Master/texmf-dist/doc/generic/FAQ-en/html/FAQ-ifpdf.html


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<head>
<title>UK TeX FAQ -- question label ifpdf</title>
</head><body>
<h3>Am I using PDFTeX?</h3>
<p/>It&rsquo;s often useful to know whether your macros are operating within
PDFTeX or within (&ldquo;normal&rdquo;) TeX; getting the right answer is
surprisingly tricky.
<p/>Suppose you need to test whether your output will be PDF or
DVI.  The natural thing is to check whether you have access to
some PDFTeX-only primitive; a good one to try (not least because it
was present in the very first releases of PDFTeX) is
<code>\</code><code>pdfoutput</code>.  So you try
<blockquote>
<pre>
\ifx\pdfoutput\undefined
  &lt;not running PDFTeX&gt;
\else
  &lt;running PDFTeX&gt;
\fi
</pre>
</blockquote><p>
Except that neither branch of this conditional is rock-solid.  The
first branch can be misleading, since the &ldquo;awkward&rdquo; user could have
written:
<blockquote>
<pre>
\let\pdfoutput\undefined
</pre>
</blockquote><p>
so that your test will falsely choose the first alternative.  While
this is a theoretical problem, it is unlikely to be a major one.
<p/>More important is the user who loads a package that uses
LaTeX-style testing for the command name&rsquo;s existence (for example,
the LaTeX <i>graphics</i> package, which is useful even to the
Plain TeX user).  Such a package may have gone ahead of you, so the
test may need to be elaborated:
<blockquote>
<pre>
\ifx\pdfoutput\undefined
  &lt;not running PDFTeX&gt;
\else
  \ifx\pdfoutput\relax
    &lt;not running PDFTeX&gt;
  \else
    &lt;running PDFTeX&gt;
  \fi
\fi
</pre>
</blockquote><p>
If you only want to know whether some PDFTeX extension (such as
marginal kerning) is present, you can stop at this point: you know as
much as you need.
<p/>However, if you need to know whether you&rsquo;re creating PDF
output, you also need to know about the value of <code>\</code><code>pdfoutput</code>:
<blockquote>
<pre>
\ifx\pdfoutput\undefined
  &lt;not running PDFTeX&gt;
\else
  \ifx\pdfoutput\relax
    &lt;not running PDFTeX&gt;
  \else
    &lt;running PDFTeX, with...&gt;
    \ifnum\pdfoutput&gt;0
      &lt;...PDF output&gt;
    \else
      &lt;...DVI output&gt;
    \fi
  \fi
\fi
</pre>
</blockquote><p>
The above is, in essence, what Heiko Oberdiek&rsquo;s <i>ifpdf</i>
package does; the reasoning is the FAQ&rsquo;s interpretation of
Heiko&rsquo;s explanation.
<dl>
<dt><tt><i>ifpdf.sty</i></tt><dd>Distributed with Heiko Oberdiek&rsquo;s packages <a href="ftp://cam.ctan.org/tex-archive/macros/latex/contrib/oberdiek.zip">macros/latex/contrib/oberdiek</a> (<a href="ftp://cam.ctan.org/tex-archive/macros/latex/contrib/oberdiek.tar.gz">gzipped tar</a>, <a href="http://www.tex.ac.uk/tex-archive/macros/latex/contrib/oberdiek/">browse</a>)
</dl>
<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=ifpdf">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=ifpdf</a>
</body>