libstdc++-v3/doc/html/faq.html

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   4       2008
   5
   6       <a class="ulink" href="http://www.fsf.org" target="_top">FSF</a>
   7     </p></div></div><hr /></div><div class="qandaset" title="Frequently Asked Questions"><a id="id523703"></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">
   8       What is libstdc++?
   9     </a></dt><dt>1.2. <a href="faq.html#faq.why">
  10       Why should I use libstdc++?
  11     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  12       Who's in charge of it?
  13     </a></dt><dt>1.4. <a href="faq.html#faq.when">
  14       When is libstdc++ going to be finished?
  15     </a></dt><dt>1.5. <a href="faq.html#faq.how">
  16       How do I contribute to the effort?
  17     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
  18       What happened to the older libg++? I need that!
  19     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
  20       What if I have more questions?
  21     </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">
  22       What are the license terms for libstdc++?
  23     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
  24       So any program which uses libstdc++ falls under the GPL?
  25     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
  26       How is that different from the GNU {Lesser,Library} GPL?
  27     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
  28       I see. So, what restrictions are there on programs that use the library?
  29     </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++?
  30     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
  31     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
  32     </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?
  33     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
  34       What's libsupc++?
  35     </a></dt><dt>3.6. <a href="faq.html#faq.size">
  36       This library is HUGE!
  37     </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">
  38       Can libstdc++ be used with non-GNU compilers?
  39     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
  40       No 'long long' type on Solaris?
  41     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
  42       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
  43     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
  44       Mac OS X ctype.h is broken! How can I fix it?
  45     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
  46       Threading is broken on i386?
  47     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
  48       MIPS atomic operations
  49     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
  50       Recent GNU/Linux glibc required?
  51     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
  52       Can't use wchar_t/wstring on FreeBSD
  53     </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">
  54       What works already?
  55     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
  56       Bugs in the ISO C++ language or library specification
  57     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
  58       Bugs in the compiler (gcc/g++) and not libstdc++
  59     </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">
  60       Reopening a stream fails
  61     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
  62       -Weffc++ complains too much
  63     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
  64       Ambiguous overloads after including an old-style header
  65     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
  66       The g++-3 headers are not ours
  67     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
  68       Errors about *Concept and
  69       constraints in the STL
  70     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
  71       Program crashes when using library code in a
  72       dynamically-loaded library
  73     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
  74       “Memory leaks” in containers
  75     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
  76       list::size() is O(n)!
  77     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
  78       Aw, that's easy to fix!
  79     </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">
  80       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
  81     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
  82       What's next after libstdc++?
  83     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
  84       What about the STL from SGI?
  85     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
  86       Extensions and Backward Compatibility
  87     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
  88       Does libstdc++ support TR1?
  89     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
  90     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
  91       What's an ABI and why is it so messy?
  92     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
  93       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
  94     </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">
  95       What is libstdc++?
  96     </a></dt><dt>1.2. <a href="faq.html#faq.why">
  97       Why should I use libstdc++?
  98     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  99       Who's in charge of it?
 100     </a></dt><dt>1.4. <a href="faq.html#faq.when">
 101       When is libstdc++ going to be finished?
 102     </a></dt><dt>1.5. <a href="faq.html#faq.how">
 103       How do I contribute to the effort?
 104     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
 105       What happened to the older libg++? I need that!
 106     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
 107       What if I have more questions?
 108     </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>
 109       What is libstdc++?
 110     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
 111      The GNU Standard C++ Library v3 is an ongoing project to
 112      implement the ISO 14882 Standard C++ library as described in
 113      chapters 17 through 27 and annex D.  For those who want to see
 114      exactly how far the project has come, or just want the latest
 115      bleeding-edge code, the up-to-date source is available over
 116      anonymous SVN, and can even be browsed over
 117      the <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top">web</a>.
 118     </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>
 119       Why should I use libstdc++?
 120     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
 121     The completion of the ISO C++ standardization gave the C++
 122     community a powerful set of reuseable tools in the form of the C++
 123     Standard Library.  However, all existing C++ implementations are
 124     (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
 125     incorrekt</span>”</span>, and many suffer from limitations of the compilers
 126     that use them.
