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

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   3       2008-2018
   4
   5       <a class="link" href="https://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 C++ Standard Library as described in
 113      clauses 20 through 33 and annex D (prior to the 2017 standard
 114      the library clauses started with 17).  For those who want to see
 115      exactly how far the project has come, or just want the latest
 116      bleeding-edge code, the up-to-date source is available over
 117      anonymous SVN, and can be browsed over the
 118      <a class="link" href="https://gcc.gnu.org/svn.html" target="_top">web</a>.
 119     </p><p>
 120     N.B. The library is called libstdc++ <span class="emphasis"><em>not</em></span> stdlibc++.
 121     </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>
 122       Why should I use libstdc++?
 123     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
 124     The completion of the initial ISO C++ standardization effort gave the C++
 125     community a powerful set of reuseable tools in the form of the C++
 126     Standard Library.  However, for several years C++ implementations were
 127     (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
 128     incorrekt</span>”</span>, and many suffered from limitations of the compilers
 129     that used them.
 130     </p><p>
 131     The GNU compiler collection
 132     (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
 133     considered to be one of the leading compilers in the world.  Its
 134     development is overseen by the
 135     <a class="link" href="https://gcc.gnu.org/" target="_top">GCC team</a>.  All of
 136     the rapid development and near-legendary
 137     <a class="link" href="https://gcc.gnu.org/buildstat.html" target="_top">portability</a>
 138     that are the hallmarks of an open-source project are applied to libstdc++.
 139     </p><p>
 140     All of the standard classes and functions from C++98/C++03, C++11 and C++14
 141     (such as <code class="classname">string</code>,
 142     <code class="classname">vector&lt;&gt;</code>, iostreams, algorithms etc.)
 143     are freely available and attempt to be fully compliant.
 144     Work is ongoing to complete support for the current revision of the
 145     ISO C++ Standard.
 146     </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>
 147       Who's in charge of it?
 148     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
 149      The libstdc++ project is contributed to by several developers
 150      all over the world, in the same way as GCC or the Linux kernel.
 151      The current maintainers are listed in the
 152      <a class="link" href="https://gcc.gnu.org/viewcvs/gcc/trunk/MAINTAINERS?view=co" target="_top"><code class="filename">MAINTAINERS</code></a>
 153      file (look for "c++ runtime libs").
 154     </p><p>
 155     Development and discussion is held on the libstdc++ mailing
 156     list.  Subscribing to the list, or searching the list
 157     archives, is open to everyone.  You can read instructions for
 158     doing so on the <a class="link" href="https://gcc.gnu.org/lists.html" target="_top">GCC mailing lists</a> page.
 159     If you have questions, ideas, code, or are just curious, sign up!
 160     </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>
 161       When is libstdc++ going to be finished?
 162     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
 163     Nathan Myers gave the best of all possible answers, responding to
 164     a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
 165     help.</em></span>
 166     </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>
 167       How do I contribute to the effort?
 168     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
 169     See the <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">Contributing</a> section in
 170     the manual. Subscribing to the mailing list (see above, or
 171     the homepage) is a very good idea if you have something to
 172     contribute, or if you have spare time and want to
 173     help. Contributions don't have to be in the form of source code;
 174     anybody who is willing to help write documentation, for example,
 175     or has found a bug in code that we all thought was working and is
 176     willing to provide details, is more than welcome!
 177     </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>
 178       What happened to the older libg++? I need that!
 179     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
 180     The last libg++ README states
 181     <span class="quote">“<span class="quote">This package is considered obsolete and is no longer
 182     being developed.</span>”</span>
 183     It should not be used for new projects, and won't even compile with
 184     recent releases of GCC (or most other C++ compilers).
 185     </p><p>
 186     More information can be found in the
 187     <a class="link" href="manual/backwards.html" title="Backwards Compatibility">Backwards
 188     Compatibility</a> section of the libstdc++ manual.
 189     </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>
 190       What if I have more questions?
 191     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
 192     If you have read the documentation, and your question remains
 193     unanswered, then just ask the mailing list. At present, you do not
 194     need to be subscribed to the list to send a message to it.  More
 195     information is available on the homepage (including how to browse
 196     the list archives); to send a message to the list,
 197     use <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code>.
 198     </p><p>
 199     If you have a question that you think should be included
 200     here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
 201     here, please send email to the libstdc++ mailing list, as above.
