Error creating header fancyhead for oneside contents

Question

I created my thesis and used this code to created heading. The document is setted to book class and oneside option. I got a page where both the left and right are number. Instead I would have the page number at the right and at the left the section

\usepackage{fancyhdr}
\pagestyle{fancy}

\makeatletter
\DeclareRobustCommand{\format@sec@number}[2]{{\normalfont\upshape#1}#2}
\renewcommand{\chaptermark}[1]{%
  \markboth{\format@sec@number{\ifnum\c@secnumdepth>\m@ne\@chapapp\ \thechapter. \fi}{#1}}{}}
\renewcommand{\sectionmark}[1]{%
  \markright{\format@sec@number{\ifnum\c@secnumdepth>\z@\thesection. \fi}{#1}}}
\makeatother

\fancyhf{}
\fancyhead[R]{\itshape\nouppercase{\leftmark}}
\fancyhead[L]{\itshape\nouppercase{\rightmark}}
\fancyhead[L,R]{\thepage}

Answer 1

You are defining both side heading to be page numbers via

\fancyhead[L,R]{\thepage}

hence you get the page numbers on both sides. Try the following code:

\documentclass[oneside]{book}
\usepackage{lipsum}
\usepackage{fancyhdr}
\pagestyle{fancy}

\makeatletter
\DeclareRobustCommand{\format@sec@number}[2]{{\normalfont\upshape#1}#2}
\renewcommand{\chaptermark}[1]{%
  \markboth{\format@sec@number{\ifnum\c@secnumdepth>\m@ne\@chapapp\ \thechapter. \fi}{#1}}{}}
\renewcommand{\sectionmark}[1]{%
  \markright{\format@sec@number{\ifnum\c@secnumdepth>\z@\thesection. \fi}{#1}}}
\makeatother

\fancyhf{}
\fancyhead[R]{\thepage}
\fancyhead[L]{\itshape\nouppercase{\rightmark}}
\begin{document}
\chapter{Some chapter}
\section{Some section}
\lipsum[1-10]
\section{Some other section}
\lipsum[11-20]
\end{document}