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

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   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*;
  80       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" 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">
  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"><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>
 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      clauses 17 through 30 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 be browsed over
 117      the <a class="link" href="https://gcc.gnu.org/svn.html" target="_top">web</a>.
 118     </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>
 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 initial ISO C++ standardization effort gave the C++
 122     community a powerful set of reuseable tools in the form of the C++
 123     Standard Library.  However, for several years C++ implementations were
 124     (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
 125     incorrekt</span>”</span>, and many suffered from limitations of the compilers
 126     that used 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="link" href="https://gcc.gnu.org/" target="_top">GCC team</a>.  All of
 133     the rapid development and near-legendary
 134     <a class="link" href="https://gcc.gnu.org/buildstat.html" target="_top">portability</a>
 135     that are the hallmarks of an open-source project are applied to libstdc++.
 136     </p><p>
 137     All of the standard classes and functions from C++98/C++03, C++11 and C++14
 138     (such as <code class="classname">string</code>,
 139     <code class="classname">vector&lt;&gt;</code>, iostreams, algorithms etc.)
 140     are freely available and attempt to be fully compliant.
 141     Work is ongoing to complete support for the current revision of the
 142     ISO C++ Standard.
 143     </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>
 144       Who's in charge of it?
 145     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
 146      The libstdc++ project is contributed to by several developers
 147      all over the world, in the same way as GCC or the Linux kernel.
 148      The current maintainers are listed in the
 149      <a class="link" href="https://gcc.gnu.org/viewcvs/gcc/trunk/MAINTAINERS?view=co" target="_top"><code class="filename">MAINTAINERS</code></a>
 150      file (look for "c++ runtime libs").
 151     </p><p>
 152     Development and discussion is held on the libstdc++ mailing
 153     list.  Subscribing to the list, or searching the list
 154     archives, is open to everyone.  You can read instructions for
 155     doing so on the <a class="link" href="https://gcc.gnu.org/lists.html" target="_top">GCC mailing lists</a> page.
 156     If you have questions, ideas, code, or are just curious, sign up!
 157     </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>
 158       When is libstdc++ going to be finished?
 159     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
 160     Nathan Myers gave the best of all possible answers, responding to
 161     a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
 162     help.</em></span>
 163     </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>
 164       How do I contribute to the effort?
 165     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
 166     See the <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">Contributing</a> section in
 167     the manual. Subscribing to the mailing list (see above, or
 168     the homepage) is a very good idea if you have something to
 169     contribute, or if you have spare time and want to
 170     help. Contributions don't have to be in the form of source code;
 171     anybody who is willing to help write documentation, for example,
 172     or has found a bug in code that we all thought was working and is
 173     willing to provide details, is more than welcome!
 174     </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>
 175       What happened to the older libg++? I need that!
 176     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
 177     The last libg++ README states
 178     <span class="quote">“<span class="quote">This package is considered obsolete and is no longer
 179     being developed.</span>”</span>
 180     It should not be used for new projects, and won't even compile with
 181     recent releases of GCC (or most other C++ compilers).
 182     </p><p>
 183     More information can be found in the
 184     <a class="link" href="manual/backwards.html" title="Backwards Compatibility">Backwards
 185     Compatibility</a> section of the libstdc++ manual.
 186     </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>
 187       What if I have more questions?
 188     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
 189     If you have read the documentation, and your question remains
 190     unanswered, then just ask the mailing list. At present, you do not
 191     need to be subscribed to the list to send a message to it.  More
 192     information is available on the homepage (including how to browse
 193     the list archives); to send a message to the list,
 194     use <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code>.
 195     </p><p>
 196     If you have a question that you think should be included
 197     here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
 198     here, please send email to the libstdc++ mailing list, as above.
 199     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
 200       What are the license terms for libstdc++?
 201     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
 202       So any program which uses libstdc++ falls under the GPL?
 203     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
 204       How is that different from the GNU {Lesser,Library} GPL?
 205     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
 206       I see. So, what restrictions are there on programs that use the library?
 207     </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>
 208       What are the license terms for libstdc++?
 209     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
 210     See <a class="link" href="manual/license.html" title="License">our license description</a>
 211     for these and related questions.
 212     </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>
 213       So any program which uses libstdc++ falls under the GPL?
 214     </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>
 215      No. The special exception permits use of the library in
 216      proprietary applications.
