libstdc++-v3/docs/html/faq/index.html

   1 <?xml version="1.0" encoding="ISO-8859-1"?>
   2 <!DOCTYPE html
   3           PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   4           "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
   5
   6 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
   7 <head>
   8    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
   9    <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++, libg++, STL" />
  10    <meta name="DESCRIPTION" content="FAQ for the GNU libstdc++ effort." />
  11    <title>libstdc++-v3 FAQ</title>
  12 <link rel="StyleSheet" href="../lib3styles.css" />
  13 <link rel="Start" rev="Help" href="../documentation.html" type="text/html"
  14  title="GNU C++ Standard Library" />
  15 <link rel="Copyright" href="../17_intro/license.html" type="text/html" />
  16 </head>
  17 <body>
  18
  19 <h1 class="centered">libstdc++ Frequently Asked Questions</h1>
  20
  21 <p class="fineprint"><em>
  22    The latest version of this document is always available at
  23    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/">
  24    http://gcc.gnu.org/onlinedocs/libstdc++/faq/</a>.  The main documentation
  25    page is at
  26    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html">
  27    http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html</a>.
  28 </em></p>
  29
  30 <p><em>
  31    To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
  32 </em></p>
  33
  34 <!-- ####################################################### -->
  35 <hr />
  36 <h1>Questions</h1>
  37 <ol>
  38    <li><a href="#1_0">General Information</a>
  39    <!-- I suspect these will mostly be links to/into existing documents. -->
  40    <ol>
  41       <li><a href="#1_1">What is libstdc++-v3?</a> </li>
  42       <li><a href="#1_2">Why should I use libstdc++?</a> </li>
  43       <li><a href="#1_3">Who's in charge of it?</a> </li>
  44       <li><a href="#1_4">How do I get libstdc++?</a> </li>
  45       <li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
  46       <li><a href="#1_6">How do I contribute to the effort?</a> </li>
  47       <li><a href="#1_7">What happened to libg++?  I need that!</a> </li>
  48       <li><a href="#1_8">What if I have more questions?</a> </li>
  49       <li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
  50    </ol>
  51    </li>
  52
  53    <li><a href="#2_0">Installation</a>
  54       <ol>
  55          <li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
  56          <li><a href="#2_2">[removed]</a> </li>
  57          <li><a href="#2_3">What is this SVN thing that you keep
  58                             mentioning?</a> </li>
  59          <li><a href="#2_4">How do I know if it works?</a> </li>
  60          <li><a href="#2_5">This library is HUGE!  And what's libsupc++?</a> </li>
  61          <li><a href="#2_6">Why do I get an error saying
  62                             <code>libstdc++.so.X</code> is missing when I
  63                             run my program?</a> </li>
  64       </ol>
  65    </li>
  66
  67    <li><a href="#3_0">Platform-Specific Issues</a>
  68       <ol>
  69          <li><a href="#3_1">Can libstdc++-v3 be used with &lt;my
  70                             favorite compiler&gt;?</a> </li>
  71          <li><a href="#3_2">[removed]</a> </li>
  72          <li><a href="#3_3">[removed]</a> </li>
  73          <li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
  74          <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
  75                             <code>_GNU_SOURCE</code> / etc is always defined</a>
  76          </li>
  77          <li><a href="#3_6">OS X ctype.h is broken!  How can I hack it?</a></li>
  78          <li><a href="#3_7">Threading is broken on i386</a></li>
  79          <li><a href="#3_8">Recent GNU/Linux glibc required?</a></li>
  80          <li><a href="#3_9">Can't use wchar_t/wstring on FreeBSD</a></li>
  81          <li><a href="#3_10">MIPS atomic operations</a></li>
  82       </ol>
  83    </li>
  84
  85    <li><a href="#4_0">Known Bugs and Non-Bugs</a>
  86       <ol>
  87          <li><a href="#4_1">What works already?</a> </li>
  88          <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
  89          <li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
  90          <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
  91            <li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
  92            <li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
  93            <li><a href="#4_4_rel_ops">&quot;ambiguous overloads&quot;
  94                                after including an old-style header</a> </li>
  95            <li><a href="#4_4_interface">The g++-3 headers are
  96                                <strong>not ours</strong></a> </li>
  97            <li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
  98            <li><a href="#4_4_checks">errors about <em>*Concept</em> and
  99                                <em>constraints</em> in the STL...</a> </li>
 100            <li><a href="#4_4_dlsym">program crashes when using library code
 101                                in a dynamically-loaded library</a> </li>
 102            <li><a href="#4_4_leak">"memory leaks" in containers</a> </li>
 103          </ul>
 104          </li>
 105          <li><a href="#4_5">Aw, that's easy to fix!</a> </li>
 106       </ol>
 107    </li>
 108
 109    <li><a href="#5_0">Miscellaneous</a>
 110       <ol>
 111          <li><a href="#5_1">string::iterator is not char*;
 112                             vector&lt;T&gt;::iterator is not T*</a> </li>
 113          <li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
 114          <li><a href="#5_3">What about the STL from SGI?</a> </li>
 115          <li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
 116          <li><a href="#5_5">Does libstdc++ support TR1?</a> </li>
 117          <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
 118          <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
 119          <li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
 120          <li><a href="#5_9">How do I make std::vector&lt;T&gt;::capacity()
 121                             == std::vector&lt;T&gt;::size?</a> </li>
 122       </ol>
 123    </li>
 124
 125 </ol>
 126
 127 <hr />
 128
 129 <!-- ####################################################### -->
 130
 131 <h1><a name="1_0">1.0 General Information</a></h1>
 132 <!-- I suspect these will mostly be links to/into existing documents. -->
 133    <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
 134       <p>The GNU Standard C++ Library v3 is an
 135          ongoing project to implement the ISO 14882 Standard C++ library
 136          as described in chapters 17 through 27 and annex D.
 137          For those who want to see exactly how
 138          far the project has come, or just want the latest
 139          bleeding-edge code, the up-to-date source is available over
 140          anonymous SVN, and can even be browsed over the Web (see
 141          <a href="#1_4">1.4</a> below).
 142       </p>
 143       <p>The older libstdc++-v2 project is no longer maintained; the code
 144          has been completely replaced and rewritten.
 145          <a href="#4_4_interface">If you are using V2</a>, then you need to
 146          report bugs to your system vendor, not to the V3 list.
 147       </p>
 148       <p>A more formal description of the V3 goals can be found in the
 149          official <a href="../17_intro/DESIGN">design document</a>.
