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2001-09-17 Phil Edwards <pme@gcc.gnu.org> * docs/html/configopts.html: HTML to XHTML change. Lowercase tags. * docs/html/documentation.html: Likewise. * docs/html/explanations.html: Likewise. * docs/html/install.html: Likewise. * docs/html/17_intro/howto.html: Likewise. * docs/html/18_support/howto.html: Likewise. * docs/html/19_diagnostics/howto.html: Likewise. * docs/html/20_util/howto.html: Likewise. * docs/html/21_strings/howto.html: Likewise. * docs/html/22_locale/codecvt.html: Likewise. * docs/html/22_locale/ctype.html: Likewise. * docs/html/22_locale/howto.html: Likewise. * docs/html/22_locale/locale.html: Likewise. * docs/html/22_locale/messages.html: Likewise. * docs/html/23_containers/howto.html: Likewise. * docs/html/24_iterators/howto.html: Likewise. * docs/html/25_algorithms/howto.html: Likewise. * docs/html/26_numerics/howto.html: Likewise. * docs/html/27_io/howto.html: Likewise. * docs/html/ext/howto.html: Likewise. * docs/html/faq/index.html: Likewise. * docs/html/faq/index.txt: Regenerated. From-SVN: r45668
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174 lines
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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<html>
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<head>
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<meta HcodeP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<meta NAME="AUTHOR" CONTENT="pme@gcc.gnu.org (Phil Edwards)">
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<meta NAME="KEYWORDS" CONTENT="HOWTO, libstdc++, GCC, g++, libg++, STL">
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<meta NAME="DESCRIPTION" CONTENT="Notes for the libstdc++ extensions.">
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<meta NAME="GENERATOR" CONTENT="vi and eight fingers">
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<title>libstdc++-v3 HOWTO: Extensions</title>
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<link REL=StyleSheet HREF="../lib3styles.css">
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<!-- $Id: howto.html,v 1.5 2001/05/30 21:55:04 pme Exp $ -->
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</head>
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<body>
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<h1 CLASS="centered"><a name="top">Extensions</a></h1>
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<p>Here we will make an attempt at describing the non-Standard extensions to
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the library. Some of these are from SGI's STL, some of these are GNU's,
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and some just seemed to appear on the doorstep.
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</p>
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<p><B>Before you leap in and use these</B>, be aware of two things:
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<ol>
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<li>Non-Standard means exactly that. The behavior, and the very
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existence, of these extensions may change with little or no
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warning. (Ideally, the really good ones will appear in the next
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revision of C++.) Also, other platforms, other compilers, other
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versions of g++ or libstdc++-v3 may not recognize these names, or
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treat them differently, or...
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<li>You should know how to <a href="../faq/index.html#5_4">access
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these headers properly</a>.
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</ol>
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</p>
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<!-- ####################################################### -->
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<hr>
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<h1>Contents</h1>
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<ul>
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<li><a href="#1">Ropes and trees and hashes, oh my!</a>
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<li><a href="#2">Added members</a>
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<li><a href="#3">Allocators</a>
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<li><a href="#4">Compile-time checks</a>
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</ul>
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<hr>
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<!-- ####################################################### -->
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<h2><a name="1">Ropes and trees and hashes, oh my!</a></h2>
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<p>The SGI headers
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<PRE>
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<bvector>
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<hash_map>
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<hash_set>
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<rope>
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<slist>
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<tree>
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</PRE> are all here; <code><bvector></code> exposes the old bit_vector
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class that was used before specialization of vector<bool> was
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available (it's actually a typedef for the specialization now).
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<code><hash_map></code> and <code><hash_set></code>
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are discussed further below. <code><rope></code> is the SGI
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specialization for large strings ("rope," "large
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strings," get it? love those SGI folks).
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<code><slist></code> is a singly-linked list, for when the
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doubly-linked <code>list<></code> is too much space overhead, and
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<code><tree></code> exposes the red-black tree classes used in the
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implementation of the standard maps and sets.
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</p>
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<p>Okay, about those hashing classes... I'm going to foist most of the
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work off onto SGI's own site.