 217     </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>
 218       How is that different from the GNU {Lesser,Library} GPL?
 219     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
 220       The LGPL requires that users be able to replace the LGPL code with a
 221      modified version; this is trivial if the library in question is a C
 222      shared library.  But there's no way to make that work with C++, where
 223      much of the library consists of inline functions and templates, which
 224      are expanded inside the code that uses the library.  So to allow people
 225      to replace the library code, someone using the library would have to
 226      distribute their own source, rendering the LGPL equivalent to the GPL.
 227     </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>
 228       I see. So, what restrictions are there on programs that use the library?
 229     </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>
 230       None.  We encourage such programs to be released as free software,
 231      but we won't punish you or sue you if you choose otherwise.
 232     </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++?
 233     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
 234     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
 235     </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?
 236     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
 237       What's libsupc++?
 238     </a></dt><dt>3.6. <a href="faq.html#faq.size">
 239       This library is HUGE!
 240     </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++?
 241     </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>
 242     Often libstdc++ comes pre-installed as an integral part of many
 243     existing GNU/Linux and Unix systems, as well as many embedded
 244     development tools. It may be necessary to install extra
 245     development packages to get the headers, or the documentation, or
 246     the source: please consult your vendor for details.
 247     </p><p>
 248     To build and install from the GNU GCC sources, please consult the
 249     <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
 250     documentation</a> for detailed
 251     instructions. You may wish to browse those files ahead
 252     of time to get a feel for what's required.
 253     </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?
 254     </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>
 255     Libstdc++ sources for all official releases can be obtained as
 256     part of the GCC sources, available from various sites and
 257     mirrors. A full <a class="link" href="https://gcc.gnu.org/mirrors.html" target="_top">list of
 258     download sites</a> is provided on the main GCC site.
 259     </p><p>
 260     Current libstdc++ sources can always be checked out of the main
 261     GCC source repository using the appropriate version control
 262     tool. At this time, that tool
 263     is <span class="application">Subversion</span>.
 264     </p><p>
 265     <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
 266     one of several revision control packages.  It was selected for GNU
 267     projects because it's free (speech), free (beer), and very high
 268     quality.  The <a class="link" href="http://subversion.tigris.org" target="_top"> Subversion
 269     home page</a> has a better description.
 270     </p><p>
 271     The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
 272     similar to anonymous FTP in that it allows anyone to retrieve
 273     the latest libstdc++ sources.
 274     </p><p>
 275     For more information
 276     see <a class="link" href="https://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
 277     details</a>.
 278     </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?
 279     </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>
 280     Libstdc++ comes with its own validation testsuite, which includes
 281     conformance testing, regression testing, ABI testing, and
 282     performance testing. Please consult the
 283     <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing
 284     documentation</a> for GCC and
 285     <a class="link" href="manual/test.html" title="Testing">Testing</a> in the libstdc++
 286     manual for more details.
 287     </p><p>
 288     If you find bugs in the testsuite programs themselves, or if you
 289     think of a new test program that should be added to the suite,
 290     <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
 291     </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?
 292     </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>
 293     Depending on your platform and library version, the error message might
 294     be similar to one of the following:
 295     </p><pre class="screen">
 296     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 297
 298     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
 299     </pre><p>
 300     This doesn't mean that the shared library isn't installed, only
 301     that the dynamic linker can't find it. When a dynamically-linked
 302     executable is run the linker finds and loads the required shared
 303     libraries by searching a pre-configured list of directories. If
 304     the directory where you've installed libstdc++ is not in this list
 305     then the libraries won't be found.
 306     </p><p>
 307     If you already have an older version of libstdc++ installed then the
 308     error might look like one of the following instead:
 309     </p><pre class="screen">
 310     ./a.out: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.20' not found
 311     ./a.out: /usr/lib/libstdc++.so.6: version `CXXABI_1.3.8' not found
 312     </pre><p>
 313     This means the linker found <code class="filename">/usr/lib/libstdc++.so.6</code>
 314     but that library belongs to an older version of GCC than was used to
 315     compile and link the program <code class="filename">a.out</code> (or some part
 316     of it). The program depends on code defined in the newer libstdc++
 317     that belongs to the newer version of GCC, so the linker must be told
 318     how to find the newer libstdc++ shared library.
