mirror of git://gcc.gnu.org/git/gcc.git
543 lines
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HTML
543 lines
20 KiB
HTML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-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" type="text/css" />
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<link rel="Start" href="../documentation.html" type="text/html"
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title="GNU C++ Standard Library" />
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<link rel="Prev" href="../27_io/howto.html" type="text/html"
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title="Input/Output" />
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<link rel="Bookmark" href="sgiexts.html" type="text/html"
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title="SGI extensions" />
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<link rel="Bookmark" href="mt_allocator.html" type="text/html"
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title="__mt_alloc" />
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<link rel="Copyright" href="../17_intro/license.html" type="text/html" />
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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><strong>Before you leap in and use these</strong>, be aware of two things:
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</p>
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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... </li>
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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>. </li>
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</ol>
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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></li>
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<li><a href="#2">Added members and types</a></li>
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<li><a href="mt_allocator.html"><code>__mt_alloc</code> </a></li>
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<li><a href="#4">Compile-time checks</a></li>
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<li><a href="#5">LWG Issues</a></li>
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<li><a href="../18_support/howto.html#6">Demangling</a></li>
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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</p>
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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>
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<p>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/tech/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/tech/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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</p>
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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>(Side note: for those of you wondering, <strong>"Why wasn't a hash
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table included in the Standard in the first #!$@ place?"</strong>
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I'll 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 and types</a></h2>
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<p>Some of the classes in the Standard Library have additional
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publicly-available members, and some classes are themselves not in
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the standard. Of those, some are intended purely for the implementors,
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for example, additional typedefs. Those won't be described here
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(or anywhere else).
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</p>
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<ul>
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<li>The extensions added by SGI are so numerous that they have
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<a href="sgiexts.html">their own page</a>. Since the SGI STL is no
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longer actively maintained, we will try and keep this code working
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ourselves.</li>
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<li>Extensions allowing <code>filebuf</code>s to be constructed from
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stdio types are described in the
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<a href="../27_io/howto.html#11">chapter 27 notes</a>.</li>
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</ul>
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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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<hr />
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<h2><a name="5">LWG Issues</a></h2>
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<p>Everybody's got issues. Even the C++ Standard Library.
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</p>
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<p>The Library Working Group, or LWG, is the ISO subcommittee responsible
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for making changes to the library. They periodically publish an
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Issues List containing problems and possible solutions. As they reach
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a consensus on proposed solutions, we often incorporate the solution
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into libstdc++-v3.
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</p>
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<p>Here are the issues which have resulted in code changes to the library.
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The links are to the specific defect reports from a <strong>partial
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copy</strong> of the Issues List. You can read the full version online
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at the <a href="http://www.open-std.org/jtc1/sc22/wg21/">ISO C++
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Committee homepage</a>, linked to on the
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<a href="http://gcc.gnu.org/readings.html">GCC "Readings"
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page</a>. If
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you spend a lot of time reading the issues, we recommend downloading
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the ZIP file and reading them locally.
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</p>
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<p>(NB: <strong>partial copy</strong> means that not all links within
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the lwg-*.html pages will work.
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Specifically, links to defect reports that have not been accorded full
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DR status will probably break. Rather than trying to mirror the
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entire issues list on our overworked web server, we recommend you go
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to the LWG homepage instead.)
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</p>
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<p>
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If a DR is not listed here, we may simply not have gotten to it yet;
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feel free to submit a patch. Search the include/bits and src
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directories for appearances of _GLIBCXX_RESOLVE_LIB_DEFECTS for
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examples of style. Note that we usually do not make changes to the code
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until an issue has reached <a href="lwg-active.html#DR">DR</a> status.
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</p>
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<dl>
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<dt><a href="lwg-defects.html#5">5</a>:
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<em>string::compare specification questionable</em>
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</dt>
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<dd>This should be two overloaded functions rather than a single function.
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</dd>
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<dt><a href="lwg-defects.html#17">17</a>:
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<em>Bad bool parsing</em>
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</dt>
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<dd>Apparently extracting Boolean values was messed up...
