# Cross Reference problem

I have a problem when I use a cross-reference from other files. I have a folder in which there is a main.tex file and a subfolder (Chapter) containing Chapter1.tex and Chapter2.tex.

In the main file, I include only the chapter files like this:

    \include{Chapters/Chapter1}
\include{Chapters/Chapter2}


My problem is that in the Chapter2.tex file I need to reference a section from Chapter1.

Chapter1.tex

\documentclass{standalone}
\begin{document}
\chapter{chapter}
\label{ch:first_chapter}

\section{first section}\label{sc:first_section}
some Text..........
\end{document}


Chapter2.tex

\documentclass{standalone}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument[C1-]{/Chapter1}
\begin{document}
\chapter{Second Chapter}
\label{ch:second_chapter}
\section{section}\label{sc:first_section_ch2}

Some text...text \ref{C1-sc:first_section}
\end{document}


When I compile the file, only ?? appears.

• I don't think \chapter is defined for the standalone document class. Besides this, for me this sounds more like a job for ctan.org/pkg/subfiles?lang=en then for standalone. – user36296 Jul 4 '17 at 16:29

## 2 Answers

I don't think \chapter is defined for the standalone document class. Besides this, for me this sounds more like a job for the subfiles package then for standalone:

main.tex:

\documentclass{book}
\usepackage{subfiles}
\usepackage{xr-hyper}
\usepackage{hyperref}
\usepackage{xstring}

\begin{document}
\subfile{chapter1}
\subfile{chapter2}
\end{document}


and chapter1.tex

% !TeX root = chapter1.tex
\documentclass[main]{subfiles}

\begin{document}
\chapter{chapter}
\label{ch:first_chapter}

\section{first section}\label{sc:first_section}
some Text..........
\end{document}


and chapter2.tex

% !TeX root = chapter2.tex
\documentclass[main]{subfiles}

\IfEq{\jobname}{\detokenize{main}}{}{%
\externaldocument{chapter1}
}

\begin{document}
\chapter{Second Chapter}
\label{ch:second_chapter}
\section{section}\label{sc:first_section_ch2}

Some text...text \ref{sc:first_section}
\end{document}


(the above example assumes that all 3 files are in the same folder, for the usage of subfolders, you have to adjust the paths of the main file and the chapter files accordingly)

• What does this do? \IfEq{\jobname}{\detokenize{main}}{}{% \externaldocument{chapter1} } – Mars Jan 1 '18 at 19:42
• @Mars This only loads the \externaldocument if the subfile is compiled. If this would be loaded when the main file is compiled, it would result in an error of labels defined multiple times. – user36296 Jan 1 '18 at 19:46
• If there were a third chapter, would we add \externaldocument{chapter2} right after \externaldocument{chapter1}? – Robert Wolfe Dec 18 '18 at 20:35
• @RobertWolfe Correct. The order does not matter, you could add the second before the first – user36296 Dec 18 '18 at 20:45

The / before Chapter1 in \externaldocument is wrong. Also standalone does not have the \chapter command.

In my point of view, there is nothing to gain to make separate documents from the individual chapter files here.

Both (or all!) files should use hyperref packages in order to provide the correct label format.

\documentclass{book}
\usepackage{xr-hyper}
\usepackage{hyperref}
\begin{document}
\chapter{chapter}
\label{ch:first_chapter}

\section{first section}\label{sc:first_section}
some Text..........
\end{document}


Chapter2.tex

\documentclass{book}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument[C1-]{Chapter1}
\begin{document}
\chapter{Second Chapter}
\label{ch:second_chapter}
\section{section}\label{sc:first_section_ch2}

Some text...text \ref{C1-sc:first_section}
\end{document}