 150       </p>
 151
 152 <hr />
 153    <h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
 154       <p>The completion of the ISO C++ standardization gave the
 155          C++ community a powerful set of reuseable tools in the form
 156          of the C++ Standard Library.  However, all existing C++
 157          implementations are (as the Draft Standard used to say)
 158          &quot;incomplet and incorrekt,&quot; and many suffer from
 159          limitations of the compilers that use them.
 160       </p>
 161       <p>The GNU C/C++/FORTRAN/&lt;pick-a-language&gt; compiler
 162          (<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
 163          one of the leading compilers in the world.  Its development
 164          is overseen by the
 165          <a href="http://gcc.gnu.org/">GCC team</a>.  All of
 166          the rapid development and near-legendary
 167          <a href="http://gcc.gnu.org/gcc-3.3/buildstat.html">portability</a>
 168          that are the hallmarks of an open-source project are being
 169          applied to libstdc++.
 170       </p>
 171       <p>That means that all of the Standard classes and functions
 172          (such as <code>string</code>, <code>vector&lt;&gt;</code>, iostreams,
 173          and algorithms) will be freely available and fully compliant.
 174          Programmers will no longer need to &quot;roll their own&quot;
 175          nor be worried about platform-specific incompatibilities.
 176       </p>
 177
 178 <hr />
 179    <h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
 180       <p>The libstdc++ project is contributed to by several developers
 181          all over the world, in the same way as GCC or Linux.
 182          Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
 183          Loren James Rittle, and Paolo Carlini are the lead maintainers of
 184          the SVN archive.
 185       </p>
 186       <p>Development and discussion is held on the libstdc++ mailing
 187          list.  Subscribing to the list, or searching the list
 188          archives, is open to everyone.  You can read instructions for
 189          doing so on the <a href="http://gcc.gnu.org/libstdc++/">homepage</a>.
 190          If you have questions, ideas, code, or are just curious, sign up!
 191       </p>
 192
 193 <hr />
 194    <h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
 195       <p>The <a href="http://gcc.gnu.org/libstdc++/">homepage</a>
 196          has instructions for retrieving the latest SVN sources, and for
 197          browsing the SVN sources over the web.
 198       </p>
 199       <p>Stable versions of libstdc++-v3 are included with releases of
 200          <a href="http://gcc.gnu.org/releases.html">the GCC compilers</a>.
 201       </p>
 202       <p>The subset commonly known as the Standard Template Library
 203          (chapters 23 through 25, mostly) is adapted from the final release
 204          of the SGI STL, with extensive changes.
 205       </p>
 206
 207 <hr />
 208    <h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
 209 <!--      <p>Nathan Myers gave the best of all possible answers in <a
 210          href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
 211          Usenet article</a>.</p>
 212 which is no longer available, thanks deja...-->
 213       <p>Nathan Myers gave the best of all possible answers, responding to a
 214          Usenet article asking this question:  <em>Sooner, if you help.</em>
 215       </p>
 216
 217 <hr />
 218    <h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
 219       <p>Here is <a href="../17_intro/contribute.html">a
 220          page devoted to this topic</a>.  Subscribing to the mailing
 221          list (see above, or the homepage) is a very good idea if you
 222          have something to contribute, or if you have spare time and
 223          want to help.  Contributions don't have to be in the form of
 224          source code; anybody who is willing to help write
 225          documentation, for example, or has found a bug in code that
 226          we all thought was working, is more than welcome!
 227       </p>
 228
 229 <hr />
 230    <h2><a name="1_7">1.7 What happened to libg++?  I need that!</a></h2>
 231       <p>The most recent libg++ README states that libg++ is no longer
 232          being actively maintained.  It should not be used for new
 233          projects, and is only being kicked along to support older code.
 234       </p>
 235       <p>The libg++ was designed and created when there was no Standard
 236          to provide guidance.  Classes like linked lists are now provided
 237          for by <code>list&lt;T&gt;</code> and do not need to be created by
 238          <code>genclass</code>.  (For that matter, templates exist now and
 239          are well-supported, whereas genclass (mostly) predates them.)
 240       </p>
 241       <p>There are other classes in libg++ that are not specified in the
 242          ISO Standard (e.g., statistical analysis).  While there are a
 243          lot of really useful things that are used by a lot of people
 244          (e.g., statistics :-), the Standards Committee couldn't include
 245          everything, and so a lot of those &quot;obvious&quot; classes
 246          didn't get included.
 247       </p>
 248       <p>Since libstdc++ is an implementation of the Standard Library, we
 249          have no plans at this time to include non-Standard utilities
 250          in the implementation, however handy they are.  (The extensions
 251          provided in the SGI STL aren't maintained by us and don't get
 252          a lot of our attention, because they don't require a lot of our
 253          time.)  It is entirely plausable that the &quot;useful stuff&quot;
 254          from libg++ might be extracted into an updated utilities library,
 255          but nobody has started such a project yet.
 256       </p>
 257       <p>(The <a href="http://www.boost.org/">Boost</a> site houses free
 258          C++ libraries that do varying things, and happened to be started
 259          by members of the Standards Committee.  Certain &quot;useful
 260          stuff&quot; classes will probably migrate there.)
 261       </p>
 262       <p>For the bold and/or desperate, the
 263          <a href="http://gcc.gnu.org/extensions.html">GCC extensions page</a>
 264          describes where to find the last libg++ source.
 265       </p>
 266
 267 <hr />
 268    <h2><a name="1_8">1.8 What if I have more questions?</a></h2>
 269       <p>If you have read the README and RELEASE-NOTES files, and your
 270          question remains unanswered, then just ask the mailing list.
 271          At present, you do not need to be subscribed to the list to
 272          send a message to it.  More information is available on the
 273          homepage (including how to browse the list archives); to send
 274          to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
 275          <code>libstdc++@gcc.gnu.org</code></a>.
 276       </p>
 277       <p>If you have a question that you think should be included here,
 278          or if you have a question <em>about</em> a question/answer here,
 279          contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
 280          or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
 281       </p>
 282
 283 <hr />
 284    <h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
 285       <p>See <a href="../17_intro/license.html">our license description</a>
 286          for these and related questions.
 287       </p>
 288
 289 <hr />
 290 <h1><a name="2_0">2.0 Installation</a></h1>
 291    <h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
 292       <p>Complete instructions are not given here (this is a FAQ, not
 293          an installation document), but the tools required are few:
 294       </p>
 295          <ul>
 296             <li> A 3.x release of GCC.  Note that building GCC is much
 297                  easier and more automated than building the GCC 2.[78]
 298                  series was.  If you are using GCC 2.95, you can still
 299                  build earlier snapshots of libstdc++.
