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  • Committer: Bazaar Package Importer
  • Author(s): Roberto C. Sanchez
  • Date: 2008-05-17 20:14:19 UTC
  • mfrom: (1.1.1 upstream)
  • Revision ID: james.westby@ubuntu.com-20080517201419-qgbuogq2ckkdisyi
Tags: 5.10.0-2
Supersede botched upload of 5.10.0-1.

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functions/unpack.html
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      <h2>Links:</h2>
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      <ul>
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        <li><a href="http://search.cpan.org">CPAN</a></li>
 
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        <li><a href="http://www.perl.org">Perl.org</a></li>
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        <li><a href="http://www.perl.com">Perl.com</a></li>
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        <li><a href="http://www.perl.org">Perl.org</a></li>
 
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        <li><a href="http://perlbuzz.com">Perl Buzz</a></li>
 
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        <li><a href="http://www.perlfoundation.org/perl5/index.cgi">Perl 5 Wiki</a></li>
 
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        <li><a href="http://jobs.perl.org">Perl Jobs</a></li>
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        <li><a href="http://www.pm.org">Perl Mongers</a></li>
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        <li><a href="http://www.perlmonks.org">Perl Monks</a></li>
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        <li><a href="http://planet.perl.org">Planet Perl</a></li>
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      <ul>
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        <li>Site maintained by<br><a href="http://perl.jonallen.info">Jon Allen</a>
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            (<a href="http://perl.jonallen.info">JJ</a>)</li>
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        <li class="spaced">Last updated on<br>23 April 2006</li>
 
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        <li class="spaced">Last updated on<br>23 December 2007</li>
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        <li class="spaced">See the <a href="http://perl.jonallen.info/projects/perldoc">project page</a> for
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        more details</li>
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      </ul>
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    <div id="centerContent">
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      <div id="contentHeader">
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        <div id="contentHeaderLeft"><a href="#" onClick="showLeft()">Show navigation</a></div>
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        <div id="contentHeaderCentre">-- Perl 5.8.8 documentation --</div>
 
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        <div id="contentHeaderCentre">-- Perl 5.10.0 documentation --</div>
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        <div id="contentHeaderRight"><a href="#" onClick="showRight()">Show toolbar</a></div>
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      </div>
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      <div id="breadCrumbs"><a href="../index.html">Home</a> &gt; <a href="../index-language.html">Language reference</a> &gt; <a href="../index-functions.html">Functions</a> &gt; unpack</div>
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      <div id="contentBody"><div class="title_container"><div class="page_title">unpack</div></div><div class="mod_az_list"><a href="../index-functions.html">Perl functions A-Z</a> | <a href="../index-functions-by-cat.html">Perl functions by category</a> | <a href="../perlfunc.html">The 'perlfunc' manpage</a></div><ul>
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<li><a name="unpack-TEMPLATE%2cEXPR"></a><b>unpack TEMPLATE,EXPR</b>
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<p></p>
 
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</li>
 
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</ul>
 
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<ul>
 
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<li><a name="unpack-TEMPLATE"></a><b>unpack TEMPLATE</b>
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<p><code class="inline"><a class="l_k" href="../functions/unpack.html">unpack</a></code> does the reverse of <code class="inline"><a class="l_k" href="../functions/pack.html">pack</a></code>: it takes a string
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and expands it out into a list of values.
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(In scalar context, it returns merely the first value produced.)</p>
 
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<p>If EXPR is omitted, unpacks the <code class="inline"><span class="i">$_</span></code>
 
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 string.</p>
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<p>The string is broken into chunks described by the TEMPLATE.  Each chunk
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is converted separately to a value.  Typically, either the string is a result
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of <code class="inline"><a class="l_k" href="../functions/pack.html">pack</a></code>, or the bytes of the string represent a C structure of some
 
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of <code class="inline"><a class="l_k" href="../functions/pack.html">pack</a></code>, or the characters of the string represent a C structure of some
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kind.</p>
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<p>The TEMPLATE has the same format as in the <code class="inline"><a class="l_k" href="../functions/pack.html">pack</a></code> function.
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Here's a subroutine that does substring:</p>
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        <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;x$where a$howmuch&quot;</span><span class="cm">,</span> <span class="i">$what</span><span class="s">)</span><span class="sc">;</span>
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    <span class="s">}</span></pre>
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<p>and then there's</p>
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<pre class="verbatim"><a name="ordinal"></a>    sub <span class="m">ordinal</span> <span class="s">{</span> <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;c&quot;</span><span class="cm">,</span><span class="i">$_</span>[<span class="n">0</span>]<span class="s">)</span><span class="sc">;</span> <span class="s">}</span> <span class="c"># same as ord()</span></pre>
 
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<pre class="verbatim"><a name="ordinal"></a>    sub <span class="m">ordinal</span> <span class="s">{</span> <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;W&quot;</span><span class="cm">,</span><span class="i">$_</span>[<span class="n">0</span>]<span class="s">)</span><span class="sc">;</span> <span class="s">}</span> <span class="c"># same as ord()</span></pre>
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<p>In addition to fields allowed in pack(), you may prefix a field with
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a %&lt;number&gt; to indicate that
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you want a &lt;number&gt;-bit checksum of the items instead of the items
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computes the same number as the System V sum program:</p>
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<pre class="verbatim">    <span class="i">$checksum</span> = <a class="l_k" href="../functions/do.html">do</a> <span class="s">{</span>
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        <a class="l_k" href="../functions/local.html">local</a> <span class="i">$/</span><span class="sc">;</span>  <span class="c"># slurp!</span>
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        <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;%32C*&quot;</span><span class="cm">,</span>&lt;&gt;<span class="s">)</span> % <span class="n">65535</span><span class="sc">;</span>
 
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        <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;%32W*&quot;</span><span class="cm">,</span>&lt;&gt;<span class="s">)</span> % <span class="n">65535</span><span class="sc">;</span>
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    <span class="s">}</span><span class="sc">;</span></pre>
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<p>The following efficiently counts the number of set bits in a bit vector:</p>
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<pre class="verbatim">    <span class="i">$setbits</span> = <a class="l_k" href="../functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;%32b*&quot;</span><span class="cm">,</span> <span class="i">$selectmask</span><span class="s">)</span><span class="sc">;</span></pre>
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<p>The <code class="inline">p</code>
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 and <code class="inline">P</code>
 
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<p>The <code class="inline"><span class="w">p</span></code>
 
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 and <code class="inline"><span class="w">P</span></code>
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 formats should be used with care.  Since Perl
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has no way of checking whether the value passed to <code class="inline"><a class="l_k" href="../functions/unpack.html">unpack()</a></code>
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corresponds to a valid memory location, passing a pointer value that's
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<code class="inline"><a class="l_k" href="../functions/unpack.html">unpack()</a></code> will produce null strings or zeroes, or terminate with an
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error. If the input string is longer than one described by the TEMPLATE,
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the rest is ignored.</p>
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<p>See <a href="pack.html">pack</a> for more examples and notes.</p>
 
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<p>See <a href="#pack">"pack"</a> for more examples and notes.</p>
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</li>
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</ul>
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</div>
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          <!--<select name="r"><option value="1" selected>Go to top result<option value="0">Show results list</select>-->
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        </form>
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      </p>
 
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      <script language="JavaScript" type="text/javascript" src="/perl-version.js"></script>
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      <h2>Labels:</h2>
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      <p>
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        <a href="#" onClick="addLabel('unpack','functions/unpack.html')">Add this page</a>