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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Frequently Asked Questions</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="bk03.html" title="" /><link rel="prev" href="bk03.html" title="" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frequently Asked Questions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><th width="60%" align="center"></th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="article" title="Frequently Asked Questions"><div class="titlepage"><div><div><h2 class="title"><a id="faq"></a>Frequently Asked Questions</h2></div><div><p class="copyright">Copyright © 
      2008
     
      <a class="ulink" href="http://www.fsf.org" target="_top">FSF</a>
    </p></div></div><hr /></div><div class="qandaset" title="Frequently Asked Questions"><a id="id571249"></a><dl><dt>1.  <a href="faq.html#faq.info">General Information</a></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
      What is libstdc++?
    </a></dt><dt>1.2. <a href="faq.html#faq.why">
      Why should I use libstdc++?
    </a></dt><dt>1.3. <a href="faq.html#faq.who">
      Who's in charge of it?
    </a></dt><dt>1.4. <a href="faq.html#faq.when">
      When is libstdc++ going to be finished?
    </a></dt><dt>1.5. <a href="faq.html#faq.how">
      How do I contribute to the effort?
    </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
      What happened to the older libg++? I need that!
    </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
      What if I have more questions?
    </a></dt></dl></dd><dt>2.  <a href="faq.html#faq.license">License</a></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
      What are the license terms for libstdc++?
    </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
      So any program which uses libstdc++ falls under the GPL?
    </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
      How is that different from the GNU {Lesser,Library} GPL?
    </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
      I see. So, what restrictions are there on programs that use the library?
    </a></dt></dl></dd><dt>3.  <a href="faq.html#faq.installation">Installation</a></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
    </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
    </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
    </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found?
    </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
      What's libsupc++?
    </a></dt><dt>3.6. <a href="faq.html#faq.size">
      This library is HUGE!
    </a></dt></dl></dd><dt>4.  <a href="faq.html#faq.platform-specific">Platform-Specific Issues</a></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
      Can libstdc++ be used with non-GNU compilers?
    </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
      No 'long long' type on Solaris?
    </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
      _XOPEN_SOURCE and _GNU_SOURCE are always defined?
    </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
      Mac OS X ctype.h is broken! How can I fix it?
    </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
      Threading is broken on i386?
    </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
      MIPS atomic operations
    </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
      Recent GNU/Linux glibc required?
    </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
      Can't use wchar_t/wstring on FreeBSD
    </a></dt></dl></dd><dt>5.  <a href="faq.html#faq.known_bugs">Known Bugs</a></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
      What works already?
    </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
      Bugs in the ISO C++ language or library specification
    </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
      Bugs in the compiler (gcc/g++) and not libstdc++
    </a></dt></dl></dd><dt>6.  <a href="faq.html#faq.known_non-bugs">Known Non-Bugs</a></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
      Reopening a stream fails
    </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
      -Weffc++ complains too much
    </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
      Ambiguous overloads after including an old-style header
    </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
      The g++-3 headers are not ours
    </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
      Errors about *Concept and
      constraints in the STL
    </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
      Program crashes when using library code in a
      dynamically-loaded library
    </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
      “Memory leaks” in containers
    </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
      list::size() is O(n)!
    </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
      Aw, that's easy to fix!
    </a></dt></dl></dd><dt>7.  <a href="faq.html#faq.misc">Miscellaneous</a></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
      string::iterator is not char*; vector<T>::iterator is not T*
    </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
      What's next after libstdc++?
    </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
      What about the STL from SGI?
    </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
      Extensions and Backward Compatibility
    </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
      Does libstdc++ support TR1?
    </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
    </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
      What's an ABI and why is it so messy?
    </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
      How do I make std::vector<T>::capacity() == std::vector<T>::size?
    </a></dt></dl></dd></dl><table border="0" width="100%" summary="Q and A Set"><col align="left" width="1%" /><col /><tbody><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.info"></a>1. General Information</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
      What is libstdc++?
    </a></dt><dt>1.2. <a href="faq.html#faq.why">
      Why should I use libstdc++?
    </a></dt><dt>1.3. <a href="faq.html#faq.who">
      Who's in charge of it?
    </a></dt><dt>1.4. <a href="faq.html#faq.when">
      When is libstdc++ going to be finished?
    </a></dt><dt>1.5. <a href="faq.html#faq.how">
      How do I contribute to the effort?
    </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
      What happened to the older libg++? I need that!
    </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
      What if I have more questions?
    </a></dt></dl></td></tr><tr class="question" title="1.1."><td align="left" valign="top"><a id="faq.what"></a><a id="faq.what.q"></a><p><b>1.1.</b></p></td><td align="left" valign="top"><p>
      What is libstdc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
     The GNU Standard C++ Library v3 is an ongoing project to
     implement the ISO 14882 Standard C++ library as described in
     chapters 17 through 27 and annex D.  For those who want to see
     exactly how far the project has come, or just want the latest
     bleeding-edge code, the up-to-date source is available over
     anonymous SVN, and can even be browsed over
     the <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top">web</a>.
    </p></td></tr><tr class="question" title="1.2."><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><b>1.2.</b></p></td><td align="left" valign="top"><p>
      Why should I use libstdc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
    The completion of the ISO C++ standardization gave the C++
    community a powerful set of reuseable tools in the form of the C++
    Standard Library.  However, all existing C++ implementations are
    (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
    incorrekt</span>”</span>, and many suffer from limitations of the compilers
    that use them.
