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 which contains necessary bugfixes.
 477          Most GNU/Linux distros make more recent versions available now.
 478       </p><p>The guideline is simple:  the more recent the C++ library, the
 479          more recent the C library.  (This is also documented in the main
 480          GCC installation instructions.)
 481       </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>
 482       Can't use wchar_t/wstring on FreeBSD
 483     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
 484     Older versions of FreeBSD's C library do not have sufficient
 485     support for wide character functions, and as a result the
 486     libstdc++ configury decides that wchar_t support should be
 487     disabled. In addition, the libstdc++ platform checks that
 488     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 489     enough to detect when the minimal support to
 490     enable <span class="type">wchar_t</span> and C++ library structures
 491     like <code class="classname">wstring</code> were present. This impacted Solaris,
 492     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 493     </p><p>
 494     </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">
 495       What works already?
 496     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 497       Bugs in the ISO C++ language or library specification
 498     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 499       Bugs in the compiler (gcc/g++) and not libstdc++
 500     </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>
 501       What works already?
 502     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 503     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 504     except for some corner cases.  Support for localization
 505     in <code class="classname">locale</code> may be incomplete on non-GNU
 506     platforms. Also dependant on the underlying platform is support
 507     for <span class="type">wchar_t</span> and <span class="type">long
 508     long</span> specializations, and details of thread support.
 509     </p><p>
 510     Long answer: See the implementation status pages for
 511     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 512     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 513     <a class="link" href="manual/status.html#status.iso.200x" title="C++ 200x">C++0x</a>.
 514     </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>
 515       Bugs in the ISO C++ language or library specification
 516     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 517     Unfortunately, there are some.
 518     </p><p>
 519     For those people who are not part of the ISO Library Group
 520     (i.e., nearly all of us needing to read this page in the first
 521     place), a public list of the library defects is occasionally
 522     published <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">here</a>.
 523     Some of these issues have resulted in code changes in libstdc++.
 524     </p><p>
 525     If you think you've discovered a new bug that is not listed,
 526     please post a message describing your problem
 527     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
 528     comp.lang.c++.moderated.
 529     </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>
 530       Bugs in the compiler (gcc/g++) and not libstdc++
 531     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 532     On occasion, the compiler is wrong. Please be advised that this
 533     happens much less often than one would think, and avoid jumping to
 534     conclusions.
 535     </p><p>
 536     First, examine the ISO C++ standard. Second, try another compiler
 537     or an older version of the GNU compilers. Third, you can find more
 538     information on the libstdc++ and the GCC mailing lists: search
 539     these lists with terms describing your issue.
 540     </p><p>
 541     Before reporting a bug, please examine the
 542     <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the
 543     category set to <span class="quote">“<span class="quote">g++</span>”</span>.
 544     </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">
 545       Reopening a stream fails
 546     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 547       -Weffc++ complains too much
 548     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 549       Ambiguous overloads after including an old-style header
 550     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 551       The g++-3 headers are not ours
 552     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 553       Errors about *Concept and
 554       constraints in the STL
 555     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 556       Program crashes when using library code in a
 557       dynamically-loaded library
 558     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 559       “Memory leaks” in containers
 560     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 561       list::size() is O(n)!
 562     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 563       Aw, that's easy to fix!
 564     </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>
 565       Reopening a stream fails
 566     </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>
 567     One of the most-reported non-bug reports. Executing a sequence like:
 568     </p><div class="literallayout"><p><br />
 569     #include &lt;fstream&gt;<br />
 570     ...<br />
 571     std::fstream  fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
 572     // .<br />
 573     // . do things with fs...<br />
 574     // .<br />
 575     fs.close();<br />
 576     fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
 577     </p></div><p>
 578     All operations on the re-opened <code class="varname">fs</code> will fail, or at
 579     least act very strangely.  Yes, they often will, especially if
 580     <code class="varname">fs</code> reached the EOF state on the previous file.  The
 581     reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
 582     on a successful call to open().  The standard unfortunately did
 583     not specify behavior in this case, and to everybody's great sorrow,
 584     the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
 585       DR #22</a> is to leave the flags unchanged.  You must insert a call
 586     to <code class="function">fs.clear()</code> between the calls to close() and open(),
 587     and then everything will work like we all expect it to work.