 300             </li>
 301             <li> GNU Make is required for GCC 3.4 and later.
 302             </li>
 303             <li> The GNU Autotools are needed if you are messing with
 304                  the configury or makefiles.
 305             </li>
 306          </ul>
 307       <p>The file <a href="../documentation.html">documentation.html</a>
 308          provides a good overview of the steps necessary to build, install,
 309          and use the library.  Instructions for configuring the library
 310          with new flags such as --enable-threads are there also, as well as
 311          patches and instructions for working with GCC 2.95.
 312       </p>
 313       <p>The top-level install.html and
 314          <a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
 315          the exact build and installation instructions.  You may wish to
 316          browse those files over ViewVC ahead of time to get a feel for
 317          what's required.  RELEASE-NOTES is located in the
 318          &quot;.../docs/17_intro/&quot; directory of the distribution.
 319       </p>
 320
 321 <hr />
 322    <h2><a name="2_2">2.2 [removed]</a></h2>
 323       <p>This question has become moot and has been removed.  The stub
 324          is here to preserve numbering (and hence links/bookmarks).
 325       </p>
 326
 327 <hr />
 328    <h2><a name="2_3">2.3 What is this SVN thing that you
 329                          keep mentioning?</a></h2>
 330       <p><em>Subversion</em> is one of several revision control packages.
 331          It was selected for GNU projects because it's free (speech), free (beer),
 332          and very high quality.  The <a href="http://subversion.tigris.org">
 333          Subversion home page</a> has a better description.
 334       </p>
 335       <p>The &quot;anonymous client checkout&quot; feature of SVN is
 336          similar to anonymous FTP in that it allows anyone to retrieve
 337          the latest libstdc++ sources.
 338       </p>
 339       <p>After the first of April, American users will have a
 340          &quot;/pharmacy&quot; command-line option...
 341          <!-- wonder how long that'll live -->
 342       </p>
 343
 344 <hr />
 345    <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
 346       <p>libstdc++-v3 comes with its own testsuite.  You do not need
 347          to actually install the library (&quot;<code>make
 348          install</code>&quot;) to run the testsuite, but you do need
 349          DejaGNU, as described
 350          <a href="http://gcc.gnu.org/install/test.html">here</a>.
 351       </p>
 352       <p>To run the testsuite on the library after building it, use
 353          &quot;make check&quot; while in your build directory.  To run
 354          the testsuite on the library after building and installing it,
 355          use &quot;make check-install&quot; instead.
 356       </p>
 357       <p>If you find bugs in the testsuite programs themselves, or if you
 358          think of a new test program that should be added to the suite,
 359          <strong>please</strong> write up your idea and send it to the list!
 360       </p>
 361
 362 <hr />
 363    <h2><a name="2_5">2.5 This library is HUGE!  And what's libsupc++?</a></h2>
 364       <p>Usually the size of libraries on disk isn't noticeable.  When a
 365          link editor (or simply &quot;linker&quot;) pulls things from a
 366          static archive library, only the necessary object files are copied
 367          into your executable, not the entire library.  Unfortunately, even
 368          if you only need a single function or variable from an object file,
 369          the entire object file is extracted.  (There's nothing unique to C++
 370          or libstdc++-v3 about this; it's just common behavior, given here
 371          for background reasons.)
 372       </p>
 373       <p>Some of the object files which make up libstdc++.a are rather large.
 374          If you create a statically-linked executable with
 375          <code> -static</code>, those large object files are suddenly part
 376          of your executable.  Historically the best way around this was to
 377          only place a very few functions (often only a single one) in each
 378          source/object file; then extracting a single function is the same
 379          as extracting a single .o file.  For libstdc++-v3 this is only
 380          possible to a certain extent; the object files in question contain
 381          template classes and template functions, pre-instantiated, and
 382          splitting those up causes severe maintenance headaches.
 383       </p>
 384       <p>It's not a bug, and it's not really a problem.  Nevertheless, some
 385          people don't like it, so here are two pseudo-solutions:
 386       </p>
 387       <p>If the only functions from libstdc++.a which you need are
 388          language support functions (those listed in <a
 389          href="../18_support/howto.html">clause 18</a> of the
 390          standard, e.g., <code>new</code> and <code>delete</code>),
 391          then try linking against <code>libsupc++.a</code> (Using
 392          <code>gcc</code> instead of <code>g++</code> and explicitly
 393          linking in <code>-lsupc++</code> for the final link step will
 394          do it).  This library contains only those support routines,
 395          one per object file.  But if you are using anything from the
 396          rest of the library, such as IOStreams or vectors, then
 397          you'll still need pieces from <code>libstdc++.a</code>.
 398       </p>
 399       <p>The second method is one we hope to incorporate into the library
 400          build process.  Some platforms can place each function and variable
 401          into its own section in a .o file.  The GNU linker can then perform
 402          garbage collection on unused sections; this reduces the situation
 403          to only copying needed functions into the executable, as before,
 404          but all happens automatically.
 405       </p>
 406       <p>Unfortunately the garbage collection in GNU ld is buggy; sections
 407          (corresponding to functions and variables) which <em>are</em> used
 408          are mistakenly removed, leading to horrible crashes when your
 409          executable starts up.  For the time being, this feature is not used
 410          when building the library.
 411       </p>
 412
 413 <hr />
 414    <h2><a name="2_6">2.6 Why do I get an error saying
 415                          <code>libstdc++.so.X</code> is missing when I run
 416                          my program?</a></h2>
 417       <p>Depending on your platform and library version, the message might
 418          be similar to one of the following:
 419       </p>
 420       <pre>
 421     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 422
 423     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found </pre>
 424
 425       <p>This doesn't mean that the shared library isn't installed, only
 426          that the dynamic linker can't find it. When a dynamically-linked
 427          executable is run the linker finds and loads the required shared
 428          libraries by searching a pre-configured list of directories. If
 429          the directory where you've installed libstdc++ is not in this
 430          list then the libraries won't be found. The simplest way to fix
 431          this is to use the <code>LD_LIBRARY_PATH</code> environment
 432          variable, which is a colon-separated list of directories in which
 433          the linker will search for shared libraries:
 434       </p>
 435       <pre>
 436     LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 437     export LD_LIBRARY_PATH </pre>
 438       <p>The exact environment variable to use will depend on your platform,
 439          e.g. DYLD_LIBRARY_PATH for Darwin,
 440          LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
 441          LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs
 442          and SHLIB_PATH for HP-UX.