    </p><p>
    The GNU compiler collection
    (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
    considered to be one of the leading compilers in the world.  Its
    development is overseen by the
    <a class="ulink" href="http://gcc.gnu.org/" target="_top">GCC team</a>.  All of
    the rapid development and near-legendary
    <a class="ulink" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a>
    that are the hallmarks of an open-source project are being
    applied to libstdc++.
    </p><p>
    That means that all of the Standard classes and functions will be
    freely available and fully compliant. (Such as
    <code class="classname">string</code>,
    <code class="classname">vector<></code>, iostreams, and algorithms.)
    Programmers will no longer need to <span class="quote">“<span class="quote">roll their own</span>”</span>
    nor be worried about platform-specific incompatibilities.
    </p></td></tr><tr class="question" title="1.3."><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><b>1.3.</b></p></td><td align="left" valign="top"><p>
      Who's in charge of it?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
     The libstdc++ project is contributed to by several developers
     all over the world, in the same way as GCC or Linux.
     Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
     Loren James Rittle, and Paolo Carlini are the lead maintainers of
     the SVN archive.
    </p><p>
    Development and discussion is held on the libstdc++ mailing
    list.  Subscribing to the list, or searching the list
    archives, is open to everyone.  You can read instructions for
    doing so on the <a class="ulink" href="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>.
    If you have questions, ideas, code, or are just curious, sign up!
    </p></td></tr><tr class="question" title="1.4."><td align="left" valign="top"><a id="faq.when"></a><a id="q-when"></a><p><b>1.4.</b></p></td><td align="left" valign="top"><p>
      When is libstdc++ going to be finished?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
    Nathan Myers gave the best of all possible answers, responding to
    a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
    help.</em></span>
    </p></td></tr><tr class="question" title="1.5."><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><b>1.5.</b></p></td><td align="left" valign="top"><p>
      How do I contribute to the effort?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
    Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">a page devoted to
    this topic</a>. Subscribing to the mailing list (see above, or
    the homepage) is a very good idea if you have something to
    contribute, or if you have spare time and want to
    help. Contributions don't have to be in the form of source code;
    anybody who is willing to help write documentation, for example,
    or has found a bug in code that we all thought was working and is
    willing to provide details, is more than welcome!
    </p></td></tr><tr class="question" title="1.6."><td align="left" valign="top"><a id="faq.whereis_old"></a><a id="q-whereis_old"></a><p><b>1.6.</b></p></td><td align="left" valign="top"><p>
      What happened to the older libg++? I need that!
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
    The most recent libg++ README states that libg++ is no longer
    being actively maintained.  It should not be used for new
    projects, and is only being kicked along to support older code.
    </p><p>
    More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a>
    </p></td></tr><tr class="question" title="1.7."><td align="left" valign="top"><a id="faq.more_questions"></a><a id="q-more_questions"></a><p><b>1.7.</b></p></td><td align="left" valign="top"><p>
      What if I have more questions?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
    If you have read the README file, and your question remains
    unanswered, then just ask the mailing list. At present, you do not
    need to be subscribed to the list to send a message to it.  More
    information is available on the homepage (including how to browse
    the list archives); to send a message to the list,
    use <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code>.
    </p><p> 
    If you have a question that you think should be included
    here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
    here, please send email to the libstdc++ mailing list, as above.
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.license"></a>2. License</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
      What are the license terms for libstdc++?
    </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
      So any program which uses libstdc++ falls under the GPL?
    </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
      How is that different from the GNU {Lesser,Library} GPL?
    </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
      I see. So, what restrictions are there on programs that use the library?
    </a></dt></dl></td></tr><tr class="question" title="2.1."><td align="left" valign="top"><a id="faq.license.what"></a><a id="q-license.what"></a><p><b>2.1.</b></p></td><td align="left" valign="top"><p>
      What are the license terms for libstdc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
    See <a class="link" href="manual/license.html" title="License">our license description</a>
    for these and related questions.
    </p></td></tr><tr class="question" title="2.2."><td align="left" valign="top"><a id="faq.license.any_program"></a><a id="q-license.any_program"></a><p><b>2.2.</b></p></td><td align="left" valign="top"><p>
      So any program which uses libstdc++ falls under the GPL?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.any_program"></a></td><td align="left" valign="top"><p>
     No. The special exception permits use of the library in
     proprietary applications.
    </p></td></tr><tr class="question" title="2.3."><td align="left" valign="top"><a id="faq.license.lgpl"></a><a id="q-license.lgpl"></a><p><b>2.3.</b></p></td><td align="left" valign="top"><p>
      How is that different from the GNU {Lesser,Library} GPL?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
      The LGPL requires that users be able to replace the LGPL code with a
     modified version; this is trivial if the library in question is a C
     shared library.  But there's no way to make that work with C++, where
     much of the library consists of inline functions and templates, which
     are expanded inside the code that uses the library.  So to allow people
     to replace the library code, someone using the library would have to
     distribute their own source, rendering the LGPL equivalent to the GPL.
    </p></td></tr><tr class="question" title="2.4."><td align="left" valign="top"><a id="faq.license.what_restrictions"></a><a id="q-license.what_restrictions"></a><p><b>2.4.</b></p></td><td align="left" valign="top"><p>
      I see. So, what restrictions are there on programs that use the library?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what_restrictions"></a></td><td align="left" valign="top"><p>
      None.  We encourage such programs to be released as open source,
     but we won't punish you or sue you if you choose otherwise.