 127     </p><p>
 128     The GNU compiler collection
 129     (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
 130     considered to be one of the leading compilers in the world.  Its
 131     development is overseen by the
 132     <a class="ulink" href="http://gcc.gnu.org/" target="_top">GCC team</a>.  All of
 133     the rapid development and near-legendary
 134     <a class="ulink" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a>
 135     that are the hallmarks of an open-source project are being
 136     applied to libstdc++.
 137     </p><p>
 138     That means that all of the Standard classes and functions will be
 139     freely available and fully compliant. (Such as
 140     <code class="classname">string</code>,
 141     <code class="classname">vector&lt;&gt;</code>, iostreams, and algorithms.)
 142     Programmers will no longer need to <span class="quote">“<span class="quote">roll their own</span>”</span>
 143     nor be worried about platform-specific incompatibilities.
 144     </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>
 145       Who's in charge of it?
 146     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
 147      The libstdc++ project is contributed to by several developers
 148      all over the world, in the same way as GCC or Linux.
 149      Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
 150      Loren James Rittle, and Paolo Carlini are the lead maintainers of
 151      the SVN archive.
 152     </p><p>
 153     Development and discussion is held on the libstdc++ mailing
 154     list.  Subscribing to the list, or searching the list
 155     archives, is open to everyone.  You can read instructions for
 156     doing so on the <a class="ulink" href="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>.
 157     If you have questions, ideas, code, or are just curious, sign up!
 158     </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>
 159       When is libstdc++ going to be finished?
 160     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
 161     Nathan Myers gave the best of all possible answers, responding to
 162     a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
 163     help.</em></span>
 164     </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>
 165       How do I contribute to the effort?
 166     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
 167     Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">a page devoted to
 168     this topic</a>. Subscribing to the mailing list (see above, or
 169     the homepage) is a very good idea if you have something to
 170     contribute, or if you have spare time and want to
 171     help. Contributions don't have to be in the form of source code;
 172     anybody who is willing to help write documentation, for example,
 173     or has found a bug in code that we all thought was working and is
 174     willing to provide details, is more than welcome!
 175     </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>
 176       What happened to the older libg++? I need that!
 177     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
 178     The most recent libg++ README states that libg++ is no longer
 179     being actively maintained.  It should not be used for new
 180     projects, and is only being kicked along to support older code.
 181     </p><p>
 182     More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a>
 183     </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>
 184       What if I have more questions?
 185     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
 186     If you have read the README file, and your question remains
 187     unanswered, then just ask the mailing list. At present, you do not
 188     need to be subscribed to the list to send a message to it.  More
 189     information is available on the homepage (including how to browse
 190     the list archives); to send a message to the list,
 191     use <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code>.
 192     </p><p>
 193     If you have a question that you think should be included
 194     here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
 195     here, please send email to the libstdc++ mailing list, as above.
 196     </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">
 197       What are the license terms for libstdc++?
 198     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
 199       So any program which uses libstdc++ falls under the GPL?
 200     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
 201       How is that different from the GNU {Lesser,Library} GPL?
 202     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
 203       I see. So, what restrictions are there on programs that use the library?
 204     </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>
 205       What are the license terms for libstdc++?
 206     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
 207     See <a class="link" href="manual/license.html" title="License">our license description</a>
 208     for these and related questions.
 209     </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>
 210       So any program which uses libstdc++ falls under the GPL?
 211     </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>
 212      No. The special exception permits use of the library in
 213      proprietary applications.
 214     </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>
 215       How is that different from the GNU {Lesser,Library} GPL?
 216     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
 217       The LGPL requires that users be able to replace the LGPL code with a
 218      modified version; this is trivial if the library in question is a C
 219      shared library.  But there's no way to make that work with C++, where
 220      much of the library consists of inline functions and templates, which
 221      are expanded inside the code that uses the library.  So to allow people
 222      to replace the library code, someone using the library would have to
 223      distribute their own source, rendering the LGPL equivalent to the GPL.
 224     </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>
 225       I see. So, what restrictions are there on programs that use the library?
 226     </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>
 227       None.  We encourage such programs to be released as open source,
 228      but we won't punish you or sue you if you choose otherwise.
 229     </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++?
 230     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
 231     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
 232     </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?
 233     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
 234       What's libsupc++?
 235     </a></dt><dt>3.6. <a href="faq.html#faq.size">
 236       This library is HUGE!
 237     </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++?
