gcc-4_9-branch/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="idm270879457456"></a><dl><dt></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
   7       What is libstdc++?
   8     </a></dt><dt>1.2. <a href="faq.html#faq.why">
   9       Why should I use libstdc++?
  10     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  11       Who's in charge of it?
  12     </a></dt><dt>1.4. <a href="faq.html#faq.when">
  13       When is libstdc++ going to be finished?
  14     </a></dt><dt>1.5. <a href="faq.html#faq.how">
  15       How do I contribute to the effort?
  16     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
  17       What happened to the older libg++? I need that!
  18     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
  19       What if I have more questions?
  20     </a></dt></dl></dd><dt></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
  21       What are the license terms for libstdc++?
  22     </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
  23       So any program which uses libstdc++ falls under the GPL?
  24     </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
  25       How is that different from the GNU {Lesser,Library} GPL?
  26     </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
  27       I see. So, what restrictions are there on programs that use the library?
  28     </a></dt></dl></dd><dt></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
  29     </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
  30     </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
  31     </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found?
  32     </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
  33       What's libsupc++?
  34     </a></dt><dt>3.6. <a href="faq.html#faq.size">
  35       This library is HUGE!
  36     </a></dt></dl></dd><dt></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
  37       Can libstdc++ be used with non-GNU compilers?
  38     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
  39       No 'long long' type on Solaris?
  40     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
  41       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
  42     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
  43       Mac OS X ctype.h is broken! How can I fix it?
  44     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
  45       Threading is broken on i386?
  46     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
  47       MIPS atomic operations
  48     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
  49       Recent GNU/Linux glibc required?
  50     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
  51       Can't use wchar_t/wstring on FreeBSD
  52     </a></dt></dl></dd><dt></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
  53       What works already?
  54     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
  55       Bugs in the ISO C++ language or library specification
  56     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
  57       Bugs in the compiler (gcc/g++) and not libstdc++
  58     </a></dt></dl></dd><dt></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
  59       Reopening a stream fails
  60     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
  61       -Weffc++ complains too much
  62     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
  63       Ambiguous overloads after including an old-style header
  64     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
  65       The g++-3 headers are not ours
  66     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
  67       Errors about *Concept and
  68       constraints in the STL
  69     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
  70       Program crashes when using library code in a
  71       dynamically-loaded library
  72     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
  73       “Memory leaks” in containers
  74     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
  75       list::size() is O(n)!
  76     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
  77       Aw, that's easy to fix!
  78     </a></dt></dl></dd><dt></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
  79       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
  80     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
  81       What's next after libstdc++?
  82     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
  83       What about the STL from SGI?
  84     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
  85       Extensions and Backward Compatibility
  86     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
  87       Does libstdc++ support TR1?
  88     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
  89     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
  90       What's an ABI and why is it so messy?
  91     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
  92       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
  93     </a></dt></dl></dd></dl><table border="0" style="width: 100%;"><colgroup><col align="left" width="1%" /><col /></colgroup><tbody><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
  94       What is libstdc++?
  95     </a></dt><dt>1.2. <a href="faq.html#faq.why">
  96       Why should I use libstdc++?
  97     </a></dt><dt>1.3. <a href="faq.html#faq.who">
  98       Who's in charge of it?
  99     </a></dt><dt>1.4. <a href="faq.html#faq.when">
 100       When is libstdc++ going to be finished?
 101     </a></dt><dt>1.5. <a href="faq.html#faq.how">
 102       How do I contribute to the effort?
 103     </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
 104       What happened to the older libg++? I need that!
 105     </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
 106       What if I have more questions?
 107     </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what"></a><a id="faq.what.q"></a><p><strong>1.1.</strong></p></td><td align="left" valign="top"><p>
 108       What is libstdc++?
 109     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
 110      The GNU Standard C++ Library v3 is an ongoing project to
 111      implement the ISO 14882 Standard C++ library as described in
 112      clauses 17 through 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 free software,
 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.