 202     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
 203       What are the license terms for libstdc++?
 204     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
 205       So any program which uses libstdc++ falls under the GPL?
 206     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
 207       How is that different from the GNU {Lesser,Library} GPL?
 208     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
 209       I see. So, what restrictions are there on programs that use the library?
 210     </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>
 211       What are the license terms for libstdc++?
 212     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
 213     See <a class="link" href="manual/license.html" title="License">our license description</a>
 214     for these and related questions.
 215     </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>
 216       So any program which uses libstdc++ falls under the GPL?
 217     </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>
 218      No. The special exception permits use of the library in
 219      proprietary applications.
 220     </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>
 221       How is that different from the GNU {Lesser,Library} GPL?
 222     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
 223       The LGPL requires that users be able to replace the LGPL code with a
 224      modified version; this is trivial if the library in question is a C
 225      shared library.  But there's no way to make that work with C++, where
 226      much of the library consists of inline functions and templates, which
 227      are expanded inside the code that uses the library.  So to allow people
 228      to replace the library code, someone using the library would have to
 229      distribute their own source, rendering the LGPL equivalent to the GPL.
 230     </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>
 231       I see. So, what restrictions are there on programs that use the library?
 232     </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>
 233       None.  We encourage such programs to be released as free software,
 234      but we won't punish you or sue you if you choose otherwise.
 235     </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++?
 236     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
 237     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
 238     </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?
 239     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
 240       What's libsupc++?
 241     </a></dt><dt>3.6. <a href="faq.html#faq.size">
 242       This library is HUGE!
 243     </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++?
 244     </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>
 245     Often libstdc++ comes pre-installed as an integral part of many
 246     existing GNU/Linux and Unix systems, as well as many embedded
 247     development tools. It may be necessary to install extra
 248     development packages to get the headers, or the documentation, or
 249     the source: please consult your vendor for details.
 250     </p><p>
 251     To build and install from the GNU GCC sources, please consult the
 252     <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
 253     documentation</a> for detailed
 254     instructions. You may wish to browse those files ahead
 255     of time to get a feel for what's required.
 256     </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?
 257     </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>
 258     Libstdc++ sources for all official releases can be obtained as
 259     part of the GCC sources, available from various sites and
 260     mirrors. A full <a class="link" href="https://gcc.gnu.org/mirrors.html" target="_top">list of
 261     download sites</a> is provided on the main GCC site.
 262     </p><p>
 263     Current libstdc++ sources can always be checked out of the main
 264     GCC source repository using the appropriate version control
 265     tool. At this time, that tool
 266     is <span class="application">Subversion</span>.
 267     </p><p>
 268     <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
 269     one of several revision control packages.  It was selected for GNU
 270     projects because it's free (speech), free (beer), and very high
 271     quality.  The <a class="link" href="http://subversion.tigris.org" target="_top"> Subversion
 272     home page</a> has a better description.
 273     </p><p>
 274     The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
 275     similar to anonymous FTP in that it allows anyone to retrieve
 276     the latest libstdc++ sources.
 277     </p><p>
 278     For more information
 279     see <a class="link" href="https://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
 280     details</a>.
 281     </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?
 282     </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>
 283     Libstdc++ comes with its own validation testsuite, which includes
 284     conformance testing, regression testing, ABI testing, and
 285     performance testing. Please consult the
 286     <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing
 287     documentation</a> for GCC and
 288     <a class="link" href="manual/test.html" title="Testing">Testing</a> in the libstdc++
 289     manual for more details.
 290     </p><p>
 291     If you find bugs in the testsuite programs themselves, or if you
 292     think of a new test program that should be added to the suite,
 293     <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
 294     </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?
 295     </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>
 296     Depending on your platform and library version, the error message might
 297     be similar to one of the following:
 298     </p><pre class="screen">
 299     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 300
 301     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
 302     </pre><p>
 303     This doesn't mean that the shared library isn't installed, only
 304     that the dynamic linker can't find it. When a dynamically-linked
 305     executable is run the linker finds and loads the required shared
 306     libraries by searching a pre-configured list of directories. If
 307     the directory where you've installed libstdc++ is not in this list
 308     then the libraries won't be found.