 238     </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>
 239     Often libstdc++ comes pre-installed as an integral part of many
 240     existing Linux and Unix systems, as well as many embedded
 241     development tools. It may be necessary to install extra
 242     development packages to get the headers, or the documentation, or
 243     the source: please consult your vendor for details.
 244     </p><p>
 245     To build and install from the GNU GCC sources, please consult the
 246     <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
 247     documentation</a> for detailed
 248     instructions. You may wish to browse those files ahead
 249     of time to get a feel for what's required.
 250     </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?
 251     </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>
 252     Libstdc++ sources for all official releases can be obtained as
 253     part of the GCC sources, available from various sites and
 254     mirrors. A full <a class="ulink" href="http://gcc.gnu.org/mirrors.html" target="_top">list of
 255     download sites</a> is provided on the main GCC site.
 256     </p><p>
 257     Current libstdc++ sources can always be checked out of the main
 258     GCC source repository using the appropriate version control
 259     tool. At this time, that tool
 260     is <span class="application">Subversion</span>.
 261     </p><p>
 262     <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
 263     one of several revision control packages.  It was selected for GNU
 264     projects because it's free (speech), free (beer), and very high
 265     quality.  The <a class="ulink" href="http://subversion.tigris.org" target="_top"> Subversion
 266     home page</a> has a better description.
 267     </p><p>
 268     The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
 269     similar to anonymous FTP in that it allows anyone to retrieve
 270     the latest libstdc++ sources.
 271     </p><p>
 272     For more information
 273     see <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
 274     details</a>.
 275     </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?
 276     </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>
 277     Libstdc++ comes with its own validation testsuite, which includes
 278     conformance testing, regression testing, ABI testing, and
 279     performance testing. Please consult the
 280     <a class="ulink" href="http://gcc.gnu.org/install/test.html" target="_top">testing
 281     documentation</a> for more details.
 282     </p><p>
 283     If you find bugs in the testsuite programs themselves, or if you
 284     think of a new test program that should be added to the suite,
 285     <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
 286     </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?
 287     </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>
 288     Depending on your platform and library version, the error message might
 289     be similar to one of the following:
 290     </p><pre class="screen">
 291     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 292
 293     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
 294     </pre><p>
 295     This doesn't mean that the shared library isn't installed, only
 296     that the dynamic linker can't find it. When a dynamically-linked
 297     executable is run the linker finds and loads the required shared
 298     libraries by searching a pre-configured list of directories. If
 299     the directory where you've installed libstdc++ is not in this list
 300     then the libraries won't be found. The simplest way to fix this is
 301     to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
 302     which is a colon-separated list of directories in which the linker
 303     will search for shared libraries:
 304     </p><pre class="screen">
 305     LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 306     export LD_LIBRARY_PATH
 307     </pre><p>
 308     The exact environment variable to use will depend on your
 309     platform, e.g. DYLD_LIBRARY_PATH for Darwin,
 310     LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
 311     LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs and
 312     SHLIB_PATH for HP-UX.
 313     </p><p>
 314     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 315     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 316     linker has different names on different platforms but the man page
 317     is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>.
 318     </p><p>
 319     Using LD_LIBRARY_PATH is not always the best solution, <a class="link" href="manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic" title="Finding Dynamic or Shared Libraries">Finding Dynamic or Shared
 320     Libraries</a> in the manual gives some alternatives.
 321     </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>
 322       What's libsupc++?
 323     </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>
 324       If the only functions from <code class="filename">libstdc++.a</code>
 325       which you need are language support functions (those listed in
 326       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 327       standard, e.g., <code class="function">new</code> and
 328       <code class="function">delete</code>), then try linking against
 329       <code class="filename">libsupc++.a</code>, which is a subset of
 330       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 331       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 332       <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
 333       for the final link step will do it).  This library contains only
 334       those support routines, one per object file.  But if you are
 335       using anything from the rest of the library, such as IOStreams
 336       or vectors, then you'll still need pieces from
 337       <code class="filename">libstdc++.a</code>.
 338     </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>
 339       This library is HUGE!
 340     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 341     Usually the size of libraries on disk isn't noticeable.  When a
 342     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 343     static archive library, only the necessary object files are copied
 344     into your executable, not the entire library.  Unfortunately, even
 345     if you only need a single function or variable from an object file,
 346     the entire object file is extracted.  (There's nothing unique to C++
 347     or libstdc++ about this; it's just common behavior, given here
 348     for background reasons.)