 300     </p><p>
 301     If you already have an older version of libstdc++ installed then the
 302     error might look like one of the following instead:
 303     </p><pre class="screen">
 304     ./a.out: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.20' not found
 305     ./a.out: /usr/lib/libstdc++.so.6: version `CXXABI_1.3.8' not found
 306     </pre><p>
 307     This means the linker found <code class="filename">/usr/lib/libstdc++.so.6</code>
 308     but that library belongs to an older version of GCC than was used to
 309     compile and link the program <code class="filename">a.out</code> (or some part
 310     of it). The program depends on code defined in the newer libstdc++
 311     that belongs to the newer version of GCC, so the linker must be told
 312     how to find the newer libstdc++ shared library.
 313     </p><p>
 314     The simplest way to fix this is
 315     to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
 316     which is a colon-separated list of directories in which the linker
 317     will search for shared libraries:
 318     </p><pre class="screen">
 319     LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
 320     export LD_LIBRARY_PATH
 321     </pre><p>
 322     Here the shell variable <span class="command"><strong>${prefix}</strong></span> is assumed to contain
 323     the directory prefix where GCC was installed to. The directory containing
 324     the library might depend on whether you want the 32-bit or 64-bit copy
 325     of the library, so for example would be
 326     <code class="filename">${prefix}/lib64</code> on some systems.
 327     The exact environment variable to use will depend on your
 328     platform, e.g. DYLD_LIBRARY_PATH for Darwin,
 329     LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit
 330     and SHLIB_PATH for HP-UX.
 331     </p><p>
 332     See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
 333     and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
 334     linker has different names on different platforms but the man page
 335     is usually called something such as <code class="filename">ld.so</code>,
 336     <code class="filename">rtld</code> or <code class="filename">dld.so</code>.
 337     </p><p>
 338     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
 339     Libraries</a> in the manual gives some alternatives.
 340     </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>
 341       What's libsupc++?
 342     </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>
 343       If the only functions from <code class="filename">libstdc++.a</code>
 344       which you need are language support functions (those listed in
 345       <a class="link" href="manual/support.html" title="Chapter 4.  Support">clause 18</a> of the
 346       standard, e.g., <code class="function">new</code> and
 347       <code class="function">delete</code>), then try linking against
 348       <code class="filename">libsupc++.a</code>, which is a subset of
 349       <code class="filename">libstdc++.a</code>.  (Using <span class="command"><strong>gcc</strong></span>
 350       instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
 351       <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
 352       for the final link step will do it).  This library contains only
 353       those support routines, one per object file.  But if you are
 354       using anything from the rest of the library, such as IOStreams
 355       or vectors, then you'll still need pieces from
 356       <code class="filename">libstdc++.a</code>.
 357     </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>
 358       This library is HUGE!
 359     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
 360     Usually the size of libraries on disk isn't noticeable.  When a
 361     link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
 362     static archive library, only the necessary object files are copied
 363     into your executable, not the entire library.  Unfortunately, even
 364     if you only need a single function or variable from an object file,
 365     the entire object file is extracted.  (There's nothing unique to C++
 366     or libstdc++ about this; it's just common behavior, given here
 367     for background reasons.)
 368     </p><p>
 369     Some of the object files which make up libstdc++.a are rather large.
 370     If you create a statically-linked executable with
 371     <code class="literal">-static</code>, those large object files are suddenly part
 372     of your executable.  Historically the best way around this was to
 373     only place a very few functions (often only a single one) in each
 374     source/object file; then extracting a single function is the same
 375     as extracting a single .o file.  For libstdc++ this is only
 376     possible to a certain extent; the object files in question contain
 377     template classes and template functions, pre-instantiated, and
 378     splitting those up causes severe maintenance headaches.
 379     </p><p>
 380     On supported platforms, libstdc++ takes advantage of garbage
 381     collection in the GNU linker to get a result similar to separating
 382     each symbol into a separate source and object files. On these platforms,
 383     GNU ld can place each function and variable into its own
 384     section in a .o file.  The GNU linker can then perform garbage
 385     collection on unused sections; this reduces the situation to only
 386     copying needed functions into the executable, as before, but all
 387     happens automatically.
 388     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
 389       Can libstdc++ be used with non-GNU compilers?
 390     </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
 391       No 'long long' type on Solaris?
 392     </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
 393       _XOPEN_SOURCE and _GNU_SOURCE are always defined?
