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+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Deprecated HP/SGI</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="ext_containers.html" title="Chapter 33. Containers" /><link rel="prev" href="bk01pt12ch33s02.html" title="HP/SGI" /><link rel="next" href="ext_utilities.html" title="Chapter 34. Utilities" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Deprecated HP/SGI</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt12ch33s02.html">Prev</a> </td><th width="60%" align="center">Chapter 33. Containers</th><td width="20%" align="right"> <a accesskey="n" href="ext_utilities.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.containers.deprecated_sgi"></a>Deprecated HP/SGI</h2></div></div></div><p>
+ The SGI hashing classes <code class="classname">hash_set</code> and
+ <code class="classname">hash_set</code> have been deprecated by the
+ unordered_set, unordered_multiset, unordered_map,
+ unordered_multimap containers in TR1 and the upcoming C++0x, and
+ may be removed in future releases.
+ </p><p>The SGI headers</p><pre class="programlisting">
+ <hash_map>
+ <hash_set>
+ <rope>
+ <slist>
+ <rb_tree>
+ </pre><p>are all here;
+ <code class="code"><hash_map></code> and <code class="code"><hash_set></code>
+ are deprecated but available as backwards-compatible extensions,
+ as discussed further below. <code class="code"><rope></code> is the
+ SGI specialization for large strings ("rope,"
+ "large strings," get it? Love that geeky humor.)
+ <code class="code"><slist></code> is a singly-linked list, for when the
+ doubly-linked <code class="code">list<></code> is too much space
+ overhead, and <code class="code"><rb_tree></code> exposes the red-black
+ tree classes used in the implementation of the standard maps and
+ sets.
+ </p><p>Each of the associative containers map, multimap, set, and multiset
+ have a counterpart which uses a
+ <a class="ulink" href="http://www.sgi.com/tech/stl/HashFunction.html" target="_top">hashing
+ function</a> to do the arranging, instead of a strict weak ordering
+ function. The classes take as one of their template parameters a
+ function object that will return the hash value; by default, an
+ instantiation of
+ <a class="ulink" href="http://www.sgi.com/tech/stl/hash.html" target="_top">hash</a>.
+ You should specialize this functor for your class, or define your own,
+ before trying to use one of the hashing classes.
+ </p><p>The hashing classes support all the usual associative container
+ functions, as well as some extra constructors specifying the number
+ of buckets, etc.
+ </p><p>Why would you want to use a hashing class instead of the
+ “<span class="quote">normal</span>”implementations? Matt Austern writes:
+ </p><div class="blockquote"><blockquote class="blockquote"><p>
+ <span class="emphasis"><em>[W]ith a well chosen hash function, hash tables
+ generally provide much better average-case performance than
+ binary search trees, and much worse worst-case performance. So
+ if your implementation has hash_map, if you don't mind using
+ nonstandard components, and if you aren't scared about the
+ possibility of pathological cases, you'll probably get better
+ performance from hash_map.
+ </em></span>
+ </p></blockquote></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt12ch33s02.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ext_containers.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ext_utilities.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">HP/SGI </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 34. Utilities</td></tr></table></div></body></html>
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