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

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   3       2008, 2010
   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="idm140623083442864"></a><dl><dt></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
   7       What is libstdc++?
   8     </a></dt><dt>1.2. <a href="faq.html#faq.why">
   9       Why should I use libstdc++?
  10     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  11       Who's in charge of it?
  12     </a></dt><dt>1.4. <a href="faq.html#faq.when">
  13       When is libstdc++ going to be finished?
  14     </a></dt><dt>1.5. <a href="faq.html#faq.how">
  15       How do I contribute to the effort?
  16     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
  17       What happened to the older libg++? I need that!
  18     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
  19       What if I have more questions?
  20     </a></dt></dl></dd><dt></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
  21       What are the license terms for libstdc++?
  22     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
  23       So any program which uses libstdc++ falls under the GPL?
  24     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
  25       How is that different from the GNU {Lesser,Library} GPL?
  26     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
  27       I see. So, what restrictions are there on programs that use the library?
  28     </a></dt></dl></dd><dt></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
  29     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
  30     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
  31     </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found?
  32     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
  33       What's libsupc++?
  34     </a></dt><dt>3.6. <a href="faq.html#faq.size">
  35       This library is HUGE!
  36     </a></dt></dl></dd><dt></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
  37       Can libstdc++ be used with non-GNU compilers?
  38     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
  39       No 'long long' type on Solaris?
  40     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
  41       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
  42     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
  43       Mac OS X ctype.h is broken! How can I fix it?
  44     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
  45       Threading is broken on i386?
  46     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
  47       MIPS atomic operations
  48     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
  49       Recent GNU/Linux glibc required?
  50     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
  51       Can't use wchar_t/wstring on FreeBSD
  52     </a></dt></dl></dd><dt></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
  53       What works already?
  54     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
  55       Bugs in the ISO C++ language or library specification
  56     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
  57       Bugs in the compiler (gcc/g++) and not libstdc++
  58     </a></dt></dl></dd><dt></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
  59       Reopening a stream fails
  60     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
  61       -Weffc++ complains too much
  62     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
  63       Ambiguous overloads after including an old-style header
  64     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
  65       The g++-3 headers are not ours
  66     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
  67       Errors about *Concept and
  68       constraints in the STL
  69     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
  70       Program crashes when using library code in a
  71       dynamically-loaded library
  72     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
  73       “Memory leaks” in containers
  74     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
  75       list::size() is O(n)!
  76     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
  77       Aw, that's easy to fix!
  78     </a></dt></dl></dd><dt></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
  79       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
  80     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
  81       What's next after libstdc++?
  82     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
  83       What about the STL from SGI?
  84     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
  85       Extensions and Backward Compatibility
  86     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
  87       Does libstdc++ support TR1?
  88     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
  89     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
  90       What's an ABI and why is it so messy?
  91     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
  92       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
  93     </a></dt></dl></dd></dl><table border="0" style="width: 100%;"><colgroup><col align="left" width="1%" /><col /></colgroup><tbody><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
  94       What is libstdc++?
  95     </a></dt><dt>1.2. <a href="faq.html#faq.why">
  96       Why should I use libstdc++?
  97     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  98       Who's in charge of it?
  99     </a></dt><dt>1.4. <a href="faq.html#faq.when">
 100       When is libstdc++ going to be finished?
 101     </a></dt><dt>1.5. <a href="faq.html#faq.how">
 102       How do I contribute to the effort?
 103     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
 104       What happened to the older libg++? I need that!
 105     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
 106       What if I have more questions?
 107     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what"></a><a id="faq.what.q"></a><p><strong>1.1.</strong></p></td><td align="left" valign="top"><p>
 108       What is libstdc++?
 109     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
 110      The GNU Standard C++ Library v3 is an ongoing project to
 111      implement the ISO 14882 Standard C++ library as described in
 112      chapters 17 through 27 and annex D.  For those who want to see
 113      exactly how far the project has come, or just want the latest
 114      bleeding-edge code, the up-to-date source is available over
 115      anonymous SVN, and can even be browsed over
 116      the <a class="link" href="http://gcc.gnu.org/svn.html" target="_top">web</a>.
