Label a lstlisting listing in the lower right corner

Question

I want to put a label in the lower right corner of my listings, in this case to indicate the kind of code listed there. I have a bad hack that works somewhat and illustrates what I want:

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}
\definecolor{light-gray}{gray}{0.95}
\newcommand{\mylabel}[1]{\raisebox{1em}[0pt][0pt]{\makebox[0pt][l]{\makebox[\linewidth][r]{\color{gray}{\sffamily #1}\hspace{3.5em}}}}\ignorespaces}
\lstnewenvironment{code}{\lstset{
    ,frame=single
    ,xleftmargin=2em
    ,xrightmargin=2em
    ,backgroundcolor=\color{light-gray}
    ,belowskip=0pt
}}{\mylabel{Code}}
\begin{document}
\begin{code}
This is
some code
set with lstlisting
\end{code}

This is again regular text.
\end{document}

Which looks like this:

The problem is that it

• does not work well with page breaks directly after the listing, i.e. the label may appear on the next page
• If the listing is followed by a blank line, the spacing is increased twice (due to the zero-sized but still existing content between the listing and the paragraph).
• It is not elegant.

Are there nicer ways of obtaining this result?

Answer 1

One easy option would be to use the escapechar option to escape to LaTeX and simply put the label generation into the last line of the listing:

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}
\definecolor{light-gray}{gray}{0.95}

\newcommand{\mylabel}[1]{\hfill{\color{gray}{\sffamily #1\strut}\hspace{1em}}}

\lstnewenvironment{code}{\lstset{
    ,frame=single
    ,xleftmargin=2em
    ,xrightmargin=2em
    ,backgroundcolor=\color{light-gray}
    ,belowskip=0pt,
    ,escapechar={§},
}}{}
\begin{document}
\begin{code}
This is
some code
set with lstlisting §\mylabel{Code}§
\end{code}

This is again regular text.
\end{document}

---

The above has – depending on the viewpoint – the (dis-)advantage that you (have to/can) specify the label in the actual listing source code.

If you want the label as a parameter to the code environment, a bit more work is necessary:

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}
\usepackage{adjustbox,tikz}
\definecolor{light-gray}{gray}{0.95}

\makeatletter
\newcommand{\mylabel}[1]{\color{gray}{\sffamily #1}\hspace{1em}}    

\lstnewenvironment{code}[1]{
    \lstset{
        ,frame=single
        ,xleftmargin=2em
        ,xrightmargin=2em
        ,backgroundcolor=\color{light-gray}
        ,belowskip=0pt,
    }%
    \def\code@arg{#1}%
    \setbox0\hbox\bgroup%
}
{%
    \egroup\usebox0% printout the listing
    \raisebox{\dimexpr-\dp0+\ht\strutbox\relax}{% move near bottom of listing
        \makebox[\dimexpr-\wd0+\lst@linewidth\relax][r]{% makebox to right border
            \mylabel{\code@arg}%
        }%
    }%
}
\makeatother

\begin{document}
\begin{code}{Label}
This is
some code
set with lstlisting
\end{code}

This is again regular text bla bla.
\end{document}