 394     </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
 395       Mac OS X ctype.h is broken! How can I fix it?
 396     </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
 397       Threading is broken on i386?
 398     </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
 399       MIPS atomic operations
 400     </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
 401       Recent GNU/Linux glibc required?
 402     </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
 403       Can't use wchar_t/wstring on FreeBSD
 404     </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>
 405       Can libstdc++ be used with non-GNU compilers?
 406     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
 407     Perhaps.
 408     </p><p>
 409     Since the goal of ISO Standardization is for all C++
 410     implementations to be able to share code, libstdc++ should be
 411     usable under any ISO-compliant compiler, at least in theory.
 412     </p><p>
 413     However, the reality is that libstdc++ is targeted and optimized
 414     for GCC/g++. This means that often libstdc++ uses specific,
 415     non-standard features of g++ that are not present in older
 416     versions of proprietary compilers. It may take as much as a year or two
 417     after an official release of GCC that contains these features for
 418     proprietary tools to support these constructs.
 419     </p><p>
 420     In the near past, specific released versions of libstdc++ have
 421     been known to work with versions of the EDG C++ compiler, and
 422     vendor-specific proprietary C++ compilers such as the Intel ICC
 423     C++ compiler.
 424     </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>
 425       No 'long long' type on Solaris?
 426     </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>
 427     By default we try to support the C99 <span class="type">long long</span> type.
 428     This requires that certain functions from your C library be present.
 429     </p><p>
 430     Up through release 3.0.2 the platform-specific tests performed by
 431     libstdc++ were too general, resulting in a conservative approach
 432     to enabling the <span class="type">long long</span> code paths. The most
 433     commonly reported platform affected was Solaris.
 434     </p><p>
 435     This has been fixed for libstdc++ releases greater than 3.0.3.
 436     </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>
 437       <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
 438     </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
 439          macro <code class="constant">_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 440          with <code class="constant">_GNU_SOURCE</code>.  (This is not an exhaustive list;
 441          other macros and other platforms are also affected.)
 442       </p><p>These macros are typically used in C library headers, guarding new
 443          versions of functions from their older versions.  The C++ standard
 444          library includes the C standard library, but it requires the C90
 445          version, which for backwards-compatibility reasons is often not the
 446          default for many vendors.
 447       </p><p>More to the point, the C++ standard requires behavior which is only
 448          available on certain platforms after certain symbols are defined.
 449          Usually the issue involves I/O-related typedefs.  In order to
 450          ensure correctness, the compiler simply predefines those symbols.
 451       </p><p>Note that it's not enough to #define them only when the library is
 452          being built (during installation).  Since we don't have an 'export'
 453          keyword, much of the library exists as headers, which means that
 454          the symbols must also be defined as your programs are parsed and
 455          compiled.
 456       </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 457          the gcc config headers for your target (and try changing them to
 458          see what happens when building complicated code).  You can also run
 459          <span class="command"><strong>g++ -E -dM - &lt; /dev/null"</strong></span> to display
 460          a list of predefined macros for any particular installation.
 461       </p><p>This has been discussed on the mailing lists
 462          <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>.
 463       </p><p>This method is something of a wart.  We'd like to find a cleaner
 464          solution, but nobody yet has contributed the time.
 465       </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>
 466       Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
 467     </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,
 468          the patch is quite simple, and well-known.
 469          <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
 470          link to the solution</a>.
 471       </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>
 472       Threading is broken on i386?
 473     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
 474     </p><p>Support for atomic integer operations is/was broken on i386
 475          platforms.  The assembly code accidentally used opcodes that are
 476          only available on the i486 and later.  So if you configured GCC
 477          to target, for example, i386-linux, but actually used the programs
 478          on an i686, then you would encounter no problems.  Only when
 479          actually running the code on a i386 will the problem appear.
 480       </p><p>This is fixed in 3.2.2.
 481       </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>
 482       MIPS atomic operations
 483     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
 484     The atomic locking routines for MIPS targets requires MIPS II
 485     and later.  A patch went in just after the 3.3 release to
 486     make mips* use the generic implementation instead.  You can also
 487     configure for mipsel-elf as a workaround.
 488     </p><p>
 489     The mips*-*-linux* port continues to use the MIPS II routines, and more
 490     work in this area is expected.