 117     </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><strong>1.2.</strong></p></td><td align="left" valign="top"><p>
 118       Why should I use libstdc++?
 119     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
 120     The completion of the ISO C++ standardization gave the C++
 121     community a powerful set of reuseable tools in the form of the C++
 122     Standard Library.  However, all existing C++ implementations are
 123     (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
 124     incorrekt</span>”</span>, and many suffer from limitations of the compilers
 125     that use them.
 126     </p><p>
 127     The GNU compiler collection
 128     (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
 129     considered to be one of the leading compilers in the world.  Its
 130     development is overseen by the
 131     <a class="link" href="http://gcc.gnu.org/" target="_top">GCC team</a>.  All of
 132     the rapid development and near-legendary
 133     <a class="link" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a>
 134     that are the hallmarks of an open-source project are being
 135     applied to libstdc++.
 136     </p><p>
 137     That means that all of the Standard classes and functions will be
 138     freely available and fully compliant. (Such as
 139     <code class="classname">string</code>,
 140     <code class="classname">vector&lt;&gt;</code>, iostreams, and algorithms.)
 141     Programmers will no longer need to <span class="quote">“<span class="quote">roll their own</span>”</span>
 142     nor be worried about platform-specific incompatibilities.
 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      Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
 149      Loren James Rittle, and Paolo Carlini are the lead maintainers of
 150      the SVN archive.
 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="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>.
 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     Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">a page devoted to
 167     this topic</a>. 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 most recent libg++ README states that libg++ is no longer
 178     being actively maintained.  It should not be used for new
 179     projects, and is only being kicked along to support older code.
 180     </p><p>
 181     More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a>
 182     </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>
 183       What if I have more questions?
 184     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
 185     If you have read the README file, and your question remains
 186     unanswered, then just ask the mailing list. At present, you do not
 187     need to be subscribed to the list to send a message to it.  More
 188     information is available on the homepage (including how to browse
 189     the list archives); to send a message to the list,
 190     use <code class="email">&lt;<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>&gt;</code>.
 191     </p><p>
 192     If you have a question that you think should be included
 193     here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
 194     here, please send email to the libstdc++ mailing list, as above.
 195     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
 196       What are the license terms for libstdc++?
 197     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
 198       So any program which uses libstdc++ falls under the GPL?
 199     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
 200       How is that different from the GNU {Lesser,Library} GPL?
 201     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
 202       I see. So, what restrictions are there on programs that use the library?
 203     </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>
 204       What are the license terms for libstdc++?
 205     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
 206     See <a class="link" href="manual/license.html" title="License">our license description</a>
 207     for these and related questions.
 208     </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>
 209       So any program which uses libstdc++ falls under the GPL?
 210     </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>
 211      No. The special exception permits use of the library in
 212      proprietary applications.
 213     </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>
 214       How is that different from the GNU {Lesser,Library} GPL?
 215     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
 216       The LGPL requires that users be able to replace the LGPL code with a
 217      modified version; this is trivial if the library in question is a C
 218      shared library.  But there's no way to make that work with C++, where
 219      much of the library consists of inline functions and templates, which
 220      are expanded inside the code that uses the library.  So to allow people
 221      to replace the library code, someone using the library would have to
 222      distribute their own source, rendering the LGPL equivalent to the GPL.
 223     </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>
 224       I see. So, what restrictions are there on programs that use the library?
 225     </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>
 226       None.  We encourage such programs to be released as open source,
 227      but we won't punish you or sue you if you choose otherwise.
 228     </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++?
 229     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
 230     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
 231     </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?
 232     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
 233       What's libsupc++?
 234     </a></dt><dt>3.6. <a href="faq.html#faq.size">
 235       This library is HUGE!
 236     </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++?
 237     </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>
 238     Often libstdc++ comes pre-installed as an integral part of many
 239     existing GNU/Linux and Unix systems, as well as many embedded
 240     development tools. It may be necessary to install extra
 241     development packages to get the headers, or the documentation, or
 242     the source: please consult your vendor for details.
 243     </p><p>
 244     To build and install from the GNU GCC sources, please consult the
 245     <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
 246     documentation</a> for detailed
 247     instructions. You may wish to browse those files ahead
 248     of time to get a feel for what's required.
 249     </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?
