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

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Frequently Asked Questions</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="index.html" title="The GNU C++ Library" /><link rel="up" href="bk03.html" title="" /><link rel="prev" href="bk03.html" title="" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frequently Asked Questions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><th width="60%" align="center"></th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="article"><div class="titlepage"><div><div><h1 class="title"><a id="faq"></a>Frequently Asked Questions</h1></div><div><p class="copyright">Copyright ©
   3       2008-2014
   4
   5       <a class="link" href="http://www.fsf.org" target="_top">FSF</a>
   6     </p></div></div><hr /></div><div class="qandaset"><a id="faq.faq"></a><dl><dt></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
   7       What is libstdc++?
   8     </a></dt><dt>1.2. <a href="faq.html#faq.why">
   9       Why should I use libstdc++?
  10     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  11       Who's in charge of it?
  12     </a></dt><dt>1.4. <a href="faq.html#faq.when">
  13       When is libstdc++ going to be finished?
  14     </a></dt><dt>1.5. <a href="faq.html#faq.how">
  15       How do I contribute to the effort?
  16     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
  17       What happened to the older libg++? I need that!
  18     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
  19       What if I have more questions?
  20     </a></dt></dl></dd><dt></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
  21       What are the license terms for libstdc++?
  22     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
  23       So any program which uses libstdc++ falls under the GPL?
  24     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
  25       How is that different from the GNU {Lesser,Library} GPL?
  26     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
  27       I see. So, what restrictions are there on programs that use the library?
  28     </a></dt></dl></dd><dt></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
  29     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
  30     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
  31     </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?
  32     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
  33       What's libsupc++?
  34     </a></dt><dt>3.6. <a href="faq.html#faq.size">
  35       This library is HUGE!
  36     </a></dt></dl></dd><dt></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
  37       Can libstdc++ be used with non-GNU compilers?
  38     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
  39       No 'long long' type on Solaris?
  40     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
  41       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
  42     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
  43       Mac OS X ctype.h is broken! How can I fix it?
  44     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
  45       Threading is broken on i386?
  46     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
  47       MIPS atomic operations
  48     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
  49       Recent GNU/Linux glibc required?
  50     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
  51       Can't use wchar_t/wstring on FreeBSD
  52     </a></dt></dl></dd><dt></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
  53       What works already?
  54     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
  55       Bugs in the ISO C++ language or library specification
  56     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
  57       Bugs in the compiler (gcc/g++) and not libstdc++
  58     </a></dt></dl></dd><dt></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
  59       Reopening a stream fails
  60     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
  61       -Weffc++ complains too much
  62     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
  63       Ambiguous overloads after including an old-style header
  64     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
  65       The g++-3 headers are not ours
  66     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
  67       Errors about *Concept and
  68       constraints in the STL
  69     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
  70       Program crashes when using library code in a
  71       dynamically-loaded library
  72     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
  73       “Memory leaks” in containers
  74     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
  75       list::size() is O(n)!
  76     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
  77       Aw, that's easy to fix!
  78     </a></dt></dl></dd><dt></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
  79       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
  80     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
  81       What's next after libstdc++?
  82     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
  83       What about the STL from SGI?
  84     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
  85       Extensions and Backward Compatibility
  86     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
  87       Does libstdc++ support TR1?
  88     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
  89     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
  90       What's an ABI and why is it so messy?
  91     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
  92       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
  93     </a></dt></dl></dd></dl><table border="0" style="width: 100%;"><colgroup><col align="left" width="1%" /><col /></colgroup><tbody><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
  94       What is libstdc++?
  95     </a></dt><dt>1.2. <a href="faq.html#faq.why">
  96       Why should I use libstdc++?
  97     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  98       Who's in charge of it?
  99     </a></dt><dt>1.4. <a href="faq.html#faq.when">
 100       When is libstdc++ going to be finished?
 101     </a></dt><dt>1.5. <a href="faq.html#faq.how">
 102       How do I contribute to the effort?
 103     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
 104       What happened to the older libg++? I need that!
 105     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
 106       What if I have more questions?
 107     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what"></a><a id="faq.what.q"></a><p><strong>1.1.</strong></p></td><td align="left" valign="top"><p>
 108       What is libstdc++?
 109     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
 110      The GNU Standard C++ Library v3 is an ongoing project to
 111      implement the ISO 14882 Standard C++ library as described in
 112      clauses 17 through 30 and annex D.  For those who want to see
 113      exactly how far the project has come, or just want the latest
 114      bleeding-edge code, the up-to-date source is available over
 115      anonymous SVN, and can be browsed over
 116      the <a class="link" href="https://gcc.gnu.org/svn.html" target="_top">web</a>.
 117     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><strong>1.2.</strong></p></td><td align="left" valign="top"><p>
 118       Why should I use libstdc++?
 119     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
 120     The completion of the initial ISO C++ standardization effort gave the C++
 121     community a powerful set of reuseable tools in the form of the C++
 122     Standard Library.  However, for several years C++ implementations were
 123     (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
 124     incorrekt</span>”</span>, and many suffered from limitations of the compilers
 125     that used them.
 126     </p><p>
 127     The GNU compiler collection
 128     (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
 129     considered to be one of the leading compilers in the world.  Its
 130     development is overseen by the
 131     <a class="link" href="https://gcc.gnu.org/" target="_top">GCC team</a>.  All of
 132     the rapid development and near-legendary
 133     <a class="link" href="https://gcc.gnu.org/buildstat.html" target="_top">portability</a>
 134     that are the hallmarks of an open-source project are applied to libstdc++.
