# Can you use beamer + minted + tikz to single-step code?

I have some C pointer code that I would like to "single-step" to show what happens with e.g. dangling pointers. I use minted for syntax highlighting, and that seems to be causing the problem.

The code below compiles (with -shell-escape), but the code that should be escaped isn't. The reason seem to be a bug in pygments (see https://github.com/gpoore/minted/issues/70). I have also tried to solution of marvin2k that re-defined !, but failed to get that code to work.I have also tried various combinations of \begin{minted}[highlightlines=\only<1>{3}\only<2>{5}]{c} to no avail.

Does anyone have a solution? Edit: My platform is ubuntu 14.04, pygmentize 1.6, minted 2.4.1.

\documentclass{beamer}
\usepackage{minted,tikz}
\begin{document}
\begin{frame}[fragile]{Pointers}
\begin{minted}[linenos,escapeinside=||]{c}
int main(void) {
char *p;
p=(char *)malloc(5); |\only<1>{$\Leftarrow$}|
/* do stuff */
p=(char *)malloc(7); |\only<2>{$\Leftarrow$}|
free(p);
return 0;
}
\end{minted}
\begin{tikzpicture}
\node<1->[rectangle,draw] (p) {p};
\node<1->[rectangle,draw,right of=p] (q1) {q1};
\draw<1>[->] (p) -- (q1);
\uncover<2->{\node[rectangle,draw,below right of=p] (q2) {q2};};
\draw<2->[->] (p) -- (q2);
\end{tikzpicture}
\end{frame}
\end{document}


• Completely unrelated but you shouldn’t cast the return value of malloc in C, it’s unnecessary and error-prone (since you could accidentally cast to the wrong pointer type and invoke inadvertent undefined behaviour): stackoverflow.com/q/605845/1968 – Konrad Rudolph Jan 23 '17 at 10:42
• @KonradRudolph, unrelated...and you are right. It was a long time since I last did C and I haven't kept track of 'best practices'. I tried to modify my question but I don't know how to modify the image. – Niclas Börlin Jan 24 '17 at 13:03

As < and > are problematic with minted, you may define the \myonly command:

\newcommand\myonly[2]{\only<#1>{#2}}


MWE:

\documentclass{beamer}
\usepackage{minted,tikz}
\newcommand\myonly[2]{\only<#1>{#2}}
\begin{document}
\begin{frame}[fragile]{Pointers}
\begin{minted}[linenos,escapeinside=||]{c}
int main(void) {
char *p;
p=(char *)malloc(5); |\myonly{1}{$\Leftarrow$}|
/* do stuff */
p=(char *)malloc(7); |\myonly{2}{$\Leftarrow$}|
free(p);
return 0;
}
\end{minted}
\begin{tikzpicture}
\node<1->[rectangle,draw] (p) {p};
\node<1->[rectangle,draw,right of=p] (q1) {q1};
\draw<1>[->] (p) -- (q1);
\uncover<2->{\node[rectangle,draw,below right of=p] (q2) {q2};};
\draw<2->[->] (p) -- (q2);
\end{tikzpicture}
\end{frame}
\end{document}


• That's odd...when I compile your solution (ubuntu 14.04, pygmentize v1.6, minted v2.4.1), my problem remains. What setup did you use? – Niclas Börlin Jan 22 '17 at 15:49
• @NiclasBörlin I use TeXLive 2016, pygmentize 2.1.3 and minted 2.4.1. – Paul Gaborit Jan 22 '17 at 17:24
• It looks like I need to upgrade pygmentize then... Do you run Linux or something else? – Niclas Börlin Jan 22 '17 at 17:29
• @NiclasBörlin I use Ubuntu 16.10. – Paul Gaborit Jan 22 '17 at 17:29

The best solution I have so far is based on @VZ.'s overprint solution (https://tex.stackexchange.com/a/51618/35602). However, it would be nice with a solution that did not require the C code to be repeated...

\documentclass{beamer}
\usepackage{minted}
\usepackage{tikz}
\begin{document}
\begin{frame}[fragile]{Foo}
\begin{overprint}
\onslide<1>
\begin{minted}[linenos,highlightlines={3}]{c}
int main(void) {
char *p;
p=(char *)malloc(5);
/* do stuff */
p=(char *)malloc(7);
free(p);
return 0;
}
\end{minted}
\onslide<2>
\begin{minted}[linenos,highlightlines={5}]{c}
int main(void) {
char *p;
p=(char *)malloc(5);
/* do stuff */
p=(char *)malloc(7);
free(p);
return 0;
}
\end{minted}
\end{overprint}
\begin{tikzpicture}
\node<1->[rectangle,draw] (p) {p};
\node<1->[rectangle,draw,right of=p] (q1) {q1};
\draw<1>[->] (p) -- (q1);
\uncover<2->{\node[rectangle,draw,below right of=p] (q2) {q2};};
\draw<2->[->] (p) -- (q2);
\end{tikzpicture}
\end{frame}
\end{document}