llvm-gcc-4.0/libstdc++-v3/docs/html/ext/howto.html - llvm-archive - Git at Google

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    <title>libstdc++-v3 HOWTO:  Extensions</title>
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 <h1 class="centered"><a name="top">Extensions</a></h1>

 <p>Here we will make an attempt at describing the non-Standard extensions to
    the library.  Some of these are from SGI's STL, some of these are GNU's,
    and some just seemed to appear on the doorstep.
 </p>
 <p><strong>Before you leap in and use these</strong>, be aware of two things:
 </p>
 <ol>
    <li>Non-Standard means exactly that.  The behavior, and the very
        existence, of these extensions may change with little or no
        warning.  (Ideally, the really good ones will appear in the next
        revision of C++.)  Also, other platforms, other compilers, other
        versions of g++ or libstdc++-v3 may not recognize these names, or
        treat them differently, or... </li>
    <li>You should know how to <a href="../faq/index.html#5_4">access
        these headers properly</a>. </li>
 </ol>


 <!-- ####################################################### -->
 <hr />
 <h1>Contents</h1>
 <ul>
    <li><a href="#1">Ropes and trees and hashes, oh my!</a></li>
    <li><a href="#2">Added members and types</a></li>
    <li><a href="mt_allocator.html"><code>__mt_alloc</code> </a></li>
    <li><a href="#4">Compile-time checks</a></li>
    <li><a href="#5">LWG Issues</a></li>
    <li><a href="../18_support/howto.html#6">Demangling</a></li>
 </ul>

 <hr />

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 <h2><a name="1">Ropes and trees and hashes, oh my!</a></h2>
    <p>The SGI headers</p>
    <pre>
      &lt;bvector&gt;
      &lt;hash_map&gt;
      &lt;hash_set&gt;
      &lt;rope&gt;
      &lt;slist&gt;
      &lt;tree&gt;
    </pre>
    <p>are all here; <code>&lt;bvector&gt;</code> exposes the old bit_vector
       class that was used before specialization of vector&lt;bool&gt; was
       available (it's actually a typedef for the specialization now).
       <code>&lt;hash_map&gt;</code> and <code>&lt;hash_set&gt;</code>
       are discussed further below.  <code>&lt;rope&gt;</code> is the SGI
       specialization for large strings (&quot;rope,&quot; &quot;large
       strings,&quot; get it?  love those SGI folks).
       <code>&lt;slist&gt;</code> is a singly-linked list, for when the
       doubly-linked <code>list&lt;&gt;</code> is too much space overhead, and
       <code>&lt;tree&gt;</code> exposes the red-black tree classes used in the
       implementation of the standard maps and sets.
    </p>
    <p>Okay, about those hashing classes...  I'm going to foist most of the
       work off onto SGI's own site.
    </p>
    <p>Each of the associative containers map, multimap, set, and multiset
       have a counterpart which uses a
       <a href="http://www.sgi.com/tech/stl/HashFunction.html">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 href="http://www.sgi.com/tech/stl/hash.html">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
       &quot;normal&quot; implementations?  Matt Austern writes:
    </p>
    <blockquote><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></blockquote>
    <p>(Side note:  for those of you wondering, <strong>&quot;Why wasn't a hash
       table included in the Standard in the first #!$@ place?&quot;</strong>
       I'll give a quick answer:  it was proposed, but too late and in too
       unorganized a fashion.  Some sort of hashing will undoubtedly be
       included in a future Standard.)
    </p>
    <p>Return <a href="#top">to top of page</a> or
       <a href="../faq/index.html">to the FAQ</a>.
    </p>

 <hr />
 <h2><a name="2">Added members and types</a></h2>
    <p>Some of the classes in the Standard Library have additional
       publicly-available members, and some classes are themselves not in
       the standard.  Of those, some are intended purely for the implementors,
       for example, additional typedefs.  Those won't be described here
       (or anywhere else).
    </p>
    <ul>
      <li>The extensions added by SGI are so numerous that they have
          <a href="sgiexts.html">their own page</a>.  Since the SGI STL is no
          longer actively maintained, we will try and keep this code working
          ourselves.</li>
      <li>Extensions allowing <code>filebuf</code>s to be constructed from
          stdio types are described in the
          <a href="../27_io/howto.html#11">chapter 27 notes</a>.</li>
    </ul>
    <p>Return <a href="#top">to top of page</a> or
       <a href="../faq/index.html">to the FAQ</a>.
    </p>

