\input command recompile error "File ended while scanning use of \@xdblarg."

Question

Hello i have an annoying problem. Its about the use of \input command

I have created a folder called Docs and within that folder i have a folder called cha for chapters.

my main file is called document.tex and reside inside the Docs folder.

in the cha folder i have a file called intro.

When i try to use the \input{./cha/intro} or \input{cha/intro} i get the error message when compiling:

File ended while scanning use of \@xdblarg. bla bla bla

The code from my document.tex is some i copied because i wanted to use a template.

If i make the exact same case from a tex file from scratch e.g. \input{1/1} (folder named '1' and file named '1') i can load it...

But i dont understand what's wrong in my case..

\documentclass[12pt,a4paper]{report}

\usepackage{graphicx}
% put all the other packages here:

%\usepackage{mystyle}
%\usepackage{hyperref} 
\begin{document}

%\input{./title}
%\maketitle



\input{cha/intro}

\end{document}

This is the error i get:

This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018) (preloaded 
format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./document.tex
LaTeX2e <2018-04-01> patch level 2
Babel <3.18> and hyphenation patterns for 84 language(s) loaded.
(/usr/local/texlive/2018/texmf-dist/tex/latex/base/report.cls
Document Class: report 2014/09/29 v1.4h Standard LaTeX document class
(/usr/local/texlive/2018/texmf-dist/tex/latex/base/size12.clo))
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/local/texlive/2018/texmf-dist/tex/latex/graphics-def/pdftex.def)))
(./document.aux)
(/usr/local/texlive/2018/texmf-dist/tex/context/base/mkii/supp-pdf.mkii
[Loading MPS to PDF converter (version 2006.09.02).]
) (/usr/local/texlive/2018/texmf-dist/tex/latex/oberdiek/epstopdf-base.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/infwarerr.sty)
(/usr/local/texlive/2018/texmf-dist/tex/latex/oberdiek/grfext.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/kvdefinekeys.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/ltxcmds.sty)))
(/usr/local/texlive/2018/texmf-dist/tex/latex/oberdiek/kvoptions.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/kvsetkeys.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/etexcmds.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/ifluatex.sty))))
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/pdftexcmds.sty
(/usr/local/texlive/2018/texmf-dist/tex/generic/oberdiek/ifpdf.sty))
(/usr/local/texlive/2018/texmf-dist/tex/latex/latexconfig/epstopdf-sys.cfg))
(./cha/intro.tex)
Runaway argument?
{Introduction) \par This is where i am going to tell you about my ini\ETC.
./document.tex:15: File ended while scanning use of \@xdblarg.
<inserted text> 
                \par 
l.15 \input{cha/intro}

Any ideas?

Br Thomas

Answer 1

Errors with \@xdblarg indicate that something is wrong with a command with an optional and a mandatory argument (dblarg=double argument).

File ended while scanning use of indicates that such a argument wasn't closed correctly.

The error message quite often tells you were the argument was opened:

Runaway argument?
{Introduction) \par

And by looking closely you can see the closing parenthese instead of the closing brace....