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</p>
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<p>Each of the associative containers map, multimap, set, and multiset
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have a counterpart which uses a
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<a href="http://www.sgi.com/Technology/STL/HashFunction.html">hashing
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function</a> to do the arranging, instead of a strict weak ordering
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function. The classes take as one of their template parameters a
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function object that will return the hash value; by default, an
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instantiation of
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<a href="http://www.sgi.com/Technology/STL/hash.html">hash</a>.
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You should specialize this functor for your class, or define your own,
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before trying to use one of the hashing classes.
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</p>
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<p>The hashing classes support all the usual associative container
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functions, as well as some extra constructors specifying the number
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of buckets, etc.
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</p>
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<p>Why would you want to use a hashing class instead of the
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"normal" implementations? Matt Austern writes:
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<BLOCKQUOTE><em>[W]ith a well chosen hash function, hash tables
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generally provide much better average-case performance than binary
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search trees, and much worse worst-case performance. So if your
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implementation has hash_map, if you don't mind using nonstandard
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components, and if you aren't scared about the possibility of
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pathological cases, you'll probably get better performance from
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hash_map.</em></BLOCKQUOTE>
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</p>
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<p>(Side note: for those of you wondering, <B>"Why wasn't a hash
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table included in the Standard in the first #!$@ place?"</B> I'll
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give a quick answer: it was proposed, but too late and in too
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unorganized a fashion. Some sort of hashing will undoubtedly be
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included in a future Standard.
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</p>
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<p>Return <a href="#top">to top of page</a> or
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<a href="../faq/index.html">to the FAQ</a>.
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</p>
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<hr>
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<h2><a name="2">Added members</a></h2>
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<p>Some of the classes in the Standard Library have additional
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publicly-available members. Of those, some are intended purely for
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the implementors, for example, additional typedefs. Those won't be
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described here (or anywhere else). This list will grow slowly, since
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we expect it to be rare -- most extensions will be self-contained.
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</p>
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<p>
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<ul>
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<li><code>filebuf</code>s have another ctor with this signature:<br>
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<code>basic_filebuf(__c_file_type*, ios_base::openmode, int_type);</code>
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<br>This comes in very handy in a number of places, such as
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attaching Unix sockets, pipes, and anything else which uses file
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descriptors, into the IOStream buffering classes. The three
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arguments are as follows:
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<ul>
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<li><code>__c_file_type* F </code>
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// the __c_file_type typedef usually boils down to stdio's FILE
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<li><code>ios_base::openmode M </code>
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// same as all the other uses of openmode
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<li><code>int_type B </code>
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// buffer size, defaults to BUFSIZ
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</ul>
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For those wanting to use file descriptors instead of FILE*'s, I
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invite you to contemplate the mysteries of C's <code>fdopen()</code>.
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</ul>
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</p>
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<p>Return <a href="#top">to top of page</a> or
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<a href="../faq/index.html">to the FAQ</a>.
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</p>
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<hr>
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<h2><a name="3">Allocators</a></h2>
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<p>This will be blank for a while. It will describe all of the different
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memory allocators, most inherited from SGI's code. Input is solicited.
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</p>
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<p>Return <a href="#top">to top of page</a> or
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<a href="../faq/index.html">to the FAQ</a>.
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</p>
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<hr>
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<h2><a name="4">Compile-time checks</a></h2>
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<p>Currently libstdc++-v3 uses the concept checkers from the Boost
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library to perform <a href="../19_diagnostics/howto.html#3">optional
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compile-time checking</a> of template instantiations of the standard
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containers. They are described in the linked-to page.
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</p>
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<p>Return <a href="#top">to top of page</a> or
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<a href="../faq/index.html">to the FAQ</a>.
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</p>
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<!-- ####################################################### -->
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<hr>
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<P CLASS="fineprint"><em>
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Comments and suggestions are welcome, and may be sent to
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<a href="mailto:libstdc++@gcc.gnu.org">the mailing list</a>.
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<br> $Id: howto.html,v 1.5 2001/05/30 21:55:04 pme Exp $
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</em></p>
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