 135     </p><p>
 136     All of the standard classes and functions from C++98/C++03
 137     (such as <code class="classname">string</code>,
 138     <code class="classname">vector&lt;&gt;</code>, iostreams, algorithms etc.)
 139     are freely available and atempt to be fully compliant.
 140     Work is ongoing to complete support for the current revision of the
 141     ISO C++ Standard.
 142     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><strong>1.3.</strong></p></td><td align="left" valign="top"><p>
 143       Who's in charge of it?
 144     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
 145      The libstdc++ project is contributed to by several developers
 146      all over the world, in the same way as GCC or the Linux kernel.
 147      The current maintainers are listed in the
 148      <a class="link" href="https://gcc.gnu.org/viewcvs/gcc/trunk/MAINTAINERS?view=co" target="_top"><code class="filename">MAINTAINERS</code></a>
 149      file (look for "c++ runtime libs").
 150     </p><p>
 151     Development and discussion is held on the libstdc++ mailing
 152     list.  Subscribing to the list, or searching the list
 153     archives, is open to everyone.  You can read instructions for
 154     doing so on the <a class="link" href="https://gcc.gnu.org/lists.html" target="_top">GCC mailing lists</a> page.
 155     If you have questions, ideas, code, or are just curious, sign up!
 156     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.when"></a><a id="q-when"></a><p><strong>1.4.</strong></p></td><td align="left" valign="top"><p>
 157       When is libstdc++ going to be finished?
 158     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
 159     Nathan Myers gave the best of all possible answers, responding to
 160     a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
 161     help.</em></span>
 162     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><strong>1.5.</strong></p></td><td align="left" valign="top"><p>
 163       How do I contribute to the effort?
 164     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
 165     See the <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">Contributing</a> section in
 166     the manual. Subscribing to the mailing list (see above, or
 167     the homepage) is a very good idea if you have something to
 168     contribute, or if you have spare time and want to
 169     help. Contributions don't have to be in the form of source code;
 170     anybody who is willing to help write documentation, for example,
 171     or has found a bug in code that we all thought was working and is
 172     willing to provide details, is more than welcome!
 173     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.whereis_old"></a><a id="q-whereis_old"></a><p><strong>1.6.</strong></p></td><td align="left" valign="top"><p>
 174       What happened to the older libg++? I need that!
 175     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
 176     The last libg++ README states
 177     <span class="quote">“<span class="quote">This package is considered obsolete and is no longer
 178     being developed.</span>”</span>
 179     It should not be used for new projects, and won't even compile with
 180     recent releases of GCC (or most other C++ compilers).
 181     </p><p>
 182     More information can be found in the
 183     <a class="link" href="manual/backwards.html" title="Backwards Compatibility">Backwards
 184     Compatibility</a> section of the libstdc++ manual.
 185     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.more_questions"></a><a id="q-more_questions"></a><p><strong>1.7.</strong></p></td><td align="left" valign="top"><p>
 186       What if I have more questions?
 187     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
 188     If you have read the documentation, and your question remains
 189     unanswered, then just ask the mailing list. At present, you do not
 190     need to be subscribed to the list to send a message to it.  More
 191     information is available on the homepage (including how to browse
 192     the list archives); to send a message to the list,
 193     use <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code>.
 194     </p><p>
 195     If you have a question that you think should be included
 196     here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
 197     here, please send email to the libstdc++ mailing list, as above.
 198     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
 199       What are the license terms for libstdc++?
 200     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
 201       So any program which uses libstdc++ falls under the GPL?
 202     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
 203       How is that different from the GNU {Lesser,Library} GPL?
 204     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
 205       I see. So, what restrictions are there on programs that use the library?
 206     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.what"></a><a id="q-license.what"></a><p><strong>2.1.</strong></p></td><td align="left" valign="top"><p>
 207       What are the license terms for libstdc++?
 208     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
 209     See <a class="link" href="manual/license.html" title="License">our license description</a>
 210     for these and related questions.
 211     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.any_program"></a><a id="q-license.any_program"></a><p><strong>2.2.</strong></p></td><td align="left" valign="top"><p>
 212       So any program which uses libstdc++ falls under the GPL?
 213     </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>
 214      No. The special exception permits use of the library in
 215      proprietary applications.
 216     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.lgpl"></a><a id="q-license.lgpl"></a><p><strong>2.3.</strong></p></td><td align="left" valign="top"><p>
 217       How is that different from the GNU {Lesser,Library} GPL?
 218     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
 219       The LGPL requires that users be able to replace the LGPL code with a
 220      modified version; this is trivial if the library in question is a C
 221      shared library.  But there's no way to make that work with C++, where
 222      much of the library consists of inline functions and templates, which
 223      are expanded inside the code that uses the library.  So to allow people
 224      to replace the library code, someone using the library would have to
 225      distribute their own source, rendering the LGPL equivalent to the GPL.
 226     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.what_restrictions"></a><a id="q-license.what_restrictions"></a><p><strong>2.4.</strong></p></td><td align="left" valign="top"><p>
 227       I see. So, what restrictions are there on programs that use the library?
 228     </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>
 229       None.  We encourage such programs to be released as free software,
 230      but we won't punish you or sue you if you choose otherwise.
 231     </p></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++?
 232     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
 233     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
 234     </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?
 235     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
 236       What's libsupc++?
 237     </a></dt><dt>3.6. <a href="faq.html#faq.size">
 238       This library is HUGE!
 239     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_install"></a><a id="q-how_to_install"></a><p><strong>3.1.</strong></p></td><td align="left" valign="top"><p>How do I install libstdc++?