 <hr />
 <h2><a name="4">Compile-time checks</a></h2>
    <p>Currently libstdc++-v3 uses the concept checkers from the Boost
       library to perform <a href="../19_diagnostics/howto.html#3">optional
       compile-time checking</a> of template instantiations of the standard
       containers.  They are described in the linked-to page.
    </p>
    <p>Return <a href="#top">to top of page</a> or
       <a href="../faq/index.html">to the FAQ</a>.
    </p>

 <hr />
 <h2><a name="5">LWG Issues</a></h2>
    <p>Everybody's got issues.  Even the C++ Standard Library.
    </p>
    <p>The Library Working Group, or LWG, is the ISO subcommittee responsible
       for making changes to the library.  They periodically publish an
       Issues List containing problems and possible solutions.  As they reach
       a consensus on proposed solutions, we often incorporate the solution
       into libstdc++-v3.
    </p>
    <p>Here are the issues which have resulted in code changes to the library.
       The links are to the specific defect reports from a <strong>partial
       copy</strong> of the Issues List.  You can read the full version online
       at the <a href="http://www.open-std.org/jtc1/sc22/wg21/">ISO C++
       Committee homepage</a>, linked to on the
       <a href="http://gcc.gnu.org/readings.html">GCC &quot;Readings&quot;
       page</a>.  If
       you spend a lot of time reading the issues, we recommend downloading
       the ZIP file and reading them locally.
    </p>
    <p>(NB:  <strong>partial copy</strong> means that not all links within
       the lwg-*.html pages will work.
       Specifically, links to defect reports that have not been accorded full
       DR status will probably break.  Rather than trying to mirror the
       entire issues list on our overworked web server, we recommend you go
       to the LWG homepage instead.)
    </p>
    <p>
       If a DR is not listed here, we may simply not have gotten to it yet;
       feel free to submit a patch.  Search the include/bits and src
       directories for appearances of _GLIBCXX_RESOLVE_LIB_DEFECTS for
       examples of style.  Note that we usually do not make changes to the code
       until an issue has reached <a href="lwg-active.html#DR">DR</a> status.
    </p>
    <dl>
     <dt><a href="lwg-defects.html#5">5</a>:
         <em>string::compare specification questionable</em>
     </dt>
     <dd>This should be two overloaded functions rather than a single function.
     </dd>

     <dt><a href="lwg-defects.html#17">17</a>:
         <em>Bad bool parsing</em>
     </dt>
     <dd>Apparently extracting Boolean values was messed up...
     </dd>

     <dt><a href="lwg-defects.html#19">19</a>:
         <em>&quot;Noconv&quot; definition too vague</em>
     </dt>
     <dd>If <code>codecvt::do_in</code> returns <code>noconv</code> there are
         no changes to the values in <code>[to, to_limit)</code>.
     </dd>

     <dt><a href="lwg-defects.html#22">22</a>:
         <em>Member open vs flags</em>
     </dt>
     <dd>Re-opening a file stream does <em>not</em> clear the state flags.
     </dd>

     <dt><a href="lwg-defects.html#25">25</a>:
         <em>String operator&lt;&lt; uses width() value wrong</em>
     </dt>
     <dd>Padding issues.
     </dd>

     <dt><a href="lwg-defects.html#48">48</a>:
         <em>Use of non-existent exception constructor</em>
     </dt>
     <dd>An instance of <code>ios_base::failure</code> is constructed instead.
     </dd>

     <dt><a href="lwg-defects.html#49">49</a>:
         <em>Underspecification of ios_base::sync_with_stdio</em>
     </dt>
     <dd>The return type is the <em>previous</em> state of synchronization.
     </dd>

     <dt><a href="lwg-defects.html#50">50</a>:
         <em>Copy constructor and assignment operator of ios_base</em>
     </dt>
     <dd>These members functions are declared <code>private</code> and are
         thus inaccessible.  Specifying the correct semantics of
         &quot;copying stream state&quot; was deemed too complicated.
     </dd>

     <dt><a href="lwg-defects.html#60">60</a>:
         <em>What is a formatted input function?</em>
     </dt>
     <dd>This DR made many widespread changes to <code>basic_istream</code>
         and <code>basic_ostream</code> all of which have been implemented.
     </dd>

     <dt><a href="lwg-defects.html#63">63</a>:
         <em>Exception-handling policy for unformatted output</em>
     </dt>
     <dd>Make the policy consistent with that of formatted input, unformatted
         input, and formatted output.
     </dd>