 309     </p><p>
 310     If you already have an older version of libstdc++ installed then the
 311     error might look like one of the following instead:
 312     </p><pre class="screen">
 313     ./a.out: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.20' not found
 314     ./a.out: /usr/lib/libstdc++.so.6: version `CXXABI_1.3.8' not found
 315     </pre><p>
 316     This means the linker found <code class="filename">/usr/lib/libstdc++.so.6</code>
 317     but that library belongs to an older version of GCC than was used to
 318     compile and link the program <code class="filename">a.out</code> (or some part
 319     of it). The program depends on code defined in the newer libstdc++
 320     that belongs to the newer version of GCC, so the linker must be told
 321     how to find the newer libstdc++ shared library.
 322     </p><p>
 323     The simplest way to fix this is
 324     to use the <code class="envar">LD_LIBRARY_PATH</code> environment variable,
 325     which is a colon-separated list of directories in which the linker
 326     will search for shared libraries:
 327     </p><pre class="screen"><span class="command"><strong>
 328     export LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 329     </strong></span></pre><p>
 330     Here the shell variable <code class="varname">${prefix}</code> is assumed to contain
 331     the directory prefix where GCC was installed to. The directory containing
 332     the library might depend on whether you want the 32-bit or 64-bit copy
 333     of the library, so for example would be
 334     <code class="filename">${prefix}/lib64</code> on some systems.
 335     The exact environment variable to use will depend on your
 336     platform, e.g. <code class="envar">DYLD_LIBRARY_PATH</code> for Darwin,
 337     <code class="envar">LD_LIBRARY_PATH_32</code>/<code class="envar">LD_LIBRARY_PATH_64</code>
 338     for Solaris 32-/64-bit,
 339     and <code class="envar">SHLIB_PATH</code> for HP-UX.
 340     </p><p>
 341     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 342     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 343     linker has different names on different platforms but the man page
 344     is usually called something such as <code class="filename">ld.so</code>,
 345     <code class="filename">rtld</code> or <code class="filename">dld.so</code>.
 346     </p><p>
 347     Using <code class="envar">LD_LIBRARY_PATH</code> is not always the best solution,
 348     <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
 349     Libraries</a> in the manual gives some alternatives.
 350     </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>
 351       What's libsupc++?
 352     </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>
 353       If the only functions from <code class="filename">libstdc++.a</code>
 354       which you need are language support functions (those listed in
 355       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 356       standard, e.g., <code class="function">new</code> and
 357       <code class="function">delete</code>), then try linking against
 358       <code class="filename">libsupc++.a</code>, which is a subset of
 359       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 360       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 361       <code class="filename">libsupc++.a</code> via <code class="option">-lsupc++</code>
 362       for the final link step will do it).  This library contains only
 363       those support routines, one per object file.  But if you are
 364       using anything from the rest of the library, such as IOStreams
 365       or vectors, then you'll still need pieces from
 366       <code class="filename">libstdc++.a</code>.
 367     </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>
 368       This library is HUGE!
 369     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 370     Usually the size of libraries on disk isn't noticeable.  When a
 371     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 372     static archive library, only the necessary object files are copied
 373     into your executable, not the entire library.  Unfortunately, even
 374     if you only need a single function or variable from an object file,
 375     the entire object file is extracted.  (There's nothing unique to C++
 376     or libstdc++ about this; it's just common behavior, given here
 377     for background reasons.)
 378     </p><p>
 379     Some of the object files which make up
 380     <code class="filename">libstdc++.a</code> are rather large.
 381     If you create a statically-linked executable with
 382     <code class="option">-static</code>, those large object files are suddenly part
 383     of your executable.  Historically the best way around this was to
 384     only place a very few functions (often only a single one) in each
 385     source/object file; then extracting a single function is the same
 386     as extracting a single <code class="filename">.o</code> file.  For libstdc++ this
 387     is only possible to a certain extent; the object files in question contain
 388     template classes and template functions, pre-instantiated, and
 389     splitting those up causes severe maintenance headaches.
 390     </p><p>
 391     On supported platforms, libstdc++ takes advantage of garbage
 392     collection in the GNU linker to get a result similar to separating
 393     each symbol into a separate source and object files. On these platforms,
 394     GNU ld can place each function and variable into its own
 395     section in a <code class="filename">.o</code> file.  The GNU linker can then perform
 396     garbage collection on unused sections; this reduces the situation to only
 397     copying needed functions into the executable, as before, but all
 398     happens automatically.
 399     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
 400       Can libstdc++ be used with non-GNU compilers?
 401     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 402       No 'long long' type on Solaris?
 403     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 404       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 405     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 406       Mac OS X ctype.h is broken! How can I fix it?
 407     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 408       Threading is broken on i386?