 349     </p><p>
 350     Some of the object files which make up libstdc++.a are rather large.
 351     If you create a statically-linked executable with
 352     <code class="literal">-static</code>, those large object files are suddenly part
 353     of your executable.  Historically the best way around this was to
 354     only place a very few functions (often only a single one) in each
 355     source/object file; then extracting a single function is the same
 356     as extracting a single .o file.  For libstdc++ this is only
 357     possible to a certain extent; the object files in question contain
 358     template classes and template functions, pre-instantiated, and
 359     splitting those up causes severe maintenance headaches.
 360     </p><p>
 361     On supported platforms, libstdc++ takes advantage of garbage
 362     collection in the GNU linker to get a result similar to separating
 363     each symbol into a separate source and object files. On these platforms,
 364     GNU ld can place each function and variable into its own
 365     section in a .o file.  The GNU linker can then perform garbage
 366     collection on unused sections; this reduces the situation to only
 367     copying needed functions into the executable, as before, but all
 368     happens automatically.
 369     </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">
 370       Can libstdc++ be used with non-GNU compilers?
 371     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 372       No 'long long' type on Solaris?
 373     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 374       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 375     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 376       Mac OS X ctype.h is broken! How can I fix it?
 377     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 378       Threading is broken on i386?
 379     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 380       MIPS atomic operations
 381     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 382       Recent GNU/Linux glibc required?
 383     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 384       Can't use wchar_t/wstring on FreeBSD
 385     </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>
 386       Can libstdc++ be used with non-GNU compilers?
 387     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 388     Perhaps.
 389     </p><p>
 390     Since the goal of ISO Standardization is for all C++
 391     implementations to be able to share code, libstdc++ should be
 392     usable under any ISO-compliant compiler, at least in theory.
 393     </p><p>
 394     However, the reality is that libstdc++ is targeted and optimized
 395     for GCC/g++. This means that often libstdc++ uses specific,
 396     non-standard features of g++ that are not present in older
 397     versions of proprietary compilers. It may take as much as a year or two
 398     after an official release of GCC that contains these features for
 399     proprietary tools support these constructs.
 400     </p><p>
 401     In the near past, specific released versions of libstdc++ have
 402     been known to work with versions of the EDG C++ compiler, and
 403     vendor-specific proprietary C++ compilers such as the Intel ICC
 404     C++ compiler.
 405     </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>
 406       No 'long long' type on Solaris?
 407     </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>
 408     By default we try to support the C99 <span class="type">long long</span> type.
 409     This requires that certain functions from your C library be present.
 410     </p><p>
 411     Up through release 3.0.2 the platform-specific tests performed by
 412     libstdc++ were too general, resulting in a conservative approach
 413     to enabling the <span class="type">long long</span> code paths. The most
 414     commonly reported platform affected was Solaris.
 415     </p><p>
 416     This has been fixed for libstdc++ releases greater than 3.0.3.
 417     </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>
 418       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 419     </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
 420          macro <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 421          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 422          other macros and other platforms are also affected.)
 423       </p><p>These macros are typically used in C library headers, guarding new
 424          versions of functions from their older versions.  The C++ standard
 425          library includes the C standard library, but it requires the C90
 426          version, which for backwards-compatibility reasons is often not the
 427          default for many vendors.
 428       </p><p>More to the point, the C++ standard requires behavior which is only
 429          available on certain platforms after certain symbols are defined.
 430          Usually the issue involves I/O-related typedefs.  In order to
 431          ensure correctness, the compiler simply predefines those symbols.
 432       </p><p>Note that it's not enough to #define them only when the library is
 433          being built (during installation).  Since we don't have an 'export'
 434          keyword, much of the library exists as headers, which means that
 435          the symbols must also be defined as your programs are parsed and
 436          compiled.
 437       </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 438          the gcc config headers for your target (and try changing them to
 439          see what happens when building complicated code).  You can also run
 440          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 441          a list of predefined macros for any particular installation.
 442       </p><p>This has been discussed on the mailing lists
 443          <a class="ulink" href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&amp;format=builtin-long&amp;sort=score&amp;words=_XOPEN_SOURCE+Solaris" target="_top">quite a bit</a>.
