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875 lines
63 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Frequently Asked Questions</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><link rel="home" href="spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="bk03.html" title="" /><link rel="prev" href="bk03.html" title="" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frequently Asked Questions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><th width="60%" align="center"></th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="article" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="faq"></a>Frequently Asked Questions</h2></div><div><p class="copyright">Copyright ©
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2008
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<a class="ulink" href="http://fsf.org" target="_top">FSF</a>
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</p></div></div><hr /></div><div class="qandaset"><dl><dt>1. <a href="faq.html#faq.info">General Information</a></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
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What is libstdc++?
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</a></dt><dt>1.2. <a href="faq.html#faq.why">
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Why should I use libstdc++?
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</a></dt><dt>1.3. <a href="faq.html#faq.who">
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Who's in charge of it?
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</a></dt><dt>1.4. <a href="faq.html#faq.when">
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When is libstdc++ going to be finished?
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</a></dt><dt>1.5. <a href="faq.html#faq.how">
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How do I contribute to the effort?
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</a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
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What happened to the older libg++? I need that!
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</a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
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What if I have more questions?
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</a></dt></dl></dd><dt>2. <a href="faq.html#faq.license">License</a></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
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What are the license terms for libstdc++?
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</a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
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So any program which uses libstdc++ falls under the GPL?
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</a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
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How is that different from the GNU {Lesser,Library} GPL?
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</a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
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I see. So, what restrictions are there on programs that use the library?
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</a></dt></dl></dd><dt>3. <a href="faq.html#faq.installation">Installation</a></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
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</a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
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</a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
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</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?
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</a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
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What's libsupc++?
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</a></dt><dt>3.6. <a href="faq.html#faq.size">
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This library is HUGE!
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</a></dt></dl></dd><dt>4. <a href="faq.html#faq.platform-specific">Platform-Specific Issues</a></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
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Can libstdc++ be used with non-GNU compilers?
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</a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
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No 'long long' type on Solaris?
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</a></dt><dt>4.3. <a href="faq.html#faq.predefined">
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_XOPEN_SOURCE and _GNU_SOURCE are always defined?
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</a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
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Mac OS X ctype.h is broken! How can I fix it?
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</a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
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Threading is broken on i386?
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</a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
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MIPS atomic operations
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</a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
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Recent GNU/Linux glibc required?
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</a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
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Can't use wchar_t/wstring on FreeBSD
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</a></dt></dl></dd><dt>5. <a href="faq.html#faq.known_bugs">Known Bugs</a></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
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What works already?
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</a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
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Bugs in the ISO C++ language or library specification
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</a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
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Bugs in the compiler (gcc/g++) and not libstdc++
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</a></dt></dl></dd><dt>6. <a href="faq.html#faq.known_non-bugs">Known Non-Bugs</a></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
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Reopening a stream fails
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</a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
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-Weffc++ complains too much
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</a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
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Ambiguous overloads after including an old-style header
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</a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
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The g++-3 headers are not ours
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</a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
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Errors about *Concept and
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constraints in the STL
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</a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
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Program crashes when using library code in a
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dynamically-loaded library
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</a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
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“Memory leaks” in containers
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</a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
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list::size() is O(n)!
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</a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
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Aw, that's easy to fix!
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</a></dt></dl></dd><dt>7. <a href="faq.html#faq.misc">Miscellaneous</a></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
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string::iterator is not char*; vector<T>::iterator is not T*
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</a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
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What's next after libstdc++?
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</a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
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What about the STL from SGI?
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</a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
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Extensions and Backward Compatibility
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</a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
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Does libstdc++ support TR1?
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</a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
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</a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
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What's an ABI and why is it so messy?
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</a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
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How do I make std::vector<T>::capacity() == std::vector<T>::size?
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</a></dt></dl></dd></dl><table border="0" summary="Q and A Set"><col align="left" width="1%" /><tbody><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.info"></a>1. General Information</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
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What is libstdc++?
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</a></dt><dt>1.2. <a href="faq.html#faq.why">
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Why should I use libstdc++?
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</a></dt><dt>1.3. <a href="faq.html#faq.who">
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Who's in charge of it?
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</a></dt><dt>1.4. <a href="faq.html#faq.when">
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When is libstdc++ going to be finished?
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</a></dt><dt>1.5. <a href="faq.html#faq.how">
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How do I contribute to the effort?
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</a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
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What happened to the older libg++? I need that!
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</a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
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What if I have more questions?
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</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><b>1.1.</b></p></td><td align="left" valign="top"><p>
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What is libstdc++?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
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The GNU Standard C++ Library v3 is an ongoing project to
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implement the ISO 14882 Standard C++ library as described in
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chapters 17 through 27 and annex D. For those who want to see
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exactly how far the project has come, or just want the latest
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bleeding-edge code, the up-to-date source is available over
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anonymous SVN, and can even be browsed over
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the <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top">web</a>.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><b>1.2.</b></p></td><td align="left" valign="top"><p>
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Why should I use libstdc++?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
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The completion of the ISO C++ standardization gave the C++
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community a powerful set of reuseable tools in the form of the C++
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Standard Library. However, all existing C++ implementations are
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(as the Draft Standard used to say) “<span class="quote">incomplet and
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incorrekt</span>”, and many suffer from limitations of the compilers
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that use them.
