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  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 CVS 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 CVS, 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 CVS 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 CVS sources, and for
 197          browsing the CVS 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 CVSweb 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 CVS thing that you
 329                          keep mentioning?</a></h2>
 330       <p>The <em>Concurrent Versions System</em> is one of several revision
 331          control packages.  It was selected for GNU projects because it's
 332          free (speech), free (beer), and very high quality.  The <a
 333          href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
 334          the GNU software catalogue</a> has a better description as
 335          well as a
 336          <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
 337       </p>
 338       <p>The &quot;anonymous client checkout&quot; feature of CVS is
 339          similar to anonymous FTP in that it allows anyone to retrieve
 340          the latest libstdc++ sources.
 341       </p>
 342       <p>After the first of April, American users will have a
 343          &quot;/pharmacy&quot; command-line option...
 344          <!-- wonder how long that'll live -->
 345       </p>
 346
 347 <hr />
 348    <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
 349       <p>libstdc++-v3 comes with its own testsuite.  You do not need
 350          to actually install the library (&quot;<code>make
 351          install</code>&quot;) to run the testsuite, but you do need
 352          DejaGNU, as described
 353          <a href="http://gcc.gnu.org/install/test.html">here</a>.
 354       </p>
 355       <p>To run the testsuite on the library after building it, use
 356          &quot;make check&quot; while in your build directory.  To run
 357          the testsuite on the library after building and installing it,
 358          use &quot;make check-install&quot; instead.
 359       </p>
 360       <p>If you find bugs in the testsuite programs themselves, or if you
 361          think of a new test program that should be added to the suite,
 362          <strong>please</strong> write up your idea and send it to the list!
 363       </p>
 364
 365 <hr />
 366    <h2><a name="2_5">2.5 This library is HUGE!  And what's libsupc++?</a></h2>
 367       <p>Usually the size of libraries on disk isn't noticeable.  When a
 368          link editor (or simply &quot;linker&quot;) pulls things from a
 369          static archive library, only the necessary object files are copied
 370          into your executable, not the entire library.  Unfortunately, even
 371          if you only need a single function or variable from an object file,
 372          the entire object file is extracted.  (There's nothing unique to C++
 373          or libstdc++-v3 about this; it's just common behavior, given here
 374          for background reasons.)
 375       </p>
 376       <p>Some of the object files which make up libstdc++.a are rather large.
 377          If you create a statically-linked executable with
 378          <code> -static</code>, those large object files are suddenly part
 379          of your executable.  Historically the best way around this was to
 380          only place a very few functions (often only a single one) in each
 381          source/object file; then extracting a single function is the same
 382          as extracting a single .o file.  For libstdc++-v3 this is only
 383          possible to a certain extent; the object files in question contain
 384          template classes and template functions, pre-instantiated, and
 385          splitting those up causes severe maintenance headaches.
 386       </p>
 387       <p>It's not a bug, and it's not really a problem.  Nevertheless, some
 388          people don't like it, so here are two pseudo-solutions:
 389       </p>
 390       <p>If the only functions from libstdc++.a which you need are
 391          language support functions (those listed in <a
 392          href="../18_support/howto.html">clause 18</a> of the
 393          standard, e.g., <code>new</code> and <code>delete</code>),
 394          then try linking against <code>libsupc++.a</code> (Using
 395          <code>gcc</code> instead of <code>g++</code> and explicitly
 396          linking in <code>-lsupc++</code> for the final link step will
 397          do it).  This library contains only those support routines,
 398          one per object file.  But if you are using anything from the
 399          rest of the library, such as IOStreams or vectors, then
 400          you'll still need pieces from <code>libstdc++.a</code>.
 401       </p>
 402       <p>The second method is one we hope to incorporate into the library
 403          build process.  Some platforms can place each function and variable
 404          into its own section in a .o file.  The GNU linker can then perform
 405          garbage collection on unused sections; this reduces the situation
 406          to only copying needed functions into the executable, as before,
 407          but all happens automatically.
 408       </p>
 409       <p>Unfortunately the garbage collection in GNU ld is buggy; sections
 410          (corresponding to functions and variables) which <em>are</em> used
 411          are mistakenly removed, leading to horrible crashes when your
 412          executable starts up.  For the time being, this feature is not used
 413          when building the library.