 409     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 410       MIPS atomic operations
 411     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 412       Recent GNU/Linux glibc required?
 413     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 414       Can't use wchar_t/wstring on FreeBSD
 415     </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>
 416       Can libstdc++ be used with non-GNU compilers?
 417     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 418     Perhaps.
 419     </p><p>
 420     Since the goal of ISO Standardization is for all C++
 421     implementations to be able to share code, libstdc++ should be
 422     usable under any ISO-compliant compiler, at least in theory.
 423     </p><p>
 424     However, the reality is that libstdc++ is targeted and optimized
 425     for GCC/G++. This means that often libstdc++ uses specific,
 426     non-standard features of G++ that are not present in older
 427     versions of proprietary compilers. It may take as much as a year or two
 428     after an official release of GCC that contains these features for
 429     proprietary tools to support these constructs.
 430     </p><p>
 431     Recent versions of libstdc++ are known to work with the Clang compiler.
 432     In the near past, specific released versions of libstdc++ have
 433     been known to work with versions of the EDG C++ compiler, and
 434     vendor-specific proprietary C++ compilers such as the Intel ICC
 435     C++ compiler.
 436     </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>
 437       No '<span class="type">long long</span>' type on Solaris?
 438     </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>
 439     By default we try to support the C99 <span class="type">long long</span> type.
 440     This requires that certain functions from your C library be present.
 441     </p><p>
 442     Up through release 3.0.2 the platform-specific tests performed by
 443     libstdc++ were too general, resulting in a conservative approach
 444     to enabling the <span class="type">long long</span> code paths. The most
 445     commonly reported platform affected was Solaris.
 446     </p><p>
 447     This has been fixed for libstdc++ releases greater than 3.0.3.
 448     </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>
 449       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 450     </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>)
 451          always defines the preprocessor macro
 452          <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 453          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 454          other macros and other platforms are also affected.)
 455       </p><p>These macros are typically used in C library headers, guarding new
 456          versions of functions from their older versions.  The C++98 standard
 457          library includes the C standard library, but it requires the C90
 458          version, which for backwards-compatibility reasons is often not the
 459          default for many vendors.
 460       </p><p>More to the point, the C++ standard requires behavior which is only
 461          available on certain platforms after certain symbols are defined.
 462          Usually the issue involves I/O-related typedefs.  In order to
 463          ensure correctness, the compiler simply predefines those symbols.
 464       </p><p>Note that it's not enough to <code class="literal">#define</code> them only when the library is
 465          being built (during installation).  Since we don't have an 'export'
 466          keyword, much of the library exists as headers, which means that
 467          the symbols must also be defined as your programs are parsed and
 468          compiled.
 469       </p><p>To see which symbols are defined, look for
 470          <code class="varname">CPLUSPLUS_CPP_SPEC</code> in
 471          the gcc config headers for your target (and try changing them to
 472          see what happens when building complicated code).  You can also run
 473          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 474          a list of predefined macros for any particular installation.
 475       </p><p>This has been discussed on the mailing lists
 476          <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>.
 477       </p><p>This method is something of a wart.  We'd like to find a cleaner
 478          solution, but nobody yet has contributed the time.
 479       </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>
 480       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 481     </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>
 482          This was a long-standing bug in the OS X support.  Fortunately, the
 483          <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top">patch</a>
 484          was quite simple, and well-known.
 485       </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>
 486       Threading is broken on i386?
 487     </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
 488          platforms.  The assembly code accidentally used opcodes that are
 489          only available on the i486 and later.  So if you configured GCC
 490          to target, for example, i386-linux, but actually used the programs
 491          on an i686, then you would encounter no problems.  Only when
 492          actually running the code on a i386 will the problem appear.
 493       </p><p>This is fixed in 3.2.2.
 494       </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>
 495       MIPS atomic operations
 496     </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>
 497     The atomic locking routines for MIPS targets requires MIPS II
 498     and later.  A patch went in just after the 3.3 release to
 499     make mips* use the generic implementation instead.  You can also
 500     configure for mipsel-elf as a workaround.
 501     </p><p>
 502     The mips*-*-linux* port continues to use the MIPS II routines, and more
 503     work in this area is expected.
 504     </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>
 505       Recent GNU/Linux glibc required?
 506     </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
 507          5.0.1) and later uses localization and formatting code from the system
 508          C library (glibc) version 2.2.5 which contains necessary bugfixes.
 509          All GNU/Linux distros make more recent versions available now.
 510          libstdc++ 4.6.0 and later require glibc 2.3 or later for this
 511          localization and formatting code.
