Problems with spacing in lstlisting with escaped code

Question

Consider the following code:

\documentclass{beamer}
\usepackage{listings}

\begin{document}

\begin{frame}[fragile]{title}
\begin{lstlisting}[escapeinside={!*}{*!},]
int add
int !*\color{red}add*!
\end{lstlisting}
\end{frame}

\end{document}

As you can see, the spacing (or the font) in the word inside the escaped code changes. How can I make it to look the same?

I need to change specific parts inside the listing, but the spacing inconsistencies is a problem.

Answer 1

In case what you want to highlight is part of the code, my suggestion would be, not to define !* and *! as escape-to-LaTeX delimiters, but to simply define them as "invisible" delimiters that highlight their content in red, instead. That way, you don't get any discrepancy in column alignment between the normal code and the highlighted code. See my MWE below.

In case the highlighted bit is not code, then I don't think you should concern yourself about such a discrepancy in column alignment. For instance, have a look at the bottom screenshot on this answer; do you find anything shocking?

\documentclass{beamer}

\usepackage{listings}

% Definition of custom delimiters
% (the `i' means the delimiters themselves don't get printed)
\lstset{moredelim=[is][\color{red}]{!*}{*!}} 

\begin{document}

\begin{frame}[fragile]{title}
\begin{lstlisting}
int add
int !*add*!
\end{lstlisting}
\end{frame}

\end{document}