 414       </p>
 415
 416 <hr />
 417    <h2><a name="2_6">2.6 Why do I get an error saying
 418                          <code>libstdc++.so.X</code> is missing when I run
 419                          my program?</a></h2>
 420       <p>Depending on your platform and library version, the message might
 421          be similar to one of the following:
 422       </p>
 423       <pre>
 424     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 425
 426     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found </pre>
 427
 428       <p>This doesn't mean that the shared library isn't installed, only
 429          that the dynamic linker can't find it. When a dynamically-linked
 430          executable is run the linker finds and loads the required shared
 431          libraries by searching a pre-configured list of directories. If
 432          the directory where you've installed libstdc++ is not in this
 433          list then the libraries won't be found. The simplest way to fix
 434          this is to use the <code>LD_LIBRARY_PATH</code> environment
 435          variable, which is a colon-separated list of directories in which
 436          the linker will search for shared libraries:
 437       </p>
 438       <pre>
 439     LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 440     export LD_LIBRARY_PATH </pre>
 441       <p>The exact environment variable to use will depend on your platform,
 442          e.g. DYLD_LIBRARY_PATH for Darwin,
 443          LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
 444          LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs
 445          and SHLIB_PATH for HP-UX.
 446       </p>
 447       <p>See the man pages for <code>ld(1)</code>, <code>ldd(1)</code> and
 448          <code>ldconfig(8)</code> for more information. The dynamic linker
 449          has different names on different platforms but the man page is
 450          usually called something such as <code>ld.so / rtld / dld.so</code>.
 451       </p>
 452
 453 <hr />
 454 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
 455    <h2><a name="3_1">3.1 Can libstdc++-v3 be used with &lt;my
 456                          favorite compiler&gt;?</a></h2>
 457       <p>Probably not.  Yet.</p>
 458       <p>Because GCC advances so rapidly, development and testing of
 459          libstdc++ is being done almost entirely under that compiler.
 460          If you are curious about whether other, lesser compilers
 461          (*grin*) support libstdc++, you are more than welcome to try.
 462          Configuring and building the library (see above) will still
 463          require certain tools, however.  Also keep in mind that
 464          <em>building</em> libstdc++ does not imply that your compiler
 465          will be able to <em>use</em> all of the features found in the
 466          C++ Standard Library.
 467       </p>
 468       <p>Since the goal of ISO Standardization is for all C++
 469          implementations to be able to share code, the final libstdc++
 470          should, in theory, be usable under any ISO-compliant
 471          compiler.  It will still be targeted and optimized for
 472          GCC/g++, however.
 473       </p>
 474
 475 <hr />
 476    <h2><a name="3_2">3.2 [removed]</a></h2>
 477       <p>This question has become moot and has been removed.  The stub
 478          is here to preserve numbering (and hence links/bookmarks).
 479       </p>
 480
 481 <hr />
 482    <h2><a name="3_3">3.3 [removed]</a></h2>
 483       <p>This question has become moot and has been removed.  The stub
 484          is here to preserve numbering (and hence links/bookmarks).
 485       </p>
 486
 487 <hr />
 488    <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
 489       <p>By default we try to support the C99 <code>long long</code> type.
 490          This requires that certain functions from your C library be present.
 491       </p>
 492       <p>Up through release 3.0.2 the tests performed were too general, and
 493          this feature was disabled when it did not need to be.  The most
 494          commonly reported platform affected was Solaris.
 495       </p>
 496       <p>This has been fixed for 3.0.3 and onwards.
 497       </p>
 498
 499 <hr />
 500    <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
 501                          / etc is always defined</a></h2>
 502       <p>On Solaris, g++ (but not gcc) always defines the preprocessor
 503          macro <code>_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 504          with <code>_GNU_SOURCE</code>.  (This is not an exhaustive list;
 505          other macros and other platforms are also affected.)
 506       </p>
 507       <p>These macros are typically used in C library headers, guarding new
 508          versions of functions from their older versions.  The C++ standard
 509          library includes the C standard library, but it requires the C90
 510          version, which for backwards-compatability reasons is often not the
 511          default for many vendors.
 512       </p>
 513       <p>More to the point, the C++ standard requires behavior which is only
 514          available on certain platforms after certain symbols are defined.
 515          Usually the issue involves I/O-related typedefs.  In order to
 516          ensure correctness, the compiler simply predefines those symbols.
 517       </p>
 518       <p>Note that it's not enough to #define them only when the library is
 519          being built (during installation).  Since we don't have an 'export'
 520          keyword, much of the library exists as headers, which means that
 521          the symbols must also be defined as your programs are parsed and
 522          compiled.
 523       </p>
 524       <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 525          the gcc config headers for your target (and try changing them to
 526          see what happens when building complicated code).  You can also run
 527          <code>&quot;g++ -E -dM - &lt; /dev/null&quot;</code> to display
 528          a list of predefined macros for any particular installation.
 529       </p>
 530       <p>This has been discussed on the mailing lists
 531          <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>.
 532       </p>
 533       <p>This method is something of a wart.  We'd like to find a cleaner
 534          solution, but nobody yet has contributed the time.
 535       </p>
 536
 537 <hr />
 538    <h2><a name="3_6">3.6 OS X ctype.h is broken!  How can I hack it?</a></h2>
 539       <p>This is a long-standing bug in the OS X support.  Fortunately,
 540          the patch is quite simple, and well-known.