 250     </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>
 251     Libstdc++ sources for all official releases can be obtained as
 252     part of the GCC sources, available from various sites and
 253     mirrors. A full <a class="link" href="http://gcc.gnu.org/mirrors.html" target="_top">list of
 254     download sites</a> is provided on the main GCC site.
 255     </p><p>
 256     Current libstdc++ sources can always be checked out of the main
 257     GCC source repository using the appropriate version control
 258     tool. At this time, that tool
 259     is <span class="application">Subversion</span>.
 260     </p><p>
 261     <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
 262     one of several revision control packages.  It was selected for GNU
 263     projects because it's free (speech), free (beer), and very high
 264     quality.  The <a class="link" href="http://subversion.tigris.org" target="_top"> Subversion
 265     home page</a> has a better description.
 266     </p><p>
 267     The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
 268     similar to anonymous FTP in that it allows anyone to retrieve
 269     the latest libstdc++ sources.
 270     </p><p>
 271     For more information
 272     see <a class="link" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
 273     details</a>.
 274     </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?
 275     </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>
 276     Libstdc++ comes with its own validation testsuite, which includes
 277     conformance testing, regression testing, ABI testing, and
 278     performance testing. Please consult the
 279     <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing
 280     documentation</a> for more details.
 281     </p><p>
 282     If you find bugs in the testsuite programs themselves, or if you
 283     think of a new test program that should be added to the suite,
 284     <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
 285     </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?
 286     </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>
 287     Depending on your platform and library version, the error message might
 288     be similar to one of the following:
 289     </p><pre class="screen">
 290     ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
 291
 292     /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
 293     </pre><p>
 294     This doesn't mean that the shared library isn't installed, only
 295     that the dynamic linker can't find it. When a dynamically-linked
 296     executable is run the linker finds and loads the required shared
 297     libraries by searching a pre-configured list of directories. If
 298     the directory where you've installed libstdc++ is not in this list
 299     then the libraries won't be found. The simplest way to fix this is
 300     to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
 301     which is a colon-separated list of directories in which the linker
 302     will search for shared libraries:
 303     </p><pre class="screen">
 304     LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 305     export LD_LIBRARY_PATH
 306     </pre><p>
 307     The exact environment variable to use will depend on your
 308     platform, e.g. DYLD_LIBRARY_PATH for Darwin,
 309     LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit
 310     and SHLIB_PATH for HP-UX.
 311     </p><p>
 312     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 313     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 314     linker has different names on different platforms but the man page
 315     is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>.
 316     </p><p>
 317     Using LD_LIBRARY_PATH is not always the best solution, <a class="link" href="manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic" title="Finding Dynamic or Shared Libraries">Finding Dynamic or Shared
 318     Libraries</a> in the manual gives some alternatives.
 319     </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>
 320       What's libsupc++?
 321     </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>
 322       If the only functions from <code class="filename">libstdc++.a</code>
 323       which you need are language support functions (those listed in
 324       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 325       standard, e.g., <code class="function">new</code> and
 326       <code class="function">delete</code>), then try linking against
 327       <code class="filename">libsupc++.a</code>, which is a subset of
 328       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 329       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 330       <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
 331       for the final link step will do it).  This library contains only
 332       those support routines, one per object file.  But if you are
 333       using anything from the rest of the library, such as IOStreams
 334       or vectors, then you'll still need pieces from
 335       <code class="filename">libstdc++.a</code>.
 336     </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>
 337       This library is HUGE!
 338     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 339     Usually the size of libraries on disk isn't noticeable.  When a
 340     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 341     static archive library, only the necessary object files are copied
 342     into your executable, not the entire library.  Unfortunately, even
 343     if you only need a single function or variable from an object file,
 344     the entire object file is extracted.  (There's nothing unique to C++
 345     or libstdc++ about this; it's just common behavior, given here
 346     for background reasons.)
 347     </p><p>
 348     Some of the object files which make up libstdc++.a are rather large.
 349     If you create a statically-linked executable with
 350     <code class="literal">-static</code>, those large object files are suddenly part
 351     of your executable.  Historically the best way around this was to
 352     only place a very few functions (often only a single one) in each
 353     source/object file; then extracting a single function is the same
 354     as extracting a single .o file.  For libstdc++ this is only
 355     possible to a certain extent; the object files in question contain
 356     template classes and template functions, pre-instantiated, and
 357     splitting those up causes severe maintenance headaches.
