Period in TOC but not in reference

Question

I want roman section numbers to be followed by a period in TOC and section titles. Here is the MWE.

\documentclass{book}
\renewcommand{\thesection}{\Roman{section}.}
\begin{document}
 \tableofcontents
 \section{First section\label{l}}
 This is Section \ref{l}.
\end{document}

This results in

An extra period in the reference appears. However, if I remove the trailing period from

\renewcommand{\thesection}{\Roman{section}.},

the dots in TOC and section label disappear with it.

How can I solve this? Thank you.

Answer 1

The writing of the dot . to the .aux file for the label must be prevented, so the trick is to attack \@currentlabel when it comes to write \p@section.

This gobbles the dot in\thesection by changing \p@section and writes \Roman{section} again for the references, but keeps the I. format for the ToC and headings.

There's no other class or package involved, the disadvantage is that the definition of \thesection must be remembered.

See Writing theorem conditions with automatic numbering and labels for another application of this 'trick'.

\documentclass{book}

\renewcommand{\thesection}{\Roman{section}.}


\makeatletter
\def\remove@@dot\csname the#1\endcsname{\Roman{#1}}
\def\p@section{\remove@@dot}
\makeatother

\begin{document}
 \tableofcontents
 \section{First section\label{l}}
 This is Section \ref{l}.
\end{document}

Answer 2

The easiest way is to change the class. scrbook from the KOMA-bundle has an "autodot" feature which adds the period only at the appropriate places:

\documentclass{scrbook}
\renewcommand{\thesection}{\Roman{section}}

\begin{document}
 \tableofcontents
 \section{First section\label{l}}
 This is Section \ref{l}.
\end{document}

Answer 3

Here's a solution that works with the book document class. It (a) uses the tocloft package and (b) resets the low-level LaTeX macro \@seccntformat for section-level entries.

\documentclass{book}

\renewcommand{\thesection}{\Roman{section}}
\makeatletter
\def\@seccntformat#1{\@ifundefined{#1@cntformat}%
   {\csname the#1\endcsname\quad}%     default
   {\csname #1@cntformat\endcsname}}%  enable individual control
\newcommand\section@cntformat{\thesection.\quad} % for section-level entries
\makeatother
\usepackage[titles]{tocloft}
\renewcommand{\cftsecaftersnum}{.} % place "." after section-level "number"

\begin{document}
\tableofcontents
\section{First section\label{l}}
This is Section \ref{l}.
\end{document}

Answer 4

You can use titlesec and titletoc. But then a dot is added to the numbers of all section levels.

\documentclass{book}
\renewcommand{\thesection}{\Roman{section}}
\usepackage{titlesec}
\titlelabel{\thetitle.\enskip}
\usepackage[dotinlabels]{titletoc}
\begin{document}
\tableofcontents
\section{First section\label{l}}
Section \ref{l} contains new definitions.
\end{document}

---

Here is an additional KOMA-Script suggestion that adds the dot only to the section level:

\documentclass[
  numbers=noenddot
  ]
  {scrbook}
\addtokomafont{disposition}{\rmfamily}
\renewcommand{\thesection}{\Roman{section}}

\usepackage{xpatch}
\xpatchcmd{\sectionformat}{\autodot}{.}{}{\PatchFailed}
\newcommand\sectionentrynumberformat[1]{\renewcommand\autodot{.}#1}
\RedeclareSectionCommand[
  tocentrynumberformat=\sectionentrynumberformat
]{section}

\usepackage{blindtext}
\begin{document}
 \tableofcontents
 \section{First section\label{l}}
 Section \ref{l} contains new definitions.
%
\blinddocument
\end{document}