Comparing two versions of programming code with LaTeX

Question

I'd like to compare two versions of program with vertical line between them. How can I do this with LaTeX?

Answer 1

One way would be to use two minipages and the listings package:

While you are at it, you can also add a bit of syntax highlighting, and import an external file which has the source code you want to show:

Notes:

• The filecontents package was used here simply to package the MWE into one file. It is not needed for your actual useage.

---

Code: Basic

\documentclass{article}
\usepackage{listings}

\begin{document}
\begin{minipage}[t]{0.45\linewidth}
\begin{lstlisting}[language=c++]
// before refactoring
class A {
  public int f;
  void m (int i) {
     f = i + f;
  }
}
\end{lstlisting}
\end{minipage}%
\hfill\vrule\hfill
\begin{minipage}[t]{0.45\linewidth}
\begin{lstlisting}[language=c++]
// after refactoring
class A {
  private int f;
  void m(int i) {
     setF(i * getF()();
  }

  public int getF() {
    return this.F;
  }

  public void setF(int f) {
    this.f = f;
  }
}
\end{lstlisting}
\end{minipage}%
\end{document} 

Code: Fancy

\documentclass{article}
\usepackage{xcolor}
\usepackage{listings}

\usepackage{filecontents}
\begin{filecontents*}{before.c}
// before refactoring
class A {
  public int f;
  void m (int i) {
     f = i + f;
  }
}
\end{filecontents*}
\begin{filecontents*}{after.c}
// after refactoring
class A {
  private int f;
  void m(int i) {
     setF(i * getF()();
  }

  public int getF() {
    return this.F;
  }

  public void setF(int f) {
    this.f = f;
  }
}
\end{filecontents*}

\lstdefinestyle{MyStyle}{ %
    language=C++,
    backgroundcolor=\color{gray!10},
    basicstyle=\small,
    basicstyle=\small\ttfamily,
    keywordstyle=\color{red}
}

\begin{document}
\begin{minipage}[t]{0.45\linewidth}
    \lstinputlisting[style=MyStyle]{before.c}
\end{minipage}%
\hfill\vrule\hfill
\begin{minipage}[t]{0.45\linewidth}
    \lstinputlisting[style=MyStyle]{after.c}
\end{minipage}
\end{document} 

Answer 2

use a simple tabular environment:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{xcolor,listings,beramono}
\lstset{basicstyle=\ttfamily\small,
        keywordstyle=\color{blue}}
\begin{document}

\begin{tabular}{@{}p{\dimexpr0.4\linewidth-\tabcolsep}% can be up to 0.5\linewidth 
                 | p{\dimexpr0.5\linewidth-\tabcolsep}@{}}
\begin{lstlisting}[language=c++]
// before refactoring
class A {
  public int f;
  void m (int i) {
     f = i + f;
  }
}
\end{lstlisting}
&
\begin{lstlisting}[language=c++]
// after refactoring
class A {
  private int f;
  void m(int i) {
     setF(i * getF()();
  }

  public int getF() {
    return this.F;
  }

  public void setF(int f) {
    this.f = f;
  }
}
\end{lstlisting}

\end{tabular}

\end{document}