 358     </p><p>
 359     On supported platforms, libstdc++ takes advantage of garbage
 360     collection in the GNU linker to get a result similar to separating
 361     each symbol into a separate source and object files. On these platforms,
 362     GNU ld can place each function and variable into its own
 363     section in a .o file.  The GNU linker can then perform garbage
 364     collection on unused sections; this reduces the situation to only
 365     copying needed functions into the executable, as before, but all
 366     happens automatically.
 367     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
 368       Can libstdc++ be used with non-GNU compilers?
 369     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 370       No 'long long' type on Solaris?
 371     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 372       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 373     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 374       Mac OS X ctype.h is broken! How can I fix it?
 375     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 376       Threading is broken on i386?
 377     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 378       MIPS atomic operations
 379     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 380       Recent GNU/Linux glibc required?
 381     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 382       Can't use wchar_t/wstring on FreeBSD
 383     </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>
 384       Can libstdc++ be used with non-GNU compilers?
 385     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 386     Perhaps.
 387     </p><p>
 388     Since the goal of ISO Standardization is for all C++
 389     implementations to be able to share code, libstdc++ should be
 390     usable under any ISO-compliant compiler, at least in theory.
 391     </p><p>
 392     However, the reality is that libstdc++ is targeted and optimized
 393     for GCC/g++. This means that often libstdc++ uses specific,
 394     non-standard features of g++ that are not present in older
 395     versions of proprietary compilers. It may take as much as a year or two
 396     after an official release of GCC that contains these features for
 397     proprietary tools to support these constructs.
 398     </p><p>
 399     In the near past, specific released versions of libstdc++ have
 400     been known to work with versions of the EDG C++ compiler, and
 401     vendor-specific proprietary C++ compilers such as the Intel ICC
 402     C++ compiler.
 403     </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>
 404       No 'long long' type on Solaris?
 405     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-solaris_long_long"></a></td><td align="left" valign="top"><p>
 406     By default we try to support the C99 <span class="type">long long</span> type.
 407     This requires that certain functions from your C library be present.
 408     </p><p>
 409     Up through release 3.0.2 the platform-specific tests performed by
 410     libstdc++ were too general, resulting in a conservative approach
 411     to enabling the <span class="type">long long</span> code paths. The most
 412     commonly reported platform affected was Solaris.
 413     </p><p>
 414     This has been fixed for libstdc++ releases greater than 3.0.3.
 415     </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>
 416       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 417     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-predefined"></a></td><td align="left" valign="top"><p>On Solaris, g++ (but not gcc) always defines the preprocessor
 418          macro <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 419          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 420          other macros and other platforms are also affected.)
 421       </p><p>These macros are typically used in C library headers, guarding new
 422          versions of functions from their older versions.  The C++ standard
 423          library includes the C standard library, but it requires the C90
 424          version, which for backwards-compatibility reasons is often not the
 425          default for many vendors.
 426       </p><p>More to the point, the C++ standard requires behavior which is only
 427          available on certain platforms after certain symbols are defined.
 428          Usually the issue involves I/O-related typedefs.  In order to
 429          ensure correctness, the compiler simply predefines those symbols.
 430       </p><p>Note that it's not enough to #define them only when the library is
 431          being built (during installation).  Since we don't have an 'export'
 432          keyword, much of the library exists as headers, which means that
 433          the symbols must also be defined as your programs are parsed and
 434          compiled.
 435       </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 436          the gcc config headers for your target (and try changing them to
 437          see what happens when building complicated code).  You can also run
 438          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 439          a list of predefined macros for any particular installation.
 440       </p><p>This has been discussed on the mailing lists
 441          <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>.
 442       </p><p>This method is something of a wart.  We'd like to find a cleaner
 443          solution, but nobody yet has contributed the time.
 444       </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>
 445       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 446     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-darwin_ctype"></a></td><td align="left" valign="top"><p>This is a long-standing bug in the OS X support.  Fortunately,
 447          the patch is quite simple, and well-known.
 448          <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
 449          link to the solution</a>.