 541          <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
 542          link to the solution.</a>
 543       </p>
 544
 545 <hr />
 546    <h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
 547       <p>Support for atomic integer operations is/was broken on i386
 548          platforms.  The assembly code accidentally used opcodes that are
 549          only available on the i486 and later.  So if you configured GCC
 550          to target, for example, i386-linux, but actually used the programs
 551          on an i686, then you would encounter no problems.  Only when
 552          actually running the code on a i386 will the problem appear.
 553       </p>
 554       <p>This is fixed in 3.2.2.
 555       </p>
 556
 557 <hr />
 558    <h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
 559       <p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version
 560          5.0.1) and later uses localization and formatting code from the system
 561          C library (glibc) version 2.2.5.  That version of glibc is over a
 562          year old and contains necessary bugfixes.  Many GNU/Linux distros make
 563          glibc version 2.3.x available now.
 564       </p>
 565       <p>The guideline is simple:  the more recent the C++ library, the
 566          more recent the C library.  (This is also documented in the main
 567          GCC installation instructions.)
 568       </p>
 569
 570 <hr />
 571    <h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
 572       <p>At the moment there are a few problems in FreeBSD's support for
 573          wide character functions, and as a result the libstdc++ configury
 574          decides that wchar_t support should be disabled.  Once the underlying
 575          problems are fixed in FreeBSD (soon), the library support will
 576          automatically enable itself.
 577       </p>
 578       <p>You can fix the problems yourself, and learn more about the situation,
 579          by reading
 580          <a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
 581          this short thread</a> (&quot;_GLIBCPP_USE_WCHAR_T undefined in
 582          FreeBSD's c++config.h?&quot;).
 583       </p>
 584
 585 <hr />
 586    <h2><a name="3_10">3.10 MIPS atomic operations</a></h2>
 587       <p>The atomic locking routines for MIPS targets requires MIPS II
 588          and later.  A patch went in just after the 3.3 release to
 589          make mips* use the generic implementation instead.  You can also
 590          configure for mipsel-elf as a workaround.
 591       </p>
 592       <p>mips*-*-linux* continues to use the MIPS II routines, and more
 593          work in this area is expected.
 594       </p>
 595
 596 <hr />
 597 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
 598    <em>Note that this section can get rapdily outdated -- such is the
 599        nature of an open-source project.  For the latest information, join
 600        the mailing list or look through recent archives.   The RELEASE-
 601        NOTES and BUGS files are generally kept up-to-date.</em>
 602
 603    <p>For 3.0.1, the most common &quot;bug&quot; is an apparently missing
 604       &quot;<code>../</code>&quot; in include/Makefile, resulting in files
 605       like gthr.h and gthr-single.h not being found.  Please read
 606       <a href="http://gcc.gnu.org/install/configure.html">the configuration
 607       instructions for GCC</a>,
 608       specifically the part about configuring in a separate build directory,
 609       and how strongly recommended it is.  Building in the source directory
 610       is fragile, is rarely tested, and tends to break, as in this case.
 611       This was fixed for 3.0.2.
 612    </p>
 613
 614    <p>For 3.1, the most common &quot;bug&quot; is a parse error when using
 615       <code>&lt;fstream&gt;</code>, ending with a message,
 616       &quot;<code>bits/basic_file.h:52: parse error before `{'
 617       token</code>.&quot;  Please read
 618       <a href="http://gcc.gnu.org/install/">the installation instructions for
 619       GCC</a>, specifically the part about not installing newer versions on
 620       top of older versions.  If you install 3.1 over a 3.0.x release, then
 621       the wrong basic_file.h header will be found (its location changed
 622       between releases).
 623    </p>
 624
 625    <p><strong>Please do not report these as bugs.  We know about them.</strong>
 626       Reporting this -- or any other problem that's already been fixed --
 627       hinders the development of GCC, because we have to take time to
 628       respond to your report.  Thank you.
 629    </p>
 630
 631 <hr />
 632    <h2><a name="4_1">4.1 What works already?</a></h2>
 633       <p>Short answer:  Pretty much everything <em>works</em> except for some
 634          corner cases.  Also, localization is incomplete.  For whether it works
 635          well, or as you expect it to work, see 5.2.
 636       </p>
 637       <p>Long answer:  See the docs/html/17_intro/CHECKLIST file, which is
 638          badly outdated...  Also see the RELEASE-NOTES file, which is kept
 639          more up to date.
 640       </p>
 641
 642 <hr />
 643    <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
 644       <p>This is by no means meant to be complete nor exhaustive, but
 645          mentions some problems that users may encounter when building
 646          or using libstdc++.  If you are experiencing one of these
 647          problems, you can find more information on the libstdc++ and
 648          the GCC mailing lists.
 649       </p>
 650       <p>Before reporting a bug, examine the
 651          <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
 652          category set to &quot;libstdc++&quot;.  The BUGS file in the source
 653          tree also tracks known serious problems.