     <dt><a href="lwg-defects.html#68">68</a>:
         <em>Extractors for char* should store null at end</em>
     </dt>
     <dd>And they do now.  An editing glitch in the last item in the list of
         [27.6.1.2.3]/7.
     </dd>

     <dt><a href="lwg-defects.html#74">74</a>:
         <em>Garbled text for codecvt::do_max_length</em>
     </dt>
     <dd>The text of the standard was gibberish.  Typos gone rampant.
     </dd>

     <dt><a href="lwg-defects.html#75">75</a>:
         <em>Contradiction in codecvt::length's argument types</em>
     </dt>
     <dd>Change the first parameter to <code>stateT&amp;</code> and implement
         the new effects paragraph.
     </dd>

     <dt><a href="lwg-defects.html#83">83</a>:
         <em>string::npos vs. string::max_size()</em>
     </dt>
     <dd>Safety checks on the size of the string should test against
         <code>max_size()</code> rather than <code>npos</code>.
     </dd>

     <dt><a href="lwg-defects.html#90">90</a>:
         <em>Incorrect description of operator&gt;&gt; for strings</em>
     </dt>
     <dd>The effect contain <code>isspace(c,getloc())</code> which must be
         replaced by <code>isspace(c,is.getloc())</code>.
     </dd>

     <dt><a href="lwg-defects.html#91">91</a>:
         <em>Description of operator&gt;&gt; and getline() for string&lt;&gt;
 	    might cause endless loop</em>
     </dt>
     <dd>They behave as a formatted input function and as an unformatted
         input function, respectively (except that <code>getline</code> is
 	not required to set <code>gcount</code>).
     </dd>

     <dt><a href="lwg-defects.html#103">103</a>:
         <em>set::iterator is required to be modifiable, but this allows
 	    modification of keys.</em>
     </dt>
     <dd>For associative containers where the value type is the same as
         the key type, both <code>iterator</code> and <code>const_iterator
 	</code> are constant iterators.
     </dd>

     <dt><a href="lwg-defects.html#109">109</a>:
         <em>Missing binders for non-const sequence elements</em>
     </dt>
     <dd>The <code>binder1st</code> and <code>binder2nd</code> didn't have an
         <code>operator()</code> taking a non-const parameter.
     </dd>

     <dt><a href="lwg-defects.html#110">110</a>:
         <em>istreambuf_iterator::equal not const</em>
     </dt>
     <dd>This was not a const member function.  Note that the DR says to
         replace the function with a const one; we have instead provided an
         overloaded version with identical contents.
     </dd>

     <dt><a href="lwg-defects.html#117">117</a>:
         <em>basic_ostream uses nonexistent num_put member functions</em>
     </dt>
     <dd><code>num_put::put()</code> was overloaded on the wrong types.
     </dd>

     <dt><a href="lwg-defects.html#118">118</a>:
         <em>basic_istream uses nonexistent num_get member functions</em>
     </dt>
     <dd>Same as 117, but for <code>num_get::get()</code>.
     </dd>

     <dt><a href="lwg-defects.html#129">129</a>:
         <em>Need error indication from seekp() and seekg()</em>
     </dt>
     <dd>These functions set <code>failbit</code> on error now.
     </dd>

     <dt><a href="lwg-defects.html#136">136</a>:
         <em>seekp, seekg setting wrong streams?</em>
     </dt>
     <dd><code>seekp</code> should only set the output stream, and
         <code>seekg</code> should only set the input stream.
     </dd>

 <!--<dt><a href="lwg-defects.html#159">159</a>:
         <em>Strange use of underflow()</em>
     </dt>
     <dd>In fstream.tcc, the basic_filebuf&lt;&gt;::showmanyc() function
         should probably not be calling <code>underflow()</code>.
     </dd> -->

     <dt><a href="lwg-defects.html#167">167</a>:
         <em>Improper use of traits_type::length()</em>
     </dt>
     <dd><code>op&lt;&lt;</code> with a <code>const char*</code> was
         calculating an incorrect number of characters to write.
     </dd>

     <dt><a href="lwg-defects.html#171">171</a>:
         <em>Strange seekpos() semantics due to joint position</em>
     </dt>
     <dd>Quite complex to summarize...
     </dd>

     <dt><a href="lwg-defects.html#181">181</a>:
         <em>make_pair() unintended behavior</em>
     </dt>
     <dd>This function used to take its arguments as reference-to-const, now
         it copies them (pass by value).
     </dd>