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.installation"></a>3. Installation</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
    </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
    </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
    </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found?
    </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
      What's libsupc++?
    </a></dt><dt>3.6. <a href="faq.html#faq.size">
      This library is HUGE!
    </a></dt></dl></td></tr><tr class="question" title="3.1."><td align="left" valign="top"><a id="faq.how_to_install"></a><a id="q-how_to_install"></a><p><b>3.1.</b></p></td><td align="left" valign="top"><p>How do I install libstdc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_install"></a></td><td align="left" valign="top"><p>
    Often libstdc++ comes pre-installed as an integral part of many
    existing Linux and Unix systems, as well as many embedded
    development tools. It may be necessary to install extra
    development packages to get the headers, or the documentation, or
    the source: please consult your vendor for details.
    </p><p> 
    To build and install from the GNU GCC sources, please consult the 
    <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
    documentation</a> for detailed
    instructions. You may wish to browse those files ahead
    of time to get a feel for what's required.
    </p></td></tr><tr class="question" title="3.2."><td align="left" valign="top"><a id="faq.how_to_get_sources"></a><a id="q-how_to_get_sources"></a><p><b>3.2.</b></p></td><td align="left" valign="top"><p>How does one get current libstdc++ sources?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_get_sources"></a></td><td align="left" valign="top"><p>
    Libstdc++ sources for all official releases can be obtained as
    part of the GCC sources, available from various sites and
    mirrors. A full <a class="ulink" href="http://gcc.gnu.org/mirrors.html" target="_top">list of 
    download sites</a> is provided on the main GCC site.
    </p><p>
    Current libstdc++ sources can always be checked out of the main
    GCC source repository using the appropriate version control
    tool. At this time, that tool
    is <span class="application">Subversion</span>.
    </p><p>
    <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
    one of several revision control packages.  It was selected for GNU
    projects because it's free (speech), free (beer), and very high
    quality.  The <a class="ulink" href="http://subversion.tigris.org" target="_top"> Subversion
    home page</a> has a better description.
    </p><p>
    The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
    similar to anonymous FTP in that it allows anyone to retrieve
    the latest libstdc++ sources.
    </p><p>
    For more information
    see <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
    details</a>.
    </p></td></tr><tr class="question" title="3.3."><td align="left" valign="top"><a id="faq.how_to_test"></a><a id="q-how_to_test"></a><p><b>3.3.</b></p></td><td align="left" valign="top"><p>How do I know if it works?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_test"></a></td><td align="left" valign="top"><p>
    Libstdc++ comes with its own validation testsuite, which includes
    conformance testing, regression testing, ABI testing, and
    performance testing. Please consult the 
    <a class="ulink" href="http://gcc.gnu.org/install/test.html" target="_top">testing
    documentation</a> for more details.
    </p><p>
    If you find bugs in the testsuite programs themselves, or if you
    think of a new test program that should be added to the suite,
    <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
    </p></td></tr><tr class="question" title="3.4."><td align="left" valign="top"><a id="faq.how_to_set_paths"></a><a id="q-how_to_set_paths"></a><p><b>3.4.</b></p></td><td align="left" valign="top"><p>How do I insure that the dynamically linked library will be found?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_set_paths"></a></td><td align="left" valign="top"><p>
    Depending on your platform and library version, the error message might
    be similar to one of the following:
    </p><pre class="screen">
    ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory

    /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
    </pre><p>
    This doesn't mean that the shared library isn't installed, only
    that the dynamic linker can't find it. When a dynamically-linked
    executable is run the linker finds and loads the required shared
    libraries by searching a pre-configured list of directories. If
    the directory where you've installed libstdc++ is not in this list
    then the libraries won't be found. The simplest way to fix this is
    to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
    which is a colon-separated list of directories in which the linker
    will search for shared libraries:
    </p><pre class="screen">
    LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
    export LD_LIBRARY_PATH
    </pre><p>
    The exact environment variable to use will depend on your
    platform, e.g. DYLD_LIBRARY_PATH for Darwin,
    LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
    LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs and
    SHLIB_PATH for HP-UX.
    </p><p>
    See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
    and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
    linker has different names on different platforms but the man page
    is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>.
    </p></td></tr><tr class="question" title="3.5."><td align="left" valign="top"><a id="faq.what_is_libsupcxx"></a><a id="q-what_is_libsupcxx"></a><p><b>3.5.</b></p></td><td align="left" valign="top"><p>
      What's libsupc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_libsupcxx"></a></td><td align="left" valign="top"><p>
      If the only functions from <code class="filename">libstdc++.a</code>
      which you need are language support functions (those listed in
      <a class="link" href="manual/support.html" title="Part II.  Support">clause 18</a> of the
      standard, e.g., <code class="function">new</code> and
      <code class="function">delete</code>), then try linking against
      <code class="filename">libsupc++.a</code>, which is a subset of
      <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
      instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
      <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
      for the final link step will do it).  This library contains only
      those support routines, one per object file.  But if you are
      using anything from the rest of the library, such as IOStreams
      or vectors, then you'll still need pieces from
      <code class="filename">libstdc++.a</code>.
    </p></td></tr><tr class="question" title="3.6."><td align="left" valign="top"><a id="faq.size"></a><a id="q-size"></a><p><b>3.6.</b></p></td><td align="left" valign="top"><p>
      This library is HUGE!