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</p><p>
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The GNU compiler collection
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(<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
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considered to be one of the leading compilers in the world. Its
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development is overseen by the
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<a class="ulink" href="http://gcc.gnu.org/" target="_top">GCC team</a>. All of
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the rapid development and near-legendary
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<a class="ulink" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a>
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that are the hallmarks of an open-source project are being
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applied to libstdc++.
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</p><p>
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That means that all of the Standard classes and functions will be
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freely available and fully compliant. (Such as
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<code class="classname">string</code>,
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<code class="classname">vector<></code>, iostreams, and algorithms.)
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Programmers will no longer need to “<span class="quote">roll their own</span>”
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nor be worried about platform-specific incompatibilities.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><b>1.3.</b></p></td><td align="left" valign="top"><p>
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Who's in charge of it?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
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The libstdc++ project is contributed to by several developers
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all over the world, in the same way as GCC or Linux.
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Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
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Loren James Rittle, and Paolo Carlini are the lead maintainers of
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the SVN archive.
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</p><p>
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Development and discussion is held on the libstdc++ mailing
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list. Subscribing to the list, or searching the list
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archives, is open to everyone. You can read instructions for
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doing so on the <a class="ulink" href="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>.
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If you have questions, ideas, code, or are just curious, sign up!
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.when"></a><a id="q-when"></a><p><b>1.4.</b></p></td><td align="left" valign="top"><p>
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When is libstdc++ going to be finished?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
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Nathan Myers gave the best of all possible answers, responding to
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a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
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help.</em></span>
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><b>1.5.</b></p></td><td align="left" valign="top"><p>
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How do I contribute to the effort?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
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Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">a page devoted to
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this topic</a>. Subscribing to the mailing list (see above, or
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the homepage) is a very good idea if you have something to
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contribute, or if you have spare time and want to
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help. Contributions don't have to be in the form of source code;
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anybody who is willing to help write documentation, for example,
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or has found a bug in code that we all thought was working and is
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willing to provide details, is more than welcome!
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.whereis_old"></a><a id="q-whereis_old"></a><p><b>1.6.</b></p></td><td align="left" valign="top"><p>
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What happened to the older libg++? I need that!
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
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The most recent libg++ README states that libg++ is no longer
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being actively maintained. It should not be used for new
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projects, and is only being kicked along to support older code.
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</p><p>
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More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a>
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.more_questions"></a><a id="q-more_questions"></a><p><b>1.7.</b></p></td><td align="left" valign="top"><p>
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What if I have more questions?
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
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If you have read the README file, and your question remains
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unanswered, then just ask the mailing list. At present, you do not
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need to be subscribed to the list to send a message to it. More
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information is available on the homepage (including how to browse
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the list archives); to send a message to the list,
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use <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code>.
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</p><p>
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If you have a question that you think should be included
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here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
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here, please send email to the libstdc++ mailing list, as above.
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</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.license"></a>2. License</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
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What are the license terms for libstdc++?
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</a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
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So any program which uses libstdc++ falls under the GPL?
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</a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
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How is that different from the GNU {Lesser,Library} GPL?
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||
</a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
|
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I see. So, what restrictions are there on programs that use the library?
|
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</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><b>2.1.</b></p></td><td align="left" valign="top"><p>
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What are the license terms for libstdc++?
|
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</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
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||
See <a class="link" href="manual/license.html" title="License">our license description</a>
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||
for these and related questions.
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||
</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><b>2.2.</b></p></td><td align="left" valign="top"><p>
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So any program which uses libstdc++ falls under the GPL?
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</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>
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No. The special exception permits use of the library in
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proprietary applications.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.lgpl"></a><a id="q-license.lgpl"></a><p><b>2.3.</b></p></td><td align="left" valign="top"><p>
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||
How is that different from the GNU {Lesser,Library} GPL?
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||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
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||
The LGPL requires that users be able to replace the LGPL code with a
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||
modified version; this is trivial if the library in question is a C
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shared library. But there's no way to make that work with C++, where
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much of the library consists of inline functions and templates, which
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are expanded inside the code that uses the library. So to allow people
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to replace the library code, someone using the library would have to
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distribute their own source, rendering the LGPL equivalent to the GPL.
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||
</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><b>2.4.</b></p></td><td align="left" valign="top"><p>
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||
I see. So, what restrictions are there on programs that use the library?
|
||
</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>
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||
None. We encourage such programs to be released as open source,
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||
but we won't punish you or sue you if you choose otherwise.
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</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.installation"></a>3. Installation</h3></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++?
|
||
</a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
|
||
</a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
|
||
</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?
|
||
</a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
|
||
What's libsupc++?
|
||
</a></dt><dt>3.6. <a href="faq.html#faq.size">
|
||
This library is HUGE!
|
||
</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><b>3.1.</b></p></td><td align="left" valign="top"><p>How do I install libstdc++?
|
||
</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>
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||
Often libstdc++ comes pre-installed as an integral part of many
|
||
existing Linux and Unix systems, as well as many embedded
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||
development tools. It may be necessary to install extra
|
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development packages to get the headers, or the documentation, or
|
||
the source: please consult your vendor for details.