 240     </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>
 241     Often libstdc++ comes pre-installed as an integral part of many
 242     existing GNU/Linux and Unix systems, as well as many embedded
 243     development tools. It may be necessary to install extra
 244     development packages to get the headers, or the documentation, or
 245     the source: please consult your vendor for details.
 246     </p><p>
 247     To build and install from the GNU GCC sources, please consult the
 248     <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
 249     documentation</a> for detailed
 250     instructions. You may wish to browse those files ahead
 251     of time to get a feel for what's required.
 252     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_get_sources"></a><a id="q-how_to_get_sources"></a><p><strong>3.2.</strong></p></td><td align="left" valign="top"><p>How does one get current libstdc++ sources?
 253     </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>
 254     Libstdc++ sources for all official releases can be obtained as
 255     part of the GCC sources, available from various sites and
 256     mirrors. A full <a class="link" href="https://gcc.gnu.org/mirrors.html" target="_top">list of
 257     download sites</a> is provided on the main GCC site.
 258     </p><p>
 259     Current libstdc++ sources can always be checked out of the main
 260     GCC source repository using the appropriate version control
 261     tool. At this time, that tool
 262     is <span class="application">Subversion</span>.
 263     </p><p>
 264     <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
 265     one of several revision control packages.  It was selected for GNU
 266     projects because it's free (speech), free (beer), and very high
 267     quality.  The <a class="link" href="http://subversion.tigris.org" target="_top"> Subversion
 268     home page</a> has a better description.
 269     </p><p>
 270     The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
 271     similar to anonymous FTP in that it allows anyone to retrieve
 272     the latest libstdc++ sources.
 273     </p><p>
 274     For more information
 275     see <a class="link" href="https://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
 276     details</a>.
 277     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_test"></a><a id="q-how_to_test"></a><p><strong>3.3.</strong></p></td><td align="left" valign="top"><p>How do I know if it works?
 278     </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>
 279     Libstdc++ comes with its own validation testsuite, which includes
 280     conformance testing, regression testing, ABI testing, and
 281     performance testing. Please consult the
 282     <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing
 283     documentation</a> for GCC and
 284     <a class="link" href="manual/test.html" title="Testing">Testing</a> in the libstdc++
 285     manual for more details.
 286     </p><p>
 287     If you find bugs in the testsuite programs themselves, or if you
 288     think of a new test program that should be added to the suite,
 289     <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
 290     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_set_paths"></a><a id="q-how_to_set_paths"></a><p><strong>3.4.</strong></p></td><td align="left" valign="top"><p>How do I insure that the dynamically linked library will be found?
 291     </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>
 292     Depending on your platform and library version, the error message might
 293     be similar to one of the following:
 294     </p><pre class="screen">
 295     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 296
 297     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
 298     </pre><p>
 299     This doesn't mean that the shared library isn't installed, only
 300     that the dynamic linker can't find it. When a dynamically-linked
 301     executable is run the linker finds and loads the required shared
 302     libraries by searching a pre-configured list of directories. If
 303     the directory where you've installed libstdc++ is not in this list
 304     then the libraries won't be found.
 305     </p><p>
 306     If you already have an older version of libstdc++ installed then the
 307     error might look like one of the following instead:
 308     </p><pre class="screen">
 309     ./a.out: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.20' not found
 310     ./a.out: /usr/lib/libstdc++.so.6: version `CXXABI_1.3.8' not found
 311     </pre><p>
 312     This means the linker found <code class="filename">/usr/lib/libstdc++.so.6</code>
 313     but that library belongs to an older version of GCC than was used to
 314     compile and link the program <code class="filename">a.out</code> (or some part
 315     of it). The program depends on code defined in the newer libstdc++
 316     that belongs to the newer version of GCC, so the linker must be told
 317     how to find the newer libstdc++ shared library.
 318     </p><p>
 319     The simplest way to fix this is
 320     to use the <code class="envar">LD_LIBRARY_PATH</code> environment variable,
 321     which is a colon-separated list of directories in which the linker
 322     will search for shared libraries:
 323     </p><pre class="screen"><span class="command"><strong>
 324     export LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 325     </strong></span></pre><p>
 326     Here the shell variable <code class="varname">${prefix}</code> is assumed to contain
 327     the directory prefix where GCC was installed to. The directory containing
 328     the library might depend on whether you want the 32-bit or 64-bit copy
 329     of the library, so for example would be
 330     <code class="filename">${prefix}/lib64</code> on some systems.
 331     The exact environment variable to use will depend on your
 332     platform, e.g. <code class="envar">DYLD_LIBRARY_PATH</code> for Darwin,
 333     <code class="envar">LD_LIBRARY_PATH_32</code>/<code class="envar">LD_LIBRARY_PATH_64</code>
 334     for Solaris 32-/64-bit,
 335     and <code class="envar">SHLIB_PATH</code> for HP-UX.
 336     </p><p>
 337     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 338     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 339     linker has different names on different platforms but the man page
 340     is usually called something such as <code class="filename">ld.so</code>,
 341     <code class="filename">rtld</code> or <code class="filename">dld.so</code>.