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
    Usually the size of libraries on disk isn't noticeable.  When a
    link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
    static archive library, only the necessary object files are copied
    into your executable, not the entire library.  Unfortunately, even
    if you only need a single function or variable from an object file,
    the entire object file is extracted.  (There's nothing unique to C++
    or libstdc++ about this; it's just common behavior, given here
    for background reasons.)
    </p><p>
    Some of the object files which make up libstdc++.a are rather large.
    If you create a statically-linked executable with
    <code class="literal">-static</code>, those large object files are suddenly part
    of your executable.  Historically the best way around this was to
    only place a very few functions (often only a single one) in each
    source/object file; then extracting a single function is the same
    as extracting a single .o file.  For libstdc++ this is only
    possible to a certain extent; the object files in question contain
    template classes and template functions, pre-instantiated, and
    splitting those up causes severe maintenance headaches.
    </p><p>
    On supported platforms, libstdc++ takes advantage of garbage
    collection in the GNU linker to get a result similar to separating
    each symbol into a separate source and object files. On these platforms,
    GNU ld can place each function and variable into its own
    section in a .o file.  The GNU linker can then perform garbage
    collection on unused sections; this reduces the situation to only
    copying needed functions into the executable, as before, but all
    happens automatically.
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.platform-specific"></a>4. Platform-Specific Issues</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
      Can libstdc++ be used with non-GNU compilers?
    </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
      No 'long long' type on Solaris?
    </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
      _XOPEN_SOURCE and _GNU_SOURCE are always defined?
    </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
      Mac OS X ctype.h is broken! How can I fix it?
    </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
      Threading is broken on i386?
    </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
      MIPS atomic operations
    </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
      Recent GNU/Linux glibc required?
    </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
      Can't use wchar_t/wstring on FreeBSD
    </a></dt></dl></td></tr><tr class="question" title="4.1."><td align="left" valign="top"><a id="faq.other_compilers"></a><a id="q-other_compilers"></a><p><b>4.1.</b></p></td><td align="left" valign="top"><p>
      Can libstdc++ be used with non-GNU compilers?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
    Perhaps.
    </p><p>
    Since the goal of ISO Standardization is for all C++
    implementations to be able to share code, libstdc++ should be
    usable under any ISO-compliant compiler, at least in theory.
    </p><p>
    However, the reality is that libstdc++ is targeted and optimized
    for GCC/g++. This means that often libstdc++ uses specific,
    non-standard features of g++ that are not present in older
    versions of proprietary compilers. It may take as much as a year or two
    after an official release of GCC that contains these features for
    proprietary tools support these constructs.
    </p><p>
    In the near past, specific released versions of libstdc++ have
    been known to work with versions of the EDG C++ compiler, and
    vendor-specific proprietary C++ compilers such as the Intel ICC
    C++ compiler.
    </p></td></tr><tr class="question" title="4.2."><td align="left" valign="top"><a id="faq.solaris_long_long"></a><a id="q-solaris_long_long"></a><p><b>4.2.</b></p></td><td align="left" valign="top"><p>
      No 'long long' type on Solaris?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-solaris_long_long"></a></td><td align="left" valign="top"><p>
    By default we try to support the C99 <span class="type">long long</span> type.
    This requires that certain functions from your C library be present.
    </p><p> 
    Up through release 3.0.2 the platform-specific tests performed by
    libstdc++ were too general, resulting in a conservative approach
    to enabling the <span class="type">long long</span> code paths. The most
    commonly reported platform affected was Solaris.
    </p><p> 
    This has been fixed for libstdc++ releases greater than 3.0.3.
    </p></td></tr><tr class="question" title="4.3."><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><b>4.3.</b></p></td><td align="left" valign="top"><p>
      <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-predefined"></a></td><td align="left" valign="top"><p>On Solaris, g++ (but not gcc) always defines the preprocessor
         macro <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
         with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
         other macros and other platforms are also affected.)
      </p><p>These macros are typically used in C library headers, guarding new
         versions of functions from their older versions.  The C++ standard
         library includes the C standard library, but it requires the C90
         version, which for backwards-compatibility reasons is often not the
         default for many vendors.
      </p><p>More to the point, the C++ standard requires behavior which is only
         available on certain platforms after certain symbols are defined.
         Usually the issue involves I/O-related typedefs.  In order to
         ensure correctness, the compiler simply predefines those symbols.
      </p><p>Note that it's not enough to #define them only when the library is
         being built (during installation).  Since we don't have an 'export'
         keyword, much of the library exists as headers, which means that
         the symbols must also be defined as your programs are parsed and
         compiled.
      </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
         the gcc config headers for your target (and try changing them to
         see what happens when building complicated code).  You can also run
         <span class="command"><strong>g++ -E -dM - < /dev/null"</strong></span> to display
         a list of predefined macros for any particular installation.
      </p><p>This has been discussed on the mailing lists
         <a class="ulink" href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris" target="_top">quite a bit</a>.
      </p><p>This method is something of a wart.  We'd like to find a cleaner
         solution, but nobody yet has contributed the time.
      </p></td></tr><tr class="question" title="4.4."><td align="left" valign="top"><a id="faq.darwin_ctype"></a><a id="q-darwin_ctype"></a><p><b>4.4.</b></p></td><td align="left" valign="top"><p>
      Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-darwin_ctype"></a></td><td align="left" valign="top"><p>This is a long-standing bug in the OS X support.  Fortunately,
         the patch is quite simple, and well-known.