 512       </p><p>The guideline is simple:  the more recent the C++ library, the
 513          more recent the C library.  (This is also documented in the main
 514          GCC installation instructions.)
 515       </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>
 516       Can't use <span class="type">wchar_t</span>/<code class="classname">wstring</code> on FreeBSD
 517     </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>
 518     Older versions of FreeBSD's C library do not have sufficient
 519     support for wide character functions, and as a result the
 520     libstdc++ configury decides that <span class="type">wchar_t</span> support should be
 521     disabled. In addition, the libstdc++ platform checks that
 522     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 523     enough to detect when the minimal support to
 524     enable <span class="type">wchar_t</span> and C++ library structures
 525     like <code class="classname">wstring</code> were present. This impacted Solaris,
 526     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 527     </p><p>
 528     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
 529       What works already?
 530     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 531       Bugs in the ISO C++ language or library specification
 532     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 533       Bugs in the compiler (gcc/g++) and not libstdc++
 534     </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>
 535       What works already?
 536     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 537     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 538     except for some corner cases.  Support for localization
 539     in <code class="classname">locale</code> may be incomplete on some non-GNU
 540     platforms. Also dependent on the underlying platform is support
 541     for <span class="type">wchar_t</span> and <span class="type">long long</span> specializations,
 542     and details of thread support.
 543     </p><p>
 544     Long answer: See the implementation status pages for
 545     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 546     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>,
 547     <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>,
 548     <a class="link" href="manual/status.html#status.iso.2014" title="C++ 2014">C++14</a>, and
 549     <a class="link" href="manual/status.html#status.iso.2017" title="C++ 2017">C++17</a>.
 550     </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>
 551       Bugs in the ISO C++ language or library specification
 552     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 553     Unfortunately, there are some.
 554     </p><p>
 555     For those people who are not part of the ISO Library Group
 556     (i.e., nearly all of us needing to read this page in the first
 557     place), a public list of the library defects is occasionally
 558     published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
 559     website</a>.
 560     Many of these issues have resulted in
 561     <a class="link" href="manual/bugs.html#manual.intro.status.bugs.iso" title="Standard Bugs">code changes in libstdc++</a>.
 562     </p><p>
 563     If you think you've discovered a new bug that is not listed,
 564     please post a message describing your problem to the author of
 565     the library issues list.
 566     </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>
 567       Bugs in the compiler (gcc/g++) and not libstdc++
 568     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 569     On occasion, the compiler is wrong. Please be advised that this
 570     happens much less often than one would think, and avoid jumping to
 571     conclusions.
 572     </p><p>
 573     First, examine the ISO C++ standard. Second, try another compiler
 574     or an older version of the GNU compilers. Third, you can find more
 575     information on the libstdc++ and the GCC mailing lists: search
 576     these lists with terms describing your issue.
 577     </p><p>
 578     Before reporting a bug, please examine the
 579     <a class="link" href="https://gcc.gnu.org/bugs/" target="_top">bugs database</a>, with the
 580     component set to <span class="quote">“<span class="quote">c++</span>”</span>.
 581     </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">
 582       Reopening a stream fails
 583     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 584       -Weffc++ complains too much
 585     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 586       Ambiguous overloads after including an old-style header
 587     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 588       The g++-3 headers are not ours
 589     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 590       Errors about *Concept and
 591       constraints in the STL
 592     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 593       Program crashes when using library code in a
 594       dynamically-loaded library
 595     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 596       “Memory leaks” in containers
 597     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 598       list::size() is O(n)!
 599     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 600       Aw, that's easy to fix!
 601     </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>
 602       Reopening a stream fails
 603     </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>
 604     Prior to GCC 4.0 this was one of the most-reported non-bug reports.
 605     Executing a sequence like this would fail:
 606     </p><pre class="programlisting">
 607     #include &lt;fstream&gt;
 608     ...
 609     std::fstream  fs("a_file");
 610     // .
 611     // . do things with fs...
 612     // .
 613     fs.close();
 614     fs.open("a_new_file");
 615     </pre><p>
 616     All operations on the re-opened <code class="varname">fs</code> would fail, or at
 617     least act very strangely, especially if <code class="varname">fs</code> reached the
 618     EOF state on the previous file.
 619     The original C++98 standard did not specify behavior in this case, and
 620     the <a class="link" href="manual/bugs.html#manual.bugs.dr22">resolution of DR #22</a> was to
 621     leave the state flags unchanged on a successful call to
 622     <code class="function">open()</code>.
