lot of people seem to achieve what I want to do by including the source code from an external file.

\begin{figure}[!htb]
\subfloat[Toto]{%
\lstinputlisting{mm_base.c}%
}
\hfill
\subfloat[Tata]{%
\lstinputlisting{mm_opt.c}%
}
\end{figure}

By manually changing the fontsize, I can get the subfloats to be side by side, but I get the following result:

The frame around the code and the perceived size of the content don't seem to match. Moreover, the code on the right hand side goes out of bound, the right frame goes off-page.

The first thing I'd like to know, out of curiosity really, is why I can't use the lstlisting environment and only the lstinputlisting when inside a subfloat.

And the more pressing matters, getting the frame to match the subfig's width. And the more challenging part maybe, automatically change the size of the code included to fit in the subfig.

Answer 1

You need to reduce the \linewidth before using \lstinputlisting, otherwise it uses the full normal line width.

You can do this using \parbox or minipage environment. For example the following code places the listing in a paragraph box with 48% of the normal line width. (Some people use \textwidth which is mostly the same.)

\parbox{.48\linewidth}{\lstinputlisting{file.c}}

---

The reason why your first example doesn't work is that lstlisting is a verbatim environment and therefore not allowed in arguments of other macros. This is because the code is read as part of the argument before \begin{lstlisting} is processed and tells LaTeX to thread the code verbatim!

If you want to have the code in the main file, you could store the listings in a box which is then used in the \subfloat. This requires minipage because \parbox would also read the listing as macro argument.

\documentclass{article}

\usepackage{xcolor}
\usepackage{subfig}
\usepackage{listings}

\lstset{%
language=C,
frame=single,
numbers=left,
numberstyle=\footnotesize,
tabsize=2,
keepspaces=true,
columns=fullflexible,
basicstyle=\ttfamily\scriptsize,
keywordstyle=\color{blue}
}

\newsavebox{\mylistingbox}

\begin{document}

\begin{figure}

\begin{lrbox}{\mylistingbox}%
\begin{minipage}{.45\linewidth}%
\begin{lstlisting}
for(int i = 0 ; i < N ; i++)
 for(int j = 0 ; j < N ; j++)
  for(int k = 0 ; k < N ; k++)
   c[i][j] += a[i][k] * b[k][j];
\end{lstlisting}%
\end{minipage}%
\end{lrbox}%
%
\subfloat[small code]{\usebox{\mylistingbox}}%
%
\hfill
%
\begin{lrbox}{\mylistingbox}%
\begin{minipage}{.45\linewidth}%
\begin{lstlisting}
for(int ii = 0 ; ii < N ; ii+=B) {
 for(int jj = 0 ; jj < N ; jj+=B) {
  for(int kk = 0 ; kk < N ; kk+=B) {
   for(int i = ii ; i < ii + B ; i++) {
    for(int k = kk ; k < kk + B ; k++){
     c_i = c[i];
     a_ik = a[i][k];
     b_k = b[k];
     for(int j = jj ; j < jj + B ; j+=2){
      c_i[j] += a_ik * b_k[j];
      c_i[j+1] += a_ik * b_k[j+1];
     }
    }
   }
  }
 }
}
\end{lstlisting}%
\end{minipage}%
\end{lrbox}%
%
\subfloat[Larger code]{\usebox{\mylistingbox}}%

\end{figure}

\end{document}

I reduces the font size here to fit both on the normal text width. For figures you could also extend it in the margin using the technique shown be me in Center figure that is wider than \textwidth and Place figures side by side, spill into outer margin. In your case either use two box registers and then:

\makebox[1.2\textwidth]{\subfloat[Shorter code]{\usebox{\mylistingboxa}}\hfill\subfloat[Larger code]{\usebox{\mylistingboxb}}}

or add the following equivalent lines before and after the whole subfloat related code:

\hbox to 1.2\textwidth\bgroup\hss
 % the whole box saving and \subfloat code above
\hss\egroup