 588     <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
 589     of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
 590     now calls <code class="function">clear()</code> on success!
 591     </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>
 592       -Weffc++ complains too much
 593     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 594     Many warnings are emitted when <code class="literal">-Weffc++</code> is used.  Making
 595     libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
 596     for a few reasons.  Mainly, that option tries to enforce
 597     object-oriented programming, while the Standard Library isn't
 598     necessarily trying to be OO.
 599     </p><p>
 600     We do, however, try to have libstdc++ sources as clean as possible. If
 601     you see some simple changes that pacify <code class="literal">-Weffc++</code>
 602     without other drawbacks, send us a patch.
 603     </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>
 604       Ambiguous overloads after including an old-style header
 605     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 606     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 607     comparison operator functions contained therein.  If they become
 608     visible in the same namespace as other comparison functions
 609     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the &lt;iterator&gt; header),
 610     then you will suddenly be faced with huge numbers of ambiguity
 611     errors.  This was discussed on the -v3 list; Nathan Myers
 612     <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 613       things up here</a>.  The collisions with vector/string iterator
 614     types have been fixed for 3.1.
 615     </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>
 616       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 617     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
 618         If you have found an extremely broken header file which is
 619         causing problems for you, look carefully before submitting a
 620         "high" priority bug report (which you probably
 621         shouldn't do anyhow; see the last paragraph of the page
 622         describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC
 623         bug database</a>).
 624       </p><p>
 625         If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
 626         if the installed library's name looks like
 627         <code class="filename">libstdc++-2.10.a</code> or
 628         <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
 629         old libstdc++-v2 library, which is nonstandard and
 630         unmaintained.  Do not report problems with -v2 to the -v3
 631         mailing list.
 632       </p><p>
 633         For GCC versions 3.0 and 3.1 the libstdc++ header files are
 634         installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
 635         'v'?).  Starting with version 3.2 the headers are installed in
 636         <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
 637         headers from previous versions being found by mistake.
 638       </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>
 639       Errors about <span class="emphasis"><em>*Concept</em></span> and
 640       <span class="emphasis"><em>constraints</em></span> in the STL
 641     </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>
 642     If you see compilation errors containing messages about
 643     <span class="errortext">foo Concept </span>and something to do with a
 644     <span class="errortext">constraints</span> member function, then most
 645     likely you have violated one of the requirements for types used
 646     during instantiation of template containers and functions.  For
 647     example, EqualityComparableConcept appears if your types must be
 648     comparable with == and you have not provided this capability (a
 649     typo, or wrong visibility, or you just plain forgot, etc).
 650     </p><p>
 651     More information, including how to optionally enable/disable the
 652     checks, is available in the
 653     <a class="link" href="manual/bk01pt02ch05s02.html" title="Concept Checking">Diagnostics</a>.
 654     chapter of the manual.
 655     </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>
 656       Program crashes when using library code in a
 657       dynamically-loaded library
 658     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 659     If you are using the C++ library across dynamically-loaded
 660     objects, make certain that you are passing the correct options
 661     when compiling and linking:
 662     </p><div class="literallayout"><p><br />
 663     // compile your library components<br />
 664     g++ -fPIC -c a.cc<br />
 665     g++ -fPIC -c b.cc<br />
 666     ...<br />
 667     g++ -fPIC -c z.cc<br />
 668 <br />
 669     // create your library<br />
 670     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
 671 <br />
 672     // link the executable<br />
 673     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
 674     </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>
 675       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 676     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
 677     A few people have reported that the standard containers appear
 678     to leak memory when tested with memory checkers such as
 679     <a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>.