 450       </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>
 451       Threading is broken on i386?
 452     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
 453     </p><p>Support for atomic integer operations is/was broken on i386
 454          platforms.  The assembly code accidentally used opcodes that are
 455          only available on the i486 and later.  So if you configured GCC
 456          to target, for example, i386-linux, but actually used the programs
 457          on an i686, then you would encounter no problems.  Only when
 458          actually running the code on a i386 will the problem appear.
 459       </p><p>This is fixed in 3.2.2.
 460       </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>
 461       MIPS atomic operations
 462     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
 463     The atomic locking routines for MIPS targets requires MIPS II
 464     and later.  A patch went in just after the 3.3 release to
 465     make mips* use the generic implementation instead.  You can also
 466     configure for mipsel-elf as a workaround.
 467     </p><p>
 468     The mips*-*-linux* port continues to use the MIPS II routines, and more
 469     work in this area is expected.
 470     </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>
 471       Recent GNU/Linux glibc required?
 472     </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
 473          5.0.1) and later uses localization and formatting code from the system
 474          C library (glibc) version 2.2.5 which contains necessary bugfixes.
 475          Most GNU/Linux distros make more recent versions available now.
 476          libstdc++ 4.6.0 and later require glibc 2.3 or later for this
 477          localization and formatting code.
 478       </p><p>The guideline is simple:  the more recent the C++ library, the
 479          more recent the C library.  (This is also documented in the main
 480          GCC installation instructions.)
 481       </p></td></tr><tr class="question"><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>
 482       Can't use wchar_t/wstring on FreeBSD
 483     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
 484     Older versions of FreeBSD's C library do not have sufficient
 485     support for wide character functions, and as a result the
 486     libstdc++ configury decides that wchar_t support should be
 487     disabled. In addition, the libstdc++ platform checks that
 488     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 489     enough to detect when the minimal support to
 490     enable <span class="type">wchar_t</span> and C++ library structures
 491     like <code class="classname">wstring</code> were present. This impacted Solaris,
 492     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 493     </p><p>
 494     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
 495       What works already?
 496     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 497       Bugs in the ISO C++ language or library specification
 498     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 499       Bugs in the compiler (gcc/g++) and not libstdc++
 500     </a></dt></dl></td></tr><tr class="question"><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>
 501       What works already?
 502     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 503     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 504     except for some corner cases.  Support for localization
 505     in <code class="classname">locale</code> may be incomplete on non-GNU
 506     platforms. Also dependent on the underlying platform is support
 507     for <span class="type">wchar_t</span> and <span class="type">long
 508     long</span> specializations, and details of thread support.
 509     </p><p>
 510     Long answer: See the implementation status pages for
 511     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 512     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 513     <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>.
 514     </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>
 515       Bugs in the ISO C++ language or library specification
 516     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 517     Unfortunately, there are some.
 518     </p><p>
 519     For those people who are not part of the ISO Library Group
 520     (i.e., nearly all of us needing to read this page in the first
 521     place), a public list of the library defects is occasionally
 522     published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
 523     website</a>.
 524     Some of these issues have resulted in code changes in libstdc++.
 525     </p><p>
 526     If you think you've discovered a new bug that is not listed,
 527     please post a message describing your problem to the author of
 528     the library issues list or the Usenet group comp.lang.c++.moderated.
 529     </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>
 530       Bugs in the compiler (gcc/g++) and not libstdc++
 531     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 532     On occasion, the compiler is wrong. Please be advised that this
 533     happens much less often than one would think, and avoid jumping to
 534     conclusions.
 535     </p><p>
 536     First, examine the ISO C++ standard. Second, try another compiler
 537     or an older version of the GNU compilers. Third, you can find more
 538     information on the libstdc++ and the GCC mailing lists: search
 539     these lists with terms describing your issue.
 540     </p><p>
 541     Before reporting a bug, please examine the
 542     <a class="link" href="http://gcc.gnu.org/bugs/" target="_top">bugs database</a> with the
 543     category set to <span class="quote">“<span class="quote">g++</span>”</span>.
 544     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
 545       Reopening a stream fails
 546     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 547       -Weffc++ complains too much
 548     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 549       Ambiguous overloads after including an old-style header
 550     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 551       The g++-3 headers are not ours
 552     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 553       Errors about *Concept and
 554       constraints in the STL
 555     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 556       Program crashes when using library code in a
 557       dynamically-loaded library
 558     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 559       “Memory leaks” in containers
 560     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 561       list::size() is O(n)!
