How to left align the section title in latex?

Question

I am using the \documentclass{ctexart}, and this document class centers the section title by default. How could I left align the section title?

Answer 1

Here are two options:

1. Add \raggedright to all \sections globally:

   \documentclass{ctexart}
   \usepackage{lipsum}
   \makeatletter
   \g@addto@macro{\CTEX@section@format}{\raggedright}
   \makeatother
   \begin{document}
   \section{A section}
   \lipsum
   \end{document}
   

2. Use sectsty and modify \sectionfont:

   \documentclass{ctexart}
   \usepackage{lipsum}
   \usepackage{sectsty}
   \sectionfont{\bfseries\Large\raggedright}
   \begin{document}
   \section{A section}
   \lipsum
   \end{document}
   

Both instances above yield as output:

One would have to follow a similar technique for other sectional units.

Answer 2

One would think that the definition

\def\CTEX@section@format{\Large\bfseries}

found on line 20 of ctex-article.def would the one valid for articles. For mysterious reasons, in the ctexcap.cfg file one finds

\def\CTEX@section@format{\Large\bfseries\centering}

The file states

% ctexcap.cfg: default Chinese caption settings

I find it confusing, but that's the situation. You can fix it by just restoring the first definition:

\documentclass{ctexart}
\usepackage{lipsum}

\makeatletter
\def\CTEX@section@format{\Large\bfseries}
\makeatother

\begin{document}
\section{A section}
\lipsum[2]
\end{document}

Answer 3

You should read the document first.

For ctex v1.02d and older version:

\CTEXsetup[format=\Large\bfseries]{section}

For ctex v2.0 and later:

\ctexset{section/format=\Large\bfseries}