 443       </p>
 444       <p>See the man pages for <code>ld(1)</code>, <code>ldd(1)</code> and
 445          <code>ldconfig(8)</code> for more information. The dynamic linker
 446          has different names on different platforms but the man page is
 447          usually called something such as <code>ld.so / rtld / dld.so</code>.
 448       </p>
 449
 450 <hr />
 451 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
 452    <h2><a name="3_1">3.1 Can libstdc++-v3 be used with &lt;my
 453                          favorite compiler&gt;?</a></h2>
 454       <p>Probably not.  Yet.</p>
 455       <p>Because GCC advances so rapidly, development and testing of
 456          libstdc++ is being done almost entirely under that compiler.
 457          If you are curious about whether other, lesser compilers
 458          (*grin*) support libstdc++, you are more than welcome to try.
 459          Configuring and building the library (see above) will still
 460          require certain tools, however.  Also keep in mind that
 461          <em>building</em> libstdc++ does not imply that your compiler
 462          will be able to <em>use</em> all of the features found in the
 463          C++ Standard Library.
 464       </p>
 465       <p>Since the goal of ISO Standardization is for all C++
 466          implementations to be able to share code, the final libstdc++
 467          should, in theory, be usable under any ISO-compliant
 468          compiler.  It will still be targeted and optimized for
 469          GCC/g++, however.
 470       </p>
 471
 472 <hr />
 473    <h2><a name="3_2">3.2 [removed]</a></h2>
 474       <p>This question has become moot and has been removed.  The stub
 475          is here to preserve numbering (and hence links/bookmarks).
 476       </p>
 477
 478 <hr />
 479    <h2><a name="3_3">3.3 [removed]</a></h2>
 480       <p>This question has become moot and has been removed.  The stub
 481          is here to preserve numbering (and hence links/bookmarks).
 482       </p>
 483
 484 <hr />
 485    <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
 486       <p>By default we try to support the C99 <code>long long</code> type.
 487          This requires that certain functions from your C library be present.
 488       </p>
 489       <p>Up through release 3.0.2 the tests performed were too general, and
 490          this feature was disabled when it did not need to be.  The most
 491          commonly reported platform affected was Solaris.
 492       </p>
 493       <p>This has been fixed for 3.0.3 and onwards.
 494       </p>
 495
 496 <hr />
 497    <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
 498                          / etc is always defined</a></h2>
 499       <p>On Solaris, g++ (but not gcc) always defines the preprocessor
 500          macro <code>_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 501          with <code>_GNU_SOURCE</code>.  (This is not an exhaustive list;
 502          other macros and other platforms are also affected.)
 503       </p>
 504       <p>These macros are typically used in C library headers, guarding new
 505          versions of functions from their older versions.  The C++ standard
 506          library includes the C standard library, but it requires the C90
 507          version, which for backwards-compatability reasons is often not the
 508          default for many vendors.
 509       </p>
 510       <p>More to the point, the C++ standard requires behavior which is only
 511          available on certain platforms after certain symbols are defined.
 512          Usually the issue involves I/O-related typedefs.  In order to
 513          ensure correctness, the compiler simply predefines those symbols.
 514       </p>
 515       <p>Note that it's not enough to #define them only when the library is
 516          being built (during installation).  Since we don't have an 'export'
 517          keyword, much of the library exists as headers, which means that
 518          the symbols must also be defined as your programs are parsed and
 519          compiled.
 520       </p>
 521       <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 522          the gcc config headers for your target (and try changing them to
 523          see what happens when building complicated code).  You can also run
 524          <code>&quot;g++ -E -dM - &lt; /dev/null&quot;</code> to display
 525          a list of predefined macros for any particular installation.
 526       </p>
 527       <p>This has been discussed on the mailing lists
 528          <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&amp;format=builtin-long&amp;sort=score&amp;words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
 529       </p>
 530       <p>This method is something of a wart.  We'd like to find a cleaner
 531          solution, but nobody yet has contributed the time.
 532       </p>
 533
 534 <hr />
 535    <h2><a name="3_6">3.6 OS X ctype.h is broken!  How can I hack it?</a></h2>
 536       <p>This is a long-standing bug in the OS X support.  Fortunately,
 537          the patch is quite simple, and well-known.
 538          <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
 539          link to the solution.</a>
 540       </p>
 541
 542 <hr />
 543    <h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
 544       <p>Support for atomic integer operations is/was broken on i386
 545          platforms.  The assembly code accidentally used opcodes that are
 546          only available on the i486 and later.  So if you configured GCC
 547          to target, for example, i386-linux, but actually used the programs
 548          on an i686, then you would encounter no problems.  Only when
 549          actually running the code on a i386 will the problem appear.
 550       </p>
 551       <p>This is fixed in 3.2.2.
 552       </p>
 553
 554 <hr />
 555    <h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
 556       <p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version
 557          5.0.1) and later uses localization and formatting code from the system
 558          C library (glibc) version 2.2.5.  That version of glibc is over a
 559          year old and contains necessary bugfixes.  Many GNU/Linux distros make
 560          glibc version 2.3.x available now.
 561       </p>
 562       <p>The guideline is simple:  the more recent the C++ library, the
 563          more recent the C library.  (This is also documented in the main
 564          GCC installation instructions.)
 565       </p>
 566
 567 <hr />
 568    <h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
 569       <p>At the moment there are a few problems in FreeBSD's support for
 570          wide character functions, and as a result the libstdc++ configury
 571          decides that wchar_t support should be disabled.  Once the underlying
 572          problems are fixed in FreeBSD (soon), the library support will
 573          automatically enable itself.
 574       </p>
 575       <p>You can fix the problems yourself, and learn more about the situation,
 576          by reading
 577          <a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
 578          this short thread</a> (&quot;_GLIBCPP_USE_WCHAR_T undefined in
 579          FreeBSD's c++config.h?&quot;).
 580       </p>
 581
 582 <hr />
 583    <h2><a name="3_10">3.10 MIPS atomic operations</a></h2>
 584       <p>The atomic locking routines for MIPS targets requires MIPS II
 585          and later.  A patch went in just after the 3.3 release to
 586          make mips* use the generic implementation instead.  You can also
 587          configure for mipsel-elf as a workaround.
 588       </p>
 589       <p>mips*-*-linux* continues to use the MIPS II routines, and more
 590          work in this area is expected.