 342     </p><p>
 343     Using <code class="envar">LD_LIBRARY_PATH</code> is not always the best solution,
 344     <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
 345     Libraries</a> in the manual gives some alternatives.
 346     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_libsupcxx"></a><a id="q-what_is_libsupcxx"></a><p><strong>3.5.</strong></p></td><td align="left" valign="top"><p>
 347       What's libsupc++?
 348     </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>
 349       If the only functions from <code class="filename">libstdc++.a</code>
 350       which you need are language support functions (those listed in
 351       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 352       standard, e.g., <code class="function">new</code> and
 353       <code class="function">delete</code>), then try linking against
 354       <code class="filename">libsupc++.a</code>, which is a subset of
 355       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 356       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 357       <code class="filename">libsupc++.a</code> via <code class="option">-lsupc++</code>
 358       for the final link step will do it).  This library contains only
 359       those support routines, one per object file.  But if you are
 360       using anything from the rest of the library, such as IOStreams
 361       or vectors, then you'll still need pieces from
 362       <code class="filename">libstdc++.a</code>.
 363     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size"></a><a id="q-size"></a><p><strong>3.6.</strong></p></td><td align="left" valign="top"><p>
 364       This library is HUGE!
 365     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 366     Usually the size of libraries on disk isn't noticeable.  When a
 367     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 368     static archive library, only the necessary object files are copied
 369     into your executable, not the entire library.  Unfortunately, even
 370     if you only need a single function or variable from an object file,
 371     the entire object file is extracted.  (There's nothing unique to C++
 372     or libstdc++ about this; it's just common behavior, given here
 373     for background reasons.)
 374     </p><p>
 375     Some of the object files which make up
 376     <code class="filename">libstdc++.a</code> are rather large.
 377     If you create a statically-linked executable with
 378     <code class="option">-static</code>, those large object files are suddenly part
 379     of your executable.  Historically the best way around this was to
 380     only place a very few functions (often only a single one) in each
 381     source/object file; then extracting a single function is the same
 382     as extracting a single <code class="filename">.o</code> file.  For libstdc++ this
 383     is only possible to a certain extent; the object files in question contain
 384     template classes and template functions, pre-instantiated, and
 385     splitting those up causes severe maintenance headaches.
 386     </p><p>
 387     On supported platforms, libstdc++ takes advantage of garbage
 388     collection in the GNU linker to get a result similar to separating
 389     each symbol into a separate source and object files. On these platforms,
 390     GNU ld can place each function and variable into its own
 391     section in a <code class="filename">.o</code> file.  The GNU linker can then perform
 392     garbage collection on unused sections; this reduces the situation to only
 393     copying needed functions into the executable, as before, but all
 394     happens automatically.
 395     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
 396       Can libstdc++ be used with non-GNU compilers?
 397     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 398       No 'long long' type on Solaris?
 399     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 400       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 401     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 402       Mac OS X ctype.h is broken! How can I fix it?
 403     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 404       Threading is broken on i386?
 405     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 406       MIPS atomic operations
 407     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 408       Recent GNU/Linux glibc required?
 409     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 410       Can't use wchar_t/wstring on FreeBSD
 411     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.other_compilers"></a><a id="q-other_compilers"></a><p><strong>4.1.</strong></p></td><td align="left" valign="top"><p>
 412       Can libstdc++ be used with non-GNU compilers?
 413     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 414     Perhaps.
 415     </p><p>
 416     Since the goal of ISO Standardization is for all C++
 417     implementations to be able to share code, libstdc++ should be
 418     usable under any ISO-compliant compiler, at least in theory.
 419     </p><p>
 420     However, the reality is that libstdc++ is targeted and optimized
 421     for GCC/G++. This means that often libstdc++ uses specific,
 422     non-standard features of G++ that are not present in older
 423     versions of proprietary compilers. It may take as much as a year or two
 424     after an official release of GCC that contains these features for
 425     proprietary tools to support these constructs.
 426     </p><p>
 427     Recent versions of libstdc++ are known to work with the Clang compiler.
 428     In the near past, specific released versions of libstdc++ have
 429     been known to work with versions of the EDG C++ compiler, and
 430     vendor-specific proprietary C++ compilers such as the Intel ICC
 431     C++ compiler.
 432     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.solaris_long_long"></a><a id="q-solaris_long_long"></a><p><strong>4.2.</strong></p></td><td align="left" valign="top"><p>
 433       No '<span class="type">long long</span>' type on Solaris?
 434     </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>
 435     By default we try to support the C99 <span class="type">long long</span> type.
 436     This requires that certain functions from your C library be present.
 437     </p><p>
 438     Up through release 3.0.2 the platform-specific tests performed by
 439     libstdc++ were too general, resulting in a conservative approach
 440     to enabling the <span class="type">long long</span> code paths. The most
 441     commonly reported platform affected was Solaris.
 442     </p><p>
 443     This has been fixed for libstdc++ releases greater than 3.0.3.
 444     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><strong>4.3.</strong></p></td><td align="left" valign="top"><p>
 445       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 446     </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, <span class="command"><strong>g++</strong></span> (but not <span class="command"><strong>gcc</strong></span>)
 447          always defines the preprocessor macro
 448          <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 449          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 450          other macros and other platforms are also affected.)
 451       </p><p>These macros are typically used in C library headers, guarding new
 452          versions of functions from their older versions.  The C++98 standard
 453          library includes the C standard library, but it requires the C90
 454          version, which for backwards-compatibility reasons is often not the
 455          default for many vendors.
 456       </p><p>More to the point, the C++ standard requires behavior which is only
 457          available on certain platforms after certain symbols are defined.
 458          Usually the issue involves I/O-related typedefs.  In order to
 459          ensure correctness, the compiler simply predefines those symbols.