         <a class="ulink" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
         link to the solution</a>.
      </p></td></tr><tr class="question" title="4.5."><td align="left" valign="top"><a id="faq.threads_i386"></a><a id="q-threads_i386"></a><p><b>4.5.</b></p></td><td align="left" valign="top"><p>
      Threading is broken on i386?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
    </p><p>Support for atomic integer operations is/was broken on i386
         platforms.  The assembly code accidentally used opcodes that are
         only available on the i486 and later.  So if you configured GCC
         to target, for example, i386-linux, but actually used the programs
         on an i686, then you would encounter no problems.  Only when
         actually running the code on a i386 will the problem appear.
      </p><p>This is fixed in 3.2.2.
      </p></td></tr><tr class="question" title="4.6."><td align="left" valign="top"><a id="faq.atomic_mips"></a><a id="q-atomic_mips"></a><p><b>4.6.</b></p></td><td align="left" valign="top"><p>
      MIPS atomic operations
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
    The atomic locking routines for MIPS targets requires MIPS II
    and later.  A patch went in just after the 3.3 release to
    make mips* use the generic implementation instead.  You can also
    configure for mipsel-elf as a workaround.
    </p><p>    
    The mips*-*-linux* port continues to use the MIPS II routines, and more
    work in this area is expected.
    </p></td></tr><tr class="question" title="4.7."><td align="left" valign="top"><a id="faq.linux_glibc"></a><a id="q-linux_glibc"></a><p><b>4.7.</b></p></td><td align="left" valign="top"><p>
      Recent GNU/Linux glibc required?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-linux_glibc"></a></td><td align="left" valign="top"><p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version
         5.0.1) and later uses localization and formatting code from the system
         C library (glibc) version 2.2.5.  That version of glibc is over a
         year old and contains necessary bugfixes.  Many GNU/Linux distros make
         glibc version 2.3.x available now.
      </p><p>The guideline is simple:  the more recent the C++ library, the
         more recent the C library.  (This is also documented in the main
         GCC installation instructions.)
      </p></td></tr><tr class="question" title="4.8."><td align="left" valign="top"><a id="faq.freebsd_wchar"></a><a id="q-freebsd_wchar"></a><p><b>4.8.</b></p></td><td align="left" valign="top"><p>
      Can't use wchar_t/wstring on FreeBSD
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
    Older versions of FreeBSD's C library do not have sufficient
    support for wide character functions, and as a result the
    libstdc++ configury decides that wchar_t support should be
    disabled. In addition, the libstdc++ platform checks that
    enabled <span class="type">wchar_t</span> were quite strict, and not granular
    enough to detect when the minimal support to
    enable <span class="type">wchar_t</span> and C++ library structures
    like <code class="classname">wstring</code> were present. This impacted Solaris,
    Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
    </p><p> 
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.known_bugs"></a>5. Known Bugs</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
      What works already?
    </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
      Bugs in the ISO C++ language or library specification
    </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
      Bugs in the compiler (gcc/g++) and not libstdc++
    </a></dt></dl></td></tr><tr class="question" title="5.1."><td align="left" valign="top"><a id="faq.what_works"></a><a id="q-what_works"></a><p><b>5.1.</b></p></td><td align="left" valign="top"><p>
      What works already?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
    Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
    except for some corner cases.  Support for localization
    in <code class="classname">locale</code> may be incomplete on non-GNU
    platforms. Also dependant on the underlying platform is support
    for <span class="type">wchar_t</span> and <span class="type">long
    long</span> specializations, and details of thread support.
    </p><p>    
    Long answer: See the implementation status pages for 
    <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
    <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and 
    <a class="link" href="manual/status.html#status.iso.200x" title="C++ 200x">C++0x</a>.
    </p></td></tr><tr class="question" title="5.2."><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><b>5.2.</b></p></td><td align="left" valign="top"><p>
      Bugs in the ISO C++ language or library specification
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
    Unfortunately, there are some. 
    </p><p>
    For those people who are not part of the ISO Library Group
    (i.e., nearly all of us needing to read this page in the first
    place), a public list of the library defects is occasionally
    published <a class="ulink" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/" target="_top">here</a>.
    Some of these issues have resulted in code changes in libstdc++.
    </p><p>
    If you think you've discovered a new bug that is not listed,
    please post a message describing your problem
    to <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code> or the Usenet group
    comp.lang.c++.moderated.
    </p></td></tr><tr class="question" title="5.3."><td align="left" valign="top"><a id="faq.compiler_bugs"></a><a id="q-compiler_bugs"></a><p><b>5.3.</b></p></td><td align="left" valign="top"><p>
      Bugs in the compiler (gcc/g++) and not libstdc++
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
    On occasion, the compiler is wrong. Please be advised that this
    happens much less often than one would think, and avoid jumping to
    conclusions.
    </p><p>
    First, examine the ISO C++ standard. Second, try another compiler
    or an older version of the GNU compilers. Third, you can find more
    information on the libstdc++ and the GCC mailing lists: search
    these lists with terms describing your issue.
    </p><p> 
    Before reporting a bug, please examine the
    <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the
    category set to <span class="quote">“<span class="quote">g++</span>”</span>. 
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.known_non-bugs"></a>6. Known Non-Bugs</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
      Reopening a stream fails
    </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
      -Weffc++ complains too much
    </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
      Ambiguous overloads after including an old-style header
    </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
      The g++-3 headers are not ours
    </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
      Errors about *Concept and
      constraints in the STL
    </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
      Program crashes when using library code in a
      dynamically-loaded library
    </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
      “Memory leaks” in containers
    </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
      list::size() is O(n)!
