Is there an equivalent to \graphicspath for listings?

Question

How can I make the \lstinputlisting to search for files in a given directory? I'm thinking of a solution along the lines of the solution to this question.

I would like to have a solution like

\lstinputpath{/some/path/in/the/system}
\lstinputlisting{file.ext}

where file.ext resides in /some/path/in/the/system. I tried to search for such solution without luck. I found that inside of the definition of \lstinputlistings the authors use a \lst@inputpath. However, a naive modification of this macro doesn't yield any results.

Answer 1

The listings package provides a key called inputpath for specifying a path where \lstinputlisting should search for source files. Note that inputpath is only documented in the listings developer's guide, not in the user manual; if you haven't compiled the developer's guide, searching for "inputpath" in listings.dtx will lead you to the definition of the inputpath key. To use the latter, simply write

\lstset{inputpath=<path-in-question>}

somewhere in your document (not necessarily in your preamble, but after loading listings, of course). If you really insist on using a macro similar to \graphicspath, you can define an \lstinputpath macro yourself, like so

\newcommand*\lstinputpath[1]{\lstset{inputpath=#1}}

The code below assumes that the file sample.c resides in a subdirectory called test of your working directory.

\documentclass{article}

\usepackage{listings}

\newcommand*\lstinputpath[1]{\lstset{inputpath=#1}}

\lstinputpath{test}

\begin{document}
\lstinputlisting[
  language   = C,
  basicstyle = \ttfamily,
  frame      = single,
  caption    = {Hello world in C},
]{sample.c}
\end{document}

Answer 2

Alternative includes using \input@path LaTeX internal macro.

See also https://tex.stackexchange.com/a/24827/250119, Can a default path be set globally for \input{...} akin to \graphicspath{...}?.

e.g.

\documentclass{article}
\usepackage{listings}

\makeatletter
\def\input@path{{SubFolder/}}
\makeatother

\begin{document}
\lstinputlisting[
  language   = C,
  basicstyle = \ttfamily,
  frame      = single,
  caption    = {Hello world in C},
]{SubTest.tex}
\end{document}

Advantage: It works, supports multiple paths, and does not suffer from the disadvantage mentioned in the comment above

One important drawback that should be noted here is that the inputpath is always prepended even if the supplied argument contains slashes (and even if it starts with one i.e. if it is an absolute path).

Disadvantage:

• As far as I can see \input@path is an internal macro of LaTeX, and its original purpose isn't even to allow users to extend the possible locations for \input...? (details later)
• This only works because listings package documentation just happens to internally use \input to process the file internally. Otherwise it wouldn't work.

_{(by the way using \active to represent the constant 13 for \endlinechar is the opposite of self-documented code.)}