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||
</p><p>
|
||
To build and install from the GNU GCC sources, please consult the
|
||
<a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
|
||
documentation</a> for detailed
|
||
instructions. You may wish to browse those files ahead
|
||
of time to get a feel for what's required.
|
||
</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><b>3.2.</b></p></td><td align="left" valign="top"><p>How does one get current libstdc++ sources?
|
||
</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>
|
||
Libstdc++ sources for all official releases can be obtained as
|
||
part of the GCC sources, available from various sites and
|
||
mirrors. A full <a class="ulink" href="http://gcc.gnu.org/mirrors.html" target="_top">list of
|
||
download sites</a> is provided on the main GCC site.
|
||
</p><p>
|
||
Current libstdc++ sources can always be checked out of the main
|
||
GCC source repository using the appropriate version control
|
||
tool. At this time, that tool
|
||
is <span class="application">Subversion</span>.
|
||
</p><p>
|
||
<span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
|
||
one of several revision control packages. It was selected for GNU
|
||
projects because it's free (speech), free (beer), and very high
|
||
quality. The <a class="ulink" href="http://subversion.tigris.org" target="_top"> Subversion
|
||
home page</a> has a better description.
|
||
</p><p>
|
||
The “<span class="quote">anonymous client checkout</span>” feature of SVN is
|
||
similar to anonymous FTP in that it allows anyone to retrieve
|
||
the latest libstdc++ sources.
|
||
</p><p>
|
||
For more information
|
||
see <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
|
||
details</a>.
|
||
</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><b>3.3.</b></p></td><td align="left" valign="top"><p>How do I know if it works?
|
||
</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>
|
||
Libstdc++ comes with its own validation testsuite, which includes
|
||
conformance testing, regression testing, ABI testing, and
|
||
performance testing. Please consult the
|
||
<a class="ulink" href="http://gcc.gnu.org/install/test.html" target="_top">testing
|
||
documentation</a> for more details.
|
||
</p><p>
|
||
If you find bugs in the testsuite programs themselves, or if you
|
||
think of a new test program that should be added to the suite,
|
||
<span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
|
||
</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><b>3.4.</b></p></td><td align="left" valign="top"><p>How do I insure that the dynamically linked library will be found?
|
||
</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>
|
||
Depending on your platform and library version, the error message might
|
||
be similar to one of the following:
|
||
</p><pre class="screen">
|
||
./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
|
||
|
||
/usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
|
||
</pre><p>
|
||
This doesn't mean that the shared library isn't installed, only
|
||
that the dynamic linker can't find it. When a dynamically-linked
|
||
executable is run the linker finds and loads the required shared
|
||
libraries by searching a pre-configured list of directories. If
|
||
the directory where you've installed libstdc++ is not in this list
|
||
then the libraries won't be found. The simplest way to fix this is
|
||
to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
|
||
which is a colon-separated list of directories in which the linker
|
||
will search for shared libraries:
|
||
</p><pre class="screen">
|
||
LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
|
||
export LD_LIBRARY_PATH
|
||
</pre><p>
|
||
The exact environment variable to use will depend on your
|
||
platform, e.g. DYLD_LIBRARY_PATH for Darwin,
|
||
LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
|
||
LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs and
|
||
SHLIB_PATH for HP-UX.
|
||
</p><p>
|
||
See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
|
||
and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
|
||
linker has different names on different platforms but the man page
|
||
is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>.
|
||
</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><b>3.5.</b></p></td><td align="left" valign="top"><p>
|
||
What's libsupc++?
|
||
</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>
|
||
If the only functions from <code class="filename">libstdc++.a</code>
|
||
which you need are language support functions (those listed in
|
||
<a class="link" href="manual/support.html" title="Part II. Support">clause 18</a> of the
|
||
standard, e.g., <code class="function">new</code> and
|
||
<code class="function">delete</code>), then try linking against
|
||
<code class="filename">libsupc++.a</code>, which is a subset of
|
||
<code class="filename">libstdc++.a</code>. (Using <span class="command"><strong>gcc</strong></span>
|
||
instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
|
||
<code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
|
||
for the final link step will do it). This library contains only
|
||
those support routines, one per object file. But if you are
|
||
using anything from the rest of the library, such as IOStreams
|
||
or vectors, then you'll still need pieces from
|
||
<code class="filename">libstdc++.a</code>.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size"></a><a id="q-size"></a><p><b>3.6.</b></p></td><td align="left" valign="top"><p>
|
||
This library is HUGE!