     <dt><a href="lwg-defects.html#195">195</a>:
         <em>Should basic_istream::sentry's constructor ever set eofbit?</em>
     </dt>
     <dd>Yes, it can, specifically if EOF is reached while skipping whitespace.
     </dd>

     <dt><a href="lwg-defects.html#211">211</a>:
         <em>operator&gt;&gt;(istream&amp;, string&amp;) doesn't set failbit</em>
     </dt>
     <dd>If nothing is extracted into the string, <code>op&gt;&gt;</code> now
         sets <code>failbit</code> (which can cause an exception, etc, etc).
     </dd>

     <dt><a href="lwg-defects.html#214">214</a>:
         <em>set::find() missing const overload</em>
     </dt>
     <dd>Both <code>set</code> and <code>multiset</code> were missing
         overloaded find, lower_bound, upper_bound, and equal_range functions
         for const instances.
     </dd>

     <dt><a href="lwg-defects.html#231">231</a>:
         <em>Precision in iostream?</em>
     </dt>
     <dd>For conversion from a floating-point type, <code>str.precision()</code>
         is specified in the conversion specification.
     </dd>

     <dt><a href="lwg-defects.html#235">235</a>:
         <em>No specification of default ctor for reverse_iterator</em>
     </dt>
     <dd>The declaration of <code>reverse_iterator</code> lists a default constructor.
         However, no specification is given what this constructor should do.
     </dd>

     <dt><a href="lwg-defects.html#243">243</a>:
         <em>get and getline when sentry reports failure</em>
     </dt>
     <dd>Store a null character only if the character array has a non-zero size.
     </dd>

     <dt><a href="lwg-defects.html#251">251</a>:
         <em>basic_stringbuf missing allocator_type</em>
     </dt>
     <dd>This nested typedef was originally not specified.
     </dd>

     <dt><a href="lwg-defects.html#253">253</a>:
         <em>valarray helper functions are almost entirely useless</em>
     </dt>
     <dd>Make the copy constructor and copy-assignment operator declarations
         public in gslice_array, indirect_array, mask_array, slice_array; provide
 	definitions.
     </dd>

     <dt><a href="lwg-defects.html#265">265</a>:
         <em>std::pair::pair() effects overly restrictive</em>
     </dt>
     <dd>The default ctor would build its members from copies of temporaries;
         now it simply uses their respective default ctors.
     </dd>

     <dt><a href="lwg-defects.html#266">266</a>:
         <em>bad_exception::~bad_exception() missing Effects clause</em>
     </dt>
     <dd>The <code>bad_</code>* classes no longer have destructors (they
         are trivial), since no description of them was ever given.
     </dd>

     <dt><a href="lwg-defects.html#271">271</a>:
         <em>basic_iostream missing typedefs</em>
     </dt>
     <dd>The typedefs it inherits from its base classes can't be used, since
         (for example) <code>basic_iostream&lt;T&gt;::traits_type</code> is ambiguous.
     </dd>

     <dt><a href="lwg-defects.html#275">275</a>:
         <em>Wrong type in num_get::get() overloads</em>
     </dt>
     <dd>Similar to 118.
     </dd>

     <dt><a href="lwg-defects.html#292">292</a>:
         <em>Effects of a.copyfmt (a)</em>
     </dt>
     <dd>If <code>(this == &amp;rhs)</code> do nothing.
     </dd>

     <dt><a href="lwg-defects.html#300">300</a>:
         <em>List::merge() specification incomplete</em>
     </dt>
     <dd>If <code>(this == &amp;x)</code> do nothing.
     </dd>

     <dt><a href="lwg-defects.html#303">303</a>:
         <em>Bitset input operator underspecified</em>
     </dt>
     <dd>Basically, compare the input character to <code>is.widen(0)</code>
         and <code>is.widen(1)</code>.
     </dd>

     <dt><a href="lwg-defects.html#305">305</a>:
         <em>Default behavior of codecvt&lt;wchar_t, char, mbstate_t&gt;::length()</em>
     </dt>
     <dd>Do not specify what <code>codecvt&lt;wchar_t, char, mbstate_t&gt;::do_length</code>
         must return.
     </dd>

     <dt><a href="lwg-defects.html#328">328</a>:
         <em>Bad sprintf format modifier in money_put&lt;&gt;::do_put()</em>
     </dt>
     <dd>Change the format string to &quot;%.0Lf&quot;.
     </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&amp;</code>.
     </dd>