 444       </p><p>This method is something of a wart.  We'd like to find a cleaner
 445          solution, but nobody yet has contributed the time.
 446       </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>
 447       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 448     </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,
 449          the patch is quite simple, and well-known.
 450          <a class="ulink" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
 451          link to the solution</a>.
 452       </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>
 453       Threading is broken on i386?
 454     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
 455     </p><p>Support for atomic integer operations is/was broken on i386
 456          platforms.  The assembly code accidentally used opcodes that are
 457          only available on the i486 and later.  So if you configured GCC
 458          to target, for example, i386-linux, but actually used the programs
 459          on an i686, then you would encounter no problems.  Only when
 460          actually running the code on a i386 will the problem appear.
 461       </p><p>This is fixed in 3.2.2.
 462       </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>
 463       MIPS atomic operations
 464     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
 465     The atomic locking routines for MIPS targets requires MIPS II
 466     and later.  A patch went in just after the 3.3 release to
 467     make mips* use the generic implementation instead.  You can also
 468     configure for mipsel-elf as a workaround.
 469     </p><p>
 470     The mips*-*-linux* port continues to use the MIPS II routines, and more
 471     work in this area is expected.
 472     </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>
 473       Recent GNU/Linux glibc required?
 474     </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
 475          5.0.1) and later uses localization and formatting code from the system
 476          C library (glibc) version 2.2.5.  That version of glibc is over a
 477          year old and contains necessary bugfixes.  Many GNU/Linux distros make
 478          glibc version 2.3.x available now.
 479       </p><p>The guideline is simple:  the more recent the C++ library, the
 480          more recent the C library.  (This is also documented in the main
 481          GCC installation instructions.)
 482       </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>
 483       Can't use wchar_t/wstring on FreeBSD
 484     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
 485     Older versions of FreeBSD's C library do not have sufficient
 486     support for wide character functions, and as a result the
 487     libstdc++ configury decides that wchar_t support should be
 488     disabled. In addition, the libstdc++ platform checks that
 489     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 490     enough to detect when the minimal support to
 491     enable <span class="type">wchar_t</span> and C++ library structures
 492     like <code class="classname">wstring</code> were present. This impacted Solaris,
 493     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 494     </p><p>
 495     </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">
 496       What works already?
 497     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 498       Bugs in the ISO C++ language or library specification
 499     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 500       Bugs in the compiler (gcc/g++) and not libstdc++
 501     </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>
 502       What works already?
 503     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 504     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 505     except for some corner cases.  Support for localization
 506     in <code class="classname">locale</code> may be incomplete on non-GNU
 507     platforms. Also dependant on the underlying platform is support
 508     for <span class="type">wchar_t</span> and <span class="type">long
 509     long</span> specializations, and details of thread support.
 510     </p><p>
 511     Long answer: See the implementation status pages for
 512     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 513     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 514     <a class="link" href="manual/status.html#status.iso.200x" title="C++ 200x">C++0x</a>.
 515     </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>
 516       Bugs in the ISO C++ language or library specification
 517     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 518     Unfortunately, there are some.
 519     </p><p>
 520     For those people who are not part of the ISO Library Group
 521     (i.e., nearly all of us needing to read this page in the first
 522     place), a public list of the library defects is occasionally
 523     published <a class="ulink" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/" target="_top">here</a>.
 524     Some of these issues have resulted in code changes in libstdc++.
 525     </p><p>
 526     If you think you've discovered a new bug that is not listed,
 527     please post a message describing your problem
 528     to <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code> or the Usenet group
 529     comp.lang.c++.moderated.
 530     </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>
 531       Bugs in the compiler (gcc/g++) and not libstdc++
 532     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 533     On occasion, the compiler is wrong. Please be advised that this
 534     happens much less often than one would think, and avoid jumping to
 535     conclusions.
 536     </p><p>
 537     First, examine the ISO C++ standard. Second, try another compiler
 538     or an older version of the GNU compilers. Third, you can find more
 539     information on the libstdc++ and the GCC mailing lists: search
 540     these lists with terms describing your issue.
 541     </p><p>
 542     Before reporting a bug, please examine the
 543     <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the
 544     category set to <span class="quote">“<span class="quote">g++</span>”</span>.