 623     You had to insert a call to <code class="function">fs.clear()</code> between the
 624     calls to <code class="function">close()</code> and <code class="function">open()</code>,
 625     and then everything will work as expected.
 626     <span class="emphasis"><em>Update:</em></span> For GCC 4.0 we implemented the resolution
 627     of <a class="link" href="manual/bugs.html#manual.bugs.dr409">DR #409</a> and
 628     <code class="function">open()</code>
 629     now calls <code class="function">clear()</code> on success.
 630     </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>
 631       -Weffc++ complains too much
 632     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 633     Many warnings are emitted when <code class="option">-Weffc++</code> is used.  Making
 634     libstdc++ <code class="option">-Weffc++</code>-clean is not a goal of the project,
 635     for a few reasons.  Mainly, that option tries to enforce
 636     object-oriented programming, while the Standard Library isn't
 637     necessarily trying to be OO. The option also enforces outdated guidelines
 638     from old editions of the books, and the advice isn't all relevant to
 639     modern C++ (especially C++11 and later).
 640     </p><p>
 641     We do, however, try to have libstdc++ sources as clean as possible. If
 642     you see some simple changes that pacify <code class="option">-Weffc++</code>
 643     without other drawbacks, send us a patch.
 644     </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>
 645       Ambiguous overloads after including an old-style header
 646     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></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>
 647     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 648     comparison operator functions contained therein.  If they become
 649     visible in the same namespace as other comparison functions
 650     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the
 651     <code class="filename">&lt;iterator&gt;</code> header),
 652     then you will suddenly be faced with huge numbers of ambiguity
 653     errors.  This was discussed on the mailing list; Nathan Myers
 654     <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 655       things up here</a>.  The collisions with vector/string iterator
 656     types have been fixed for 3.1.
 657     </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>
 658       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 659     </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>
 660         If you are using headers in
 661         <code class="filename">${prefix}/include/g++-3</code>, or if
 662         the installed library's name looks like
 663         <code class="filename">libstdc++-2.10.a</code> or
 664         <code class="filename">libstdc++-libc6-2.10.so</code>, then
 665         you are using the old libstdc++-v2 library, which is non-standard and
 666         unmaintained.  Do not report problems with -v2 to the -v3
 667         mailing list.
 668       </p><p>
 669         For GCC versions 3.0 and 3.1 the libstdc++ header files are installed in
 670         <code class="filename">${prefix}/include/g++-v3</code>
 671         (see the 'v'?).  Starting with version 3.2 the headers are installed in
 672         <code class="filename">${prefix}/include/c++/${version}</code>
 673         as this prevents headers from previous versions being found by mistake.
 674       </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>
 675       Errors about <span class="emphasis"><em>*Concept</em></span> and
 676       <span class="emphasis"><em>constraints</em></span> in the STL
 677     </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>
 678     If you see compilation errors containing messages about
 679     <span class="errortext">foo Concept</span> and something to do with a
 680     <span class="errortext">constraints</span> member function, then most
 681     likely you have violated one of the requirements for types used
 682     during instantiation of template containers and functions.  For
 683     example, EqualityComparableConcept appears if your types must be
 684     comparable with == and you have not provided this capability (a
 685     typo, or wrong visibility, or you just plain forgot, etc).
 686     </p><p>
 687     More information, including how to optionally enable/disable the
 688     checks, is available in the
 689     <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
 690     chapter of the manual.
 691     </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>
 692       Program crashes when using library code in a
 693       dynamically-loaded library
 694     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 695     If you are using the C++ library across dynamically-loaded
 696     objects, make certain that you are passing the correct options
 697     when compiling and linking:
 698     </p><div class="literallayout"><p><br />
 699     Compile your library components:<br />
 700     <span class="command"><strong>g++ -fPIC -c a.cc</strong></span><br />
 701     <span class="command"><strong>g++ -fPIC -c b.cc</strong></span><br />
 702     ...<br />
 703     <span class="command"><strong>g++ -fPIC -c z.cc</strong></span><br />
 704 <br />
 705     Create your library:<br />
 706     <span class="command"><strong>g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o</strong></span><br />
 707 <br />
 708     Link the executable:<br />
 709     <span class="command"><strong>g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</strong></span><br />
 710     </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>
 711       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 712     </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>
 713     A few people have reported that the standard containers appear
 714     to leak memory when tested with memory checkers such as
 715     <a class="link" href="http://valgrind.org/" target="_top"><span class="command"><strong>valgrind</strong></span></a>.