 460       </p><p>Note that it's not enough to <code class="literal">#define</code> them only when the library is
 461          being built (during installation).  Since we don't have an 'export'
 462          keyword, much of the library exists as headers, which means that
 463          the symbols must also be defined as your programs are parsed and
 464          compiled.
 465       </p><p>To see which symbols are defined, look for
 466          <code class="varname">CPLUSPLUS_CPP_SPEC</code> in
 467          the gcc config headers for your target (and try changing them to
 468          see what happens when building complicated code).  You can also run
 469          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 470          a list of predefined macros for any particular installation.
 471       </p><p>This has been discussed on the mailing lists
 472          <a class="link" 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>.
 473       </p><p>This method is something of a wart.  We'd like to find a cleaner
 474          solution, but nobody yet has contributed the time.
 475       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.darwin_ctype"></a><a id="q-darwin_ctype"></a><p><strong>4.4.</strong></p></td><td align="left" valign="top"><p>
 476       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 477     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-darwin_ctype"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p>
 478          This was a long-standing bug in the OS X support.  Fortunately, the
 479          <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top">patch</a>
 480          was quite simple, and well-known.
 481       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.threads_i386"></a><a id="q-threads_i386"></a><p><strong>4.5.</strong></p></td><td align="left" valign="top"><p>
 482       Threading is broken on i386?
 483     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p>Support for atomic integer operations was broken on i386
 484          platforms.  The assembly code accidentally used opcodes that are
 485          only available on the i486 and later.  So if you configured GCC
 486          to target, for example, i386-linux, but actually used the programs
 487          on an i686, then you would encounter no problems.  Only when
 488          actually running the code on a i386 will the problem appear.
 489       </p><p>This is fixed in 3.2.2.
 490       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.atomic_mips"></a><a id="q-atomic_mips"></a><p><strong>4.6.</strong></p></td><td align="left" valign="top"><p>
 491       MIPS atomic operations
 492     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p>
 493     The atomic locking routines for MIPS targets requires MIPS II
 494     and later.  A patch went in just after the 3.3 release to
 495     make mips* use the generic implementation instead.  You can also
 496     configure for mipsel-elf as a workaround.
 497     </p><p>
 498     The mips*-*-linux* port continues to use the MIPS II routines, and more
 499     work in this area is expected.
 500     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.linux_glibc"></a><a id="q-linux_glibc"></a><p><strong>4.7.</strong></p></td><td align="left" valign="top"><p>
 501       Recent GNU/Linux glibc required?
 502     </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
 503          5.0.1) and later uses localization and formatting code from the system
 504          C library (glibc) version 2.2.5 which contains necessary bugfixes.
 505          All GNU/Linux distros make more recent versions available now.
 506          libstdc++ 4.6.0 and later require glibc 2.3 or later for this
 507          localization and formatting code.
 508       </p><p>The guideline is simple:  the more recent the C++ library, the
 509          more recent the C library.  (This is also documented in the main
 510          GCC installation instructions.)
 511       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.freebsd_wchar"></a><a id="q-freebsd_wchar"></a><p><strong>4.8.</strong></p></td><td align="left" valign="top"><p>
 512       Can't use wchar_t/wstring on FreeBSD
 513     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p>
 514     Older versions of FreeBSD's C library do not have sufficient
 515     support for wide character functions, and as a result the
 516     libstdc++ configury decides that <span class="type">wchar_t</span> support should be
 517     disabled. In addition, the libstdc++ platform checks that
 518     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 519     enough to detect when the minimal support to
 520     enable <span class="type">wchar_t</span> and C++ library structures
 521     like <code class="classname">wstring</code> were present. This impacted Solaris,
 522     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 523     </p><p>
 524     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
 525       What works already?
 526     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 527       Bugs in the ISO C++ language or library specification
 528     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 529       Bugs in the compiler (gcc/g++) and not libstdc++
 530     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_works"></a><a id="q-what_works"></a><p><strong>5.1.</strong></p></td><td align="left" valign="top"><p>
 531       What works already?
 532     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 533     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 534     except for some corner cases.  Support for localization
 535     in <code class="classname">locale</code> may be incomplete on some non-GNU
 536     platforms. Also dependent on the underlying platform is support
 537     for <span class="type">wchar_t</span> and <span class="type">long
 538     long</span> specializations, and details of thread support.
 539     </p><p>
 540     Long answer: See the implementation status pages for
 541     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 542     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 543     <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>.
 544     <a class="link" href="manual/status.html#status.iso.2014" title="C++ 2014">C++14</a>.
 545     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><strong>5.2.</strong></p></td><td align="left" valign="top"><p>
 546       Bugs in the ISO C++ language or library specification
 547     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 548     Unfortunately, there are some.
 549     </p><p>
 550     For those people who are not part of the ISO Library Group
 551     (i.e., nearly all of us needing to read this page in the first
 552     place), a public list of the library defects is occasionally
 553     published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
 554     website</a>.
 555     Many of these issues have resulted in code changes in libstdc++.
 556     </p><p>
 557     If you think you've discovered a new bug that is not listed,
 558     please post a message describing your problem to the author of
 559     the library issues list.
 560     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.compiler_bugs"></a><a id="q-compiler_bugs"></a><p><strong>5.3.</strong></p></td><td align="left" valign="top"><p>
 561       Bugs in the compiler (gcc/g++) and not libstdc++
 562     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 563     On occasion, the compiler is wrong. Please be advised that this
 564     happens much less often than one would think, and avoid jumping to
 565     conclusions.