 545     </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">
 546       Reopening a stream fails
 547     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 548       -Weffc++ complains too much
 549     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 550       Ambiguous overloads after including an old-style header
 551     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 552       The g++-3 headers are not ours
 553     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 554       Errors about *Concept and
 555       constraints in the STL
 556     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 557       Program crashes when using library code in a
 558       dynamically-loaded library
 559     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 560       “Memory leaks” in containers
 561     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 562       list::size() is O(n)!
 563     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 564       Aw, that's easy to fix!
 565     </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>
 566       Reopening a stream fails
 567     </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>
 568     One of the most-reported non-bug reports. Executing a sequence like:
 569     </p><div class="literallayout"><p><br />
 570     #include &lt;fstream&gt;<br />
 571     ...<br />
 572     std::fstream  fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
 573     // .<br />
 574     // . do things with fs...<br />
 575     // .<br />
 576     fs.close();<br />
 577     fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
 578     </p></div><p>
 579     All operations on the re-opened <code class="varname">fs</code> will fail, or at
 580     least act very strangely.  Yes, they often will, especially if
 581     <code class="varname">fs</code> reached the EOF state on the previous file.  The
 582     reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
 583     on a successful call to open().  The standard unfortunately did
 584     not specify behavior in this case, and to everybody's great sorrow,
 585     the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
 586       DR #22</a> is to leave the flags unchanged.  You must insert a call
 587     to <code class="function">fs.clear()</code> between the calls to close() and open(),
 588     and then everything will work like we all expect it to work.
 589     <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
 590     of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
 591     now calls <code class="function">clear()</code> on success!
 592     </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>
 593       -Weffc++ complains too much
 594     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 595     Many warnings are emitted when <code class="literal">-Weffc++</code> is used.  Making
 596     libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
 597     for a few reasons.  Mainly, that option tries to enforce
 598     object-oriented programming, while the Standard Library isn't
 599     necessarily trying to be OO.
 600     </p><p>
 601     We do, however, try to have libstdc++ sources as clean as possible. If
 602     you see some simple changes that pacify <code class="literal">-Weffc++</code>
 603     without other drawbacks, send us a patch.
 604     </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>
 605       Ambiguous overloads after including an old-style header
 606     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 607     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 608     comparison operator functions contained therein.  If they become
 609     visible in the same namespace as other comparison functions
 610     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the &lt;iterator&gt; header),
 611     then you will suddenly be faced with huge numbers of ambiguity
 612     errors.  This was discussed on the -v3 list; Nathan Myers
 613     <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 614       things up here</a>.  The collisions with vector/string iterator
 615     types have been fixed for 3.1.
 616     </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>
 617       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 618     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
 619         If you have found an extremely broken header file which is
 620         causing problems for you, look carefully before submitting a
 621         "high" priority bug report (which you probably
 622         shouldn't do anyhow; see the last paragraph of the page
 623         describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC
 624         bug database</a>).
 625       </p><p>
 626         If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
 627         if the installed library's name looks like
 628         <code class="filename">libstdc++-2.10.a</code> or
 629         <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
 630         old libstdc++-v2 library, which is nonstandard and
 631         unmaintained.  Do not report problems with -v2 to the -v3
 632         mailing list.
 633       </p><p>
 634         For GCC versions 3.0 and 3.1 the libstdc++ header files are
 635         installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
 636         'v'?).  Starting with version 3.2 the headers are installed in
 637         <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
 638         headers from previous versions being found by mistake.
 639       </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>
 640       Errors about <span class="emphasis"><em>*Concept</em></span> and
 641       <span class="emphasis"><em>constraints</em></span> in the STL
 642     </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>
 643     If you see compilation errors containing messages about
 644     <span class="errortext">foo Concept </span>and something to do with a
 645     <span class="errortext">constraints</span> member function, then most
 646     likely you have violated one of the requirements for types used
 647     during instantiation of template containers and functions.  For
 648     example, EqualityComparableConcept appears if your types must be
 649     comparable with == and you have not provided this capability (a
 650     typo, or wrong visibility, or you just plain forgot, etc).
 651     </p><p>
 652     More information, including how to optionally enable/disable the
 653     checks, is available in the
 654     <a class="link" href="manual/bk01pt02ch05s02.html" title="Concept Checking">Diagnostics</a>.
 655     chapter of the manual.