 680     The library's default allocators keep free memory in a pool
 681     for later reuse, rather than returning it to the OS.  Although
 682     this memory is always reachable by the library and is never
 683     lost, memory debugging tools can report it as a leak.  If you
 684     want to test the library for memory leaks please read
 685     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 686     first.
 687     </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>
 688       list::size() is O(n)!
 689     </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>
 690     See
 691     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 692     chapter.
 693     </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>
 694       Aw, that's easy to fix!
 695     </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>
 696     If you have found a bug in the library and you think you have
 697     a working fix, then send it in!  The main GCC site has a page
 698     on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 699     patches</a> that covers the procedure, but for libstdc++ you
 700     should also send the patch to our mailing list in addition to
 701     the GCC patches mailing list.  The libstdc++
 702     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 703     also talks about how to submit patches.
 704     </p><p>
 705     In addition to the description, the patch, and the ChangeLog
 706     entry, it is a Good Thing if you can additionally create a small
 707     test program to test for the presence of the bug that your
 708     patch fixes.  Bugs have a way of being reintroduced; if an old
 709     bug creeps back in, it will be caught immediately by the
 710     <a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists.
 711     </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">
 712       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 713     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 714       What's next after libstdc++?
 715     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 716       What about the STL from SGI?
 717     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 718       Extensions and Backward Compatibility
 719     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 720       Does libstdc++ support TR1?
 721     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 722     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 723       What's an ABI and why is it so messy?
 724     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 725       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 726     </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>
 727       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 728     </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>
 729     If you have code that depends on container&lt;T&gt; iterators
 730     being implemented as pointer-to-T, your code is broken. It's
 731     considered a feature, not a bug, that libstdc++ points this out.
 732     </p><p>
 733     While there are arguments for iterators to be implemented in
 734     that manner, A) they aren't very good ones in the long term,
 735     and B) they were never guaranteed by the Standard anyway.  The
 736     type-safety achieved by making iterators a real class rather
 737     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 738     arguments.
 739     </p><p>
 740     Code which does assume that a vector iterator <code class="varname">i</code>
 741     is a pointer can often be fixed by changing <code class="varname">i</code> in
 742     certain expressions to <code class="varname">&amp;*i</code>.  Future revisions
 743     of the Standard are expected to bless this usage for
 744     vector&lt;&gt; (but not for basic_string&lt;&gt;).
 745     </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>
 746       What's next after libstdc++?
 747     </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>
 748         Hopefully, not much.  The goal of libstdc++ is to produce a
 749         fully-compliant, fully-portable Standard Library.  After that,
 750         we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
 751         more compliance work to do.
 752       </p><p>
 753         There is an effort underway to add significant extensions to
 754         the standard library specification.  The latest version of
 755         this effort is described in
 756          <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 757          The C++ Library Technical Report 1</a>.
 758       </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>
 759       What about the STL from SGI?
 760     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 761       The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
 762     version 3.3, was the final merge of the STL codebase.  The
 763     code in libstdc++ contains many fixes and changes, and
 764     the SGI code is no longer under active
 765     development.  We expect that no future merges will take place.
 766     </p><p>
 767     In particular, <code class="classname">string</code> is not from SGI and makes no
 768     use of their "rope" class (which is included as an
 769     optional extension), nor is <code class="classname">valarray</code> and some others.
 770     Classes like <code class="classname">vector&lt;&gt;</code> are, but have been
 771     extensively modified.
 772     </p><p>
 773     More information on the evolution of libstdc++ can be found at the
 774     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 775     evolution</a>
 776     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 777     compatibility</a> documentation.
 778     </p><p>
 779     The FAQ for SGI's STL (one jump off of their main page) is
 780     still recommended reading.
 781     </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>
 782       Extensions and Backward Compatibility
 783     </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>
 784       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.
 785     </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>
 786       Does libstdc++ support TR1?
 787     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 788     Yes.