 654       </p>
 655       <ul>
 656          <li>Debugging is problematic, due to bugs in line-number generation
 657              (mostly fixed in the compiler) and gdb lagging behind the
 658              compiler (lack of personnel).  We recommend configuring the
 659              compiler using <code>--with-dwarf2</code> if the DWARF2
 660              debugging format is not already the default on your platform.
 661              Also,
 662 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
 663              GDB settings</a> can have a profound effect on your C++ debugging
 664              experiences.  :-)</li>
 665       </ul>
 666
 667 <hr />
 668    <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
 669       <p>Yes, unfortunately, there are some.  In a
 670          <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
 671          to the list</a>, Nathan Myers announced that he has started a list of
 672          problems in the ISO C++ Standard itself, especially with
 673          regard to the chapters that concern the library.  The list
 674          itself is
 675          <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
 676          website</a>.  Developers who are having problems interpreting
 677          the Standard may wish to consult his notes.
 678       </p>
 679       <p>For those people who are not part of the ISO Library Group
 680          (i.e., nearly all of us needing to read this page in the first
 681          place :-), a public list of the library defects is occasionally
 682          published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
 683          Some of these have resulted in <a href="#5_2">code changes</a>.
 684       </p>
 685
 686 <hr />
 687    <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
 688       <p>There are things which are not bugs in the compiler (4.2) nor
 689          the language specification (4.3), but aren't really bugs in
 690          libstdc++, either.  Really!  Please do not report these as bugs.
 691       </p>
 692       <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
 693          The biggest of these is the quadzillions of warnings about the
 694          library headers emitted when <code>-Weffc++</code> is used.  Making
 695          libstdc++ &quot;-Weffc++-clean&quot; is not a goal of the project,
 696          for a few reasons.  Mainly, that option tries to enforce
 697          object-oriented programming, while the Standard Library isn't
 698          necessarily trying to be OO.
 699       </p>
 700       <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
 701          </a> Did I just say that -Weffc++ was our biggest false-bug report?
 702          I lied.  (It used to be.)  Today it seems to be reports that after
 703          executing a sequence like
 704       </p>
 705       <pre>
 706     #include &lt;fstream&gt;
 707     ...
 708     std::fstream  fs(&quot;a_file&quot;);
 709     // .
 710     // . do things with fs...
 711     // .
 712     fs.close();
 713     fs.open(&quot;a_new_file&quot;);</pre>
 714       <p>all operations on the re-opened <code>fs</code> will fail, or at
 715          least act very strangely.  Yes, they often will, especially if
 716          <code>fs</code> reached the EOF state on the previous file.  The
 717          reason is that the state flags are <strong>not</strong> cleared
 718          on a successful call to open().  The standard unfortunately did
 719          not specify behavior in this case, and to everybody's great sorrow,
 720          the <a href="../ext/howto.html#5">proposed LWG resolution in
 721          DR #22</a> is to leave the flags unchanged.  You must insert a call
 722          to <code>fs.clear()</code> between the calls to close() and open(),
 723          and then everything will work like we all expect it to work.
 724          <strong>Update:</strong> for GCC 4.0 we implemented the resolution
 725          of <a href="../ext/howto.html#5">DR #409</a> and open() now calls
 726          <code>clear()</code> on success!
 727       </p>
 728       <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
 729          Another is the <code>rel_ops</code> namespace and the template
 730          comparison operator functions contained therein.  If they become
 731          visible in the same namespace as other comparison functions
 732          (e.g., '<code>using</code>' them and the &lt;iterator&gt; header),
 733          then you will suddenly be faced with huge numbers of ambiguity
 734          errors.  This was discussed on the -v3 list; Nathan Myers
 735          <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
 736          things up here</a>.  The collisions with vector/string iterator
 737          types have been fixed for 3.1.  <!-- more links to email here -->
 738       </p>
 739       <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
 740       <p>If you have found an extremely broken header file which is
 741          causing problems for you, look carefully before submitting a
 742          &quot;high&quot; priority bug report (which you probably shouldn't
 743          do anyhow; see the last paragraph of the page describing
 744          <a href="http://gcc.gnu.org/bugs.html">the GCC bug database</a>).
 745       </p>
 746       <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
 747          the installed library's name looks like <code>libstdc++-2.10.a</code>
 748          or <code>libstdc++-libc6-2.10.so</code>, then you are using the old
 749          libstdc++-v2 library, which is nonstandard and unmaintained.  Do not
 750          report problems with -v2 to the -v3 mailing list.
 751       </p>
 752       <p>For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are
 753          installed in <code>${prefix}/include/g++-v3</code> (see the 'v'?).
 754          Starting with version 3.2 the headers are installed in
 755          <code>${prefix}/include/c++/${version}</code> as this prevents
 756          headers from previous versions being found by mistake.