    </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
      Aw, that's easy to fix!
    </a></dt></dl></td></tr><tr class="question" title="6.1."><td align="left" valign="top"><a id="faq.stream_reopening_fails"></a><a id="q-stream_reopening_fails"></a><p><b>6.1.</b></p></td><td align="left" valign="top"><p>
      Reopening a stream fails
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-stream_reopening_fails"></a></td><td align="left" valign="top"><p>
    One of the most-reported non-bug reports. Executing a sequence like:
    </p><div class="literallayout"><p><br />
    #include <fstream><br />
    ...<br />
    std::fstream  fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
    // .<br />
    // . do things with fs...<br />
    // .<br />
    fs.close();<br />
    fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
    </p></div><p>
    All operations on the re-opened <code class="varname">fs</code> will fail, or at
    least act very strangely.  Yes, they often will, especially if
    <code class="varname">fs</code> reached the EOF state on the previous file.  The
    reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
    on a successful call to open().  The standard unfortunately did
    not specify behavior in this case, and to everybody's great sorrow,
    the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
      DR #22</a> is to leave the flags unchanged.  You must insert a call
    to <code class="function">fs.clear()</code> between the calls to close() and open(),
    and then everything will work like we all expect it to work.
    <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
    of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open() 
    now calls <code class="function">clear()</code> on success!
    </p></td></tr><tr class="question" title="6.2."><td align="left" valign="top"><a id="faq.wefcxx_verbose"></a><a id="q-wefcxx_verbose"></a><p><b>6.2.</b></p></td><td align="left" valign="top"><p>
      -Weffc++ complains too much
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
    Many warnings are emitted when <code class="literal">-Weffc++</code> is used.  Making
    libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
    for a few reasons.  Mainly, that option tries to enforce
    object-oriented programming, while the Standard Library isn't
    necessarily trying to be OO.
    </p><p>
    We do, however, try to have libstdc++ sources as clean as possible. If
    you see some simple changes that pacify <code class="literal">-Weffc++</code>
    without other drawbacks, send us a patch.
    </p></td></tr><tr class="question" title="6.3."><td align="left" valign="top"><a id="faq.ambiguous_overloads"></a><a id="q-ambiguous_overloads"></a><p><b>6.3.</b></p></td><td align="left" valign="top"><p>
      Ambiguous overloads after including an old-style header
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
    Another problem is the <code class="literal">rel_ops</code> namespace and the template
    comparison operator functions contained therein.  If they become
    visible in the same namespace as other comparison functions
    (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the <iterator> header),
    then you will suddenly be faced with huge numbers of ambiguity
    errors.  This was discussed on the -v3 list; Nathan Myers
    <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
      things up here</a>.  The collisions with vector/string iterator
    types have been fixed for 3.1.
    </p></td></tr><tr class="question" title="6.4."><td align="left" valign="top"><a id="faq.v2_headers"></a><a id="q-v2_headers"></a><p><b>6.4.</b></p></td><td align="left" valign="top"><p>
      The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
	If you have found an extremely broken header file which is
	causing problems for you, look carefully before submitting a
	"high" priority bug report (which you probably
	shouldn't do anyhow; see the last paragraph of the page
	describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC
	bug database</a>).
      </p><p>
	If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
	if the installed library's name looks like
	<code class="filename">libstdc++-2.10.a</code> or
	<code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
	old libstdc++-v2 library, which is nonstandard and
	unmaintained.  Do not report problems with -v2 to the -v3
	mailing list.
      </p><p>
	For GCC versions 3.0 and 3.1 the libstdc++ header files are
	installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
	'v'?).  Starting with version 3.2 the headers are installed in
	<code class="filename">${prefix}/include/c++/${version}</code> as this prevents
	headers from previous versions being found by mistake.
      </p></td></tr><tr class="question" title="6.5."><td align="left" valign="top"><a id="faq.boost_concept_checks"></a><a id="q-boost_concept_checks"></a><p><b>6.5.</b></p></td><td align="left" valign="top"><p>
      Errors about <span class="emphasis"><em>*Concept</em></span> and
      <span class="emphasis"><em>constraints</em></span> in the STL
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-boost_concept_checks"></a></td><td align="left" valign="top"><p>
    If you see compilation errors containing messages about
    <span class="errortext">foo Concept </span>and something to do with a
    <span class="errortext">constraints</span> member function, then most
    likely you have violated one of the requirements for types used
    during instantiation of template containers and functions.  For
    example, EqualityComparableConcept appears if your types must be
    comparable with == and you have not provided this capability (a
    typo, or wrong visibility, or you just plain forgot, etc).
    </p><p>
    More information, including how to optionally enable/disable the
    checks, is available
    <a class="link" href="manual/bk01pt03ch08.html" title="Chapter 8. Concept Checking">here</a>.