 591       </p>
 592
 593 <hr />
 594 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
 595    <em>Note that this section can get rapdily outdated -- such is the
 596        nature of an open-source project.  For the latest information, join
 597        the mailing list or look through recent archives.   The RELEASE-
 598        NOTES and BUGS files are generally kept up-to-date.</em>
 599
 600    <p>For 3.0.1, the most common &quot;bug&quot; is an apparently missing
 601       &quot;<code>../</code>&quot; in include/Makefile, resulting in files
 602       like gthr.h and gthr-single.h not being found.  Please read
 603       <a href="http://gcc.gnu.org/install/configure.html">the configuration
 604       instructions for GCC</a>,
 605       specifically the part about configuring in a separate build directory,
 606       and how strongly recommended it is.  Building in the source directory
 607       is fragile, is rarely tested, and tends to break, as in this case.
 608       This was fixed for 3.0.2.
 609    </p>
 610
 611    <p>For 3.1, the most common &quot;bug&quot; is a parse error when using
 612       <code>&lt;fstream&gt;</code>, ending with a message,
 613       &quot;<code>bits/basic_file.h:52: parse error before `{'
 614       token</code>.&quot;  Please read
 615       <a href="http://gcc.gnu.org/install/">the installation instructions for
 616       GCC</a>, specifically the part about not installing newer versions on
 617       top of older versions.  If you install 3.1 over a 3.0.x release, then
 618       the wrong basic_file.h header will be found (its location changed
 619       between releases).
 620    </p>
 621
 622    <p><strong>Please do not report these as bugs.  We know about them.</strong>
 623       Reporting this -- or any other problem that's already been fixed --
 624       hinders the development of GCC, because we have to take time to
 625       respond to your report.  Thank you.
 626    </p>
 627
 628 <hr />
 629    <h2><a name="4_1">4.1 What works already?</a></h2>
 630       <p>Short answer:  Pretty much everything <em>works</em> except for some
 631          corner cases.  Also, localization is incomplete.  For whether it works
 632          well, or as you expect it to work, see 5.2.
 633       </p>
 634       <p>Long answer:  See the docs/html/17_intro/CHECKLIST file, which is
 635          badly outdated...  Also see the RELEASE-NOTES file, which is kept
 636          more up to date.
 637       </p>
 638
 639 <hr />
 640    <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
 641       <p>This is by no means meant to be complete nor exhaustive, but
 642          mentions some problems that users may encounter when building
 643          or using libstdc++.  If you are experiencing one of these
 644          problems, you can find more information on the libstdc++ and
 645          the GCC mailing lists.
 646       </p>
 647       <p>Before reporting a bug, examine the
 648          <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
 649          category set to &quot;libstdc++&quot;.  The BUGS file in the source
 650          tree also tracks known serious problems.
 651       </p>
 652       <ul>
 653          <li>Debugging is problematic, due to bugs in line-number generation
 654              (mostly fixed in the compiler) and gdb lagging behind the
 655              compiler (lack of personnel).  We recommend configuring the
 656              compiler using <code>--with-dwarf2</code> if the DWARF2
 657              debugging format is not already the default on your platform.
 658              Also,
 659 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
 660              GDB settings</a> can have a profound effect on your C++ debugging
 661              experiences.  :-)</li>
 662       </ul>
 663
 664 <hr />
 665    <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
 666       <p>Yes, unfortunately, there are some.  In a
 667          <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
 668          to the list</a>, Nathan Myers announced that he has started a list of
 669          problems in the ISO C++ Standard itself, especially with
 670          regard to the chapters that concern the library.  The list
 671          itself is
 672          <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
 673          website</a>.  Developers who are having problems interpreting
 674          the Standard may wish to consult his notes.
 675       </p>
 676       <p>For those people who are not part of the ISO Library Group
 677          (i.e., nearly all of us needing to read this page in the first
 678          place :-), a public list of the library defects is occasionally
 679          published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
 680          Some of these have resulted in <a href="#5_2">code changes</a>.
 681       </p>
 682
 683 <hr />
 684    <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
 685       <p>There are things which are not bugs in the compiler (4.2) nor
 686          the language specification (4.3), but aren't really bugs in
 687          libstdc++, either.  Really!  Please do not report these as bugs.
 688       </p>
 689       <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
 690          The biggest of these is the quadzillions of warnings about the
 691          library headers emitted when <code>-Weffc++</code> is used.  Making
 692          libstdc++ &quot;-Weffc++-clean&quot; is not a goal of the project,
 693          for a few reasons.  Mainly, that option tries to enforce
 694          object-oriented programming, while the Standard Library isn't
 695          necessarily trying to be OO.
 696       </p>
 697       <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
 698          </a> Did I just say that -Weffc++ was our biggest false-bug report?
 699          I lied.  (It used to be.)  Today it seems to be reports that after
 700          executing a sequence like
 701       </p>
 702       <pre>
 703     #include &lt;fstream&gt;
 704     ...
 705     std::fstream  fs(&quot;a_file&quot;);
 706     // .
 707     // . do things with fs...
 708     // .
 709     fs.close();
 710     fs.open(&quot;a_new_file&quot;);</pre>
 711       <p>all operations on the re-opened <code>fs</code> will fail, or at
 712          least act very strangely.  Yes, they often will, especially if
 713          <code>fs</code> reached the EOF state on the previous file.  The
 714          reason is that the state flags are <strong>not</strong> cleared
 715          on a successful call to open().  The standard unfortunately did
 716          not specify behavior in this case, and to everybody's great sorrow,
 717          the <a href="../ext/howto.html#5">proposed LWG resolution in
 718          DR #22</a> is to leave the flags unchanged.  You must insert a call
 719          to <code>fs.clear()</code> between the calls to close() and open(),
 720          and then everything will work like we all expect it to work.
 721          <strong>Update:</strong> for GCC 4.0 we implemented the resolution
 722          of <a href="../ext/howto.html#5">DR #409</a> and open() now calls
 723          <code>clear()</code> on success!
 724       </p>
 725       <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
 726          Another is the <code>rel_ops</code> namespace and the template
 727          comparison operator functions contained therein.  If they become
 728          visible in the same namespace as other comparison functions
 729          (e.g., '<code>using</code>' them and the &lt;iterator&gt; header),
 730          then you will suddenly be faced with huge numbers of ambiguity
 731          errors.  This was discussed on the -v3 list; Nathan Myers
 732          <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
 733          things up here</a>.  The collisions with vector/string iterator
 734          types have been fixed for 3.1.  <!-- more links to email here -->
 735       </p>
 736       <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
 737       <p>If you have found an extremely broken header file which is
 738          causing problems for you, look carefully before submitting a
 739          &quot;high&quot; priority bug report (which you probably shouldn't
 740          do anyhow; see the last paragraph of the page describing
 741          <a href="http://gcc.gnu.org/bugs.html">the GCC bug database</a>).