 757       </p>
 758       <p><a name="4_4_glibc"><strong>glibc</strong></a>
 759          If you're on a GNU/Linux system and have just upgraded to
 760          glibc 2.2, but are still using gcc 2.95.2, then you should have
 761          read the glibc FAQ, specifically 2.34:
 762       </p>
 763       <pre>
 764 2.34.   When compiling C++ programs, I get a compilation error in streambuf.h.
 765
 766 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
 767 apply a patch to the include files in /usr/include/g++, because the fpos_t
 768 type has changed in glibc 2.2.  The patch is at
 769 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
 770    </pre>
 771       <p>Note that 2.95.x shipped with the
 772          <a href="#4_4_interface">old v2 library</a> which is no longer
 773          maintained.  Also note that gcc 2.95.3 fixes this problem, but
 774          requires a separate patch for libstdc++-v3.
 775       </p>
 776       <p><a name="4_4_checks"><strong>concept checks</strong></a>
 777          If you see compilation errors containing messages about
 778          <code> <em>foo</em>Concept </code>and a<code> constraints </code>
 779          member function, then most likely you have violated one of the
 780          requirements for types used during instantiation of template
 781          containers and functions.  For example, EqualityComparableConcept
 782          appears if your types must be comparable with == and you have not
 783          provided this capability (a typo, or wrong visibility, or you
 784          just plain forgot, etc).
 785       </p>
 786       <p>More information, including how to optionally enable/disable the
 787          checks, is available
 788          <a href="../19_diagnostics/howto.html#3">here</a>.
 789       </p>
 790       <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
 791          If you are using the C++ library across dynamically-loaded
 792          objects, make certain that you are passing the correct options
 793          when compiling and linking:
 794       </p>
 795       <pre>
 796     // compile your library components
 797     g++ -fPIC -c a.cc
 798     g++ -fPIC -c b.cc
 799     ...
 800     g++ -fPIC -c z.cc
 801
 802     // create your library
 803     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
 804
 805     // link the executable
 806     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
 807       <p><a name="4_4_leak"><strong>"memory leaks" in containers</strong></a>
 808          A few people have reported that the standard containers appear
 809          to leak memory when tested with memory checkers such as
 810          <a href="http://developer.kde.org/~sewardj/">valgrind</a>.
 811          The library's default allocators keep free memory in a pool
 812          for later reuse, rather than returning it to the OS.  Although
 813          this memory is always reachable by the library and is never
 814          lost, memory debugging tools can report it as a leak.  If you
 815          want to test the library for memory leaks please read
 816          <a href="../debug.html#mem">Tips for memory leak hunting</a>
 817          first.
 818       </p>
 819
 820 <hr />
 821    <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
 822       <p>If you have found a bug in the library and you think you have
 823          a working fix, then send it in!  The main GCC site has a page
 824          on <a href="http://gcc.gnu.org/contribute.html">submitting
 825          patches</a> that covers the procedure, but for libstdc++ you
 826          should also send the patch to our mailing list in addition to
 827          the GCC patches mailing list.  The libstdc++
 828          <a href="../17_intro/contribute.html">contributors' page</a>
 829          also talks about how to submit patches.
 830       </p>
 831       <p>In addition to the description, the patch, and the ChangeLog
 832          entry, it is a Good Thing if you can additionally create a small
 833          test program to test for the presence of the bug that your
 834          patch fixes.  Bugs have a way of being reintroduced; if an old
 835          bug creeps back in, it will be caught immediately by the
 836          <a href="#2_4">testsuite</a> -- but only if such a test exists.
 837       </p>
 838
 839 <hr />
 840 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
 841    <h2><a name="5_1">5.1 string::iterator is not char*;
 842                      vector&lt;T&gt;::iterator is not T*</a></h2>
 843       <p>If you have code that depends on container&lt;T&gt; iterators
 844          being implemented as pointer-to-T, your code is broken.
 845       </p>
 846       <p>While there are arguments for iterators to be implemented in
 847          that manner, A) they aren't very good ones in the long term,
 848          and B) they were never guaranteed by the Standard anyway.  The
 849          type-safety achieved by making iterators a real class rather
 850          than a typedef for <code>T*</code> outweighs nearly all opposing
 851          arguments.
 852       </p>
 853       <p>Code which does assume that a vector iterator <code> i </code>
 854          is a pointer can often be fixed by changing <code> i </code> in
 855          certain expressions to <code> &amp;*i </code>.  Future revisions
 856          of the Standard are expected to bless this usage for
 857          vector&lt;&gt; (but not for basic_string&lt;&gt;).