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</dd>
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<dt><a href="lwg-defects.html#19">19</a>:
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<em>"Noconv" definition too vague</em>
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</dt>
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<dd>If <code>codecvt::do_in</code> returns <code>noconv</code> there are
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no changes to the values in <code>[to, to_limit)</code>.
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</dd>
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<dt><a href="lwg-defects.html#22">22</a>:
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<em>Member open vs flags</em>
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</dt>
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<dd>Re-opening a file stream does <em>not</em> clear the state flags.
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</dd>
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<dt><a href="lwg-defects.html#25">25</a>:
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<em>String operator<< uses width() value wrong</em>
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</dt>
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<dd>Padding issues.
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</dd>
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<dt><a href="lwg-defects.html#48">48</a>:
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<em>Use of non-existent exception constructor</em>
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</dt>
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<dd>An instance of <code>ios_base::failure</code> is constructed instead.
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</dd>
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<dt><a href="lwg-defects.html#49">49</a>:
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<em>Underspecification of ios_base::sync_with_stdio</em>
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</dt>
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<dd>The return type is the <em>previous</em> state of synchronization.
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</dd>
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<dt><a href="lwg-defects.html#50">50</a>:
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<em>Copy constructor and assignment operator of ios_base</em>
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</dt>
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<dd>These members functions are declared <code>private</code> and are
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thus inaccessible. Specifying the correct semantics of
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"copying stream state" was deemed too complicated.
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</dd>
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<dt><a href="lwg-defects.html#60">60</a>:
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<em>What is a formatted input function?</em>
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</dt>
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<dd>This DR made many widespread changes to <code>basic_istream</code>
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and <code>basic_ostream</code> all of which have been implemented.
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</dd>
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<dt><a href="lwg-defects.html#63">63</a>:
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<em>Exception-handling policy for unformatted output</em>
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</dt>
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<dd>Make the policy consistent with that of formatted input, unformatted
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input, and formatted output.
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</dd>
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<dt><a href="lwg-defects.html#68">68</a>:
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<em>Extractors for char* should store null at end</em>
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</dt>
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<dd>And they do now. An editing glitch in the last item in the list of
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[27.6.1.2.3]/7.
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</dd>
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<dt><a href="lwg-defects.html#74">74</a>:
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<em>Garbled text for codecvt::do_max_length</em>
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</dt>
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<dd>The text of the standard was gibberish. Typos gone rampant.
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</dd>
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<dt><a href="lwg-defects.html#75">75</a>:
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<em>Contradiction in codecvt::length's argument types</em>
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</dt>
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<dd>Change the first parameter to <code>stateT&</code> and implement
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the new effects paragraph.
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</dd>
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<dt><a href="lwg-defects.html#83">83</a>:
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<em>string::npos vs. string::max_size()</em>
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</dt>
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<dd>Safety checks on the size of the string should test against
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<code>max_size()</code> rather than <code>npos</code>.
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</dd>
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<dt><a href="lwg-defects.html#90">90</a>:
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<em>Incorrect description of operator>> for strings</em>
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</dt>
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<dd>The effect contain <code>isspace(c,getloc())</code> which must be
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replaced by <code>isspace(c,is.getloc())</code>.
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</dd>
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<dt><a href="lwg-defects.html#91">91</a>:
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<em>Description of operator>> and getline() for string<>
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might cause endless loop</em>
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</dt>
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<dd>They behave as a formatted input function and as an unformatted
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input function, respectively (except that <code>getline</code> is
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not required to set <code>gcount</code>).
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</dd>
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<dt><a href="lwg-defects.html#103">103</a>:
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<em>set::iterator is required to be modifiable, but this allows
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modification of keys.</em>
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</dt>
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<dd>For associative containers where the value type is the same as
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the key type, both <code>iterator</code> and <code>const_iterator
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</code> are constant iterators.
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</dd>
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<dt><a href="lwg-defects.html#109">109</a>:
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<em>Missing binders for non-const sequence elements</em>
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</dt>
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<dd>The <code>binder1st</code> and <code>binder2nd</code> didn't have an
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<code>operator()</code> taking a non-const parameter.