 742       </p>
 743       <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
 744          the installed library's name looks like <code>libstdc++-2.10.a</code>
 745          or <code>libstdc++-libc6-2.10.so</code>, then you are using the old
 746          libstdc++-v2 library, which is nonstandard and unmaintained.  Do not
 747          report problems with -v2 to the -v3 mailing list.
 748       </p>
 749       <p>For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are
 750          installed in <code>${prefix}/include/g++-v3</code> (see the 'v'?).
 751          Starting with version 3.2 the headers are installed in
 752          <code>${prefix}/include/c++/${version}</code> as this prevents
 753          headers from previous versions being found by mistake.
 754       </p>
 755       <p><a name="4_4_glibc"><strong>glibc</strong></a>
 756          If you're on a GNU/Linux system and have just upgraded to
 757          glibc 2.2, but are still using gcc 2.95.2, then you should have
 758          read the glibc FAQ, specifically 2.34:
 759       </p>
 760       <pre>
 761 2.34.   When compiling C++ programs, I get a compilation error in streambuf.h.
 762
 763 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
 764 apply a patch to the include files in /usr/include/g++, because the fpos_t
 765 type has changed in glibc 2.2.  The patch is at
 766 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
 767    </pre>
 768       <p>Note that 2.95.x shipped with the
 769          <a href="#4_4_interface">old v2 library</a> which is no longer
 770          maintained.  Also note that gcc 2.95.3 fixes this problem, but
 771          requires a separate patch for libstdc++-v3.
 772       </p>
 773       <p><a name="4_4_checks"><strong>concept checks</strong></a>
 774          If you see compilation errors containing messages about
 775          <code> <em>foo</em>Concept </code>and a<code> constraints </code>
 776          member function, then most likely you have violated one of the
 777          requirements for types used during instantiation of template
 778          containers and functions.  For example, EqualityComparableConcept
 779          appears if your types must be comparable with == and you have not
 780          provided this capability (a typo, or wrong visibility, or you
 781          just plain forgot, etc).
 782       </p>
 783       <p>More information, including how to optionally enable/disable the
 784          checks, is available
 785          <a href="../19_diagnostics/howto.html#3">here</a>.
 786       </p>
 787       <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
 788          If you are using the C++ library across dynamically-loaded
 789          objects, make certain that you are passing the correct options
 790          when compiling and linking:
 791       </p>
 792       <pre>
 793     // compile your library components
 794     g++ -fPIC -c a.cc
 795     g++ -fPIC -c b.cc
 796     ...
 797     g++ -fPIC -c z.cc
 798
 799     // create your library
 800     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
 801
 802     // link the executable
 803     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
 804       <p><a name="4_4_leak"><strong>"memory leaks" in containers</strong></a>
 805          A few people have reported that the standard containers appear
 806          to leak memory when tested with memory checkers such as
 807          <a href="http://developer.kde.org/~sewardj/">valgrind</a>.
 808          The library's default allocators keep free memory in a pool
 809          for later reuse, rather than returning it to the OS.  Although
 810          this memory is always reachable by the library and is never
 811          lost, memory debugging tools can report it as a leak.  If you
 812          want to test the library for memory leaks please read
 813          <a href="../debug.html#mem">Tips for memory leak hunting</a>
 814          first.
 815       </p>
 816
 817 <hr />
 818    <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
 819       <p>If you have found a bug in the library and you think you have
 820          a working fix, then send it in!  The main GCC site has a page
 821          on <a href="http://gcc.gnu.org/contribute.html">submitting
 822          patches</a> that covers the procedure, but for libstdc++ you
 823          should also send the patch to our mailing list in addition to
 824          the GCC patches mailing list.  The libstdc++
 825          <a href="../17_intro/contribute.html">contributors' page</a>
 826          also talks about how to submit patches.
 827       </p>
 828       <p>In addition to the description, the patch, and the ChangeLog
 829          entry, it is a Good Thing if you can additionally create a small
 830          test program to test for the presence of the bug that your
 831          patch fixes.  Bugs have a way of being reintroduced; if an old
 832          bug creeps back in, it will be caught immediately by the
 833          <a href="#2_4">testsuite</a> -- but only if such a test exists.
 834       </p>
 835
 836 <hr />
 837 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
 838    <h2><a name="5_1">5.1 string::iterator is not char*;
 839                      vector&lt;T&gt;::iterator is not T*</a></h2>
 840       <p>If you have code that depends on container&lt;T&gt; iterators
 841          being implemented as pointer-to-T, your code is broken.
 842       </p>
 843       <p>While there are arguments for iterators to be implemented in
 844          that manner, A) they aren't very good ones in the long term,
 845          and B) they were never guaranteed by the Standard anyway.  The
 846          type-safety achieved by making iterators a real class rather
 847          than a typedef for <code>T*</code> outweighs nearly all opposing
 848          arguments.
 849       </p>
 850       <p>Code which does assume that a vector iterator <code> i </code>
 851          is a pointer can often be fixed by changing <code> i </code> in
 852          certain expressions to <code> &amp;*i </code>.  Future revisions
 853          of the Standard are expected to bless this usage for
 854          vector&lt;&gt; (but not for basic_string&lt;&gt;).
 855       </p>
 856
 857 <hr />
 858    <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
 859       <p>Hopefully, not much.  The goal of libstdc++-v3 is to produce
 860          a fully-compliant, fully-portable Standard Library.  After that,
 861          we're mostly done:  there won't <em>be</em> any more compliance
 862          work to do.  However:
 863       </p>
 864       <ol>
 865       <li><p>The ISO Committee will meet periodically to review Defect Reports
 866          in the C++ Standard.  Undoubtedly some of these will result in
 867          changes to the Standard, which will be reflected in patches to
 868          libstdc++.  Some of that is already happening, see <a href="#4_3">4.3</a>.  Some of
 869          those changes are being predicted by the library maintainers, and
 870          we add code to the library based on what the current proposed
 871          resolution specifies.  Those additions are listed in
 872          <a href="../ext/howto.html#5">the extensions page</a>.
 873       </p></li>
 874       <li><p>Performance tuning.  Lots of performance tuning.  This too is
 875          already underway for post-3.0 releases, starting with memory
 876          expansion in container classes and buffer usage in synchronized
 877          stream objects.
 878       </p></li>
 879       <li><p>An ABI for libstdc++ is being developed, so that
 880          multiple binary-incompatible copies of the library can be replaced
 881          with a single backwards-compatible library, like libgcc_s.so is.
 882       </p></li>
 883       <li><p>The current libstdc++ contains extensions to the Library which
 884          must be explicitly requested by client code (for example, the
 885          hash tables from SGI).  Other extensions may be added to
 886          libstdc++-v3 if they seem to be &quot;standard&quot; enough.