 858       </p>
 859
 860 <hr />
 861    <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
 862       <p>Hopefully, not much.  The goal of libstdc++-v3 is to produce
 863          a fully-compliant, fully-portable Standard Library.  After that,
 864          we're mostly done:  there won't <em>be</em> any more compliance
 865          work to do.  However:
 866       </p>
 867       <ol>
 868       <li><p>The ISO Committee will meet periodically to review Defect Reports
 869          in the C++ Standard.  Undoubtedly some of these will result in
 870          changes to the Standard, which will be reflected in patches to
 871          libstdc++.  Some of that is already happening, see <a href="#4_3">4.3</a>.  Some of
 872          those changes are being predicted by the library maintainers, and
 873          we add code to the library based on what the current proposed
 874          resolution specifies.  Those additions are listed in
 875          <a href="../ext/howto.html#5">the extensions page</a>.
 876       </p></li>
 877       <li><p>Performance tuning.  Lots of performance tuning.  This too is
 878          already underway for post-3.0 releases, starting with memory
 879          expansion in container classes and buffer usage in synchronized
 880          stream objects.
 881       </p></li>
 882       <li><p>An ABI for libstdc++ is being developed, so that
 883          multiple binary-incompatible copies of the library can be replaced
 884          with a single backwards-compatible library, like libgcc_s.so is.
 885       </p></li>
 886       <li><p>The current libstdc++ contains extensions to the Library which
 887          must be explicitly requested by client code (for example, the
 888          hash tables from SGI).  Other extensions may be added to
 889          libstdc++-v3 if they seem to be &quot;standard&quot; enough.
 890          (For example, the &quot;long long&quot; type from C99.)
 891          Bugfixes and rewrites (to improve or fix thread safety, for
 892          instance) will of course be a continuing task.
 893       </p></li>
 894       <li><p>There is an effort underway to add significant extensions to
 895          the standard library specification.  The latest version of this effort is
 896          described in
 897          <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
 898          The C++ Library Technical Report 1</a>.
 899          See <a href="#5_5">5.5</a>.
 900       </p></li>
 901       </ol>
 902       <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
 903          question</a> about the next libstdc++ prompted some brief but
 904          interesting
 905          <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
 906       </p>
 907
 908 <hr />
 909    <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
 910       <p>The <a href="http://www.sgi.com/tech/stl/">STL from SGI</a>,
 911          version 3.3, was the final merge of the STL codebase.  The
 912          code in libstdc++ contains many fixes and changes, and
 913          the SGI code is no longer under active
 914          development.  We expect that no future merges will take place.
 915       </p>
 916       <p>In particular, <code>string</code> is not from SGI and makes no
 917          use of their &quot;rope&quot; class (which is included as an
 918          optional extension), nor is <code>valarray</code> and some others.
 919          Classes like <code>vector&lt;&gt;</code> are, however we have
 920          made significant changes to them since then.
 921       </p>
 922       <p>The FAQ for SGI's STL (one jump off of their main page) is
 923          recommended reading.
 924       </p>
 925
 926 <hr />
 927    <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
 928       <p>Headers in the <code>ext</code> and <code>backward</code>
 929          subdirectories should be referred to by their relative paths:
 930          <!-- Careful, the leading spaces in PRE show up directly. -->
 931       </p>
 932       <pre>
 933       #include &lt;ext/hash_map&gt; </pre>
 934       <p>rather than using <code>-I</code> or other options.  This is more
 935          portable and forward-compatible.  (The situation is the same as
 936          that of other headers whose directories are not searched directly,
 937          e.g., <code>&lt;sys/stat.h&gt;</code>, <code>&lt;X11/Xlib.h&gt;</code>.
 938       </p>
 939
 940       <p>At this time most of the features of the SGI STL extension have been
 941          replaced by standardized libraries.
 942          In particular, the unordered_map and unordered_set containers of TR1
 943          are suitable replacement for the non-standard hash_map and hash_set
 944          containers in the SGI STL.  See <a href="#5_5">5.5</a> for more details.
 945       </p>
 946
 947       <p>The extensions are no longer in the global or <code>std</code>
 948          namespaces, instead they are declared in the <code>__gnu_cxx</code>
 949          namespace. For maximum portability, consider defining a namespace
 950          alias to use to talk about extensions, e.g.:
 951       </p>
 952       <pre>
 953       #ifdef __GNUC__
 954       #if __GNUC__ &lt; 3
 955         #include &lt;hash_map.h&gt;
 956         namespace Sgi { using ::hash_map; }; // inherit globals
 957       #else
 958         #include &lt;ext/hash_map&gt;
 959         #if __GNUC_MINOR__ == 0
 960           namespace Sgi = std;               // GCC 3.0
 961         #else
 962           namespace Sgi = ::__gnu_cxx;       // GCC 3.1 and later
 963         #endif
 964       #endif
 965       #else      // ...  there are other compilers, right?
 966         namespace Sgi = std;
 967       #endif
 968
 969       Sgi::hash_map&lt;int,int&gt; my_map; </pre>
 970       <p>This is a bit cleaner than defining typedefs for all the
 971          instantiations you might need.
