Special characters in QR code

Question

I am trying to read a list of URLs from a file and create QR codes for them. If they contain a # like in the example, I get an

Illegal parameter number in definition of \qr@texttoencode

error. Is it possible to make this work without having to edit the input file and escape the special characters there?

\documentclass{article}
\usepackage{qrcode}
\begin{filecontents}{urls.txt}
http://example.org/foo#bar
\end{filecontents}
\def\loadurls#1{%
    \newread\file
    \openin\file=#1
    \begingroup\endlinechar=-1
    \loop\unless\ifeof\file
    \read\file to \fileline
    \qrcode{\fileline}
    \repeat
    \endgroup
    \closein\file
}
\begin{document}
    \loadurls{urls.txt}
\end{document}

Answer 1

An alternative solution using csvsimple. Look at the section 3.6 Special Characters of the csvsimple documentation for other options to escape the special characters. Here I used the respect sharp=true to interpret # as a normal character:

\documentclass{article}
\usepackage{csvsimple}
\usepackage{qrcode}
\begin{filecontents}[overwrite,noheader]{urls.txt}
http://example.org/foo#bar
http://www.ctan.org
\end{filecontents}
\begin{document}
\csvreader[nohead,respect sharp=true]{urls.txt}{}{\qrcode{\csvcoli}\quad}
\end{document}

Answer 2

You should use \readstring rather than \read. By the way, \newread should go outside the definition of \loadurls (and you should use a different name than \file).

Here's an expl3 version:

\begin{filecontents*}[overwrite]{\jobname.dat}
http://example.org/foo#bar
https://tex.stackexchange.com/questions/594413/special-characters-in-qr-code#594426
\end{filecontents*}
\documentclass{article}
\usepackage{qrcode}
\ExplSyntaxOn
\NewDocumentCommand{\loadurls}{m}
 {
  \patheticpat_loadurls:n { #1 }
 }
\ior_new:N \g_patheticpat_loadurls_ior
\cs_new_protected:Nn \patheticpat_loadurls:n
 {
  \ior_open:Nn \g_patheticpat_loadurls_ior { #1 }
  \ior_str_map_inline:Nn \g_patheticpat_loadurls_ior
   {
    \qrcode{##1}\par\medskip
   }
 }
\ExplSyntaxOff
\begin{document}
\loadurls{\jobname.dat}
\end{document}