 491     </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>
 492       Recent GNU/Linux glibc required?
 493     </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
 494          5.0.1) and later uses localization and formatting code from the system
 495          C library (glibc) version 2.2.5 which contains necessary bugfixes.
 496          Most GNU/Linux distros make more recent versions available now.
 497          libstdc++ 4.6.0 and later require glibc 2.3 or later for this
 498          localization and formatting code.
 499       </p><p>The guideline is simple:  the more recent the C++ library, the
 500          more recent the C library.  (This is also documented in the main
 501          GCC installation instructions.)
 502       </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>
 503       Can't use wchar_t/wstring on FreeBSD
 504     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
 505     Older versions of FreeBSD's C library do not have sufficient
 506     support for wide character functions, and as a result the
 507     libstdc++ configury decides that wchar_t support should be
 508     disabled. In addition, the libstdc++ platform checks that
 509     enabled <span class="type">wchar_t</span> were quite strict, and not granular
 510     enough to detect when the minimal support to
 511     enable <span class="type">wchar_t</span> and C++ library structures
 512     like <code class="classname">wstring</code> were present. This impacted Solaris,
 513     Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
 514     </p><p>
 515     </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
 516       What works already?
 517     </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
 518       Bugs in the ISO C++ language or library specification
 519     </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
 520       Bugs in the compiler (gcc/g++) and not libstdc++
 521     </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>
 522       What works already?
 523     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
 524     Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
 525     except for some corner cases.  Support for localization
 526     in <code class="classname">locale</code> may be incomplete on non-GNU
 527     platforms. Also dependent on the underlying platform is support
 528     for <span class="type">wchar_t</span> and <span class="type">long
 529     long</span> specializations, and details of thread support.
 530     </p><p>
 531     Long answer: See the implementation status pages for
 532     <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
 533     <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
 534     <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>.
 535     <a class="link" href="manual/status.html#status.iso.2014" title="C++ 2014">C++14</a>.
 536     </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>
 537       Bugs in the ISO C++ language or library specification
 538     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
 539     Unfortunately, there are some.
 540     </p><p>
 541     For those people who are not part of the ISO Library Group
 542     (i.e., nearly all of us needing to read this page in the first
 543     place), a public list of the library defects is occasionally
 544     published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
 545     website</a>.
 546     Some of these issues have resulted in code changes in libstdc++.
 547     </p><p>
 548     If you think you've discovered a new bug that is not listed,
 549     please post a message describing your problem to the author of
 550     the library issues list or the Usenet group comp.lang.c++.moderated.
 551     </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>
 552       Bugs in the compiler (gcc/g++) and not libstdc++
 553     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
 554     On occasion, the compiler is wrong. Please be advised that this
 555     happens much less often than one would think, and avoid jumping to
 556     conclusions.
 557     </p><p>
 558     First, examine the ISO C++ standard. Second, try another compiler
 559     or an older version of the GNU compilers. Third, you can find more
 560     information on the libstdc++ and the GCC mailing lists: search
 561     these lists with terms describing your issue.
 562     </p><p>
 563     Before reporting a bug, please examine the
 564     <a class="link" href="http://gcc.gnu.org/bugs/" target="_top">bugs database</a> with the
 565     category set to <span class="quote">“<span class="quote">g++</span>”</span>.
 566     </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">
 567       Reopening a stream fails
 568     </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
 569       -Weffc++ complains too much
 570     </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
 571       Ambiguous overloads after including an old-style header
 572     </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
 573       The g++-3 headers are not ours
 574     </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
 575       Errors about *Concept and
 576       constraints in the STL
 577     </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
 578       Program crashes when using library code in a
 579       dynamically-loaded library
 580     </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
 581       “Memory leaks” in containers
 582     </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
 583       list::size() is O(n)!