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
|
||
Usually the size of libraries on disk isn't noticeable. When a
|
||
link editor (or simply “<span class="quote">linker</span>”) pulls things from a
|
||
static archive library, only the necessary object files are copied
|
||
into your executable, not the entire library. Unfortunately, even
|
||
if you only need a single function or variable from an object file,
|
||
the entire object file is extracted. (There's nothing unique to C++
|
||
or libstdc++ about this; it's just common behavior, given here
|
||
for background reasons.)
|
||
</p><p>
|
||
Some of the object files which make up libstdc++.a are rather large.
|
||
If you create a statically-linked executable with
|
||
<code class="literal">-static</code>, those large object files are suddenly part
|
||
of your executable. Historically the best way around this was to
|
||
only place a very few functions (often only a single one) in each
|
||
source/object file; then extracting a single function is the same
|
||
as extracting a single .o file. For libstdc++ this is only
|
||
possible to a certain extent; the object files in question contain
|
||
template classes and template functions, pre-instantiated, and
|
||
splitting those up causes severe maintenance headaches.
|
||
</p><p>
|
||
On supported platforms, libstdc++ takes advantage of garbage
|
||
collection in the GNU linker to get a result similar to separating
|
||
each symbol into a separate source and object files. On these platforms,
|
||
GNU ld can place each function and variable into its own
|
||
section in a .o file. The GNU linker can then perform garbage
|
||
collection on unused sections; this reduces the situation to only
|
||
copying needed functions into the executable, as before, but all
|
||
happens automatically.
|
||
</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.platform-specific"></a>4. Platform-Specific Issues</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
|
||
Can libstdc++ be used with non-GNU compilers?
|
||
</a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
|
||
No 'long long' type on Solaris?
|
||
</a></dt><dt>4.3. <a href="faq.html#faq.predefined">
|
||
_XOPEN_SOURCE and _GNU_SOURCE are always defined?
|
||
</a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
|
||
Mac OS X ctype.h is broken! How can I fix it?
|
||
</a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
|
||
Threading is broken on i386?
|
||
</a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
|
||
MIPS atomic operations
|
||
</a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
|
||
Recent GNU/Linux glibc required?
|
||
</a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
|
||
Can't use wchar_t/wstring on FreeBSD
|
||
</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><b>4.1.</b></p></td><td align="left" valign="top"><p>
|
||
Can libstdc++ be used with non-GNU compilers?
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
|
||
Perhaps.
|
||
</p><p>
|
||
Since the goal of ISO Standardization is for all C++
|
||
implementations to be able to share code, libstdc++ should be
|
||
usable under any ISO-compliant compiler, at least in theory.
|
||
</p><p>
|
||
However, the reality is that libstdc++ is targeted and optimized
|
||
for GCC/g++. This means that often libstdc++ uses specific,
|
||
non-standard features of g++ that are not present in older
|
||
versions of proprietary compilers. It may take as much as a year or two
|
||
after an official release of GCC that contains these features for
|
||
proprietary tools support these constructs.
|
||
</p><p>
|
||
In the near past, specific released versions of libstdc++ have
|
||
been known to work with versions of the EDG C++ compiler, and
|
||
vendor-specific proprietary C++ compilers such as the Intel ICC
|
||
C++ compiler.
|
||
</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><b>4.2.</b></p></td><td align="left" valign="top"><p>
|
||
No 'long long' type on Solaris?
|
||
</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>
|
||
By default we try to support the C99 <span class="type">long long</span> type.
|
||
This requires that certain functions from your C library be present.
|
||
</p><p>
|
||
Up through release 3.0.2 the platform-specific tests performed by
|
||
libstdc++ were too general, resulting in a conservative approach
|
||
to enabling the <span class="type">long long</span> code paths. The most
|
||
commonly reported platform affected was Solaris.
|
||
</p><p>
|
||
This has been fixed for libstdc++ releases greater than 3.0.3.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><b>4.3.</b></p></td><td align="left" valign="top"><p>
|
||
<code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
|
||
</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
|
||
macro <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
|
||
with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list;
|
||
other macros and other platforms are also affected.)
|
||
</p><p>These macros are typically used in C library headers, guarding new
|
||
versions of functions from their older versions. The C++ standard
|
||
library includes the C standard library, but it requires the C90
|
||
version, which for backwards-compatibility reasons is often not the
|
||
default for many vendors.
|
||
</p><p>More to the point, the C++ standard requires behavior which is only
|
||
available on certain platforms after certain symbols are defined.
|
||
Usually the issue involves I/O-related typedefs. In order to
|
||
ensure correctness, the compiler simply predefines those symbols.
|
||
</p><p>Note that it's not enough to #define them only when the library is
|
||
being built (during installation). Since we don't have an 'export'
|
||
keyword, much of the library exists as headers, which means that
|
||
the symbols must also be defined as your programs are parsed and
|
||
compiled.
|
||
</p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
|
||
the gcc config headers for your target (and try changing them to
|
||
see what happens when building complicated code). You can also run
|
||
<span class="command"><strong>g++ -E -dM - < /dev/null"</strong></span> to display
|
||
a list of predefined macros for any particular installation.
|
||
</p><p>This has been discussed on the mailing lists
|
||
<a class="ulink" href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris" target="_top">quite a bit</a>.
|
||
</p><p>This method is something of a wart. We'd like to find a cleaner
|
||
solution, but nobody yet has contributed the time.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.darwin_ctype"></a><a id="q-darwin_ctype"></a><p><b>4.4.</b></p></td><td align="left" valign="top"><p>
|
||
Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
|
||
</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,
|
||
the patch is quite simple, and well-known.
|
||
<a class="ulink" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
|
||
link to the solution</a>.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.threads_i386"></a><a id="q-threads_i386"></a><p><b>4.5.</b></p></td><td align="left" valign="top"><p>
|
||
Threading is broken on i386?