 887          (For example, the &quot;long long&quot; type from C99.)
 888          Bugfixes and rewrites (to improve or fix thread safety, for
 889          instance) will of course be a continuing task.
 890       </p></li>
 891       <li><p>There is an effort underway to add significant extensions to
 892          the standard library specification.  The latest version of this effort is
 893          described in
 894          <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
 895          The C++ Library Technical Report 1</a>.
 896          See <a href="#5_5">5.5</a>.
 897       </p></li>
 898       </ol>
 899       <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
 900          question</a> about the next libstdc++ prompted some brief but
 901          interesting
 902          <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
 903       </p>
 904
 905 <hr />
 906    <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
 907       <p>The <a href="http://www.sgi.com/tech/stl/">STL from SGI</a>,
 908          version 3.3, was the final merge of the STL codebase.  The
 909          code in libstdc++ contains many fixes and changes, and
 910          the SGI code is no longer under active
 911          development.  We expect that no future merges will take place.
 912       </p>
 913       <p>In particular, <code>string</code> is not from SGI and makes no
 914          use of their &quot;rope&quot; class (which is included as an
 915          optional extension), nor is <code>valarray</code> and some others.
 916          Classes like <code>vector&lt;&gt;</code> are, however we have
 917          made significant changes to them since then.
 918       </p>
 919       <p>The FAQ for SGI's STL (one jump off of their main page) is
 920          recommended reading.
 921       </p>
 922
 923 <hr />
 924    <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
 925       <p>Headers in the <code>ext</code> and <code>backward</code>
 926          subdirectories should be referred to by their relative paths:
 927          <!-- Careful, the leading spaces in PRE show up directly. -->
 928       </p>
 929       <pre>
 930       #include &lt;ext/hash_map&gt; </pre>
 931       <p>rather than using <code>-I</code> or other options.  This is more
 932          portable and forward-compatible.  (The situation is the same as
 933          that of other headers whose directories are not searched directly,
 934          e.g., <code>&lt;sys/stat.h&gt;</code>, <code>&lt;X11/Xlib.h&gt;</code>.
 935       </p>
 936
 937       <p>At this time most of the features of the SGI STL extension have been
 938          replaced by standardized libraries.
 939          In particular, the unordered_map and unordered_set containers of TR1
 940          are suitable replacement for the non-standard hash_map and hash_set
 941          containers in the SGI STL.  See <a href="#5_5">5.5</a> for more details.
 942       </p>
 943
 944       <p>The extensions are no longer in the global or <code>std</code>
 945          namespaces, instead they are declared in the <code>__gnu_cxx</code>
 946          namespace. For maximum portability, consider defining a namespace
 947          alias to use to talk about extensions, e.g.:
 948       </p>
 949       <pre>
 950       #ifdef __GNUC__
 951       #if __GNUC__ &lt; 3
 952         #include &lt;hash_map.h&gt;
 953         namespace Sgi { using ::hash_map; }; // inherit globals
 954       #else
 955         #include &lt;ext/hash_map&gt;
 956         #if __GNUC_MINOR__ == 0
 957           namespace Sgi = std;               // GCC 3.0
 958         #else
 959           namespace Sgi = ::__gnu_cxx;       // GCC 3.1 and later
 960         #endif
 961       #endif
 962       #else      // ...  there are other compilers, right?
 963         namespace Sgi = std;
 964       #endif
 965
 966       Sgi::hash_map&lt;int,int&gt; my_map; </pre>
 967       <p>This is a bit cleaner than defining typedefs for all the
 968          instantiations you might need.
 969       </p>
 970       <p><strong>Note:</strong> explicit template specializations must
 971          be declared in the same namespace as the original template.
 972          This means you cannot use a namespace alias when declaring
 973          an explicit specialization.
 974       </p>
 975       <p>Extensions to the library have
 976          <a href="../ext/howto.html">their own page</a>.
 977       </p>
 978
 979 <hr />
 980    <h2><a name="5_5">5.5 Does libstdc++ support TR1?</a></h2>
 981
 982       <p>The C++ Standard Library Technical Report adds many new features to
 983          the library.  The latest version of this effort is described in
 984          <a href=
 985          "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
 986          Technical Report 1</a>.
 987       </p>
 988
 989       <p>libstdc++ strives to implement all of TR1.
 990          An <a href="../ext/tr1.html">overview</a> of the implementation status
 991          is available.
 992       </p>
 993
 994       <p>Briefly, the features of TR1 and the current status are:
 995       </p>
 996
 997       <p><strong>Unordered containers - Complete -</strong>
 998          The unordered_set, unordered_map, unordered_multiset, and
 999          unordered_multimap containers are hashed versions of the map, set,
1000          multimap, and multiset containers respectively.  These classes are
1001          suitable replacements for the SGI STL hash_map and hash_set
1002          extensions.
1003       </p>
1004
1005       <p><strong>Reference-counted smart pointers - Complete -</strong>
1006          The shared_ptr and weak_ptr allow several object to know about a
1007          pointer and whether it is valid.  When the last reference to the
1008          pointer is destroyed the pointer is freed.
1009       </p>
1010
1011       <p><strong>Type traits - Complete -</strong>
1012          The type_traits class gives templates the ability to probe
1013          information about the input type and enable type-dependent logic
1014          to be performed without the need of template specializations.
1015       </p>
1016
1017       <p><strong>Fixed-size arrays - Complete -</strong>
1018          The array class implements small fixed-sized arrays with container
1019          semantics.
1020       </p>
1021
1022       <p><strong>Tuples - Complete -</strong>
1023          The tuple class implements small heterogeneous arrays.  This is an
1024          enhanced pair.  In fact, the standard pair is enhanced with a tuple
1025          interface.
1026       </p>
1027
1028       <p><strong>A regular expression engine</strong>
1029          This library provides for regular expression objects with traversal
1030          of text with return of subexpressions.
1031       </p>
1032
1033       <p><strong>A random number engine</strong>
1034          This library contains randow number generators with several different
1035          choices of distribution.
1036       </p>
1037
1038       <p><strong>Special functions - Under construction - </strong>
1039          Twenty-three mathematical functions familiar to physicists and
1040          engineers are included:  cylindrical and spherical Bessel and Neumann
1041          functions, hypergeometric functions, Laguerre polynomials, Legendre
1042          functions, elliptic integrals, exponential integrals and the Riemann
1043          zeta function all for your computing pleasure.