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</dd>
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<dt><a href="lwg-defects.html#110">110</a>:
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<em>istreambuf_iterator::equal not const</em>
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</dt>
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<dd>This was not a const member function. Note that the DR says to
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replace the function with a const one; we have instead provided an
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overloaded version with identical contents.
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</dd>
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<dt><a href="lwg-defects.html#117">117</a>:
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<em>basic_ostream uses nonexistent num_put member functions</em>
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</dt>
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<dd><code>num_put::put()</code> was overloaded on the wrong types.
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</dd>
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<dt><a href="lwg-defects.html#118">118</a>:
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<em>basic_istream uses nonexistent num_get member functions</em>
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</dt>
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<dd>Same as 117, but for <code>num_get::get()</code>.
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</dd>
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<dt><a href="lwg-defects.html#129">129</a>:
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<em>Need error indication from seekp() and seekg()</em>
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</dt>
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<dd>These functions set <code>failbit</code> on error now.
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</dd>
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<dt><a href="lwg-defects.html#136">136</a>:
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<em>seekp, seekg setting wrong streams?</em>
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</dt>
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<dd><code>seekp</code> should only set the output stream, and
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<code>seekg</code> should only set the input stream.
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</dd>
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<!--<dt><a href="lwg-defects.html#159">159</a>:
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<em>Strange use of underflow()</em>
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</dt>
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<dd>In fstream.tcc, the basic_filebuf<>::showmanyc() function
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should probably not be calling <code>underflow()</code>.
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</dd> -->
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<dt><a href="lwg-defects.html#167">167</a>:
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<em>Improper use of traits_type::length()</em>
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</dt>
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<dd><code>op<<</code> with a <code>const char*</code> was
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calculating an incorrect number of characters to write.
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</dd>
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<dt><a href="lwg-defects.html#171">171</a>:
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<em>Strange seekpos() semantics due to joint position</em>
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</dt>
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<dd>Quite complex to summarize...
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</dd>
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<dt><a href="lwg-defects.html#181">181</a>:
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<em>make_pair() unintended behavior</em>
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</dt>
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<dd>This function used to take its arguments as reference-to-const, now
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it copies them (pass by value).
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</dd>
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<dt><a href="lwg-defects.html#195">195</a>:
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<em>Should basic_istream::sentry's constructor ever set eofbit?</em>
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</dt>
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<dd>Yes, it can, specifically if EOF is reached while skipping whitespace.
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</dd>
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<dt><a href="lwg-defects.html#211">211</a>:
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<em>operator>>(istream&, string&) doesn't set failbit</em>
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</dt>
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<dd>If nothing is extracted into the string, <code>op>></code> now
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sets <code>failbit</code> (which can cause an exception, etc, etc).
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</dd>
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<dt><a href="lwg-defects.html#214">214</a>:
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<em>set::find() missing const overload</em>
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</dt>
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<dd>Both <code>set</code> and <code>multiset</code> were missing
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overloaded find, lower_bound, upper_bound, and equal_range functions
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for const instances.
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</dd>
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<dt><a href="lwg-defects.html#231">231</a>:
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<em>Precision in iostream?</em>
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</dt>
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<dd>For conversion from a floating-point type, <code>str.precision()</code>
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is specified in the conversion specification.
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</dd>
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<dt><a href="lwg-defects.html#235">235</a>:
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<em>No specification of default ctor for reverse_iterator</em>
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</dt>
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<dd>The declaration of <code>reverse_iterator</code> lists a default constructor.
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However, no specification is given what this constructor should do.
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</dd>
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<dt><a href="lwg-defects.html#243">243</a>:
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<em>get and getline when sentry reports failure</em>
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</dt>
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<dd>Store a null character only if the character array has a non-zero size.
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</dd>
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<dt><a href="lwg-defects.html#251">251</a>:
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<em>basic_stringbuf missing allocator_type</em>
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</dt>
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<dd>This nested typedef was originally not specified.
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</dd>
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<dt><a href="lwg-defects.html#253">253</a>:
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<em>valarray helper functions are almost entirely useless</em>
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</dt>
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<dd>Make the copy constructor and copy-assignment operator declarations
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public in gslice_array, indirect_array, mask_array, slice_array; provide
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definitions.