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
|
||
</p><p>Support for atomic integer operations is/was broken on i386
|
||
platforms. The assembly code accidentally used opcodes that are
|
||
only available on the i486 and later. So if you configured GCC
|
||
to target, for example, i386-linux, but actually used the programs
|
||
on an i686, then you would encounter no problems. Only when
|
||
actually running the code on a i386 will the problem appear.
|
||
</p><p>This is fixed in 3.2.2.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.atomic_mips"></a><a id="q-atomic_mips"></a><p><b>4.6.</b></p></td><td align="left" valign="top"><p>
|
||
MIPS atomic operations
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
|
||
The atomic locking routines for MIPS targets requires MIPS II
|
||
and later. A patch went in just after the 3.3 release to
|
||
make mips* use the generic implementation instead. You can also
|
||
configure for mipsel-elf as a workaround.
|
||
</p><p>
|
||
The mips*-*-linux* port continues to use the MIPS II routines, and more
|
||
work in this area is expected.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.linux_glibc"></a><a id="q-linux_glibc"></a><p><b>4.7.</b></p></td><td align="left" valign="top"><p>
|
||
Recent GNU/Linux glibc required?
|
||
</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
|
||
5.0.1) and later uses localization and formatting code from the system
|
||
C library (glibc) version 2.2.5. That version of glibc is over a
|
||
year old and contains necessary bugfixes. Many GNU/Linux distros make
|
||
glibc version 2.3.x available now.
|
||
</p><p>The guideline is simple: the more recent the C++ library, the
|
||
more recent the C library. (This is also documented in the main
|
||
GCC installation instructions.)
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.freebsd_wchar"></a><a id="q-freebsd_wchar"></a><p><b>4.8.</b></p></td><td align="left" valign="top"><p>
|
||
Can't use wchar_t/wstring on FreeBSD
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
|
||
Older versions of FreeBSD's C library do not have sufficient
|
||
support for wide character functions, and as a result the
|
||
libstdc++ configury decides that wchar_t support should be
|
||
disabled. In addition, the libstdc++ platform checks that
|
||
enabled <span class="type">wchar_t</span> were quite strict, and not granular
|
||
enough to detect when the minimal support to
|
||
enable <span class="type">wchar_t</span> and C++ library structures
|
||
like <code class="classname">wstring</code> were present. This impacted Solaris,
|
||
Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
|
||
</p><p>
|
||
</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.known_bugs"></a>5. Known Bugs</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
|
||
What works already?
|
||
</a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
|
||
Bugs in the ISO C++ language or library specification
|
||
</a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
|
||
Bugs in the compiler (gcc/g++) and not libstdc++
|
||
</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><b>5.1.</b></p></td><td align="left" valign="top"><p>
|
||
What works already?
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
|
||
Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
|
||
except for some corner cases. Support for localization
|
||
in <code class="classname">locale</code> may be incomplete on non-GNU
|
||
platforms. Also dependant on the underlying platform is support
|
||
for <span class="type">wchar_t</span> and <span class="type">long
|
||
long</span> specializations, and details of thread support.
|
||
</p><p>
|
||
Long answer: See the implementation status pages for
|
||
<a class="link" href="manual/status.html#manual.intro.status.standard.1998" title="C++ 1998/2003">C++98</a>,
|
||
<a class="link" href="manual/status.html#manual.intro.status.standard.tr1" title="C++ TR1">TR1</a>, and
|
||
<a class="link" href="manual/status.html#manual.intro.status.standard.200x" title="C++ 200x">C++0x</a>.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><b>5.2.</b></p></td><td align="left" valign="top"><p>
|
||
Bugs in the ISO C++ language or library specification
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
|
||
Unfortunately, there are some.
|
||
</p><p>
|
||
For those people who are not part of the ISO Library Group
|
||
(i.e., nearly all of us needing to read this page in the first
|
||
place), a public list of the library defects is occasionally
|
||
published <a class="ulink" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/" target="_top">here</a>.
|
||
Some of these issues have resulted in code changes in libstdc++.
|
||
</p><p>
|
||
If you think you've discovered a new bug that is not listed,
|
||
please post a message describing your problem
|
||
to <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code> or the Usenet group
|
||
comp.lang.c++.moderated.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.compiler_bugs"></a><a id="q-compiler_bugs"></a><p><b>5.3.</b></p></td><td align="left" valign="top"><p>
|
||
Bugs in the compiler (gcc/g++) and not libstdc++
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
|
||
On occasion, the compiler is wrong. Please be advised that this
|
||
happens much less often than one would think, and avoid jumping to
|
||
conclusions.
|
||
</p><p>
|
||
First, examine the ISO C++ standard. Second, try another compiler
|
||
or an older version of the GNU compilers. Third, you can find more
|
||
information on the libstdc++ and the GCC mailing lists: search
|
||
these lists with terms describing your issue.
|
||
</p><p>
|
||
Before reporting a bug, please examine the
|
||
<a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the
|
||
category set to “<span class="quote">g++</span>”.