 319     </p><p>
 320     The simplest way to fix this is
 321     to use the <code class="envar">LD_LIBRARY_PATH</code> environment variable,
 322     which is a colon-separated list of directories in which the linker
 323     will search for shared libraries:
 324     </p><pre class="screen"><span class="command"><strong>
 325     export LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 326     </strong></span></pre><p>
 327     Here the shell variable <code class="varname">${prefix}</code> is assumed to contain
 328     the directory prefix where GCC was installed to. The directory containing
 329     the library might depend on whether you want the 32-bit or 64-bit copy
 330     of the library, so for example would be
 331     <code class="filename">${prefix}/lib64</code> on some systems.
 332     The exact environment variable to use will depend on your
 333     platform, e.g. <code class="envar">DYLD_LIBRARY_PATH</code> for Darwin,
 334     <code class="envar">LD_LIBRARY_PATH_32</code>/<code class="envar">LD_LIBRARY_PATH_64</code>
 335     for Solaris 32-/64-bit,
 336     and <code class="envar">SHLIB_PATH</code> for HP-UX.
 337     </p><p>
 338     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 339     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 340     linker has different names on different platforms but the man page
 341     is usually called something such as <code class="filename">ld.so</code>,
 342     <code class="filename">rtld</code> or <code class="filename">dld.so</code>.
 343     </p><p>
 344     Using <code class="envar">LD_LIBRARY_PATH</code> is not always the best solution,
 345     <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
 346     Libraries</a> in the manual gives some alternatives.
 347     </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>
 348       What's libsupc++?
 349     </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>
 350       If the only functions from <code class="filename">libstdc++.a</code>
 351       which you need are language support functions (those listed in
 352       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 353       standard, e.g., <code class="function">new</code> and
 354       <code class="function">delete</code>), then try linking against
 355       <code class="filename">libsupc++.a</code>, which is a subset of
 356       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 357       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 358       <code class="filename">libsupc++.a</code> via <code class="option">-lsupc++</code>
 359       for the final link step will do it).  This library contains only
 360       those support routines, one per object file.  But if you are
 361       using anything from the rest of the library, such as IOStreams
 362       or vectors, then you'll still need pieces from
 363       <code class="filename">libstdc++.a</code>.
 364     </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>
 365       This library is HUGE!
 366     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 367     Usually the size of libraries on disk isn't noticeable.  When a
 368     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 369     static archive library, only the necessary object files are copied
 370     into your executable, not the entire library.  Unfortunately, even
 371     if you only need a single function or variable from an object file,
 372     the entire object file is extracted.  (There's nothing unique to C++
 373     or libstdc++ about this; it's just common behavior, given here
 374     for background reasons.)
 375     </p><p>
 376     Some of the object files which make up
 377     <code class="filename">libstdc++.a</code> are rather large.
 378     If you create a statically-linked executable with
 379     <code class="option">-static</code>, those large object files are suddenly part
 380     of your executable.  Historically the best way around this was to
 381     only place a very few functions (often only a single one) in each
 382     source/object file; then extracting a single function is the same
 383     as extracting a single <code class="filename">.o</code> file.  For libstdc++ this
 384     is only possible to a certain extent; the object files in question contain
 385     template classes and template functions, pre-instantiated, and
 386     splitting those up causes severe maintenance headaches.
 387     </p><p>
 388     On supported platforms, libstdc++ takes advantage of garbage
 389     collection in the GNU linker to get a result similar to separating
 390     each symbol into a separate source and object files. On these platforms,
 391     GNU ld can place each function and variable into its own
 392     section in a <code class="filename">.o</code> file.  The GNU linker can then perform
 393     garbage collection on unused sections; this reduces the situation to only
 394     copying needed functions into the executable, as before, but all
 395     happens automatically.
 396     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
 397       Can libstdc++ be used with non-GNU compilers?
 398     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 399       No 'long long' type on Solaris?
 400     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 401       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 402     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 403       Mac OS X ctype.h is broken! How can I fix it?
 404     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 405       Threading is broken on i386?
 406     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 407       MIPS atomic operations
 408     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 409       Recent GNU/Linux glibc required?
 410     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 411       Can't use wchar_t/wstring on FreeBSD
 412     </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>
 413       Can libstdc++ be used with non-GNU compilers?
 414     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 415     Perhaps.
 416     </p><p>
 417     Since the goal of ISO Standardization is for all C++
 418     implementations to be able to share code, libstdc++ should be
 419     usable under any ISO-compliant compiler, at least in theory.