 562     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 563       Aw, that's easy to fix!
 564     </a></dt></dl></td></tr><tr class="question"><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>
 565       Reopening a stream fails
 566     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-stream_reopening_fails"></a></td><td align="left" valign="top"><p>
 567     One of the most-reported non-bug reports. Executing a sequence like:
 568     </p><div class="literallayout"><p><br />
 569     #include &lt;fstream&gt;<br />
 570     ...<br />
 571     std::fstream  fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
 572     // .<br />
 573     // . do things with fs...<br />
 574     // .<br />
 575     fs.close();<br />
 576     fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
 577     </p></div><p>
 578     All operations on the re-opened <code class="varname">fs</code> will fail, or at
 579     least act very strangely.  Yes, they often will, especially if
 580     <code class="varname">fs</code> reached the EOF state on the previous file.  The
 581     reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
 582     on a successful call to open().  The standard unfortunately did
 583     not specify behavior in this case, and to everybody's great sorrow,
 584     the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
 585       DR #22</a> is to leave the flags unchanged.  You must insert a call
 586     to <code class="function">fs.clear()</code> between the calls to close() and open(),
 587     and then everything will work like we all expect it to work.
 588     <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
 589     of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
 590     now calls <code class="function">clear()</code> on success!
 591     </p></td></tr><tr class="question"><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>
 592       -Weffc++ complains too much
 593     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 594     Many warnings are emitted when <code class="literal">-Weffc++</code> is used.  Making
 595     libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
 596     for a few reasons.  Mainly, that option tries to enforce
 597     object-oriented programming, while the Standard Library isn't
 598     necessarily trying to be OO.
 599     </p><p>
 600     We do, however, try to have libstdc++ sources as clean as possible. If
 601     you see some simple changes that pacify <code class="literal">-Weffc++</code>
 602     without other drawbacks, send us a patch.
 603     </p></td></tr><tr class="question"><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>
 604       Ambiguous overloads after including an old-style header
 605     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 606     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 607     comparison operator functions contained therein.  If they become
 608     visible in the same namespace as other comparison functions
 609     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the &lt;iterator&gt; header),
 610     then you will suddenly be faced with huge numbers of ambiguity
 611     errors.  This was discussed on the -v3 list; Nathan Myers
 612     <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 613       things up here</a>.  The collisions with vector/string iterator
 614     types have been fixed for 3.1.
 615     </p></td></tr><tr class="question"><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>
 616       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 617     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
 618         If you are using headers in
 619         <code class="filename">${prefix}/include/g++-3</code>, or if the installed
 620         library's name looks like <code class="filename">libstdc++-2.10.a</code> or
 621         <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
 622         old libstdc++-v2 library, which is nonstandard and
 623         unmaintained.  Do not report problems with -v2 to the -v3
 624         mailing list.
 625       </p><p>
 626         For GCC versions 3.0 and 3.1 the libstdc++ header files are
 627         installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
 628         'v'?).  Starting with version 3.2 the headers are installed in
 629         <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
 630         headers from previous versions being found by mistake.
 631       </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>
 632       Errors about <span class="emphasis"><em>*Concept</em></span> and
 633       <span class="emphasis"><em>constraints</em></span> in the STL
 634     </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>
 635     If you see compilation errors containing messages about
 636     <span class="errortext">foo Concept </span>and something to do with a
 637     <span class="errortext">constraints</span> member function, then most
 638     likely you have violated one of the requirements for types used
 639     during instantiation of template containers and functions.  For
 640     example, EqualityComparableConcept appears if your types must be
 641     comparable with == and you have not provided this capability (a
 642     typo, or wrong visibility, or you just plain forgot, etc).
 643     </p><p>
 644     More information, including how to optionally enable/disable the
 645     checks, is available in the
 646     <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
 647     chapter of the manual.