|
||
</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.known_non-bugs"></a>6. Known Non-Bugs</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
|
||
Reopening a stream fails
|
||
</a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
|
||
-Weffc++ complains too much
|
||
</a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
|
||
Ambiguous overloads after including an old-style header
|
||
</a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
|
||
The g++-3 headers are not ours
|
||
</a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
|
||
Errors about *Concept and
|
||
constraints in the STL
|
||
</a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
|
||
Program crashes when using library code in a
|
||
dynamically-loaded library
|
||
</a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
|
||
“Memory leaks” in containers
|
||
</a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
|
||
list::size() is O(n)!
|
||
</a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
|
||
Aw, that's easy to fix!
|
||
</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><b>6.1.</b></p></td><td align="left" valign="top"><p>
|
||
Reopening a stream fails
|
||
</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>
|
||
One of the most-reported non-bug reports. Executing a sequence like:
|
||
</p><div class="literallayout"><p><br />
|
||
#include <fstream><br />
|
||
...<br />
|
||
std::fstream fs(“<span class="quote">a_file</span>”);<br />
|
||
// .<br />
|
||
// . do things with fs...<br />
|
||
// .<br />
|
||
fs.close();<br />
|
||
fs.open(“<span class="quote">a_new_file</span>”);<br />
|
||
</p></div><p>
|
||
All operations on the re-opened <code class="varname">fs</code> will fail, or at
|
||
least act very strangely. Yes, they often will, especially if
|
||
<code class="varname">fs</code> reached the EOF state on the previous file. The
|
||
reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
|
||
on a successful call to open(). The standard unfortunately did
|
||
not specify behavior in this case, and to everybody's great sorrow,
|
||
the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
|
||
DR #22</a> is to leave the flags unchanged. You must insert a call
|
||
to <code class="function">fs.clear()</code> between the calls to close() and open(),
|
||
and then everything will work like we all expect it to work.
|
||
<span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
|
||
of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
|
||
now calls <code class="function">clear()</code> on success!
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.wefcxx_verbose"></a><a id="q-wefcxx_verbose"></a><p><b>6.2.</b></p></td><td align="left" valign="top"><p>
|
||
-Weffc++ complains too much
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
|
||
Many warnings are emitted when <code class="literal">-Weffc++</code> is used. Making
|
||
libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
|
||
for a few reasons. Mainly, that option tries to enforce
|
||
object-oriented programming, while the Standard Library isn't
|
||
necessarily trying to be OO.
|
||
</p><p>
|
||
We do, however, try to have libstdc++ sources as clean as possible. If
|
||
you see some simple changes that pacify <code class="literal">-Weffc++</code>
|
||
without other drawbacks, send us a patch.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.ambiguous_overloads"></a><a id="q-ambiguous_overloads"></a><p><b>6.3.</b></p></td><td align="left" valign="top"><p>
|
||
Ambiguous overloads after including an old-style header
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
|
||
Another problem is the <code class="literal">rel_ops</code> namespace and the template
|
||
comparison operator functions contained therein. If they become
|
||
visible in the same namespace as other comparison functions
|
||
(e.g., “<span class="quote">using</span>” them and the <iterator> header),
|
||
then you will suddenly be faced with huge numbers of ambiguity
|
||
errors. This was discussed on the -v3 list; Nathan Myers
|
||
<a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
|
||
things up here</a>. The collisions with vector/string iterator
|
||
types have been fixed for 3.1.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.v2_headers"></a><a id="q-v2_headers"></a><p><b>6.4.</b></p></td><td align="left" valign="top"><p>
|
||
The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
|
||
If you have found an extremely broken header file which is
|
||
causing problems for you, look carefully before submitting a
|
||
"high" priority bug report (which you probably
|
||
shouldn't do anyhow; see the last paragraph of the page
|
||
describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC
|
||
bug database</a>).
|
||
</p><p>
|
||
If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
|
||
if the installed library's name looks like
|
||
<code class="filename">libstdc++-2.10.a</code> or
|
||
<code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
|
||
old libstdc++-v2 library, which is nonstandard and
|
||
unmaintained. Do not report problems with -v2 to the -v3
|
||
mailing list.
|
||
</p><p>
|
||
For GCC versions 3.0 and 3.1 the libstdc++ header files are
|
||
installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
|
||
'v'?). Starting with version 3.2 the headers are installed in
|
||
<code class="filename">${prefix}/include/c++/${version}</code> as this prevents
|
||
headers from previous versions being found by mistake.
|
||
</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><b>6.5.</b></p></td><td align="left" valign="top"><p>
|
||
Errors about <span class="emphasis"><em>*Concept</em></span> and
|
||
<span class="emphasis"><em>constraints</em></span> in the STL
|
||
</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>
|
||
If you see compilation errors containing messages about
|
||
<span class="errortext">foo Concept </span>and something to do with a
|
||
<span class="errortext">constraints</span> member function, then most
|
||
likely you have violated one of the requirements for types used
|
||
during instantiation of template containers and functions. For
|
||
example, EqualityComparableConcept appears if your types must be
|
||
comparable with == and you have not provided this capability (a
|
||
typo, or wrong visibility, or you just plain forgot, etc).