     <dt><a href="lwg-defects.html#402">402</a>:
         <em>Wrong new expression in [some_]allocator::construct</em>
     </dt>
     <dd>Replace &quot;new&quot; with &quot;::new&quot;.
     </dd>

     <dt><a href="lwg-active.html#409">409</a>:
         <em>Closing an fstream should clear the error state</em>
     </dt>
     <dd>Have <code>open</code> clear the error flags.
     </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>
 <!--
     <dt><a href="lwg-defects.html#"></a>:
         <em></em>
     </dt>
     <dd>
     </dd>

 -->
    </dl>
    <p>Return <a href="#top">to top of page</a> or
       <a href="../faq/index.html">to the FAQ</a>.
    </p>


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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>.
 </em></p>


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	<h1 class="centered"><a name="top">Extensions</a></h1>

	<p>Here we will make an attempt at describing the non-Standard extensions to
	the library. Some of these are from SGI's STL, some of these are GNU's,
	and some just seemed to appear on the doorstep.
	</p>
	<p><strong>Before you leap in and use these</strong>, be aware of two things:
	</p>
	<ol>
	<li>Non-Standard means exactly that. The behavior, and the very
	existence, of these extensions may change with little or no
	warning. (Ideally, the really good ones will appear in the next
	revision of C++.) Also, other platforms, other compilers, other
	versions of g++ or libstdc++-v3 may not recognize these names, or
	treat them differently, or... </li>
	<li>You should know how to <a href="../faq/index.html#5_4">access
	these headers properly</a>. </li>
	</ol>


	<!-- ####################################################### -->
	<hr />
	<h1>Contents</h1>
	<ul>
	<li><a href="#1">Ropes and trees and hashes, oh my!</a></li>
	<li><a href="#2">Added members and types</a></li>
	<li><a href="mt_allocator.html"><code>__mt_alloc</code> </a></li>
	<li><a href="#4">Compile-time checks</a></li>
	<li><a href="#5">LWG Issues</a></li>
	<li><a href="../18_support/howto.html#6">Demangling</a></li>
	</ul>

	<hr />

	<!-- ####################################################### -->

	<h2><a name="1">Ropes and trees and hashes, oh my!</a></h2>
	<p>The SGI headers</p>
	<pre>
	<bvector>
	<hash_map>
	<hash_set>
	<rope>
	<slist>
	<tree>
	</pre>
	<p>are all here; <code><bvector></code> exposes the old bit_vector
	class that was used before specialization of vector<bool> was
	available (it's actually a typedef for the specialization now).
	<code><hash_map></code> and <code><hash_set></code>
	are discussed further below. <code><rope></code> is the SGI
	specialization for large strings ("rope," "large
	strings," get it? love those SGI folks).
	<code><slist></code> is a singly-linked list, for when the
	doubly-linked <code>list<></code> is too much space overhead, and
	<code><tree></code> exposes the red-black tree classes used in the
	implementation of the standard maps and sets.
	</p>
	<p>Okay, about those hashing classes... I'm going to foist most of the
	work off onto SGI's own site.
	</p>
	<p>Each of the associative containers map, multimap, set, and multiset
	have a counterpart which uses a
	<a href="http://www.sgi.com/tech/stl/HashFunction.html">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 href="http://www.sgi.com/tech/stl/hash.html">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
	"normal" implementations? Matt Austern writes:
	</p>
	<blockquote><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></blockquote>
	<p>(Side note: for those of you wondering, <strong>"Why wasn't a hash
	table included in the Standard in the first #!$@ place?"</strong>
	I'll give a quick answer: it was proposed, but too late and in too
	unorganized a fashion. Some sort of hashing will undoubtedly be
	included in a future Standard.)
	</p>
	<p>Return <a href="#top">to top of page</a> or
	<a href="../faq/index.html">to the FAQ</a>.
	</p>

	<hr />
	<h2><a name="2">Added members and types</a></h2>
	<p>Some of the classes in the Standard Library have additional
	publicly-available members, and some classes are themselves not in
	the standard. Of those, some are intended purely for the implementors,
	for example, additional typedefs. Those won't be described here
	(or anywhere else).
	</p>
	<ul>
	<li>The extensions added by SGI are so numerous that they have
	<a href="sgiexts.html">their own page</a>. Since the SGI STL is no
	longer actively maintained, we will try and keep this code working
	ourselves.</li>
	<li>Extensions allowing <code>filebuf</code>s to be constructed from
	stdio types are described in the
	<a href="../27_io/howto.html#11">chapter 27 notes</a>.</li>
	</ul>
	<p>Return <a href="#top">to top of page</a> or
	<a href="../faq/index.html">to the FAQ</a>.
	</p>