    </p></td></tr><tr class="question" title="6.6."><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><b>6.6.</b></p></td><td align="left" valign="top"><p>
      Program crashes when using library code in a
      dynamically-loaded library
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
    If you are using the C++ library across dynamically-loaded
    objects, make certain that you are passing the correct options
    when compiling and linking:
    </p><div class="literallayout"><p><br />
    // compile your library components<br />
    g++ -fPIC -c a.cc<br />
    g++ -fPIC -c b.cc<br />
    ...<br />
    g++ -fPIC -c z.cc<br />
<br />
    // create your library<br />
    g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
<br />
    // link the executable<br />
    g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
    </p></div></td></tr><tr class="question" title="6.7."><td align="left" valign="top"><a id="faq.memory_leaks"></a><a id="q-memory_leaks"></a><p><b>6.7.</b></p></td><td align="left" valign="top"><p>
      <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
    A few people have reported that the standard containers appear
    to leak memory when tested with memory checkers such as
    <a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>.
    The library's default allocators keep free memory in a pool
    for later reuse, rather than returning it to the OS.  Although
    this memory is always reachable by the library and is never
    lost, memory debugging tools can report it as a leak.  If you
    want to test the library for memory leaks please read
    <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
    first.
    </p></td></tr><tr class="question" title="6.8."><td align="left" valign="top"><a id="faq.list_size_on"></a><a id="q-list_size_on"></a><p><b>6.8.</b></p></td><td align="left" valign="top"><p>
      list::size() is O(n)!
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-list_size_on"></a></td><td align="left" valign="top"><p>
    See
    the <a class="link" href="manual/containers.html" title="Part VII.  Containers">Containers</a>
    chapter.
    </p></td></tr><tr class="question" title="6.9."><td align="left" valign="top"><a id="faq.easy_to_fix"></a><a id="q-easy_to_fix"></a><p><b>6.9.</b></p></td><td align="left" valign="top"><p>
      Aw, that's easy to fix!
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-easy_to_fix"></a></td><td align="left" valign="top"><p>
    If you have found a bug in the library and you think you have
    a working fix, then send it in!  The main GCC site has a page
    on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
    patches</a> that covers the procedure, but for libstdc++ you
    should also send the patch to our mailing list in addition to
    the GCC patches mailing list.  The libstdc++
    <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
    also talks about how to submit patches.
    </p><p>
    In addition to the description, the patch, and the ChangeLog
    entry, it is a Good Thing if you can additionally create a small
    test program to test for the presence of the bug that your
    patch fixes.  Bugs have a way of being reintroduced; if an old
    bug creeps back in, it will be caught immediately by the
    <a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists.
    </p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.misc"></a>7. Miscellaneous</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
      string::iterator is not char*; vector<T>::iterator is not T*
    </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
      What's next after libstdc++?
    </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
      What about the STL from SGI?
    </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
      Extensions and Backward Compatibility
    </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
      Does libstdc++ support TR1?
    </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
    </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
      What's an ABI and why is it so messy?
    </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
      How do I make std::vector<T>::capacity() == std::vector<T>::size?
    </a></dt></dl></td></tr><tr class="question" title="7.1."><td align="left" valign="top"><a id="faq.iterator_as_pod"></a><a id="faq.iterator_as_pod_q"></a><p><b>7.1.</b></p></td><td align="left" valign="top"><p>
      string::iterator is not char*; vector<T>::iterator is not T*
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.iterator_as_pod_a"></a></td><td align="left" valign="top"><p>
    If you have code that depends on container<T> iterators
    being implemented as pointer-to-T, your code is broken. It's
    considered a feature, not a bug, that libstdc++ points this out.
    </p><p>
    While there are arguments for iterators to be implemented in
    that manner, A) they aren't very good ones in the long term,
    and B) they were never guaranteed by the Standard anyway.  The
    type-safety achieved by making iterators a real class rather
    than a typedef for <span class="type">T*</span> outweighs nearly all opposing
    arguments.
    </p><p>
    Code which does assume that a vector iterator <code class="varname">i</code>
    is a pointer can often be fixed by changing <code class="varname">i</code> in
    certain expressions to <code class="varname">&*i</code>.  Future revisions
    of the Standard are expected to bless this usage for
    vector<> (but not for basic_string<>).
    </p></td></tr><tr class="question" title="7.2."><td align="left" valign="top"><a id="faq.what_is_next"></a><a id="q-what_is_next"></a><p><b>7.2.</b></p></td><td align="left" valign="top"><p>
      What's next after libstdc++?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_next"></a></td><td align="left" valign="top"><p>
	Hopefully, not much.  The goal of libstdc++ is to produce a
	fully-compliant, fully-portable Standard Library.  After that,
	we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
	more compliance work to do.
      </p><p>
	There is an effort underway to add significant extensions to
	the standard library specification.  The latest version of
	this effort is described in
         <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
         The C++ Library Technical Report 1</a>.
      </p></td></tr><tr class="question" title="7.3."><td align="left" valign="top"><a id="faq.sgi_stl"></a><a id="q-sgi_stl"></a><p><b>7.3.</b></p></td><td align="left" valign="top"><p>
      What about the STL from SGI?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
      The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
    version 3.3, was the final merge of the STL codebase.  The
    code in libstdc++ contains many fixes and changes, and
    the SGI code is no longer under active
    development.  We expect that no future merges will take place.
    </p><p>
    In particular, <code class="classname">string</code> is not from SGI and makes no
    use of their "rope" class (which is included as an
    optional extension), nor is <code class="classname">valarray</code> and some others.
    Classes like <code class="classname">vector<></code> are, but have been
    extensively modified.
    </p><p>
    More information on the evolution of libstdc++ can be found at the
    <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
    evolution</a>
    and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
    compatibility</a> documentation.
    </p><p>
    The FAQ for SGI's STL (one jump off of their main page) is
    still recommended reading.