 648     </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>
 649       Program crashes when using library code in a
 650       dynamically-loaded library
 651     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 652     If you are using the C++ library across dynamically-loaded
 653     objects, make certain that you are passing the correct options
 654     when compiling and linking:
 655     </p><div class="literallayout"><p><br />
 656     // compile your library components<br />
 657     g++ -fPIC -c a.cc<br />
 658     g++ -fPIC -c b.cc<br />
 659     ...<br />
 660     g++ -fPIC -c z.cc<br />
 661 <br />
 662     // create your library<br />
 663     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
 664 <br />
 665     // link the executable<br />
 666     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
 667     </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>
 668       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 669     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
 670     A few people have reported that the standard containers appear
 671     to leak memory when tested with memory checkers such as
 672     <a class="link" href="http://valgrind.org/" target="_top">valgrind</a>.
 673     Under some configurations the library's allocators keep free memory in a
 674     pool for later reuse, rather than returning it to the OS.  Although
 675     this memory is always reachable by the library and is never
 676     lost, memory debugging tools can report it as a leak.  If you
 677     want to test the library for memory leaks please read
 678     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 679     first.
 680     </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>
 681       list::size() is O(n)!
 682     </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>
 683     See
 684     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 685     chapter.
 686     </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>
 687       Aw, that's easy to fix!
 688     </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>
 689     If you have found a bug in the library and you think you have
 690     a working fix, then send it in!  The main GCC site has a page
 691     on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 692     patches</a> that covers the procedure, but for libstdc++ you
 693     should also send the patch to our mailing list in addition to
 694     the GCC patches mailing list.  The libstdc++
 695     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 696     also talks about how to submit patches.
 697     </p><p>
 698     In addition to the description, the patch, and the ChangeLog
 699     entry, it is a Good Thing if you can additionally create a small
 700     test program to test for the presence of the bug that your patch
 701     fixes.  Bugs have a way of being reintroduced; if an old bug
 702     creeps back in, it will be caught immediately by the testsuite -
 703     but only if such a test exists.
 704     </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">
 705       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 706     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 707       What's next after libstdc++?
 708     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 709       What about the STL from SGI?
 710     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 711       Extensions and Backward Compatibility
 712     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 713       Does libstdc++ support TR1?
 714     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 715     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 716       What's an ABI and why is it so messy?
 717     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 718       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 719     </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>
 720       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 721     </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>
 722     If you have code that depends on container&lt;T&gt; iterators
 723     being implemented as pointer-to-T, your code is broken. It's
 724     considered a feature, not a bug, that libstdc++ points this out.
 725     </p><p>
 726     While there are arguments for iterators to be implemented in
 727     that manner, A) they aren't very good ones in the long term,
 728     and B) they were never guaranteed by the Standard anyway.  The
 729     type-safety achieved by making iterators a real class rather
 730     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 731     arguments.
 732     </p><p>
 733     Code which does assume that a vector iterator <code class="varname">i</code>
 734     is a pointer can often be fixed by changing <code class="varname">i</code> in
 735     certain expressions to <code class="varname">&amp;*i</code>.  Future revisions
 736     of the Standard are expected to bless this usage for
 737     vector&lt;&gt; (but not for basic_string&lt;&gt;).
 738     </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>
 739       What's next after libstdc++?
 740     </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>
 741         Hopefully, not much.  The goal of libstdc++ is to produce a
 742         fully-compliant, fully-portable Standard Library.  After that,
 743         we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
 744         more compliance work to do.
 745       </p><p>
 746         There is an effort underway to add significant extensions to
 747         the standard library specification.  The latest version of
 748         this effort is described in
 749          <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 750          The C++ Library Technical Report 1</a>.
 751       </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>
 752       What about the STL from SGI?
 753     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 754       The <a class="link" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
 755     version 3.3, was the final merge of the STL codebase.  The
 756     code in libstdc++ contains many fixes and changes, and
 757     the SGI code is no longer under active
 758     development.  We expect that no future merges will take place.
 759     </p><p>
 760     In particular, <code class="classname">string</code> is not from SGI and makes no
 761     use of their "rope" class (which is included as an
 762     optional extension), nor is <code class="classname">valarray</code> and some others.
 763     Classes like <code class="classname">vector&lt;&gt;</code> are, but have been
 764     extensively modified.
 765     </p><p>
 766     More information on the evolution of libstdc++ can be found at the
 767     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 768     evolution</a>
 769     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 770     compatibility</a> documentation.
 771     </p><p>
 772     The FAQ for SGI's STL (one jump off of their main page) is
 773     still recommended reading.