|
||
</p><p>
|
||
More information, including how to optionally enable/disable the
|
||
checks, is available
|
||
<a class="link" href="manual/bk01pt03ch08.html" title="Chapter 8. Concept Checking">here</a>.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><b>6.6.</b></p></td><td align="left" valign="top"><p>
|
||
Program crashes when using library code in a
|
||
dynamically-loaded library
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
|
||
If you are using the C++ library across dynamically-loaded
|
||
objects, make certain that you are passing the correct options
|
||
when compiling and linking:
|
||
</p><div class="literallayout"><p><br />
|
||
// compile your library components<br />
|
||
g++ -fPIC -c a.cc<br />
|
||
g++ -fPIC -c b.cc<br />
|
||
...<br />
|
||
g++ -fPIC -c z.cc<br />
|
||
<br />
|
||
// create your library<br />
|
||
g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
|
||
<br />
|
||
// link the executable<br />
|
||
g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
|
||
</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><b>6.7.</b></p></td><td align="left" valign="top"><p>
|
||
“<span class="quote">Memory leaks</span>” in containers
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
|
||
A few people have reported that the standard containers appear
|
||
to leak memory when tested with memory checkers such as
|
||
<a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>.
|
||
The library's default allocators keep free memory in a pool
|
||
for later reuse, rather than returning it to the OS. Although
|
||
this memory is always reachable by the library and is never
|
||
lost, memory debugging tools can report it as a leak. If you
|
||
want to test the library for memory leaks please read
|
||
<a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
|
||
first.
|
||
</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><b>6.8.</b></p></td><td align="left" valign="top"><p>
|
||
list::size() is O(n)!
|
||
</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>
|
||
See
|
||
the <a class="link" href="manual/containers.html" title="Part VII. Containers">Containers</a>
|
||
chapter.
|
||
</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><b>6.9.</b></p></td><td align="left" valign="top"><p>
|
||
Aw, that's easy to fix!
|
||
</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>
|
||
If you have found a bug in the library and you think you have
|
||
a working fix, then send it in! The main GCC site has a page
|
||
on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
|
||
patches</a> that covers the procedure, but for libstdc++ you
|
||
should also send the patch to our mailing list in addition to
|
||
the GCC patches mailing list. The libstdc++
|
||
<a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">contributors' page</a>
|
||
also talks about how to submit patches.
|
||
</p><p>
|
||
In addition to the description, the patch, and the ChangeLog
|
||
entry, it is a Good Thing if you can additionally create a small
|
||
test program to test for the presence of the bug that your
|
||
patch fixes. Bugs have a way of being reintroduced; if an old
|
||
bug creeps back in, it will be caught immediately by the
|
||
<a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists.
|
||
</p></td></tr><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.misc"></a>7. Miscellaneous</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
|
||
string::iterator is not char*; vector<T>::iterator is not T*
|
||
</a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
|
||
What's next after libstdc++?
|
||
</a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
|
||
What about the STL from SGI?
|
||
</a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
|
||
Extensions and Backward Compatibility
|
||
</a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
|
||
Does libstdc++ support TR1?
|
||
</a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
|
||
</a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
|
||
What's an ABI and why is it so messy?
|
||
</a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
|
||
How do I make std::vector<T>::capacity() == std::vector<T>::size?
|
||
</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><b>7.1.</b></p></td><td align="left" valign="top"><p>
|
||
string::iterator is not char*; vector<T>::iterator is not T*
|
||
</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>
|
||
If you have code that depends on container<T> iterators
|
||
being implemented as pointer-to-T, your code is broken. It's
|
||
considered a feature, not a bug, that libstdc++ points this out.
|
||
</p><p>
|
||
While there are arguments for iterators to be implemented in
|
||
that manner, A) they aren't very good ones in the long term,
|
||
and B) they were never guaranteed by the Standard anyway. The
|
||
type-safety achieved by making iterators a real class rather
|
||
than a typedef for <span class="type">T*</span> outweighs nearly all opposing
|
||
arguments.
|
||
</p><p>
|
||
Code which does assume that a vector iterator <code class="varname">i</code>
|
||
is a pointer can often be fixed by changing <code class="varname">i</code> in
|
||
certain expressions to <code class="varname">&*i</code>. Future revisions
|
||
of the Standard are expected to bless this usage for
|
||
vector<> (but not for basic_string<>).
|
||
</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><b>7.2.</b></p></td><td align="left" valign="top"><p>
|
||
What's next after libstdc++?
|
||
</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>
|
||
Hopefully, not much. The goal of libstdc++ is to produce a
|
||
fully-compliant, fully-portable Standard Library. After that,
|
||
we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
|
||
more compliance work to do.
|
||
</p><p>
|
||
There is an effort underway to add significant extensions to
|
||
the standard library specification. The latest version of
|
||
this effort is described in
|
||
<a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
|
||
The C++ Library Technical Report 1</a>.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.sgi_stl"></a><a id="q-sgi_stl"></a><p><b>7.3.</b></p></td><td align="left" valign="top"><p>
|
||
What about the STL from SGI?