    </p></td></tr><tr class="question" title="7.4."><td align="left" valign="top"><a id="faq.extensions_and_backwards_compat"></a><a id="q-extensions_and_backwards_compat"></a><p><b>7.4.</b></p></td><td align="left" valign="top"><p>
      Extensions and Backward Compatibility
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-extensions_and_backwards_compat"></a></td><td align="left" valign="top"><p>
      See the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">link</a> on backwards compatibility and <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">link</a> on evolution.
    </p></td></tr><tr class="question" title="7.5."><td align="left" valign="top"><a id="faq.tr1_support"></a><a id="q-tr1_support"></a><p><b>7.5.</b></p></td><td align="left" valign="top"><p>
      Does libstdc++ support TR1?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
    Yes.
    </p><p>
    The C++ Standard Library Technical Report adds many new features to 
    the library.  The latest version of this effort is described in
    <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
         Technical Report 1</a>.
    </p><p>
    The implementation status of TR1 in libstdc++ can be tracked <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status
    page</a>.
    </p></td></tr><tr class="question" title="7.6."><td align="left" valign="top"><a id="faq.get_iso_cxx"></a><a id="q-get_iso_cxx"></a><p><b>7.6.</b></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-get_iso_cxx"></a></td><td align="left" valign="top"><p>
    Copies of the full ISO 14882 standard are available on line via
    the ISO mirror site for committee members.  Non-members, or those
    who have not paid for the privilege of sitting on the committee
    and sustained their two-meeting commitment for voting rights, may
    get a copy of the standard from their respective national
    standards organization.  In the USA, this national standards
    organization is ANSI and their website is
    right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>.  (And if
    you've already registered with them, clicking this link will take
    you to directly to the place where you can
    <a class="ulink" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
    </p><p>
    Who is your country's member body?  Visit the
    <a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
    </p><p>
    The 2003 version of the standard (the 1998 version plus TC1) is
    available in print, ISBN 0-470-84674-7.
    </p></td></tr><tr class="question" title="7.7."><td align="left" valign="top"><a id="faq.what_is_abi"></a><a id="q-what_is_abi"></a><p><b>7.7.</b></p></td><td align="left" valign="top"><p>
      What's an ABI and why is it so messy?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_abi"></a></td><td align="left" valign="top"><p>
    <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
     Interface</span>”</span>.  Conventionally, it refers to a great
    mass of details about how arguments are arranged on the call
    stack and/or in registers, and how various types are arranged
    and padded in structs.  A single CPU design may suffer
    multiple ABIs designed by different development tool vendors
    who made different choices, or even by the same vendor for
    different target applications or compiler versions.  In ideal
    circumstances the CPU designer presents one ABI and all the
    OSes and compilers use it.  In practice every ABI omits
    details that compiler implementers (consciously or
    accidentally) must choose for themselves.
    </p><p>
    That ABI definition suffices for compilers to generate code so a
    program can interact safely with an OS and its lowest-level libraries.
    Users usually want an ABI to encompass more detail, allowing libraries
    built with different compilers (or different releases of the same
    compiler!) to be linked together.  For C++, this includes many more
    details than for C, and CPU designers (for good reasons elaborated
    below) have not stepped up to publish C++ ABIs.  The details include
    virtual function implementation, struct inheritance layout, name
    mangling, and exception handling.  Such an ABI has been defined for
    GNU C++, and is immediately useful for embedded work relying only on
    a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
    of) the standard library.  It is a good basis for the work to come.
    </p><p>
    A useful C++ ABI must also incorporate many details of the standard
    library implementation.  For a C ABI, the layouts of a few structs
    (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
    For C++, the details include the complete set of names of functions
    and types used, the offsets of class members and virtual functions,
    and the actual definitions of all inlines.  C++ exposes many more
    library details to the caller than C does.  It makes defining
    a complete ABI a much bigger undertaking, and requires not just
    documenting library implementation details, but carefully designing
    those details so that future bug fixes and optimizations don't
    force breaking the ABI.
    </p><p>
    There are ways to help isolate library implementation details from the
    ABI, but they trade off against speed.  Library details used in
    inner loops (e.g., getchar) must be exposed and frozen for all
    time, but many others may reasonably be kept hidden from user code,
    so they may later be changed.  Deciding which, and implementing
    the decisions, must happen before you can reasonably document a
    candidate C++ ABI that encompasses the standard library.
    </p></td></tr><tr class="question" title="7.8."><td align="left" valign="top"><a id="faq.size_equals_capacity"></a><a id="q-size_equals_capacity"></a><p><b>7.8.</b></p></td><td align="left" valign="top"><p>
      How do I make std::vector<T>::capacity() == std::vector<T>::size?
    </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size_equals_capacity"></a></td><td align="left" valign="top"><p>
    The standard idiom for deallocating a <code class="classname">vector<T></code>'s
    unused memory is to create a temporary copy of the vector and swap their
    contents, e.g. for <code class="classname">vector<T> v</code>
    </p><div class="literallayout"><p><br />
     std::vector<T>(v).swap(v);<br />
    </p></div><p>
    The copy will take O(n) time and the swap is constant time.
    </p><p>
    See <a class="link" href="manual/bk01pt05ch13s05.html" title="Shrink to Fit">Shrink-to-fit
    strings</a> for a similar solution for strings.
    </p></td></tr></tbody></table></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk03.html">Up</a></td><td width="40%" align="right"> </td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="spine.html">
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