 972       </p>
 973       <p><strong>Note:</strong> explicit template specializations must
 974          be declared in the same namespace as the original template.
 975          This means you cannot use a namespace alias when declaring
 976          an explicit specialization.
 977       </p>
 978       <p>Extensions to the library have
 979          <a href="../ext/howto.html">their own page</a>.
 980       </p>
 981
 982 <hr />
 983    <h2><a name="5_5">5.5 Does libstdc++ support TR1?</a></h2>
 984
 985       <p>The C++ Standard Library Technical Report adds many new features to
 986          the library.  The latest version of this effort is described in
 987          <a href=
 988          "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
 989          Technical Report 1</a>.
 990       </p>
 991
 992       <p>libstdc++ strives to implement all of TR1.
 993          An <a href="../ext/tr1.html">overview</a> of the implementation status
 994          is available.
 995       </p>
 996
 997       <p>Briefly, the features of TR1 and the current status are:
 998       </p>
 999
1000       <p><strong>Unordered containers - Complete -</strong>
1001          The unordered_set, unordered_map, unordered_multiset, and
1002          unordered_multimap containers are hashed versions of the map, set,
1003          multimap, and multiset containers respectively.  These classes are
1004          suitable replacements for the SGI STL hash_map and hash_set
1005          extensions.
1006       </p>
1007
1008       <p><strong>Reference-counted smart pointers - Complete -</strong>
1009          The shared_ptr and weak_ptr allow several object to know about a
1010          pointer and whether it is valid.  When the last reference to the
1011          pointer is destroyed the pointer is freed.
1012       </p>
1013
1014       <p><strong>Type traits - Complete -</strong>
1015          The type_traits class gives templates the ability to probe
1016          information about the input type and enable type-dependent logic
1017          to be performed without the need of template specializations.
1018       </p>
1019
1020       <p><strong>Fixed-size arrays - Complete -</strong>
1021          The array class implements small fixed-sized arrays with container
1022          semantics.
1023       </p>
1024
1025       <p><strong>Tuples - Complete -</strong>
1026          The tuple class implements small heterogeneous arrays.  This is an
1027          enhanced pair.  In fact, the standard pair is enhanced with a tuple
1028          interface.
1029       </p>
1030
1031       <p><strong>A regular expression engine</strong>
1032          This library provides for regular expression objects with traversal
1033          of text with return of subexpressions.
1034       </p>
1035
1036       <p><strong>A random number engine</strong>
1037          This library contains randow number generators with several different
1038          choices of distribution.
1039       </p>
1040
1041       <p><strong>Special functions - Under construction - </strong>
1042          Twenty-three mathematical functions familiar to physicists and
1043          engineers are included:  cylindrical and spherical Bessel and Neumann
1044          functions, hypergeometric functions, Laguerre polynomials, Legendre
1045          functions, elliptic integrals, exponential integrals and the Riemann
1046          zeta function all for your computing pleasure.
1047       </p>
1048
1049       <p><strong>C99 compatibility - Under construction - </strong>
1050          There are many features designed to minimize the divergence of the C
1051          and the C++ languages.
1052       </p>
1053
1054 <hr />
1055    <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
1056       <p>libstdc++-v3 strives to be thread-safe when all of the following
1057          conditions are met:
1058       </p>
1059       <ul>
1060        <li>The system's libc is itself thread-safe,</li>
1061        <li><code>gcc -v</code> reports a thread model other than 'single',</li>
1062        <li>[pre-3.3 only] a non-generic implementation of atomicity.h
1063            exists for the architecture in question.</li>
1064       </ul>
1065       <p>The user-code must guard against concurrent method calls which may
1066          access any particular library object's state.  Typically, the
1067          application programmer may infer what object locks must be held
1068          based on the objects referenced in a method call.  Without getting
1069          into great detail, here is an example which requires user-level
1070          locks:
1071       </p>
1072       <pre>
1073      library_class_a shared_object_a;
1074
1075      thread_main () {
1076        library_class_b *object_b = new library_class_b;
1077        shared_object_a.add_b (object_b);   // must hold lock for shared_object_a
1078        shared_object_a.mutate ();          // must hold lock for shared_object_a
1079      }
1080
1081      // Multiple copies of thread_main() are started in independent threads.</pre>
1082       <p>Under the assumption that object_a and object_b are never exposed to
1083          another thread, here is an example that should not require any
1084          user-level locks:
1085       </p>
1086       <pre>
1087      thread_main () {
1088        library_class_a object_a;
1089        library_class_b *object_b = new library_class_b;
1090        object_a.add_b (object_b);
1091        object_a.mutate ();
1092      } </pre>
1093       <p>All library objects are safe to use in a multithreaded program as
1094          long as each thread carefully locks out access by any other
1095          thread while it uses any object visible to another thread, i.e.,
1096          treat library objects like any other shared resource.  In general,
1097          this requirement includes both read and write access to objects;
1098          unless otherwise documented as safe, do not assume that two threads
1099          may access a shared standard library object at the same time.