 566     </p><p>
 567     First, examine the ISO C++ standard. Second, try another compiler
 568     or an older version of the GNU compilers. Third, you can find more
 569     information on the libstdc++ and the GCC mailing lists: search
 570     these lists with terms describing your issue.
 571     </p><p>
 572     Before reporting a bug, please examine the
 573     <a class="link" href="http://gcc.gnu.org/bugs/" target="_top">bugs database</a> with the
 574     category set to <span class="quote">“<span class="quote">g++</span>”</span>.
 575     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
 576       Reopening a stream fails
 577     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 578       -Weffc++ complains too much
 579     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 580       Ambiguous overloads after including an old-style header
 581     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 582       The g++-3 headers are not ours
 583     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 584       Errors about *Concept and
 585       constraints in the STL
 586     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 587       Program crashes when using library code in a
 588       dynamically-loaded library
 589     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 590       “Memory leaks” in containers
 591     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 592       list::size() is O(n)!
 593     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 594       Aw, that's easy to fix!
 595     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.stream_reopening_fails"></a><a id="q-stream_reopening_fails"></a><p><strong>6.1.</strong></p></td><td align="left" valign="top"><p>
 596       Reopening a stream fails
 597     </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>
 598     One of the most-reported non-bug reports. Executing a sequence like:
 599     </p><pre class="programlisting">
 600     #include &lt;fstream&gt;
 601     ...
 602     std::fstream  fs("a_file");
 603     // .
 604     // . do things with fs...
 605     // .
 606     fs.close();
 607     fs.open("a_new_file");
 608     </pre><p>
 609     All operations on the re-opened <code class="varname">fs</code> will fail, or at
 610     least act very strangely.  Yes, they often will, especially if
 611     <code class="varname">fs</code> reached the EOF state on the previous file.  The
 612     reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
 613     on a successful call to open().  The standard unfortunately did
 614     not specify behavior in this case, and to everybody's great sorrow,
 615     the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
 616       DR #22</a> is to leave the flags unchanged.  You must insert a call
 617     to <code class="function">fs.clear()</code> between the calls to close() and open(),
 618     and then everything will work like we all expect it to work.
 619     <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
 620     of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
 621     now calls <code class="function">clear()</code> on success!
 622     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.wefcxx_verbose"></a><a id="q-wefcxx_verbose"></a><p><strong>6.2.</strong></p></td><td align="left" valign="top"><p>
 623       -Weffc++ complains too much
 624     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 625     Many warnings are emitted when <code class="option">-Weffc++</code> is used.  Making
 626     libstdc++ <code class="option">-Weffc++</code>-clean is not a goal of the project,
 627     for a few reasons.  Mainly, that option tries to enforce
 628     object-oriented programming, while the Standard Library isn't
 629     necessarily trying to be OO.
 630     </p><p>
 631     We do, however, try to have libstdc++ sources as clean as possible. If
 632     you see some simple changes that pacify <code class="option">-Weffc++</code>
 633     without other drawbacks, send us a patch.
 634     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.ambiguous_overloads"></a><a id="q-ambiguous_overloads"></a><p><strong>6.3.</strong></p></td><td align="left" valign="top"><p>
 635       Ambiguous overloads after including an old-style header
 636     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 637     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 638     comparison operator functions contained therein.  If they become
 639     visible in the same namespace as other comparison functions
 640     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the &lt;iterator&gt; header),
 641     then you will suddenly be faced with huge numbers of ambiguity
 642     errors.  This was discussed on the -v3 list; Nathan Myers
 643     <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 644       things up here</a>.  The collisions with vector/string iterator
 645     types have been fixed for 3.1.
 646     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.v2_headers"></a><a id="q-v2_headers"></a><p><strong>6.4.</strong></p></td><td align="left" valign="top"><p>
 647       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 648     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
 649         If you are using headers in
 650         <code class="filename">${prefix}/include/g++-3</code>, or if
 651         the installed library's name looks like
 652         <code class="filename">libstdc++-2.10.a</code> or
 653         <code class="filename">libstdc++-libc6-2.10.so</code>, then
 654         you are using the old libstdc++-v2 library, which is non-standard and
 655         unmaintained.  Do not report problems with -v2 to the -v3
 656         mailing list.
 657       </p><p>
 658         For GCC versions 3.0 and 3.1 the libstdc++ header files are installed in
 659         <code class="filename">${prefix}/include/g++-v3</code>
 660         (see the 'v'?).  Starting with version 3.2 the headers are installed in
 661         <code class="filename">${prefix}/include/c++/${version}</code>
 662         as this prevents headers from previous versions being found by mistake.
 663       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.boost_concept_checks"></a><a id="q-boost_concept_checks"></a><p><strong>6.5.</strong></p></td><td align="left" valign="top"><p>
 664       Errors about <span class="emphasis"><em>*Concept</em></span> and
 665       <span class="emphasis"><em>constraints</em></span> in the STL
 666     </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>
 667     If you see compilation errors containing messages about
 668     <span class="errortext">foo Concept</span> and something to do with a
 669     <span class="errortext">constraints</span> member function, then most
 670     likely you have violated one of the requirements for types used
 671     during instantiation of template containers and functions.  For
 672     example, EqualityComparableConcept appears if your types must be
 673     comparable with == and you have not provided this capability (a
 674     typo, or wrong visibility, or you just plain forgot, etc).
 675     </p><p>
 676     More information, including how to optionally enable/disable the
 677     checks, is available in the
 678     <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
 679     chapter of the manual.
