ext_sgi.html revision 1.3
1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Deprecated</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="ext_containers.html" title="Chapter��23.��HP/SGI Extensions" /><link rel="prev" href="ext_containers.html" title="Chapter��23.��HP/SGI Extensions" /><link rel="next" href="ext_utilities.html" title="Chapter��24.��Utilities" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Deprecated</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_containers.html">Prev</a>��</td><th width="60%" align="center">Chapter��23.��HP/SGI Extensions</th><td width="20%" align="right">��<a accesskey="n" href="ext_utilities.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.containers.deprecated_sgi"></a>Deprecated</h2></div></div></div><p> 3 The SGI hashing classes <code class="classname">hash_set</code> and 4 <code class="classname">hash_set</code> have been deprecated by the 5 unordered_set, unordered_multiset, unordered_map, 6 unordered_multimap containers in TR1 and C++11, and 7 may be removed in future releases. 8 </p><p>The SGI headers</p><pre class="programlisting"> 9 <hash_map> 10 <hash_set> 11 <rope> 12 <slist> 13 <rb_tree> 14 </pre><p>are all here; 15 <code class="filename"><backwards/hash_map></code> and 16 <code class="filename"><backwards/hash_set></code> 17 are deprecated but available as backwards-compatible extensions, 18 as discussed further below. 19 <code class="filename"><ext/rope></code> is the SGI 20 specialization for large strings ("rope," "large strings," get it? Love 21 that geeky humor.) 22 <code class="filename"><ext/slist></code> (superseded in 23 C++11 by <code class="filename"><forward_list></code>) 24 is a singly-linked list, for when the doubly-linked <code class="code">list<></code> 25 is too much space overhead, and 26 <code class="filename"><ext/rb_tree></code> exposes the 27 red-black tree classes used in the implementation of the standard maps 28 and sets. 29 </p><p>Each of the associative containers map, multimap, set, and multiset 30 have a counterpart which uses a 31 <a class="link" href="http://www.sgi.com/tech/stl/HashFunction.html" target="_top">hashing 32 function</a> to do the arranging, instead of a strict weak ordering 33 function. The classes take as one of their template parameters a 34 function object that will return the hash value; by default, an 35 instantiation of 36 <a class="link" href="http://www.sgi.com/tech/stl/hash.html" target="_top">hash</a>. 37 You should specialize this functor for your class, or define your own, 38 before trying to use one of the hashing classes. 39 </p><p>The hashing classes support all the usual associative container 40 functions, as well as some extra constructors specifying the number 41 of buckets, etc. 42 </p><p>Why would you want to use a hashing class instead of the 43 <span class="quote">���<span class="quote">normal</span>���</span>implementations? Matt Austern writes: 44 </p><div class="blockquote"><blockquote class="blockquote"><p> 45 <span class="emphasis"><em>[W]ith a well chosen hash function, hash tables 46 generally provide much better average-case performance than 47 binary search trees, and much worse worst-case performance. So 48 if your implementation has hash_map, if you don't mind using 49 nonstandard components, and if you aren't scared about the 50 possibility of pathological cases, you'll probably get better 51 performance from hash_map. 52 </em></span> 53 </p></blockquote></div><p> 54 The deprecated hash tables are superseded by the standard unordered 55 associative containers defined in the ISO C++ 2011 standard in the 56 headers <code class="filename"><unordered_map></code> 57 and <code class="filename"><unordered_set></code>. 58 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_containers.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">Chapter��23.��HP/SGI Extensions��</td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top">��Chapter��24.��Utilities</td></tr></table></div></body></html>