	<hr />
	<h2><a name="4">Compile-time checks</a></h2>
	<p>Currently libstdc++-v3 uses the concept checkers from the Boost
	library to perform <a href="../19_diagnostics/howto.html#3">optional
	compile-time checking</a> of template instantiations of the standard
	containers. They are described in the linked-to page.
	</p>
	<p>Return <a href="#top">to top of page</a> or
	<a href="../faq/index.html">to the FAQ</a>.
	</p>

	<hr />
	<h2><a name="5">LWG Issues</a></h2>
	<p>Everybody's got issues. Even the C++ Standard Library.
	</p>
	<p>The Library Working Group, or LWG, is the ISO subcommittee responsible
	for making changes to the library. They periodically publish an
	Issues List containing problems and possible solutions. As they reach
	a consensus on proposed solutions, we often incorporate the solution
	into libstdc++-v3.
	</p>
	<p>Here are the issues which have resulted in code changes to the library.
	The links are to the specific defect reports from a <strong>partial
	copy</strong> of the Issues List. You can read the full version online
	at the <a href="http://www.open-std.org/jtc1/sc22/wg21/">ISO C++
	Committee homepage</a>, linked to on the
	<a href="http://gcc.gnu.org/readings.html">GCC "Readings"
	page</a>. If
	you spend a lot of time reading the issues, we recommend downloading
	the ZIP file and reading them locally.
	</p>
	<p>(NB: <strong>partial copy</strong> means that not all links within
	the lwg-*.html pages will work.
	Specifically, links to defect reports that have not been accorded full
	DR status will probably break. Rather than trying to mirror the
	entire issues list on our overworked web server, we recommend you go
	to the LWG homepage instead.)
	</p>
	<p>
	If a DR is not listed here, we may simply not have gotten to it yet;
	feel free to submit a patch. Search the include/bits and src
	directories for appearances of _GLIBCXX_RESOLVE_LIB_DEFECTS for
	examples of style. Note that we usually do not make changes to the code
	until an issue has reached <a href="lwg-active.html#DR">DR</a> status.
	</p>
	<dl>
	<dt><a href="lwg-defects.html#5">5</a>:
	<em>string::compare specification questionable</em>
	</dt>
	<dd>This should be two overloaded functions rather than a single function.
	</dd>

	<dt><a href="lwg-defects.html#17">17</a>:
	<em>Bad bool parsing</em>
	</dt>
	<dd>Apparently extracting Boolean values was messed up...
	</dd>

	<dt><a href="lwg-defects.html#19">19</a>:
	<em>"Noconv" definition too vague</em>
	</dt>
	<dd>If <code>codecvt::do_in</code> returns <code>noconv</code> there are
	no changes to the values in <code>[to, to_limit)</code>.
	</dd>

	<dt><a href="lwg-defects.html#22">22</a>:
	<em>Member open vs flags</em>
	</dt>
	<dd>Re-opening a file stream does <em>not</em> clear the state flags.
	</dd>

	<dt><a href="lwg-defects.html#25">25</a>:
	<em>String operator<< uses width() value wrong</em>
	</dt>
	<dd>Padding issues.
	</dd>

	<dt><a href="lwg-defects.html#48">48</a>:
	<em>Use of non-existent exception constructor</em>
	</dt>
	<dd>An instance of <code>ios_base::failure</code> is constructed instead.
	</dd>

	<dt><a href="lwg-defects.html#49">49</a>:
	<em>Underspecification of ios_base::sync_with_stdio</em>
	</dt>
	<dd>The return type is the <em>previous</em> state of synchronization.
	</dd>

	<dt><a href="lwg-defects.html#50">50</a>:
	<em>Copy constructor and assignment operator of ios_base</em>
	</dt>
	<dd>These members functions are declared <code>private</code> and are
	thus inaccessible. Specifying the correct semantics of
	"copying stream state" was deemed too complicated.
	</dd>

	<dt><a href="lwg-defects.html#60">60</a>:
	<em>What is a formatted input function?</em>
	</dt>
	<dd>This DR made many widespread changes to <code>basic_istream</code>
	and <code>basic_ostream</code> all of which have been implemented.
	</dd>

	<dt><a href="lwg-defects.html#63">63</a>:
	<em>Exception-handling policy for unformatted output</em>
	</dt>
	<dd>Make the policy consistent with that of formatted input, unformatted
	input, and formatted output.
	</dd>