 584     </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
 585       Aw, that's easy to fix!
 586     </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>
 587       Reopening a stream fails
 588     </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>
 589     One of the most-reported non-bug reports. Executing a sequence like:
 590     </p><div class="literallayout"><p><br />
 591     #include &lt;fstream&gt;<br />
 592     ...<br />
 593     std::fstream  fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
 594     // .<br />
 595     // . do things with fs...<br />
 596     // .<br />
 597     fs.close();<br />
 598     fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
 599     </p></div><p>
 600     All operations on the re-opened <code class="varname">fs</code> will fail, or at
 601     least act very strangely.  Yes, they often will, especially if
 602     <code class="varname">fs</code> reached the EOF state on the previous file.  The
 603     reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
 604     on a successful call to open().  The standard unfortunately did
 605     not specify behavior in this case, and to everybody's great sorrow,
 606     the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
 607       DR #22</a> is to leave the flags unchanged.  You must insert a call
 608     to <code class="function">fs.clear()</code> between the calls to close() and open(),
 609     and then everything will work like we all expect it to work.
 610     <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
 611     of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
 612     now calls <code class="function">clear()</code> on success!
 613     </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>
 614       -Weffc++ complains too much
 615     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
 616     Many warnings are emitted when <code class="literal">-Weffc++</code> is used.  Making
 617     libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
 618     for a few reasons.  Mainly, that option tries to enforce
 619     object-oriented programming, while the Standard Library isn't
 620     necessarily trying to be OO.
 621     </p><p>
 622     We do, however, try to have libstdc++ sources as clean as possible. If
 623     you see some simple changes that pacify <code class="literal">-Weffc++</code>
 624     without other drawbacks, send us a patch.
 625     </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>
 626       Ambiguous overloads after including an old-style header
 627     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
 628     Another problem is the <code class="literal">rel_ops</code> namespace and the template
 629     comparison operator functions contained therein.  If they become
 630     visible in the same namespace as other comparison functions
 631     (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the &lt;iterator&gt; header),
 632     then you will suddenly be faced with huge numbers of ambiguity
 633     errors.  This was discussed on the -v3 list; Nathan Myers
 634     <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
 635       things up here</a>.  The collisions with vector/string iterator
 636     types have been fixed for 3.1.
 637     </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>
 638       The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
 639     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
 640         If you are using headers in
 641         <code class="filename">${prefix}/include/g++-3</code>, or if the installed
 642         library's name looks like <code class="filename">libstdc++-2.10.a</code> or
 643         <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
 644         old libstdc++-v2 library, which is nonstandard and
 645         unmaintained.  Do not report problems with -v2 to the -v3
 646         mailing list.
 647       </p><p>
 648         For GCC versions 3.0 and 3.1 the libstdc++ header files are
 649         installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
 650         'v'?).  Starting with version 3.2 the headers are installed in
 651         <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
 652         headers from previous versions being found by mistake.
 653       </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>
 654       Errors about <span class="emphasis"><em>*Concept</em></span> and
 655       <span class="emphasis"><em>constraints</em></span> in the STL
 656     </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>
 657     If you see compilation errors containing messages about
 658     <span class="errortext">foo Concept </span>and something to do with a
 659     <span class="errortext">constraints</span> member function, then most
 660     likely you have violated one of the requirements for types used
 661     during instantiation of template containers and functions.  For
 662     example, EqualityComparableConcept appears if your types must be
 663     comparable with == and you have not provided this capability (a
 664     typo, or wrong visibility, or you just plain forgot, etc).
 665     </p><p>
 666     More information, including how to optionally enable/disable the
 667     checks, is available in the
 668     <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
 669     chapter of the manual.
 670     </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>
 671       Program crashes when using library code in a
 672       dynamically-loaded library
 673     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
 674     If you are using the C++ library across dynamically-loaded
 675     objects, make certain that you are passing the correct options
 676     when compiling and linking:
 677     </p><div class="literallayout"><p><br />
 678     // compile your library components<br />
 679     g++ -fPIC -c a.cc<br />
 680     g++ -fPIC -c b.cc<br />
 681     ...<br />
 682     g++ -fPIC -c z.cc<br />
 683 <br />
 684     // create your library<br />
 685     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
 686 <br />
 687     // link the executable<br />
 688     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
 689     </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>
 690       <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
 691     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
 692     A few people have reported that the standard containers appear
 693     to leak memory when tested with memory checkers such as
 694     <a class="link" href="http://valgrind.org/" target="_top">valgrind</a>.