 420     </p><p>
 421     However, the reality is that libstdc++ is targeted and optimized
 422     for GCC/G++. This means that often libstdc++ uses specific,
 423     non-standard features of G++ that are not present in older
 424     versions of proprietary compilers. It may take as much as a year or two
 425     after an official release of GCC that contains these features for
 426     proprietary tools to support these constructs.
 427     </p><p>
 428     Recent versions of libstdc++ are known to work with the Clang compiler.
 429     In the near past, specific released versions of libstdc++ have
 430     been known to work with versions of the EDG C++ compiler, and
 431     vendor-specific proprietary C++ compilers such as the Intel ICC
 432     C++ compiler.
 433     </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>
 434       No '<span class="type">long long</span>' type on Solaris?
 435     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-solaris_long_long"></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>
 436     By default we try to support the C99 <span class="type">long long</span> type.
 437     This requires that certain functions from your C library be present.
 438     </p><p>
 439     Up through release 3.0.2 the platform-specific tests performed by
 440     libstdc++ were too general, resulting in a conservative approach
 441     to enabling the <span class="type">long long</span> code paths. The most
 442     commonly reported platform affected was Solaris.
 443     </p><p>
 444     This has been fixed for libstdc++ releases greater than 3.0.3.
 445     </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>
 446       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 447     </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>)
 448          always defines the preprocessor macro
 449          <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 450          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 451          other macros and other platforms are also affected.)
 452       </p><p>These macros are typically used in C library headers, guarding new
 453          versions of functions from their older versions.  The C++98 standard
 454          library includes the C standard library, but it requires the C90
 455          version, which for backwards-compatibility reasons is often not the
 456          default for many vendors.
 457       </p><p>More to the point, the C++ standard requires behavior which is only
 458          available on certain platforms after certain symbols are defined.
 459          Usually the issue involves I/O-related typedefs.  In order to
 460          ensure correctness, the compiler simply predefines those symbols.
 461       </p><p>Note that it's not enough to <code class="literal">#define</code> them only when the library is
 462          being built (during installation).  Since we don't have an 'export'
 463          keyword, much of the library exists as headers, which means that
 464          the symbols must also be defined as your programs are parsed and
 465          compiled.
 466       </p><p>To see which symbols are defined, look for
 467          <code class="varname">CPLUSPLUS_CPP_SPEC</code> in
 468          the gcc config headers for your target (and try changing them to
 469          see what happens when building complicated code).  You can also run
 470          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 471          a list of predefined macros for any particular installation.
 472       </p><p>This has been discussed on the mailing lists
 473          <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>.
 474       </p><p>This method is something of a wart.  We'd like to find a cleaner
 475          solution, but nobody yet has contributed the time.
 476       </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>
 477       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 478     </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>
 479          This was a long-standing bug in the OS X support.  Fortunately, the
 480          <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top">patch</a>
 481          was quite simple, and well-known.
 482       </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>
 483       Threading is broken on i386?
 484     </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
 485          platforms.  The assembly code accidentally used opcodes that are
 486          only available on the i486 and later.  So if you configured GCC
 487          to target, for example, i386-linux, but actually used the programs
 488          on an i686, then you would encounter no problems.  Only when
 489          actually running the code on a i386 will the problem appear.
 490       </p><p>This is fixed in 3.2.2.
 491       </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>
 492       MIPS atomic operations
 493     </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>
 494     The atomic locking routines for MIPS targets requires MIPS II
 495     and later.  A patch went in just after the 3.3 release to
 496     make mips* use the generic implementation instead.  You can also
 497     configure for mipsel-elf as a workaround.
 498     </p><p>
 499     The mips*-*-linux* port continues to use the MIPS II routines, and more
 500     work in this area is expected.
 501     </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>
 502       Recent GNU/Linux glibc required?
 503     </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
 504          5.0.1) and later uses localization and formatting code from the system
 505          C library (glibc) version 2.2.5 which contains necessary bugfixes.
 506          All GNU/Linux distros make more recent versions available now.
 507          libstdc++ 4.6.0 and later require glibc 2.3 or later for this
 508          localization and formatting code.