 774     </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>
 775       Extensions and Backward Compatibility
 776     </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>
 777       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.
 778     </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>
 779       Does libstdc++ support TR1?
 780     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 781     Yes.
 782     </p><p>
 783     The C++ Standard Library Technical Report adds many new features to
 784     the library.  The latest version of this effort is described in
 785     <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 786          Technical Report 1</a>.
 787     </p><p>
 788     The implementation status of TR1 in libstdc++ can be tracked <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status
 789     page</a>.
 790     </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?
 791     </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>
 792     Copies of the full ISO 14882 standard are available on line via
 793     the ISO mirror site for committee members.  Non-members, or those
 794     who have not paid for the privilege of sitting on the committee
 795     and sustained their two-meeting commitment for voting rights, may
 796     get a copy of the standard from their respective national
 797     standards organization.  In the USA, this national standards
 798     organization is ANSI and their website is
 799     right <a class="link" href="http://www.ansi.org" target="_top">here</a>.  (And if
 800     you've already registered with them, clicking this link will take
 801     you to directly to the place where you can
 802     <a class="link" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
 803     </p><p>
 804     Who is your country's member body?  Visit the
 805     <a class="link" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
 806     </p><p>
 807     The 2003 version of the standard (the 1998 version plus TC1) is
 808     available in print, ISBN 0-470-84674-7.
 809     </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>
 810       What's an ABI and why is it so messy?
 811     </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>
 812     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 813      Interface</span>”</span>.  Conventionally, it refers to a great
 814     mass of details about how arguments are arranged on the call
 815     stack and/or in registers, and how various types are arranged
 816     and padded in structs.  A single CPU design may suffer
 817     multiple ABIs designed by different development tool vendors
 818     who made different choices, or even by the same vendor for
 819     different target applications or compiler versions.  In ideal
 820     circumstances the CPU designer presents one ABI and all the
 821     OSes and compilers use it.  In practice every ABI omits
 822     details that compiler implementers (consciously or
 823     accidentally) must choose for themselves.
 824     </p><p>
 825     That ABI definition suffices for compilers to generate code so a
 826     program can interact safely with an OS and its lowest-level libraries.
 827     Users usually want an ABI to encompass more detail, allowing libraries
 828     built with different compilers (or different releases of the same
 829     compiler!) to be linked together.  For C++, this includes many more
 830     details than for C, and CPU designers (for good reasons elaborated
 831     below) have not stepped up to publish C++ ABIs.  The details include
 832     virtual function implementation, struct inheritance layout, name
 833     mangling, and exception handling.  Such an ABI has been defined for
 834     GNU C++, and is immediately useful for embedded work relying only on
 835     a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
 836     of) the standard library.  It is a good basis for the work to come.
 837     </p><p>
 838     A useful C++ ABI must also incorporate many details of the standard
 839     library implementation.  For a C ABI, the layouts of a few structs
 840     (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 841     For C++, the details include the complete set of names of functions
 842     and types used, the offsets of class members and virtual functions,
 843     and the actual definitions of all inlines.  C++ exposes many more
 844     library details to the caller than C does.  It makes defining
 845     a complete ABI a much bigger undertaking, and requires not just
 846     documenting library implementation details, but carefully designing
 847     those details so that future bug fixes and optimizations don't
 848     force breaking the ABI.
 849     </p><p>
 850     There are ways to help isolate library implementation details from the
 851     ABI, but they trade off against speed.  Library details used in
 852     inner loops (e.g., getchar) must be exposed and frozen for all
 853     time, but many others may reasonably be kept hidden from user code,
 854     so they may later be changed.  Deciding which, and implementing
 855     the decisions, must happen before you can reasonably document a
 856     candidate C++ ABI that encompasses the standard library.
 857     </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>
 858       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 859     </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>
 860     The standard idiom for deallocating a <code class="classname">vector&lt;T&gt;</code>'s
 861     unused memory is to create a temporary copy of the vector and swap their
 862     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 863     </p><div class="literallayout"><p><br />
 864      std::vector&lt;T&gt;(v).swap(v);<br />
 865     </p></div><p>
 866     The copy will take O(n) time and the swap is constant time.
 867     </p><p>
 868     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 869     strings</a> for a similar solution for strings.
 870     </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>