 656     </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>
 657       Program crashes when using library code in a
 658       dynamically-loaded library
 659     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 660     If you are using the C++ library across dynamically-loaded
 661     objects, make certain that you are passing the correct options
 662     when compiling and linking:
 663     </p><div class="literallayout"><p><br />
 664     // compile your library components<br />
 665     g++ -fPIC -c a.cc<br />
 666     g++ -fPIC -c b.cc<br />
 667     ...<br />
 668     g++ -fPIC -c z.cc<br />
 669 <br />
 670     // create your library<br />
 671     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
 672 <br />
 673     // link the executable<br />
 674     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
 675     </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>
 676       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 677     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
 678     A few people have reported that the standard containers appear
 679     to leak memory when tested with memory checkers such as
 680     <a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>.
 681     The library's default allocators keep free memory in a pool
 682     for later reuse, rather than returning it to the OS.  Although
 683     this memory is always reachable by the library and is never
 684     lost, memory debugging tools can report it as a leak.  If you
 685     want to test the library for memory leaks please read
 686     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 687     first.
 688     </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>
 689       list::size() is O(n)!
 690     </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>
 691     See
 692     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 693     chapter.
 694     </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>
 695       Aw, that's easy to fix!
 696     </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>
 697     If you have found a bug in the library and you think you have
 698     a working fix, then send it in!  The main GCC site has a page
 699     on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 700     patches</a> that covers the procedure, but for libstdc++ you
 701     should also send the patch to our mailing list in addition to
 702     the GCC patches mailing list.  The libstdc++
 703     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 704     also talks about how to submit patches.
 705     </p><p>
 706     In addition to the description, the patch, and the ChangeLog
 707     entry, it is a Good Thing if you can additionally create a small
 708     test program to test for the presence of the bug that your
 709     patch fixes.  Bugs have a way of being reintroduced; if an old
 710     bug creeps back in, it will be caught immediately by the
 711     <a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists.
 712     </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">
 713       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 714     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 715       What's next after libstdc++?
 716     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 717       What about the STL from SGI?
 718     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 719       Extensions and Backward Compatibility
 720     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 721       Does libstdc++ support TR1?
 722     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 723     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 724       What's an ABI and why is it so messy?
 725     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 726       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 727     </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>
 728       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 729     </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>
 730     If you have code that depends on container&lt;T&gt; iterators
 731     being implemented as pointer-to-T, your code is broken. It's
 732     considered a feature, not a bug, that libstdc++ points this out.
 733     </p><p>
 734     While there are arguments for iterators to be implemented in
 735     that manner, A) they aren't very good ones in the long term,
 736     and B) they were never guaranteed by the Standard anyway.  The
 737     type-safety achieved by making iterators a real class rather
 738     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 739     arguments.
 740     </p><p>
 741     Code which does assume that a vector iterator <code class="varname">i</code>
 742     is a pointer can often be fixed by changing <code class="varname">i</code> in
 743     certain expressions to <code class="varname">&amp;*i</code>.  Future revisions
 744     of the Standard are expected to bless this usage for
 745     vector&lt;&gt; (but not for basic_string&lt;&gt;).
 746     </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>
 747       What's next after libstdc++?
 748     </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>
 749         Hopefully, not much.  The goal of libstdc++ is to produce a
 750         fully-compliant, fully-portable Standard Library.  After that,
 751         we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
 752         more compliance work to do.
 753       </p><p>
 754         There is an effort underway to add significant extensions to
 755         the standard library specification.  The latest version of
 756         this effort is described in
 757          <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 758          The C++ Library Technical Report 1</a>.
 759       </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>
 760       What about the STL from SGI?
 761     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 762       The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
 763     version 3.3, was the final merge of the STL codebase.  The
 764     code in libstdc++ contains many fixes and changes, and
 765     the SGI code is no longer under active
 766     development.  We expect that no future merges will take place.
 767     </p><p>
 768     In particular, <code class="classname">string</code> is not from SGI and makes no
 769     use of their "rope" class (which is included as an
 770     optional extension), nor is <code class="classname">valarray</code> and some others.
 771     Classes like <code class="classname">vector&lt;&gt;</code> are, but have been
 772     extensively modified.
 773     </p><p>
 774     More information on the evolution of libstdc++ can be found at the
 775     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 776     evolution</a>
 777     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 778     compatibility</a> documentation.