	<dt><a href="lwg-defects.html#68">68</a>:
	<em>Extractors for char* should store null at end</em>
	</dt>
	<dd>And they do now. An editing glitch in the last item in the list of
	[27.6.1.2.3]/7.
	</dd>

	<dt><a href="lwg-defects.html#74">74</a>:
	<em>Garbled text for codecvt::do_max_length</em>
	</dt>
	<dd>The text of the standard was gibberish. Typos gone rampant.
	</dd>

	<dt><a href="lwg-defects.html#75">75</a>:
	<em>Contradiction in codecvt::length's argument types</em>
	</dt>
	<dd>Change the first parameter to <code>stateT&</code> and implement
	the new effects paragraph.
	</dd>

	<dt><a href="lwg-defects.html#83">83</a>:
	<em>string::npos vs. string::max_size()</em>
	</dt>
	<dd>Safety checks on the size of the string should test against
	<code>max_size()</code> rather than <code>npos</code>.
	</dd>

	<dt><a href="lwg-defects.html#90">90</a>:
	<em>Incorrect description of operator>> for strings</em>
	</dt>
	<dd>The effect contain <code>isspace(c,getloc())</code> which must be
	replaced by <code>isspace(c,is.getloc())</code>.
	</dd>

	<dt><a href="lwg-defects.html#91">91</a>:
	<em>Description of operator>> and getline() for string<>
	might cause endless loop</em>
	</dt>
	<dd>They behave as a formatted input function and as an unformatted
	input function, respectively (except that <code>getline</code> is
	not required to set <code>gcount</code>).
	</dd>

	<dt><a href="lwg-defects.html#103">103</a>:
	<em>set::iterator is required to be modifiable, but this allows
	modification of keys.</em>
	</dt>
	<dd>For associative containers where the value type is the same as
	the key type, both <code>iterator</code> and <code>const_iterator
	</code> are constant iterators.
	</dd>

	<dt><a href="lwg-defects.html#109">109</a>:
	<em>Missing binders for non-const sequence elements</em>
	</dt>
	<dd>The <code>binder1st</code> and <code>binder2nd</code> didn't have an
	<code>operator()</code> taking a non-const parameter.
	</dd>

	<dt><a href="lwg-defects.html#110">110</a>:
	<em>istreambuf_iterator::equal not const</em>
	</dt>
	<dd>This was not a const member function. Note that the DR says to
	replace the function with a const one; we have instead provided an
	overloaded version with identical contents.
	</dd>

	<dt><a href="lwg-defects.html#117">117</a>:
	<em>basic_ostream uses nonexistent num_put member functions</em>
	</dt>
	<dd><code>num_put::put()</code> was overloaded on the wrong types.
	</dd>

	<dt><a href="lwg-defects.html#118">118</a>:
	<em>basic_istream uses nonexistent num_get member functions</em>
	</dt>
	<dd>Same as 117, but for <code>num_get::get()</code>.
	</dd>

	<dt><a href="lwg-defects.html#129">129</a>:
	<em>Need error indication from seekp() and seekg()</em>
	</dt>
	<dd>These functions set <code>failbit</code> on error now.
	</dd>

	<dt><a href="lwg-defects.html#136">136</a>:
	<em>seekp, seekg setting wrong streams?</em>
	</dt>
	<dd><code>seekp</code> should only set the output stream, and
	<code>seekg</code> should only set the input stream.
	</dd>

	<!--<dt><a href="lwg-defects.html#159">159</a>:
	<em>Strange use of underflow()</em>
	</dt>
	<dd>In fstream.tcc, the basic_filebuf<>::showmanyc() function
	should probably not be calling <code>underflow()</code>.
	</dd> -->

	<dt><a href="lwg-defects.html#167">167</a>:
	<em>Improper use of traits_type::length()</em>
	</dt>
	<dd><code>op<<</code> with a <code>const char*</code> was
	calculating an incorrect number of characters to write.
	</dd>

	<dt><a href="lwg-defects.html#171">171</a>:
	<em>Strange seekpos() semantics due to joint position</em>
	</dt>
	<dd>Quite complex to summarize...
	</dd>

	<dt><a href="lwg-defects.html#181">181</a>:
	<em>make_pair() unintended behavior</em>
	</dt>
	<dd>This function used to take its arguments as reference-to-const, now
	it copies them (pass by value).
	</dd>

