summaryrefslogtreecommitdiff
path: root/Master/texmf-dist/doc/generic/FAQ-en/html/FAQ-oddpage.html
blob: 4e7f785ced8ffadc51e1b4a60bfea2c87f6baf73 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
<head>
<title>UK TeX FAQ -- question label oddpage</title>
</head><body>
<h3>Finding if you&rsquo;re on an odd or an even page</h3>
<p/><a href="FAQ-marginparside.html">Another question</a> discusses the issue
of getting <code>\</code><code>marginpar</code> commands to put their output in the correct
margin of two-sided documents.  This is an example of the general
problem of knowing where a particular bit of text lies: the output
routine is asynchronous, and (La)TeX will usually process quite a
bit of the &ldquo;next&rdquo; page before deciding to output any page.  As a
result, the <code>page</code> counter (known internally in LaTeX as
<code>\</code><code>c@page</code>) is normally only reliable when you&rsquo;re actually <em>in</em>
the output routine.
<p/>The solution is to use some version of the <code>\</code><code>label</code> mechanism to
determine which side of the page you&rsquo;re on; the value of the page
counter that appears in a <code>\</code><code>pageref</code> command has been inserted in
the course of the output routine, and is therefore safe.
<p/>However, <code>\</code><code>pageref</code> itself isn&rsquo;t reliable: one might hope that
<pre>
\ifthenelse{\isodd{\pageref{foo}}}{odd}{even}
</pre>
would do the necessary, but both the <i>babel</i> and
<i>hyperref</i> packages have been known to interfere with the
output of <code>\</code><code>pageref</code>; be careful!
<p/>The <i>changepage</i> package needs to provide this functionality for
its own use, and therefore provides a command <code>\</code><code>checkoddpage</code>; this
sets a private-use label, and the page reference part of that label is
then examined (in a <i>hyperref</i>-safe way) to set a conditional 
<code>\</code><code>ifoddpage</code> true if the command was issued on an odd page.  The
<i>memoir</i> class has the same command setting a conditional
<code>\</code><code>ifoddpage</code>.  Of course, the <code>\</code><code>label</code> contributes to LaTeX&rsquo;s
&ldquo;Rerun to get cross-references right&rdquo; error messages&hellip;
<p/>The Koma-Script classes have an <code>addmargin*</code> environment
that also provides the sorts of facilities that the <i>changepage</i>
offers.  Koma-Script&rsquo;s supporting command is 
<code>\</code><code>ifthispageodd{&lt;true&gt;}{&lt;false&gt;}</code> executes different things
depending on the page number.
<dl>
<dt><tt><i>changepage.sty</i></tt><dd><a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/misc/changepage.sty">macros/latex/contrib/misc/changepage.sty</a>
<dt><tt><i>KOMA script bundle</i></tt><dd><a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/koma-script.zip">macros/latex/contrib/koma-script</a> (or <a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/koma-script/">browse the directory</a>)
<dt><tt><i>memoir.cls</i></tt><dd><a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/memoir.zip">macros/latex/contrib/memoir</a> (or <a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/memoir/">browse the directory</a>)
</dl>
<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=oddpage">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=oddpage</a>
</body>