 695     Under some configurations the library's allocators keep free memory in a
 696     pool for later reuse, rather than returning it to the OS.  Although
 697     this memory is always reachable by the library and is never
 698     lost, memory debugging tools can report it as a leak.  If you
 699     want to test the library for memory leaks please read
 700     <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
 701     first.
 702     </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>
 703       list::size() is O(n)!
 704     </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>
 705     See
 706     the <a class="link" href="manual/containers.html" title="Chapter 9.  Containers">Containers</a>
 707     chapter.
 708     </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>
 709       Aw, that's easy to fix!
 710     </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>
 711     If you have found a bug in the library and you think you have
 712     a working fix, then send it in!  The main GCC site has a page
 713     on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
 714     patches</a> that covers the procedure, but for libstdc++ you
 715     should also send the patch to our mailing list in addition to
 716     the GCC patches mailing list.  The libstdc++
 717     <a class="link" href="manual/appendix_contributing.html" title="Appendix A.  Contributing">contributors' page</a>
 718     also talks about how to submit patches.
 719     </p><p>
 720     In addition to the description, the patch, and the ChangeLog
 721     entry, it is a Good Thing if you can additionally create a small
 722     test program to test for the presence of the bug that your patch
 723     fixes.  Bugs have a way of being reintroduced; if an old bug
 724     creeps back in, it will be caught immediately by the testsuite -
 725     but only if such a test exists.
 726     </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">
 727       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 728     </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
 729       What's next after libstdc++?
 730     </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
 731       What about the STL from SGI?
 732     </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
 733       Extensions and Backward Compatibility
 734     </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
 735       Does libstdc++ support TR1?
 736     </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
 737     </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
 738       What's an ABI and why is it so messy?
 739     </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
 740       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 741     </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>
 742       string::iterator is not char*; vector&lt;T&gt;::iterator is not T*
 743     </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>
 744     If you have code that depends on container&lt;T&gt; iterators
 745     being implemented as pointer-to-T, your code is broken. It's
 746     considered a feature, not a bug, that libstdc++ points this out.
 747     </p><p>
 748     While there are arguments for iterators to be implemented in
 749     that manner, A) they aren't very good ones in the long term,
 750     and B) they were never guaranteed by the Standard anyway.  The
 751     type-safety achieved by making iterators a real class rather
 752     than a typedef for <span class="type">T*</span> outweighs nearly all opposing
 753     arguments.
 754     </p><p>
 755     Code which does assume that a vector iterator <code class="varname">i</code>
 756     is a pointer can often be fixed by changing <code class="varname">i</code> in
 757     certain expressions to <code class="varname">&amp;*i</code>.  Future revisions
 758     of the Standard are expected to bless this usage for
 759     vector&lt;&gt; (but not for basic_string&lt;&gt;).
 760     </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>
 761       What's next after libstdc++?
 762     </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>
 763         Hopefully, not much.  The goal of libstdc++ is to produce a
 764         fully-compliant, fully-portable Standard Library.  After that,
 765         we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
 766         more compliance work to do.
 767       </p><p>
 768         There is an effort underway to add significant extensions to
 769         the standard library specification.  The latest version of
 770         this effort is described in
 771          <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 772          The C++ Library Technical Report 1</a>.
 773       </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>
 774       What about the STL from SGI?
 775     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
 776       The <a class="link" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
 777     version 3.3, was the final merge of the STL codebase.  The
 778     code in libstdc++ contains many fixes and changes, and
 779     the SGI code is no longer under active
 780     development.  We expect that no future merges will take place.
 781     </p><p>
 782     In particular, <code class="classname">string</code> is not from SGI and makes no
 783     use of their "rope" class (which is included as an
 784     optional extension), nor is <code class="classname">valarray</code> and some others.
 785     Classes like <code class="classname">vector&lt;&gt;</code> are, but have been
 786     extensively modified.
 787     </p><p>
 788     More information on the evolution of libstdc++ can be found at the
 789     <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
 790     evolution</a>
 791     and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
 792     compatibility</a> documentation.
 793     </p><p>
 794     The FAQ for SGI's STL (one jump off of their main page) is
 795     still recommended reading.
 796     </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>
 797       Extensions and Backward Compatibility
 798     </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>
 799       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.