 509       </p><p>The guideline is simple:  the more recent the C++ library, the
 510          more recent the C library.  (This is also documented in the main
 511          GCC installation instructions.)
 512       </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>
 513       Can't use <span class="type">wchar_t</span>/<code class="classname">wstring</code> on FreeBSD
 514     </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>
 515     Older versions of FreeBSD's C library do not have sufficient
 516     support for wide character functions, and as a result the
 517     libstdc++ configury decides that <span class="type">wchar_t</span> support should be
 518     disabled. In addition, the libstdc++ platform checks that
 519     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 520     enough to detect when the minimal support to
 521     enable <span class="type">wchar_t</span> and C++ library structures
 522     like <code class="classname">wstring</code> were present. This impacted Solaris,
 523     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 524     </p><p>
 525     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
 526       What works already?
 527     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 528       Bugs in the ISO C++ language or library specification
 529     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 530       Bugs in the compiler (gcc/g++) and not libstdc++
 531     </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>
 532       What works already?
 533     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 534     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 535     except for some corner cases.  Support for localization
 536     in <code class="classname">locale</code> may be incomplete on some non-GNU
 537     platforms. Also dependent on the underlying platform is support
 538     for <span class="type">wchar_t</span> and <span class="type">long
 539     long</span> specializations, and details of thread support.
 540     </p><p>
 541     Long answer: See the implementation status pages for
 542     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 543     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 544     <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>.
 545     <a class="link" href="manual/status.html#status.iso.2014" title="C++ 2014">C++14</a>.
 546     </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>
 547       Bugs in the ISO C++ language or library specification
 548     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 549     Unfortunately, there are some.
 550     </p><p>
 551     For those people who are not part of the ISO Library Group
 552     (i.e., nearly all of us needing to read this page in the first
 553     place), a public list of the library defects is occasionally
 554     published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
 555     website</a>.
 556     Many of these issues have resulted in
 557     <a class="link" href="manual/bugs.html#manual.intro.status.bugs.iso" title="Standard Bugs">code changes in libstdc++</a>.
 558     </p><p>
 559     If you think you've discovered a new bug that is not listed,
 560     please post a message describing your problem to the author of
 561     the library issues list.
 562     </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>
 563       Bugs in the compiler (gcc/g++) and not libstdc++
 564     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 565     On occasion, the compiler is wrong. Please be advised that this
 566     happens much less often than one would think, and avoid jumping to
 567     conclusions.
 568     </p><p>
 569     First, examine the ISO C++ standard. Second, try another compiler
 570     or an older version of the GNU compilers. Third, you can find more
 571     information on the libstdc++ and the GCC mailing lists: search
 572     these lists with terms describing your issue.
 573     </p><p>
 574     Before reporting a bug, please examine the
 575     <a class="link" href="https://gcc.gnu.org/bugs/" target="_top">bugs database</a>, with the
 576     component set to <span class="quote">“<span class="quote">c++</span>”</span>.
 577     </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">
 578       Reopening a stream fails
 579     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 580       -Weffc++ complains too much
 581     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 582       Ambiguous overloads after including an old-style header
 583     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 584       The g++-3 headers are not ours
 585     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 586       Errors about *Concept and
 587       constraints in the STL
 588     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 589       Program crashes when using library code in a
 590       dynamically-loaded library
 591     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 592       “Memory leaks” in containers
 593     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 594       list::size() is O(n)!
 595     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 596       Aw, that's easy to fix!
 597     </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>
 598       Reopening a stream fails
 599     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-stream_reopening_fails"></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>
 600     Prior to GCC 4.0 this was one of the most-reported non-bug reports.
 601     Executing a sequence like this would fail:
 602     </p><pre class="programlisting">
 603     #include &lt;fstream&gt;
 604     ...
 605     std::fstream  fs("a_file");
 606     // .
 607     // . do things with fs...
 608     // .
 609     fs.close();
 610     fs.open("a_new_file");
 611     </pre><p>
 612     All operations on the re-opened <code class="varname">fs</code> would fail, or at
 613     least act very strangely, especially if <code class="varname">fs</code> reached the
 614     EOF state on the previous file.
 615     The original C++98 standard did not specify behavior in this case, and
 616     the <a class="link" href="manual/bugs.html#manual.bugs.dr22">resolution of DR #22</a> was to
 617     leave the state flags unchanged on a successful call to
 618     <code class="function">open()</code>.
 619     You had to insert a call to <code class="function">fs.clear()</code> between the
 620     calls to <code class="function">close()</code> and <code class="function">open()</code>,
 621     and then everything will work as expected.