 779     </p><p>
 780     The FAQ for SGI's STL (one jump off of their main page) is
 781     still recommended reading.
 782     </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>
 783       Extensions and Backward Compatibility
 784     </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>
 785       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.
 786     </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>
 787       Does libstdc++ support TR1?
 788     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 789     Yes.
 790     </p><p>
 791     The C++ Standard Library Technical Report adds many new features to
 792     the library.  The latest version of this effort is described in
 793     <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 794          Technical Report 1</a>.
 795     </p><p>
 796     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
 797     page</a>.
 798     </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?
 799     </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>
 800     Copies of the full ISO 14882 standard are available on line via
 801     the ISO mirror site for committee members.  Non-members, or those
 802     who have not paid for the privilege of sitting on the committee
 803     and sustained their two-meeting commitment for voting rights, may
 804     get a copy of the standard from their respective national
 805     standards organization.  In the USA, this national standards
 806     organization is ANSI and their website is
 807     right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>.  (And if
 808     you've already registered with them, clicking this link will take
 809     you to directly to the place where you can
 810     <a class="ulink" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
 811     </p><p>
 812     Who is your country's member body?  Visit the
 813     <a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
 814     </p><p>
 815     The 2003 version of the standard (the 1998 version plus TC1) is
 816     available in print, ISBN 0-470-84674-7.
 817     </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>
 818       What's an ABI and why is it so messy?
 819     </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>
 820     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 821      Interface</span>”</span>.  Conventionally, it refers to a great
 822     mass of details about how arguments are arranged on the call
 823     stack and/or in registers, and how various types are arranged
 824     and padded in structs.  A single CPU design may suffer
 825     multiple ABIs designed by different development tool vendors
 826     who made different choices, or even by the same vendor for
 827     different target applications or compiler versions.  In ideal
 828     circumstances the CPU designer presents one ABI and all the
 829     OSes and compilers use it.  In practice every ABI omits
 830     details that compiler implementers (consciously or
 831     accidentally) must choose for themselves.
 832     </p><p>
 833     That ABI definition suffices for compilers to generate code so a
 834     program can interact safely with an OS and its lowest-level libraries.
 835     Users usually want an ABI to encompass more detail, allowing libraries
 836     built with different compilers (or different releases of the same
 837     compiler!) to be linked together.  For C++, this includes many more
 838     details than for C, and CPU designers (for good reasons elaborated
 839     below) have not stepped up to publish C++ ABIs.  The details include
 840     virtual function implementation, struct inheritance layout, name
 841     mangling, and exception handling.  Such an ABI has been defined for
 842     GNU C++, and is immediately useful for embedded work relying only on
 843     a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
 844     of) the standard library.  It is a good basis for the work to come.
 845     </p><p>
 846     A useful C++ ABI must also incorporate many details of the standard
 847     library implementation.  For a C ABI, the layouts of a few structs
 848     (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 849     For C++, the details include the complete set of names of functions
 850     and types used, the offsets of class members and virtual functions,
 851     and the actual definitions of all inlines.  C++ exposes many more
 852     library details to the caller than C does.  It makes defining
 853     a complete ABI a much bigger undertaking, and requires not just
 854     documenting library implementation details, but carefully designing
 855     those details so that future bug fixes and optimizations don't
 856     force breaking the ABI.
 857     </p><p>
 858     There are ways to help isolate library implementation details from the
 859     ABI, but they trade off against speed.  Library details used in
 860     inner loops (e.g., getchar) must be exposed and frozen for all
 861     time, but many others may reasonably be kept hidden from user code,
 862     so they may later be changed.  Deciding which, and implementing
 863     the decisions, must happen before you can reasonably document a
 864     candidate C++ ABI that encompasses the standard library.
 865     </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>
 866       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 867     </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>
 868     The standard idiom for deallocating a <code class="classname">vector&lt;T&gt;</code>'s
 869     unused memory is to create a temporary copy of the vector and swap their
 870     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 871     </p><div class="literallayout"><p><br />
 872      std::vector&lt;T&gt;(v).swap(v);<br />
 873     </p></div><p>
 874     The copy will take O(n) time and the swap is constant time.
 875     </p><p>
 876     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 877     strings</a> for a similar solution for strings.
 878     </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">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html>