 680     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><strong>6.6.</strong></p></td><td align="left" valign="top"><p>
 681       Program crashes when using library code in a
 682       dynamically-loaded library
 683     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 684     If you are using the C++ library across dynamically-loaded
 685     objects, make certain that you are passing the correct options
 686     when compiling and linking:
 687     </p><div class="literallayout"><p><br />
 688     Compile your library components:<br />
 689     <span class="command"><strong>g++ -fPIC -c a.cc</strong></span><br />
 690     <span class="command"><strong>g++ -fPIC -c b.cc</strong></span><br />
 691     ...<br />
 692     <span class="command"><strong>g++ -fPIC -c z.cc</strong></span><br />
 693 <br />
 694     Create your library:<br />
 695     <span class="command"><strong>g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o</strong></span><br />
 696 <br />
 697     Link the executable:<br />
 698     <span class="command"><strong>g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</strong></span><br />
 699     </p></div></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.memory_leaks"></a><a id="q-memory_leaks"></a><p><strong>6.7.</strong></p></td><td align="left" valign="top"><p>
 700       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 701     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
 702     A few people have reported that the standard containers appear
 703     to leak memory when tested with memory checkers such as
 704     <a class="link" href="http://valgrind.org/" target="_top"><span class="command"><strong>valgrind</strong></span></a>.
 705     Under some configurations the library's allocators keep free memory in a
 706     pool for later reuse, rather than returning it to the OS.  Although
 707     this memory is always reachable by the library and is never
 708     lost, memory debugging tools can report it as a leak.  If you
 709     want to test the library for memory leaks please read
 710     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 711     first.
 712     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.list_size_on"></a><a id="q-list_size_on"></a><p><strong>6.8.</strong></p></td><td align="left" valign="top"><p>
 713       list::size() is O(n)!
 714     </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>
 715     See
 716     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 717     chapter.
 718     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.easy_to_fix"></a><a id="q-easy_to_fix"></a><p><strong>6.9.</strong></p></td><td align="left" valign="top"><p>
 719       Aw, that's easy to fix!
 720     </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>
 721     If you have found a bug in the library and you think you have
 722     a working fix, then send it in!  The main GCC site has a page
 723     on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 724     patches</a> that covers the procedure, but for libstdc++ you
 725     should also send the patch to our mailing list in addition to
 726     the GCC patches mailing list.  The libstdc++
 727     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 728     also talks about how to submit patches.
 729     </p><p>
 730     In addition to the description, the patch, and the ChangeLog
 731     entry, it is a Good Thing if you can additionally create a small
 732     test program to test for the presence of the bug that your patch
 733     fixes.  Bugs have a way of being reintroduced; if an old bug
 734     creeps back in, it will be caught immediately by the testsuite -
 735     but only if such a test exists.
 736     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
 737       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 738     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 739       What's next after libstdc++?
 740     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 741       What about the STL from SGI?
 742     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 743       Extensions and Backward Compatibility
 744     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 745       Does libstdc++ support TR1?
 746     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 747     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 748       What's an ABI and why is it so messy?
 749     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 750       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 751     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.iterator_as_pod"></a><a id="faq.iterator_as_pod_q"></a><p><strong>7.1.</strong></p></td><td align="left" valign="top"><p>
 752       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 753     </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>
 754     If you have code that depends on container&lt;T&gt; iterators
 755     being implemented as pointer-to-T, your code is broken. It's
 756     considered a feature, not a bug, that libstdc++ points this out.
 757     </p><p>
 758     While there are arguments for iterators to be implemented in
 759     that manner, A) they aren't very good ones in the long term,
 760     and B) they were never guaranteed by the Standard anyway.  The
 761     type-safety achieved by making iterators a real class rather
 762     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 763     arguments.
 764     </p><p>
 765     Code which does assume that a vector iterator <code class="varname">i</code>
 766     is a pointer can often be fixed by changing <code class="varname">i</code> in
 767     certain expressions to <code class="varname">&amp;*i</code>.  Future revisions
 768     of the Standard are expected to bless this usage for
 769     vector&lt;&gt; (but not for basic_string&lt;&gt;).
 770     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_next"></a><a id="q-what_is_next"></a><p><strong>7.2.</strong></p></td><td align="left" valign="top"><p>
 771       What's next after libstdc++?
 772     </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>
 773         Hopefully, not much.  The goal of libstdc++ is to produce a
 774         fully-compliant, fully-portable Standard Library.  After that,
 775         we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
 776         more compliance work to do.
 777       </p><p>
 778         There is an effort underway to add significant extensions to
 779         the standard library specification.  The latest version of
 780         this effort is described in
 781          <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 782          The C++ Library Technical Report 1</a>.
 783       </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.sgi_stl"></a><a id="q-sgi_stl"></a><p><strong>7.3.</strong></p></td><td align="left" valign="top"><p>
 784       What about the STL from SGI?
 785     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 786       The <a class="link" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
 787     version 3.3, was the final merge of the STL codebase.  The
 788     code in libstdc++ contains many fixes and changes, and
 789     the SGI code is no longer under active
 790     development.  We expect that no future merges will take place.
 791     </p><p>
 792     In particular, <code class="classname">string</code> is not from SGI and makes no
 793     use of their "rope" class (which is included as an
 794     optional extension), nor is <code class="classname">valarray</code> and some others.
 795     Classes like <code class="classname">vector&lt;&gt;</code> are, but have been
 796     extensively modified.
 797     </p><p>
 798     More information on the evolution of libstdc++ can be found at the
 799     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 800     evolution</a>
 801     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 802     compatibility</a> documentation.
