Misplaced \noalign when centering tabularx cell

Question

I have a minimal LaTeX document like this:

\documentclass{article}
\usepackage{tabularx}
\begin{document}
  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \centering A & B \\ \hline
    1.0 & 2.0 \\
  \end{tabularx}
\end{document}

I would like to center the table headers but left-align the columns. However, when I add \centering to the B header, like this:

\documentclass{article}
\usepackage{tabularx}
\begin{document}
  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \centering A & \centering B \\ \hline
    1.0 & 2.0 \\
  \end{tabularx}
\end{document}

I get this error:

! Misplaced \noalign.
\hline ->\noalign
                  {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth \futurelet...
l.8   \end{tabularx}

! Extra alignment tab has been changed to \cr.
<recently read> \endtemplate

l.8   \end{tabularx}

! Misplaced \noalign.
\hline ->\noalign
                  {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth \futurelet...
l.8   \end{tabularx}

! Extra alignment tab has been changed to \cr.
<recently read> \endtemplate

l.8   \end{tabularx}

! Misplaced \noalign.
\hline ->\noalign
                  {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth \futurelet...
l.8   \end{tabularx}

! Extra alignment tab has been changed to \cr.
<recently read> \endtemplate

l.8   \end{tabularx}

Not a duplicate, that's centering an entire column instead of individual cells. — Nathaniel M. Beaver, Feb 20 '19 at 22:15
So it's more general since the same procedure is applied to all cells within the same column. :-| — Werner, Feb 20 '19 at 22:21
Related: https://tex.stackexchange.com/questions/109206/misplaced-noalign — Nathaniel M. Beaver, Jul 27 '19 at 15:31

score 3 · Accepted Answer · edited Jul 26 '19 at 22:23

Page 2 of the tabularx documentation says that you have to use \arraybackslash after \centering (or \raggedright or \ragggedleft). Use like this:

\documentclass{article}
\usepackage{tabularx}
\begin{document}
  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \centering\arraybackslash A & \centering\arraybackslash B \\ \hline
    1.0 & 2.0 \\
  \end{tabularx}
\end{document}

LaTeX's text alignment commands redefine \\ so that they don't mean “a new line in the table” anymore. The \arraybackslash command does \let\\\tabularnewline so that it will work again.

Alternatively, you can use \tabularnewline instead of \\ at the end of the first row.

\documentclass{article}
\usepackage{tabularx}
\begin{document}
  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \centering A & \centering B \tabularnewline \hline
    1.0 & 2.0 \\
  \end{tabularx}
\end{document}

Bernard · Answer 2 · 2019-02-20T19:28:53.283

You can simply use a \multicolumn{1}{c}{...} for the column heads. Or load makecell and use its thead command (by default, its content is centred, both horizontally and vertically), which has the possibility to define a common formatting of all theads arguments. Here is an example of both methods:

\documentclass{article}
\usepackage{tabularx, makecell, xcolor}
\renewcommand{\theadfont}{\normalsize\bfseries\color{red}}

\begin{document}

  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \multicolumn{1}{c}{A} & \multicolumn{1}{c}{B} \\ \hline
    1.0 & 2.0 \\
  \end{tabularx}
\vspace{4ex}

  \noindent
  \begin{tabularx}{\linewidth}{ X | X }
    \thead{A} & \thead{B} \\ \hline
    1.0 & 2.0 \\
  \end{tabularx}

\end{document}

Misplaced \noalign when centering tabularx cell

2 Answers2