 800     </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>
 801       Does libstdc++ support TR1?
 802     </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
 803     Yes.
 804     </p><p>
 805     The C++ Standard Library Technical Report adds many new features to
 806     the library.  The latest version of this effort is described in
 807     <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
 808          Technical Report 1</a>.
 809     </p><p>
 810     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
 811     page</a>.
 812     </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?
 813     </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>
 814     Copies of the full ISO 14882 standard are available on line via
 815     the ISO mirror site for committee members.  Non-members, or those
 816     who have not paid for the privilege of sitting on the committee
 817     and sustained their two-meeting commitment for voting rights, may
 818     get a copy of the standard from their respective national
 819     standards organization.  In the USA, this national standards
 820     organization is ANSI and their website is
 821     right <a class="link" href="http://www.ansi.org" target="_top">here</a>.  (And if
 822     you've already registered with them, clicking this link will take
 823     you to directly to the place where you can
 824     <a class="link" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
 825     </p><p>
 826     Who is your country's member body?  Visit the
 827     <a class="link" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
 828     </p><p>
 829     The 2003 version of the standard (the 1998 version plus TC1) is
 830     available in print, ISBN 0-470-84674-7.
 831     </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>
 832       What's an ABI and why is it so messy?
 833     </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>
 834     <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
 835      Interface</span>”</span>.  Conventionally, it refers to a great
 836     mass of details about how arguments are arranged on the call
 837     stack and/or in registers, and how various types are arranged
 838     and padded in structs.  A single CPU design may suffer
 839     multiple ABIs designed by different development tool vendors
 840     who made different choices, or even by the same vendor for
 841     different target applications or compiler versions.  In ideal
 842     circumstances the CPU designer presents one ABI and all the
 843     OSes and compilers use it.  In practice every ABI omits
 844     details that compiler implementers (consciously or
 845     accidentally) must choose for themselves.
 846     </p><p>
 847     That ABI definition suffices for compilers to generate code so a
 848     program can interact safely with an OS and its lowest-level libraries.
 849     Users usually want an ABI to encompass more detail, allowing libraries
 850     built with different compilers (or different releases of the same
 851     compiler!) to be linked together.  For C++, this includes many more
 852     details than for C, and CPU designers (for good reasons elaborated
 853     below) have not stepped up to publish C++ ABIs.  The details include
 854     virtual function implementation, struct inheritance layout, name
 855     mangling, and exception handling.  Such an ABI has been defined for
 856     GNU C++, and is immediately useful for embedded work relying only on
 857     a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
 858     of) the standard library.  It is a good basis for the work to come.
 859     </p><p>
 860     A useful C++ ABI must also incorporate many details of the standard
 861     library implementation.  For a C ABI, the layouts of a few structs
 862     (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 863     For C++, the details include the complete set of names of functions
 864     and types used, the offsets of class members and virtual functions,
 865     and the actual definitions of all inlines.  C++ exposes many more
 866     library details to the caller than C does.  It makes defining
 867     a complete ABI a much bigger undertaking, and requires not just
 868     documenting library implementation details, but carefully designing
 869     those details so that future bug fixes and optimizations don't
 870     force breaking the ABI.
 871     </p><p>
 872     There are ways to help isolate library implementation details from the
 873     ABI, but they trade off against speed.  Library details used in
 874     inner loops (e.g., getchar) must be exposed and frozen for all
 875     time, but many others may reasonably be kept hidden from user code,
 876     so they may later be changed.  Deciding which, and implementing
 877     the decisions, must happen before you can reasonably document a
 878     candidate C++ ABI that encompasses the standard library.
 879     </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>
 880       How do I make std::vector&lt;T&gt;::capacity() == std::vector&lt;T&gt;::size?
 881     </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>
 882     The standard idiom for deallocating a <code class="classname">vector&lt;T&gt;</code>'s
 883     unused memory is to create a temporary copy of the vector and swap their
 884     contents, e.g. for <code class="classname">vector&lt;T&gt; v</code>
 885     </p><div class="literallayout"><p><br />
 886      std::vector&lt;T&gt;(v).swap(v);<br />
 887     </p></div><p>
 888     The copy will take O(n) time and the swap is constant time.
 889     </p><p>
 890     See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
 891     strings</a> for a similar solution for strings.
 892     </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>