 789     </p><p>
 790     The C++ Standard Library Technical Report adds many new features to
 791     the library.  The latest version of this effort is described in
 792     <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 793          Technical Report 1</a>.
 794     </p><p>
 795     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
 796     page</a>.
 797     </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?
 798     </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>
 799     Copies of the full ISO 14882 standard are available on line via
 800     the ISO mirror site for committee members.  Non-members, or those
 801     who have not paid for the privilege of sitting on the committee
 802     and sustained their two-meeting commitment for voting rights, may
 803     get a copy of the standard from their respective national
 804     standards organization.  In the USA, this national standards
 805     organization is ANSI and their website is
 806     right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>.  (And if
 807     you've already registered with them, clicking this link will take
 808     you to directly to the place where you can
 809     <a class="ulink" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
 810     </p><p>
 811     Who is your country's member body?  Visit the
 812     <a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
 813     </p><p>
 814     The 2003 version of the standard (the 1998 version plus TC1) is
 815     available in print, ISBN 0-470-84674-7.
 816     </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>
 817       What's an ABI and why is it so messy?
 818     </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>
 819     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 820      Interface</span>”</span>.  Conventionally, it refers to a great
 821     mass of details about how arguments are arranged on the call
 822     stack and/or in registers, and how various types are arranged
 823     and padded in structs.  A single CPU design may suffer
 824     multiple ABIs designed by different development tool vendors
 825     who made different choices, or even by the same vendor for
 826     different target applications or compiler versions.  In ideal
 827     circumstances the CPU designer presents one ABI and all the
 828     OSes and compilers use it.  In practice every ABI omits
 829     details that compiler implementers (consciously or
 830     accidentally) must choose for themselves.
 831     </p><p>
 832     That ABI definition suffices for compilers to generate code so a
 833     program can interact safely with an OS and its lowest-level libraries.
 834     Users usually want an ABI to encompass more detail, allowing libraries
 835     built with different compilers (or different releases of the same
 836     compiler!) to be linked together.  For C++, this includes many more
 837     details than for C, and CPU designers (for good reasons elaborated
 838     below) have not stepped up to publish C++ ABIs.  The details include
 839     virtual function implementation, struct inheritance layout, name
 840     mangling, and exception handling.  Such an ABI has been defined for
 841     GNU C++, and is immediately useful for embedded work relying only on
 842     a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
 843     of) the standard library.  It is a good basis for the work to come.
 844     </p><p>
 845     A useful C++ ABI must also incorporate many details of the standard
 846     library implementation.  For a C ABI, the layouts of a few structs
 847     (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 848     For C++, the details include the complete set of names of functions
 849     and types used, the offsets of class members and virtual functions,
 850     and the actual definitions of all inlines.  C++ exposes many more
 851     library details to the caller than C does.  It makes defining
 852     a complete ABI a much bigger undertaking, and requires not just
 853     documenting library implementation details, but carefully designing
 854     those details so that future bug fixes and optimizations don't
 855     force breaking the ABI.
 856     </p><p>
 857     There are ways to help isolate library implementation details from the
 858     ABI, but they trade off against speed.  Library details used in
 859     inner loops (e.g., getchar) must be exposed and frozen for all
 860     time, but many others may reasonably be kept hidden from user code,
 861     so they may later be changed.  Deciding which, and implementing
 862     the decisions, must happen before you can reasonably document a
 863     candidate C++ ABI that encompasses the standard library.
 864     </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>
 865       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 866     </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>
 867     The standard idiom for deallocating a <code class="classname">vector&lt;T&gt;</code>'s
 868     unused memory is to create a temporary copy of the vector and swap their
 869     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 870     </p><div class="literallayout"><p><br />
 871      std::vector&lt;T&gt;(v).swap(v);<br />
 872     </p></div><p>
 873     The copy will take O(n) time and the swap is constant time.
 874     </p><p>
 875     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 876     strings</a> for a similar solution for strings.
 877     </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>