 803     </p><p>
 804     The <a class="link" href="http://www.sgi.com/tech/stl/FAQ.html" target="_top">FAQ</a>
 805     for SGI's STL is still recommended reading.
 806     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.extensions_and_backwards_compat"></a><a id="q-extensions_and_backwards_compat"></a><p><strong>7.4.</strong></p></td><td align="left" valign="top"><p>
 807       Extensions and Backward Compatibility
 808     </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>
 809       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.
 810     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.tr1_support"></a><a id="q-tr1_support"></a><p><strong>7.5.</strong></p></td><td align="left" valign="top"><p>
 811       Does libstdc++ support TR1?
 812     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 813     Yes.
 814     </p><p>
 815     The C++ Standard Library Technical Report adds many new features to
 816     the library.  The latest version of this effort is described in
 817     <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 818          Technical Report 1</a>.
 819     </p><p>
 820     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
 821     page</a>.
 822     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.get_iso_cxx"></a><a id="q-get_iso_cxx"></a><p><strong>7.6.</strong></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard?
 823     </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>
 824     Copies of the full ISO 14882 standard are available on line via
 825     the ISO mirror site for committee members.  Non-members, or those
 826     who have not paid for the privilege of sitting on the committee
 827     and sustained their two-meeting commitment for voting rights, may
 828     get a copy of the standard from their respective national
 829     standards organization.  In the USA, this national standards
 830     organization is ANSI and their website is
 831     right <a class="link" href="http://www.ansi.org" target="_top">here</a>.  (And if
 832     you've already registered with them, clicking this link will take
 833     you to directly to the place where you can
 834     <a class="link" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
 835     </p><p>
 836     Who is your country's member body?  Visit the
 837     <a class="link" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
 838     </p><p>
 839     The 2003 version of the standard (the 1998 version plus TC1) is
 840     available in print, ISBN 0-470-84674-7.
 841     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_abi"></a><a id="q-what_is_abi"></a><p><strong>7.7.</strong></p></td><td align="left" valign="top"><p>
 842       What's an ABI and why is it so messy?
 843     </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>
 844     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 845     Interface</span>”</span>.  Conventionally, it refers to a great
 846     mass of details about how arguments are arranged on the call
 847     stack and/or in registers, and how various types are arranged
 848     and padded in structs.  A single CPU design may suffer
 849     multiple ABIs designed by different development tool vendors
 850     who made different choices, or even by the same vendor for
 851     different target applications or compiler versions.  In ideal
 852     circumstances the CPU designer presents one ABI and all the
 853     OSes and compilers use it.  In practice every ABI omits
 854     details that compiler implementers (consciously or
 855     accidentally) must choose for themselves.
 856     </p><p>
 857     That ABI definition suffices for compilers to generate code so a
 858     program can interact safely with an OS and its lowest-level libraries.
 859     Users usually want an ABI to encompass more detail, allowing libraries
 860     built with different compilers (or different releases of the same
 861     compiler!) to be linked together.  For C++, this includes many more
 862     details than for C, and most CPU designers (for good reasons elaborated
 863     below) have not stepped up to publish C++ ABIs.  Such an ABI has been
 864     defined for the Itanium architecture (see
 865     <a class="link" href="http://www.codesourcery.com/cxx-abi/" target="_top">C++
 866     ABI for Itanium</a>) and that is used by G++ and other compilers
 867     as the de facto standard ABI on many common architectures (including x86).
 868     G++ can also use the ARM architecture's EABI, for embedded
 869     systems relying only on a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that
 870     doesn't include (much of) the standard library, and the GNU EABI for
 871     hosted implementations on ARM.  Those ABIs cover low-level details
 872     such as virtual function implementation, struct inheritance layout,
 873     name mangling, and exception handling.
 874    </p><p>
 875     A useful C++ ABI must also incorporate many details of the standard
 876     library implementation.  For a C ABI, the layouts of a few structs
 877     (such as <span class="type">FILE</span>, <span class="type">stat</span>, <span class="type">jmpbuf</span>,
 878     and the like) and a few macros suffice.
 879     For C++, the details include the complete set of names of functions
 880     and types used, the offsets of class members and virtual functions,
 881     and the actual definitions of all inlines.  C++ exposes many more
 882     library details to the caller than C does.  It makes defining
 883     a complete ABI a much bigger undertaking, and requires not just
 884     documenting library implementation details, but carefully designing
 885     those details so that future bug fixes and optimizations don't
 886     force breaking the ABI.
 887     </p><p>
 888     There are ways to help isolate library implementation details from the
 889     ABI, but they trade off against speed.  Library details used in inner
 890     loops (e.g., <code class="function">getchar</code>) must be exposed and frozen for
 891     all time, but many others may reasonably be kept hidden from user code,
 892     so they may later be changed.  Deciding which, and implementing
 893     the decisions, must happen before you can reasonably document a
 894     candidate C++ ABI that encompasses the standard library.
 895     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size_equals_capacity"></a><a id="q-size_equals_capacity"></a><p><strong>7.8.</strong></p></td><td align="left" valign="top"><p>
 896       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 897     </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>
 898     The standard idiom for deallocating a <code class="classname">vector&lt;T&gt;</code>'s
 899     unused memory is to create a temporary copy of the vector and swap their
 900     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 901     </p><div class="literallayout"><p><br />
 902      std::vector&lt;T&gt;(v).swap(v);<br />
 903     </p></div><p>
 904     The copy will take O(n) time and the swap is constant time.
 905     </p><p>
 906     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 907     strings</a> for a similar solution for strings.
 908     </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="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html>