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</dd>
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<dt><a href="lwg-defects.html#265">265</a>:
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<em>std::pair::pair() effects overly restrictive</em>
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</dt>
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<dd>The default ctor would build its members from copies of temporaries;
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now it simply uses their respective default ctors.
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</dd>
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<dt><a href="lwg-defects.html#266">266</a>:
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<em>bad_exception::~bad_exception() missing Effects clause</em>
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</dt>
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<dd>The <code>bad_</code>* classes no longer have destructors (they
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are trivial), since no description of them was ever given.
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</dd>
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|
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<dt><a href="lwg-defects.html#271">271</a>:
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<em>basic_iostream missing typedefs</em>
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</dt>
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<dd>The typedefs it inherits from its base classes can't be used, since
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(for example) <code>basic_iostream<T>::traits_type</code> is ambiguous.
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</dd>
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|
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<dt><a href="lwg-defects.html#275">275</a>:
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<em>Wrong type in num_get::get() overloads</em>
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</dt>
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<dd>Similar to 118.
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</dd>
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<dt><a href="lwg-defects.html#292">292</a>:
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<em>Effects of a.copyfmt (a)</em>
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</dt>
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<dd>If <code>(this == &rhs)</code> do nothing.
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</dd>
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|
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<dt><a href="lwg-defects.html#300">300</a>:
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<em>List::merge() specification incomplete</em>
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</dt>
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<dd>If <code>(this == &x)</code> do nothing.
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|
</dd>
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|
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|
<dt><a href="lwg-defects.html#303">303</a>:
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|
<em>Bitset input operator underspecified</em>
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|
</dt>
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|
<dd>Basically, compare the input character to <code>is.widen(0)</code>
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|
and <code>is.widen(1)</code>.
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|
</dd>
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|
|
|
<dt><a href="lwg-defects.html#305">305</a>:
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|
<em>Default behavior of codecvt<wchar_t, char, mbstate_t>::length()</em>
|
|
</dt>
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|
<dd>Do not specify what <code>codecvt<wchar_t, char, mbstate_t>::do_length</code>
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|
must return.
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|
</dd>
|
|
|
|
<dt><a href="lwg-defects.html#328">328</a>:
|
|
<em>Bad sprintf format modifier in money_put<>::do_put()</em>
|
|
</dt>
|
|
<dd>Change the format string to "%.0Lf".
|
|
</dd>
|
|
|
|
<dt><a href="lwg-defects.html#365">365</a>:
|
|
<em>Lack of const-qualification in clause 27</em>
|
|
</dt>
|
|
<dd>Add const overloads of <code>is_open</code>.
|
|
</dd>
|
|
|
|
<dt><a href="lwg-defects.html#389">389</a>:
|
|
<em>Const overload of valarray::operator[] returns by value</em>
|
|
</dt>
|
|
<dd>Change it to return a <code>const T&</code>.
|
|
</dd>
|
|
|
|
<dt><a href="lwg-defects.html#402">402</a>:
|
|
<em>Wrong new expression in [some_]allocator::construct</em>
|
|
</dt>
|
|
<dd>Replace "new" with "::new".
|
|
</dd>
|
|
|
|
<dt><a href="lwg-active.html#434">434</a>:
|
|
<em>bitset::to_string() hard to use</em>
|
|
</dt>
|
|
<dd>Add three overloads, taking fewer template arguments.
|
|
</dd>
|
|
|
|
<dt><a href="lwg-active.html#453">453</a>:
|
|
<em>basic_stringbuf::seekoff need not always fail for an empty stream</em>
|
|
</dt>
|
|
<dd>Don't fail if the next pointer is null and newoff is zero.
|
|
</dd>
|
|
<!--
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|
<dt><a href="lwg-defects.html#"></a>:
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<em></em>
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</dt>
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<dd>
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</dd>
|
|
|
|
-->
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|
</dl>
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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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<!-- ####################################################### -->
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<hr />
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<p class="fineprint"><em>
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|
See <a href="../17_intro/license.html">license.html</a> for copying conditions.
|
|
Comments and suggestions are welcome, and may be sent to
|
|
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
|
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</em></p>
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</body>
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</html>
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