1044       </p>
1045
1046       <p><strong>C99 compatibility - Under construction - </strong>
1047          There are many features designed to minimize the divergence of the C
1048          and the C++ languages.
1049       </p>
1050
1051 <hr />
1052    <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
1053       <p>libstdc++-v3 strives to be thread-safe when all of the following
1054          conditions are met:
1055       </p>
1056       <ul>
1057        <li>The system's libc is itself thread-safe,</li>
1058        <li><code>gcc -v</code> reports a thread model other than 'single',</li>
1059        <li>[pre-3.3 only] a non-generic implementation of atomicity.h
1060            exists for the architecture in question.</li>
1061       </ul>
1062       <p>The user-code must guard against concurrent method calls which may
1063          access any particular library object's state.  Typically, the
1064          application programmer may infer what object locks must be held
1065          based on the objects referenced in a method call.  Without getting
1066          into great detail, here is an example which requires user-level
1067          locks:
1068       </p>
1069       <pre>
1070      library_class_a shared_object_a;
1071
1072      thread_main () {
1073        library_class_b *object_b = new library_class_b;
1074        shared_object_a.add_b (object_b);   // must hold lock for shared_object_a
1075        shared_object_a.mutate ();          // must hold lock for shared_object_a
1076      }
1077
1078      // Multiple copies of thread_main() are started in independent threads.</pre>
1079       <p>Under the assumption that object_a and object_b are never exposed to
1080          another thread, here is an example that should not require any
1081          user-level locks:
1082       </p>
1083       <pre>
1084      thread_main () {
1085        library_class_a object_a;
1086        library_class_b *object_b = new library_class_b;
1087        object_a.add_b (object_b);
1088        object_a.mutate ();
1089      } </pre>
1090       <p>All library objects are safe to use in a multithreaded program as
1091          long as each thread carefully locks out access by any other
1092          thread while it uses any object visible to another thread, i.e.,
1093          treat library objects like any other shared resource.  In general,
1094          this requirement includes both read and write access to objects;
1095          unless otherwise documented as safe, do not assume that two threads
1096          may access a shared standard library object at the same time.
1097       </p>
1098       <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
1099          introduction), <a href="../23_containers/howto.html#3">23</a>
1100          (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
1101          more information.
1102       </p>
1103
1104 <hr />
1105    <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
1106       <p>Copies of the full ISO 14882 standard are available on line via the
1107          ISO mirror site for committee members.  Non-members, or those who
1108          have not paid for the privilege of sitting on the committee and
1109          sustained their two-meeting commitment for voting rights, may get a
1110          copy of the standard from their respective national standards
1111          organization.  In the USA, this national standards organization is
1112          ANSI and their website is right <a href="http://www.ansi.org">here</a>.
1113          (And if you've already registered with them, clicking this link will
1114          take you to directly to the place where you can
1115 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003">buy
1116          the standard on-line</a>.
1117       </p>
1118       <p>Who is your country's member body?  Visit the
1119          <a href="http://www.iso.ch/">ISO homepage</a> and find out!
1120       </p>
1121
1122 <hr />
1123    <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
1124       <p>&quot;ABI&quot; stands for &quot;Application Binary Interface.&quot;
1125          Conventionally, it refers to a great mass of details about how
1126          arguments are arranged on the call stack and/or in registers, and
1127          how various types are arranged and padded in structs.  A single CPU
1128          design may suffer multiple ABIs designed by different development
1129          tool vendors who made different choices, or even by the same vendor
1130          for different target applications or compiler versions.  In ideal
1131          circumstances the CPU designer presents one ABI and all the OSes and
1132          compilers use it.  In practice every ABI omits details that compiler
1133          implementers (consciously or accidentally) must choose for themselves.
1134       </p>
1135       <p>That ABI definition suffices for compilers to generate code so a
1136          program can interact safely with an OS and its lowest-level libraries.
1137          Users usually want an ABI to encompass more detail, allowing libraries
1138          built with different compilers (or different releases of the same
1139          compiler!) to be linked together.  For C++, this includes many more
1140          details than for C, and CPU designers (for good reasons elaborated
1141          below) have not stepped up to publish C++ ABIs.  The details include
1142          virtual function implementation, struct inheritance layout, name
1143          mangling, and exception handling.  Such an ABI has been defined for
1144          GNU C++, and is immediately useful for embedded work relying only on
1145          a &quot;free-standing implementation&quot; that doesn't include (much
1146          of) the standard library.  It is a good basis for the work to come.
1147       </p>
1148       <p>A useful C++ ABI must also incorporate many details of the standard
1149          library implementation.  For a C ABI, the layouts of a few structs
1150          (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
1151          For C++, the details include the complete set of names of functions
1152          and types used, the offsets of class members and virtual functions,
1153          and the actual definitions of all inlines.  C++ exposes many more
1154          library details to the caller than C does.  It makes defining
1155          a complete ABI a much bigger undertaking, and requires not just
1156          documenting library implementation details, but carefully designing
1157          those details so that future bug fixes and optimizations don't
1158          force breaking the ABI.
1159       </p>
1160       <p>There are ways to help isolate library implementation details from the
1161          ABI, but they trade off against speed.  Library details used in
1162          inner loops (e.g., getchar) must be exposed and frozen for all
1163          time, but many others may reasonably be kept hidden from user code,
1164          so they may later be changed.  Deciding which, and implementing
1165          the decisions, must happen before you can reasonably document a
1166          candidate C++ ABI that encompasses the standard library.
1167       </p>
1168
1169 <hr />
1170    <h2><a name="5_9">5.9 How do I make std::vector&lt;T&gt;::capacity()
1171                      == std::vector&lt;T&gt;::size()?</a> </h2>
1172    <!-- referenced by 21_strings/howto.html#6 -->
1173    <p>The standard idiom for deallocating a <code>std::vector&lt;T&gt;</code>'s
1174       unused memory is to create a temporary copy of the vector and swap their
1175       contents, e.g. for <code>std::vector&lt;T&gt; v</code>
1176    </p>
1177    <pre>
1178      std::vector&lt;T&gt;(v).swap(v);
1179    </pre>
1180    <p>The copy will take O(n) time and the swap is constant time.
1181    </p>
1182    <p>See <a href='../21_strings/howto.html#6'>Shrink-to-fit strings</a> for
1183       a similar solution for strings.
1184    </p>
1185
1186 <!-- ####################################################### -->
1187
1188 <hr />
1189 <p class="fineprint"><em>
1190 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
1191 Comments and suggestions are welcome, and may be sent to
1192 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
1193 </em></p>
1194
1195
1196 </body>
1197 </html>
1198