What is the use of \clearpage{\thispagestyle{empty}\cleardoublepage}

Question

I saw the command \clearpage{\thispagestyle{empty}\cleardoublepage} on a project and I didn't understand clearly what it was doing so I tried to use it in a minimal project. If I create document of class book I get numbers in the header at the right on odd pages and at the left on even pages.

If I put the command before including fun-1.tex file it will hide the header number of that file. Here is main.tex showing that:

\documentclass[12pt, a4paper]{book}

\begin{document}

\clearpage{\thispagestyle{empty}\cleardoublepage}

\include{fun-1}

\include{fun-2}

\include{fun-3}

\include{fun-4}

\end{document}

If I put the command after the include fun-1.tex file it will add a blank page after this fun-1 file and that blank page will increase count number despite that page having no number. main.tex looks like this:

\documentclass[12pt, a4paper]{book}

\begin{document}

\include{fun-1}

\clearpage{\thispagestyle{empty}\cleardoublepage}

\include{fun-2}

\include{fun-3}

\include{fun-4}

\end{document}

The other files:

fun-1.tex:

This is fun-1

fun-2.tex:

This is fun-2

fun-3.tex:

This is fun-3

fun-4.tex:

This is fun-4

I would like to know how this command works and where it is useful. It's the first time I see two commands inside curly braces, I don't quite get what is going on there.

Answer 1

Here's what the commands are supposed to do.

1. \clearpage ends the current page and prepares LaTeX to build a new one

2. { opens a group

3. \thispagestyle{empty} tells LaTeX to avoid adorning the current page with headers and footers

4. \cleardoublepage tells LaTeX to issue a new page if the current one (the fresh page initiated after \clearpage) is odd numbered

5. } closes the group

What happens is that if the fresh page is odd numbered, \cleardoublepage does add a new page, which will be empty; otherwise, the effect of \thispagestyle{empty} will finish as soon as } is processed, so if the page is even numbered, nothing happens.

Anyway, it's much easier to add

\usepackage{emptypage}

in the document preamble, rather than

\clearpage{\thispagestyle{empty}\cleardoublepage}

before starting each chapter.