 622     <span class="emphasis"><em>Update:</em></span> For GCC 4.0 we implemented the resolution
 623     of <a class="link" href="manual/bugs.html#manual.bugs.dr409">DR #409</a> and
 624     <code class="function">open()</code>
 625     now calls <code class="function">clear()</code> on success.
 626     </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>
 627       -Weffc++ complains too much
 628     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 629     Many warnings are emitted when <code class="option">-Weffc++</code> is used.  Making
 630     libstdc++ <code class="option">-Weffc++</code>-clean is not a goal of the project,
 631     for a few reasons.  Mainly, that option tries to enforce
 632     object-oriented programming, while the Standard Library isn't
 633     necessarily trying to be OO. The option also enforces outdated guidelines
 634     from old editions of the books, and the advice isn't all relevant to
 635     modern C++ (especially C++11 and later).
 636     </p><p>
 637     We do, however, try to have libstdc++ sources as clean as possible. If
 638     you see some simple changes that pacify <code class="option">-Weffc++</code>
 639     without other drawbacks, send us a patch.
 640     </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>
 641       Ambiguous overloads after including an old-style header
 642     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 643     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 644     comparison operator functions contained therein.  If they become
 645     visible in the same namespace as other comparison functions
 646     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the
 647     <code class="filename">&lt;iterator&gt;</code> header),
 648     then you will suddenly be faced with huge numbers of ambiguity
 649     errors.  This was discussed on the mailing list; Nathan Myers
 650     <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 651       things up here</a>.  The collisions with vector/string iterator
 652     types have been fixed for 3.1.
 653     </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>
 654       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 655     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></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>
 656         If you are using headers in
 657         <code class="filename">${prefix}/include/g++-3</code>, or if
 658         the installed library's name looks like
 659         <code class="filename">libstdc++-2.10.a</code> or
 660         <code class="filename">libstdc++-libc6-2.10.so</code>, then
 661         you are using the old libstdc++-v2 library, which is non-standard and
 662         unmaintained.  Do not report problems with -v2 to the -v3
 663         mailing list.
 664       </p><p>
 665         For GCC versions 3.0 and 3.1 the libstdc++ header files are installed in
 666         <code class="filename">${prefix}/include/g++-v3</code>
 667         (see the 'v'?).  Starting with version 3.2 the headers are installed in
 668         <code class="filename">${prefix}/include/c++/${version}</code>
 669         as this prevents headers from previous versions being found by mistake.
 670       </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>
 671       Errors about <span class="emphasis"><em>*Concept</em></span> and
 672       <span class="emphasis"><em>constraints</em></span> in the STL
 673     </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>
 674     If you see compilation errors containing messages about
 675     <span class="errortext">foo Concept</span> and something to do with a
 676     <span class="errortext">constraints</span> member function, then most
 677     likely you have violated one of the requirements for types used
 678     during instantiation of template containers and functions.  For
 679     example, EqualityComparableConcept appears if your types must be
 680     comparable with == and you have not provided this capability (a
 681     typo, or wrong visibility, or you just plain forgot, etc).
 682     </p><p>
 683     More information, including how to optionally enable/disable the
 684     checks, is available in the
 685     <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
 686     chapter of the manual.
 687     </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>
 688       Program crashes when using library code in a
 689       dynamically-loaded library
 690     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 691     If you are using the C++ library across dynamically-loaded
 692     objects, make certain that you are passing the correct options
 693     when compiling and linking:
 694     </p><div class="literallayout"><p><br />
 695     Compile your library components:<br />
 696     <span class="command"><strong>g++ -fPIC -c a.cc</strong></span><br />
 697     <span class="command"><strong>g++ -fPIC -c b.cc</strong></span><br />
 698     ...<br />
 699     <span class="command"><strong>g++ -fPIC -c z.cc</strong></span><br />
 700 <br />
 701     Create your library:<br />
 702     <span class="command"><strong>g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o</strong></span><br />
 703 <br />
 704     Link the executable:<br />
 705     <span class="command"><strong>g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</strong></span><br />
 706     </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>
 707       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 708     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></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>
 709     A few people have reported that the standard containers appear
 710     to leak memory when tested with memory checkers such as
 711     <a class="link" href="http://valgrind.org/" target="_top"><span class="command"><strong>valgrind</strong></span></a>.