1100       </p>
1101       <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
1102          introduction), <a href="../23_containers/howto.html#3">23</a>
1103          (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
1104          more information.
1105       </p>
1106
1107 <hr />
1108    <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
1109       <p>Copies of the full ISO 14882 standard are available on line via the
1110          ISO mirror site for committee members.  Non-members, or those who
1111          have not paid for the privilege of sitting on the committee and
1112          sustained their two-meeting commitment for voting rights, may get a
1113          copy of the standard from their respective national standards
1114          organization.  In the USA, this national standards organization is
1115          ANSI and their website is right <a href="http://www.ansi.org">here</a>.
1116          (And if you've already registered with them, clicking this link will
1117          take you to directly to the place where you can
1118 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003">buy
1119          the standard on-line</a>.
1120       </p>
1121       <p>Who is your country's member body?  Visit the
1122          <a href="http://www.iso.ch/">ISO homepage</a> and find out!
1123       </p>
1124
1125 <hr />
1126    <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
1127       <p>&quot;ABI&quot; stands for &quot;Application Binary Interface.&quot;
1128          Conventionally, it refers to a great mass of details about how
1129          arguments are arranged on the call stack and/or in registers, and
1130          how various types are arranged and padded in structs.  A single CPU
1131          design may suffer multiple ABIs designed by different development
1132          tool vendors who made different choices, or even by the same vendor
1133          for different target applications or compiler versions.  In ideal
1134          circumstances the CPU designer presents one ABI and all the OSes and
1135          compilers use it.  In practice every ABI omits details that compiler
1136          implementers (consciously or accidentally) must choose for themselves.
1137       </p>
1138       <p>That ABI definition suffices for compilers to generate code so a
1139          program can interact safely with an OS and its lowest-level libraries.
1140          Users usually want an ABI to encompass more detail, allowing libraries
1141          built with different compilers (or different releases of the same
1142          compiler!) to be linked together.  For C++, this includes many more
1143          details than for C, and CPU designers (for good reasons elaborated
1144          below) have not stepped up to publish C++ ABIs.  The details include
1145          virtual function implementation, struct inheritance layout, name
1146          mangling, and exception handling.  Such an ABI has been defined for
1147          GNU C++, and is immediately useful for embedded work relying only on
1148          a &quot;free-standing implementation&quot; that doesn't include (much
1149          of) the standard library.  It is a good basis for the work to come.
1150       </p>
1151       <p>A useful C++ ABI must also incorporate many details of the standard
1152          library implementation.  For a C ABI, the layouts of a few structs
1153          (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
1154          For C++, the details include the complete set of names of functions
1155          and types used, the offsets of class members and virtual functions,
1156          and the actual definitions of all inlines.  C++ exposes many more
1157          library details to the caller than C does.  It makes defining
1158          a complete ABI a much bigger undertaking, and requires not just
1159          documenting library implementation details, but carefully designing
1160          those details so that future bug fixes and optimizations don't
1161          force breaking the ABI.
1162       </p>
1163       <p>There are ways to help isolate library implementation details from the
1164          ABI, but they trade off against speed.  Library details used in
1165          inner loops (e.g., getchar) must be exposed and frozen for all
1166          time, but many others may reasonably be kept hidden from user code,
1167          so they may later be changed.  Deciding which, and implementing
1168          the decisions, must happen before you can reasonably document a
1169          candidate C++ ABI that encompasses the standard library.
1170       </p>
1171
1172 <hr />
1173    <h2><a name="5_9">5.9 How do I make std::vector&lt;T&gt;::capacity()
1174                      == std::vector&lt;T&gt;::size()?</a> </h2>
1175    <!-- referenced by 21_strings/howto.html#6 -->
1176    <p>The standard idiom for deallocating a <code>std::vector&lt;T&gt;</code>'s
1177       unused memory is to create a temporary copy of the vector and swap their
1178       contents, e.g. for <code>std::vector&lt;T&gt; v</code>
1179    </p>
1180    <pre>
1181      std::vector&lt;T&gt;(v).swap(v);
1182    </pre>
1183    <p>The copy will take O(n) time and the swap is constant time.
1184    </p>
1185    <p>See <a href='../21_strings/howto.html#6'>Shrink-to-fit strings</a> for
1186       a similar solution for strings.
1187    </p>
1188
1189 <!-- ####################################################### -->
1190
1191 <hr />
1192 <p class="fineprint"><em>
1193 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
1194 Comments and suggestions are welcome, and may be sent to
1195 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
1196 </em></p>
1197
1198
1199 </body>
1200 </html>
1201