 716     Under some (non-default) configurations the library's allocators keep
 717     free memory in a
 718     pool for later reuse, rather than returning it to the OS.  Although
 719     this memory is always reachable by the library and is never
 720     lost, memory debugging tools can report it as a leak.  If you
 721     want to test the library for memory leaks please read
 722     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 723     first.
 724     </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>
 725       <code class="code">list::size()</code> is O(n)!
 726     </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>
 727     See
 728     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 729     chapter.
 730     </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>
 731       Aw, that's easy to fix!
 732     </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>
 733     If you have found a bug in the library and you think you have
 734     a working fix, then send it in!  The main GCC site has a page
 735     on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 736     patches</a> that covers the procedure, but for libstdc++ you
 737     should also send the patch to our mailing list in addition to
 738     the GCC patches mailing list.  The libstdc++
 739     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 740     also talks about how to submit patches.
 741     </p><p>
 742     In addition to the description, the patch, and the ChangeLog
 743     entry, it is a Good Thing if you can additionally create a small
 744     test program to test for the presence of the bug that your patch
 745     fixes.  Bugs have a way of being reintroduced; if an old bug
 746     creeps back in, it will be caught immediately by the testsuite -
 747     but only if such a test exists.
 748     </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">
 749       string::iterator is not char*;
 750       vector&lt;T&gt;::iterator is not T*
 751     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 752       What's next after libstdc++?
 753     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 754       What about the STL from SGI?
 755     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 756       Extensions and Backward Compatibility
 757     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 758       Does libstdc++ support TR1?
 759     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 760     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 761       What's an ABI and why is it so messy?
 762     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 763       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 764     </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>
 765       <code class="classname">string::iterator</code> is not <code class="code">char*</code>;
 766       <code class="classname">vector&lt;T&gt;::iterator</code> is not <code class="code">T*</code>
 767     </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>
 768     If you have code that depends on container&lt;T&gt; iterators
 769     being implemented as pointer-to-T, your code is broken. It's
 770     considered a feature, not a bug, that libstdc++ points this out.
 771     </p><p>
 772     While there are arguments for iterators to be implemented in
 773     that manner, A) they aren't very good ones in the long term,
 774     and B) they were never guaranteed by the Standard anyway.  The
 775     type-safety achieved by making iterators a real class rather
 776     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 777     arguments.
 778     </p><p>
 779     Code which does assume that a vector/string iterator <code class="varname">i</code>
 780     is a pointer can often be fixed by changing <code class="varname">i</code> in
 781     certain expressions to <code class="varname">&amp;*i</code>.
 782     </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>
 783       What's next after libstdc++?
 784     </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>
 785         The goal of libstdc++ is to produce a
 786         fully-compliant, fully-portable Standard Library.
 787         While the C++ Standard continues to evolve the libstdc++ will
 788         continue to track it.
 789       </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>
 790       What about the STL from SGI?
 791     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 792     The STL (Standard Template Library) was the inspiration for large chunks
 793     of the C++ Standard Library, but the terms are not interchangeable and
 794     they don't mean the same thing. The C++ Standard Library includes lots of
 795     things that didn't come from the STL, and some of them aren't even
 796     templates, such as <code class="classname">std::locale</code> and
 797     <code class="classname">std::thread</code>.
 798     </p><p>
 799     Libstdc++-v3 incorporates a lot of code from
 800     <a class="link" href="https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/" target="_top">the SGI STL</a>
 801     (the final merge was from
 802     <a class="link" href="https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/whats_new.html" target="_top">release 3.3</a>).
 803     The code in libstdc++ contains many fixes and changes compared to the
 804     original SGI code.
 805     </p><p>
 806     In particular, <code class="classname">string</code> is not from SGI and makes no
 807     use of their "rope" class (although that is included as an optional
 808     extension), neither is <code class="classname">valarray</code> nor some others.
 809     Classes like <code class="classname">vector&lt;&gt;</code> were from SGI, but have
 810     been extensively modified.
 811     </p><p>
 812     More information on the evolution of libstdc++ can be found at the
 813     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 814     evolution</a>
 815     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 816     compatibility</a> documentation.
 817     </p><p>
 818     The <a class="link" href="https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/FAQ.html" target="_top">FAQ</a>
 819     for SGI's STL is still recommended reading.