 712     Under some (non-default) configurations the library's allocators keep
 713     free memory in a
 714     pool for later reuse, rather than returning it to the OS.  Although
 715     this memory is always reachable by the library and is never
 716     lost, memory debugging tools can report it as a leak.  If you
 717     want to test the library for memory leaks please read
 718     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 719     first.
 720     </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>
 721       <code class="code">list::size()</code> is O(n)!
 722     </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>
 723     See
 724     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 725     chapter.
 726     </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>
 727       Aw, that's easy to fix!
 728     </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>
 729     If you have found a bug in the library and you think you have
 730     a working fix, then send it in!  The main GCC site has a page
 731     on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 732     patches</a> that covers the procedure, but for libstdc++ you
 733     should also send the patch to our mailing list in addition to
 734     the GCC patches mailing list.  The libstdc++
 735     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 736     also talks about how to submit patches.
 737     </p><p>
 738     In addition to the description, the patch, and the ChangeLog
 739     entry, it is a Good Thing if you can additionally create a small
 740     test program to test for the presence of the bug that your patch
 741     fixes.  Bugs have a way of being reintroduced; if an old bug
 742     creeps back in, it will be caught immediately by the testsuite -
 743     but only if such a test exists.
 744     </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">
 745       string::iterator is not char*;
 746       vector&lt;T&gt;::iterator is not T*
 747     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 748       What's next after libstdc++?
 749     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 750       What about the STL from SGI?
 751     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 752       Extensions and Backward Compatibility
 753     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 754       Does libstdc++ support TR1?
 755     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 756     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 757       What's an ABI and why is it so messy?
 758     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 759       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 760     </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>
 761       <code class="classname">string::iterator</code> is not <code class="code">char*</code>;
 762       <code class="classname">vector&lt;T&gt;::iterator</code> is not <code class="code">T*</code>
 763     </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>
 764     If you have code that depends on container&lt;T&gt; iterators
 765     being implemented as pointer-to-T, your code is broken. It's
 766     considered a feature, not a bug, that libstdc++ points this out.
 767     </p><p>
 768     While there are arguments for iterators to be implemented in
 769     that manner, A) they aren't very good ones in the long term,
 770     and B) they were never guaranteed by the Standard anyway.  The
 771     type-safety achieved by making iterators a real class rather
 772     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 773     arguments.
 774     </p><p>
 775     Code which does assume that a vector/string iterator <code class="varname">i</code>
 776     is a pointer can often be fixed by changing <code class="varname">i</code> in
 777     certain expressions to <code class="varname">&amp;*i</code>.
 778     </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>
 779       What's next after libstdc++?
 780     </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>
 781         The goal of libstdc++ is to produce a
 782         fully-compliant, fully-portable Standard Library.
 783         While the C++ Standard continues to evolve the libstdc++ will
 784         continue to track it.
 785       </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>
 786       What about the STL from SGI?
 787     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 788     The STL (Standard Template Library) was the inspiration for large chunks
 789     of the C++ Standard Library, but the terms are not interchangeable and
 790     they don't mean the same thing. The C++ Standard Library includes lots of
 791     things that didn't come from the STL, and some of them aren't even
 792     templates, such as <code class="classname">std::locale</code> and
 793     <code class="classname">std::thread</code>.
 794     </p><p>
 795     Libstdc++-v3 incorporates a lot of code from
 796     <a class="link" href="http://www.sgi.com/tech/stl/" target="_top">the SGI STL</a>
 797     (the final merge was from
 798     <a class="link" href="http://www.sgi.com/tech/stl/whats_new.html" target="_top">release 3.3</a>).
 799     The code in libstdc++ contains many fixes and changes compared to the
 800     original SGI code.
 801     </p><p>
 802     In particular, <code class="classname">string</code> is not from SGI and makes no
 803     use of their "rope" class (although that is included as an optional
 804     extension), neither is <code class="classname">valarray</code> nor some others.
 805     Classes like <code class="classname">vector&lt;&gt;</code> were from SGI, but have
 806     been extensively modified.
 807     </p><p>
 808     More information on the evolution of libstdc++ can be found at the
 809     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 810     evolution</a>
 811     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 812     compatibility</a> documentation.
 813     </p><p>
 814     The <a class="link" href="http://www.sgi.com/tech/stl/FAQ.html" target="_top">FAQ</a>
 815     for SGI's STL is still recommended reading.
 816     </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>
 817       Extensions and Backward Compatibility
 818     </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>
 819       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.
