Section numbering problem in toc when using tocloft

Question

When using \part with tocloft (without fontspec) in pdflatex as suggested in the answer in this post Separate book into parts and chapters, I encounter a problem in the section numbering in the tableofcontents like this.

Contents

First Part

1 Chapter1

1 Sections1.1

1.1 Subsection1.1.1

2 Chapter2

1 Section2.1

1 Section2.2

1.1 Subsection2.2.1

Second part

3 Chapter3

2 Section3.1

2.1 Subsection3.1.1

The sectioning in the text however is fine.

Can someone help me out? Thanks.

The preamble is the following

\documentclass[a4paper,10pt]{book}
\usepackage{amsmath,amssymb,amsfonts,amsthm}
\usepackage{inputenc}
\usepackage{tabularx}
\usepackage{mathtools}
\usepackage{booktabs}
\usepackage{siunitx}
\usepackage{textcomp}
\usepackage{xpatch}
\usepackage{tikz}
\usepackage{tocloft}
\usepackage{inputenc}
\usepackage{xspace}
\usepackage{fancyhdr} 
\pagestyle{fancy}
\fancyhf{}
\fancyhead[LE,RO]{}
\fancyhead[RE,LO]{\textcopyright~ Prints 2019}
\fancyfoot[CE,CO]{}
\fancyfoot[LE,RO]{\thepage}

\everymath{\displaystyle}

\newtheorem{prop}{Proposition}[chapter]
\newtheorem{defn}{Definition}[chapter]
\newtheorem{lemma}{Lemma}
\newtheorem{theorem}{Theorem}[chapter]
\newtheorem{corollary}[prop]{Corollary}
\newtheorem{remark}{Remark}
\newtheorem{example}{Example}[chapter]

\newcommand{\floorceil}[1]{\lceil #1 \rfloor}

\makeatletter
\xpatchcmd{\@thm}{\thm@headpunct{.}}{\thm@headpunct{}}{}{}
\makeatother

\renewcommand{\cftpartfont}{\bfseries\Large\hrule}%add line above part
\renewcommand{\cftpartpagefont}{\bfseries}
\renewcommand{\cftbeforepartskip}{5mm}
\renewcommand{\cftpartafterpnum}{\\\hrule}%add line below part
\cftpagenumbersoff{part}%get rid of part page numbers
\renewcommand{\cftsecindent}{8mm}%control spacing between number and sec title
\renewcommand{\cftsecnumwidth}{4mm}%section indent
\renewcommand{\cftparskip}{4mm}%control line spacing

\begin{document}
\tableofcontents
\part{First part}
\chapter{Chapter1}
\section{Sections1.1}
\subsection{Subsection1.1.1}
\chapter{Chapter2}
\section{Section2.1}
\section{Section2.2}
\subsection{Subsection2.2.1}
\part{Second part}
\chapter{Chapter3}
\section{Section3.1}
\subsection{Subsection3.1.1}
\end{document}

A snapshot of the toc is here.]2

Answer 1

Some comments and suggestions:

• length parameters of the tocloft package should be modified via \setlength, not \renewcommand

• consider replacing

  \renewcommand{\cftsecindent}{8mm}%control spacing between number and sec title
  \renewcommand{\cftsecnumwidth}{4mm}%section indent
  

  with

  \cftsetindents{chap}{0em}{1.5em}
  \cftsetindents{sec}{1.5em}{2em}
  \cftsetindents{subsec}{3.5em}{2.75em}
  

  You are obviously free to modify these settings to suit your preferences and typesetting needs.

---

\documentclass[a4paper,10pt]{book}
\usepackage{mathtools,amssymb,amsthm}
\usepackage[utf8]{inputenc}
\usepackage{tabularx}
\usepackage{booktabs}
\usepackage{siunitx}
\usepackage{textcomp}
\usepackage{xpatch}
\usepackage{tikz}
\usepackage{tocloft}
\usepackage{xspace}

\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhf{}
\fancyhead[LE,RO]{}
\fancyhead[RE,LO]{\textcopyright~ Prints 2019}
\fancyfoot[CE,CO]{}
\fancyfoot[LE,RO]{\thepage}

\everymath{\displaystyle}

\newtheorem{prop}{Proposition}[chapter]
\newtheorem{defn}{Definition}[chapter]
\newtheorem{lemma}{Lemma}
\newtheorem{theorem}{Theorem}[chapter]
\newtheorem{corollary}[prop]{Corollary}
\newtheorem{remark}{Remark}
\newtheorem{example}{Example}[chapter]

\newcommand{\floorceil}[1]{\lceil #1 \rfloor}

\makeatletter
\xpatchcmd{\@thm}{\thm@headpunct{.}}{\thm@headpunct{}}{}{}
\makeatother

\renewcommand{\cftpartfont}{\hrule\bfseries\Large}%add line above part
\renewcommand{\cftpartpagefont}{\bfseries}
\setlength{\cftbeforepartskip}{5mm}
\renewcommand{\cftpartafterpnum}{\\\hrule}%add line below part
\cftpagenumbersoff{part}%no page numbers for part-level entries

%% commented out:
%\setlength{\cftsecindent}{8mm}% spacing between number and sec title
%\setlength{\cftsecnumwidth}{6mm}%section indent

%% new instructions:
\cftsetindents{chap}{0em}{1.5em}
\cftsetindents{sec}{1.5em}{2em}  % 1st length should be sum of lengths on preceding line
\cftsetindents{subsec}{3.5em}{2.75em}

\setlength{\cftparskip}{4mm}%control line spacing

\begin{document}
\tableofcontents

\part{First part}
\chapter{Chapter1}
\section{Section1.1}
\subsection{Subsection1.1.1}
\chapter{Chapter2}
\section{Section2.1}
\section{Section2.2}
\subsection{Subsection2.2.1}
\part{Second part}
\chapter{Chapter3}
\section{Section3.1}
\subsection{Subsection3.1.1}
\end{document}