 820     </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>
 821       Extensions and Backward Compatibility
 822     </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>
 823       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.
 824     </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>
 825       Does libstdc++ support TR1?
 826     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 827     Yes.
 828     </p><p>
 829     The C++ Standard Library
 830     <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 831     Technical Report 1</a> added many new features to the library.
 832     </p><p>
 833     The implementation status of TR1 in libstdc++ can be tracked
 834     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status page</a>.
 835     </p><p>
 836     New code should probably not use TR1, because almost everything in it has
 837     been added to the main C++ Standard Library (usually with significant
 838     improvements).
 839     The TR1 implementation in libstdc++ is no longer actively maintained.
 840     </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?
 841     </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>
 842     Please refer to the <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">Contributing</a>
 843     section in our manual.
 844     </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>
 845       What's an ABI and why is it so messy?
 846     </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>
 847     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 848     Interface</span>”</span>.  Conventionally, it refers to a great
 849     mass of details about how arguments are arranged on the call
 850     stack and/or in registers, and how various types are arranged
 851     and padded in structs.  A single CPU design may suffer
 852     multiple ABIs designed by different development tool vendors
 853     who made different choices, or even by the same vendor for
 854     different target applications or compiler versions.  In ideal
 855     circumstances the CPU designer presents one ABI and all the
 856     OSes and compilers use it.  In practice every ABI omits
 857     details that compiler implementers (consciously or
 858     accidentally) must choose for themselves.
 859     </p><p>
 860     That ABI definition suffices for compilers to generate code so a
 861     program can interact safely with an OS and its lowest-level libraries.
 862     Users usually want an ABI to encompass more detail, allowing libraries
 863     built with different compilers (or different releases of the same
 864     compiler!) to be linked together.  For C++, this includes many more
 865     details than for C, and most CPU designers (for good reasons elaborated
 866     below) have not stepped up to publish C++ ABIs.  Such an ABI has been
 867     defined for the Itanium architecture (see
 868     <a class="link" href="https://itanium-cxx-abi.github.io/cxx-abi/" target="_top">C++
 869     ABI for Itanium</a>) and that is used by G++ and other compilers
 870     as the de facto standard ABI on many common architectures (including x86).
 871     G++ can also use the ARM architecture's EABI, for embedded
 872     systems relying only on a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that
 873     doesn't include (much of) the standard library, and the GNU EABI for
 874     hosted implementations on ARM.  Those ABIs cover low-level details
 875     such as virtual function implementation, struct inheritance layout,
 876     name mangling, and exception handling.
 877    </p><p>
 878     A useful C++ ABI must also incorporate many details of the standard
 879     library implementation.  For a C ABI, the layouts of a few structs
 880     (such as <span class="type">FILE</span>, <span class="type">stat</span>, <span class="type">jmpbuf</span>,
 881     and the like) and a few macros suffice.
 882     For C++, the details include the complete set of names of functions
 883     and types used, the offsets of class members and virtual functions,
 884     and the actual definitions of all inlines.  C++ exposes many more
 885     library details to the caller than C does.  It makes defining
 886     a complete ABI a much bigger undertaking, and requires not just
 887     documenting library implementation details, but carefully designing
 888     those details so that future bug fixes and optimizations don't
 889     force breaking the ABI.
 890     </p><p>
 891     There are ways to help isolate library implementation details from the
 892     ABI, but they trade off against speed.  Library details used in inner
 893     loops (e.g., <code class="function">getchar</code>) must be exposed and frozen for
 894     all time, but many others may reasonably be kept hidden from user code,
 895     so they may later be changed.  Deciding which, and implementing
 896     the decisions, must happen before you can reasonably document a
 897     candidate C++ ABI that encompasses the standard library.
 898     </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>
 899       How do I make <code class="code">std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size</code>?
 900     </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>
 901     Since C++11 just call the <code class="function">shrink_to_fit()</code> member
 902     function.
 903     </p><p>
 904     Before C++11, the standard idiom for deallocating a
 905     <code class="classname">vector&lt;T&gt;</code>'s
 906     unused memory was to create a temporary copy of the vector and swap their
 907     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 908     </p><div class="literallayout"><p><br />
 909      std::vector&lt;T&gt;(v).swap(v);<br />
 910     </p></div><p>
 911     The copy will take O(n) time and the swap is constant time.
 912     </p><p>
 913     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 914     strings</a> for a similar solution for strings.
 915     </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>