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<head>
<title>UK TeX FAQ -- question label tabcellalign</title>
</head><body>
<h3>How to alter the alignment of tabular cells</h3>
<p>One often needs to alter the alignment of a tabular <code>p</code> (‘paragraph’)
cell, but problems at the end of a table row are common. With a
<code>p</code> cell that looks like:
<blockquote>
<pre>
... & \centering blah ... \\
</pre>
</blockquote><p>
one is liable to encounter errors that complain about a “misplaced
<code>\</code><code>noalign</code>” or “<a href="FAQ-altabcr.html">extra alignment tab</a>”, or the like.
The problem is that the command <code>\\</code> means different things in
different circumstances: the <code>tabular</code> environment
switches the meaning to a value for use in the table, and
<code>\</code><code>centering</code>, <code>\</code><code>raggedright</code> and <code>\</code><code>raggedleft</code> all change the
meaning to something incompatible. Note that the problem only
arises in the last cell of a row: since each cell is set into a box,
its settings are lost at the <code>&</code> (or <code>\\</code>) that
terminates it.
<p>The simple (old) solution is to preserve the meaning of <code>\\</code>:
<blockquote>
<pre>
\newcommand\PBS[1]{\let\temp=\\%
#1%
\let\\=\temp
}
</pre>
</blockquote><p>
which one uses as:
<blockquote>
<pre>
... & \PBS\centering blah ... \\
</pre>
</blockquote><p>
(for example).
<p>The technique using <code>\</code><code>PBS</code> was developed in the days of LaTeX 2.09
because the actual value of <code>\\</code> that the <code>tabular</code>
environment uses was only available as an internal command. Nowadays,
the value is a public command, and you can in principle use it
explicitly:
<blockquote>
<pre>
... & \centering blah ... \tabularnewline
</pre>
</blockquote><p>
which may be incorporated into a simple macro as:
<blockquote>
<pre>
\newcommand{\RBS}{\let\\=\tabularnewline}
</pre>
</blockquote><p>
and used as
<blockquote>
<pre>
... & \centering\RBS blah ... \\
</pre>
</blockquote><p>
(note, you Preserve backslash with <code>\</code><code>PBS</code> <em>before</em> the command
that changes it, and Restore it with <code>\</code><code>RBS</code> <em>after</em> the
command; in fact, <code>\</code><code>RBS</code> is marginally preferable, but the old
trick lingers on).
<p>The <code>\</code><code>PBS</code> and <code>\</code><code>RBS</code> tricks also serve well in <i>array</i>
package “field format” preamble specifications:
<blockquote>
<pre>
\begin{tabular}{... >{\centering\RBS}p{50mm}}
...
</pre>
</blockquote><p>
or
<blockquote>
</blockquote><p>
<blockquote>
<pre>
\begin{tabular}{... >{\PBS\centering}p{50mm}}
...
</pre>
</blockquote><p>
In the <i>tabularx</i> and <i>tabulary</i> packages, there’s a
command <code>\</code><code>arraybackslash</code> that has same effect as <code>\</code><code>RBS</code> (above);
so in those packages, one might say:
<blockquote>
<pre>
\begin{tabular}{... >{\centering\arraybackslash}p{50mm}}
...
</pre>
</blockquote><p>
in place of the example above; in fact, the very latest (2003/12/01)
release of array.sty also provides a <code>\</code><code>tabularnewline</code> command,
that has the “basic tabular/array” meaning of ‘\\’.
The command does rather lack brevity, but at least you don’t have to
define it for yourself.
<dl>
<dt><tt><i>array.sty</i></tt><dd>Distributed as part of <a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/tools.zip">macros/latex/required/tools</a> (<a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/tools.tar.gz">gzipped tar</a>, <a href="http://www.tex.ac.uk/tex-archive/macros/latex/required/tools/">browse</a>)
<dt><tt><i>tabularx.sty</i></tt><dd>Distributed as part of <a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/tools.zip">macros/latex/required/tools</a> (<a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/tools.tar.gz">gzipped tar</a>, <a href="http://www.tex.ac.uk/tex-archive/macros/latex/required/tools/">browse</a>)
<dt><tt><i>tabulary.sty</i></tt><dd><a href="ftp://cam.ctan.org/tex-archive/macros/latex/contrib/tabulary.zip">macros/latex/contrib/tabulary</a> (<a href="ftp://cam.ctan.org/tex-archive/macros/latex/contrib/tabulary.tar.gz">gzipped tar</a>, <a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/tabulary/">browse</a>)
</dl>
<p><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=tabcellalign">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=tabcellalign</a>
</body>
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