 820     </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>
 821       Does libstdc++ support TR1?
 822     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 823     Yes.
 824     </p><p>
 825     The C++ Standard Library
 826     <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 827     Technical Report 1</a> added many new features to the library.
 828     </p><p>
 829     The implementation status of TR1 in libstdc++ can be tracked
 830     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status page</a>.
 831     </p><p>
 832     New code should probably not use TR1, because almost everything in it has
 833     been added to the main C++ Standard Library (usually with significant
 834     improvements).
 835     The TR1 implementation in libstdc++ is no longer actively maintained.
 836     </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?
 837     </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>
 838     Please refer to the <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">Contributing</a>
 839     section in our manual.
 840     </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>
 841       What's an ABI and why is it so messy?
 842     </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>
 843     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 844     Interface</span>”</span>.  Conventionally, it refers to a great
 845     mass of details about how arguments are arranged on the call
 846     stack and/or in registers, and how various types are arranged
 847     and padded in structs.  A single CPU design may suffer
 848     multiple ABIs designed by different development tool vendors
 849     who made different choices, or even by the same vendor for
 850     different target applications or compiler versions.  In ideal
 851     circumstances the CPU designer presents one ABI and all the
 852     OSes and compilers use it.  In practice every ABI omits
 853     details that compiler implementers (consciously or
 854     accidentally) must choose for themselves.
 855     </p><p>
 856     That ABI definition suffices for compilers to generate code so a
 857     program can interact safely with an OS and its lowest-level libraries.
 858     Users usually want an ABI to encompass more detail, allowing libraries
 859     built with different compilers (or different releases of the same
 860     compiler!) to be linked together.  For C++, this includes many more
 861     details than for C, and most CPU designers (for good reasons elaborated
 862     below) have not stepped up to publish C++ ABIs.  Such an ABI has been
 863     defined for the Itanium architecture (see
 864     <a class="link" href="https://itanium-cxx-abi.github.io/cxx-abi/" target="_top">C++
 865     ABI for Itanium</a>) and that is used by G++ and other compilers
 866     as the de facto standard ABI on many common architectures (including x86).
 867     G++ can also use the ARM architecture's EABI, for embedded
 868     systems relying only on a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that
 869     doesn't include (much of) the standard library, and the GNU EABI for
 870     hosted implementations on ARM.  Those ABIs cover low-level details
 871     such as virtual function implementation, struct inheritance layout,
 872     name mangling, and exception handling.
 873    </p><p>
 874     A useful C++ ABI must also incorporate many details of the standard
 875     library implementation.  For a C ABI, the layouts of a few structs
 876     (such as <span class="type">FILE</span>, <span class="type">stat</span>, <span class="type">jmpbuf</span>,
 877     and the like) and a few macros suffice.
 878     For C++, the details include the complete set of names of functions
 879     and types used, the offsets of class members and virtual functions,
 880     and the actual definitions of all inlines.  C++ exposes many more
 881     library details to the caller than C does.  It makes defining
 882     a complete ABI a much bigger undertaking, and requires not just
 883     documenting library implementation details, but carefully designing
 884     those details so that future bug fixes and optimizations don't
 885     force breaking the ABI.
 886     </p><p>
 887     There are ways to help isolate library implementation details from the
 888     ABI, but they trade off against speed.  Library details used in inner
 889     loops (e.g., <code class="function">getchar</code>) must be exposed and frozen for
 890     all time, but many others may reasonably be kept hidden from user code,
 891     so they may later be changed.  Deciding which, and implementing
 892     the decisions, must happen before you can reasonably document a
 893     candidate C++ ABI that encompasses the standard library.
 894     </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>
 895       How do I make <code class="code">std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size</code>?
 896     </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>
 897     Since C++11 just call the <code class="function">shrink_to_fit()</code> member
 898     function.
 899     </p><p>
 900     Before C++11, the standard idiom for deallocating a
 901     <code class="classname">vector&lt;T&gt;</code>'s
 902     unused memory was to create a temporary copy of the vector and swap their
 903     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 904     </p><div class="literallayout"><p><br />
 905      std::vector&lt;T&gt;(v).swap(v);<br />
 906     </p></div><p>
 907     The copy will take O(n) time and the swap is constant time.
 908     </p><p>
 909     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 910     strings</a> for a similar solution for strings.
 911     </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>