	<dt><a href="lwg-defects.html#195">195</a>:
	<em>Should basic_istream::sentry's constructor ever set eofbit?</em>
	</dt>
	<dd>Yes, it can, specifically if EOF is reached while skipping whitespace.
	</dd>

	<dt><a href="lwg-defects.html#211">211</a>:
	<em>operator>>(istream&, string&) doesn't set failbit</em>
	</dt>
	<dd>If nothing is extracted into the string, <code>op>></code> now
	sets <code>failbit</code> (which can cause an exception, etc, etc).
	</dd>

	<dt><a href="lwg-defects.html#214">214</a>:
	<em>set::find() missing const overload</em>
	</dt>
	<dd>Both <code>set</code> and <code>multiset</code> were missing
	overloaded find, lower_bound, upper_bound, and equal_range functions
	for const instances.
	</dd>

	<dt><a href="lwg-defects.html#231">231</a>:
	<em>Precision in iostream?</em>
	</dt>
	<dd>For conversion from a floating-point type, <code>str.precision()</code>
	is specified in the conversion specification.
	</dd>

	<dt><a href="lwg-defects.html#235">235</a>:
	<em>No specification of default ctor for reverse_iterator</em>
	</dt>
	<dd>The declaration of <code>reverse_iterator</code> lists a default constructor.
	However, no specification is given what this constructor should do.
	</dd>

	<dt><a href="lwg-defects.html#243">243</a>:
	<em>get and getline when sentry reports failure</em>
	</dt>
	<dd>Store a null character only if the character array has a non-zero size.
	</dd>

	<dt><a href="lwg-defects.html#251">251</a>:
	<em>basic_stringbuf missing allocator_type</em>
	</dt>
	<dd>This nested typedef was originally not specified.
	</dd>

	<dt><a href="lwg-defects.html#253">253</a>:
	<em>valarray helper functions are almost entirely useless</em>
	</dt>
	<dd>Make the copy constructor and copy-assignment operator declarations
	public in gslice_array, indirect_array, mask_array, slice_array; provide
	definitions.
	</dd>

	<dt><a href="lwg-defects.html#265">265</a>:
	<em>std::pair::pair() effects overly restrictive</em>
	</dt>
	<dd>The default ctor would build its members from copies of temporaries;
	now it simply uses their respective default ctors.
	</dd>

	<dt><a href="lwg-defects.html#266">266</a>:
	<em>bad_exception::~bad_exception() missing Effects clause</em>
	</dt>
	<dd>The <code>bad_</code>* classes no longer have destructors (they
	are trivial), since no description of them was ever given.
	</dd>

	<dt><a href="lwg-defects.html#271">271</a>:
	<em>basic_iostream missing typedefs</em>
	</dt>
	<dd>The typedefs it inherits from its base classes can't be used, since
	(for example) <code>basic_iostream<T>::traits_type</code> is ambiguous.
	</dd>

	<dt><a href="lwg-defects.html#275">275</a>:
	<em>Wrong type in num_get::get() overloads</em>
	</dt>
	<dd>Similar to 118.
	</dd>

	<dt><a href="lwg-defects.html#292">292</a>:
	<em>Effects of a.copyfmt (a)</em>
	</dt>
	<dd>If <code>(this == &rhs)</code> do nothing.
	</dd>

	<dt><a href="lwg-defects.html#300">300</a>:
	<em>List::merge() specification incomplete</em>
	</dt>
	<dd>If <code>(this == &x)</code> do nothing.
	</dd>

	<dt><a href="lwg-defects.html#303">303</a>:
	<em>Bitset input operator underspecified</em>
	</dt>
	<dd>Basically, compare the input character to <code>is.widen(0)</code>
	and <code>is.widen(1)</code>.
	</dd>

	<dt><a href="lwg-defects.html#305">305</a>:
	<em>Default behavior of codecvt<wchar_t, char, mbstate_t>::length()</em>
	</dt>
	<dd>Do not specify what <code>codecvt<wchar_t, char, mbstate_t>::do_length</code>
	must return.
	</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#409">409</a>:
	<em>Closing an fstream should clear the error state</em>
	</dt>
	<dd>Have <code>open</code> clear the error flags.
	</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>
	<!--
	<dt><a href="lwg-defects.html#"></a>:
	<em></em>
	</dt>
	<dd>
	</dd>

	-->
	</dl>
	<p>Return <a href="#top">to top of page</a> or
	<a href="../faq/index.html">to the FAQ</a>.
	</p>


	<!-- ####################################################### -->

	<hr />
	<p class="fineprint"><em>
	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>.
	</em></p>


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