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
|
||
The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
|
||
version 3.3, was the final merge of the STL codebase. The
|
||
code in libstdc++ contains many fixes and changes, and
|
||
the SGI code is no longer under active
|
||
development. We expect that no future merges will take place.
|
||
</p><p>
|
||
In particular, <code class="classname">string</code> is not from SGI and makes no
|
||
use of their "rope" class (which is included as an
|
||
optional extension), nor is <code class="classname">valarray</code> and some others.
|
||
Classes like <code class="classname">vector<></code> are, but have been
|
||
extensively modified.
|
||
</p><p>
|
||
More information on the evolution of libstdc++ can be found at the
|
||
<a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
|
||
evolution</a>
|
||
and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
|
||
compatibility</a> documentation.
|
||
</p><p>
|
||
The FAQ for SGI's STL (one jump off of their main page) is
|
||
still recommended reading.
|
||
</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><b>7.4.</b></p></td><td align="left" valign="top"><p>
|
||
Extensions and Backward Compatibility
|
||
</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>
|
||
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.
|
||
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.tr1_support"></a><a id="q-tr1_support"></a><p><b>7.5.</b></p></td><td align="left" valign="top"><p>
|
||
Does libstdc++ support TR1?
|
||
</p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
|
||
Yes.
|
||
</p><p>
|
||
The C++ Standard Library Technical Report adds many new features to
|
||
the library. The latest version of this effort is described in
|
||
<a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
|
||
Technical Report 1</a>.
|
||
</p><p>
|
||
The implementation status of TR1 in libstdc++ can be tracked <a class="link" href="manual/status.html#manual.intro.status.standard.tr1" title="C++ TR1">on the TR1 status
|
||
page</a>.
|
||
</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><b>7.6.</b></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard?
|
||
</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>
|
||
Copies of the full ISO 14882 standard are available on line via
|
||
the ISO mirror site for committee members. Non-members, or those
|
||
who have not paid for the privilege of sitting on the committee
|
||
and sustained their two-meeting commitment for voting rights, may
|
||
get a copy of the standard from their respective national
|
||
standards organization. In the USA, this national standards
|
||
organization is ANSI and their website is
|
||
right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>. (And if
|
||
you've already registered with them, clicking this link will take
|
||
you to directly to the place where you can
|
||
<a class="ulink" href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003" target="_top">buy the standard on-line</a>.
|
||
</p><p>
|
||
Who is your country's member body? Visit the
|
||
<a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
|
||
</p><p>
|
||
The 2003 version of the standard (the 1998 version plus TC1) is
|
||
available in print, ISBN 0-470-84674-7.
|
||
</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><b>7.7.</b></p></td><td align="left" valign="top"><p>
|
||
What's an ABI and why is it so messy?
|
||
</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>
|
||
<acronym class="acronym">ABI</acronym> stands for “<span class="quote">Application Binary
|
||
Interface</span>”. Conventionally, it refers to a great
|
||
mass of details about how arguments are arranged on the call
|
||
stack and/or in registers, and how various types are arranged
|
||
and padded in structs. A single CPU design may suffer
|
||
multiple ABIs designed by different development tool vendors
|
||
who made different choices, or even by the same vendor for
|
||
different target applications or compiler versions. In ideal
|
||
circumstances the CPU designer presents one ABI and all the
|
||
OSes and compilers use it. In practice every ABI omits
|
||
details that compiler implementers (consciously or
|
||
accidentally) must choose for themselves.
|
||
</p><p>
|
||
That ABI definition suffices for compilers to generate code so a
|
||
program can interact safely with an OS and its lowest-level libraries.
|
||
Users usually want an ABI to encompass more detail, allowing libraries
|
||
built with different compilers (or different releases of the same
|
||
compiler!) to be linked together. For C++, this includes many more
|
||
details than for C, and CPU designers (for good reasons elaborated
|
||
below) have not stepped up to publish C++ ABIs. The details include
|
||
virtual function implementation, struct inheritance layout, name
|
||
mangling, and exception handling. Such an ABI has been defined for
|
||
GNU C++, and is immediately useful for embedded work relying only on
|
||
a “<span class="quote">free-standing implementation</span>” that doesn't include (much
|
||
of) the standard library. It is a good basis for the work to come.
|
||
</p><p>
|
||
A useful C++ ABI must also incorporate many details of the standard
|
||
library implementation. For a C ABI, the layouts of a few structs
|
||
(such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
|
||
For C++, the details include the complete set of names of functions
|
||
and types used, the offsets of class members and virtual functions,
|
||
and the actual definitions of all inlines. C++ exposes many more
|
||
library details to the caller than C does. It makes defining
|
||
a complete ABI a much bigger undertaking, and requires not just
|
||
documenting library implementation details, but carefully designing
|
||
those details so that future bug fixes and optimizations don't
|
||
force breaking the ABI.
|
||
</p><p>
|
||
There are ways to help isolate library implementation details from the
|
||
ABI, but they trade off against speed. Library details used in
|
||
inner loops (e.g., getchar) must be exposed and frozen for all
|
||
time, but many others may reasonably be kept hidden from user code,
|
||
so they may later be changed. Deciding which, and implementing
|
||
the decisions, must happen before you can reasonably document a
|
||
candidate C++ ABI that encompasses the standard library.
|
||
</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><b>7.8.</b></p></td><td align="left" valign="top"><p>
|
||
How do I make std::vector<T>::capacity() == std::vector<T>::size?
|
||
</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>
|
||
The standard idiom for deallocating a <code class="classname">vector<T></code>'s
|
||
unused memory is to create a temporary copy of the vector and swap their
|
||
contents, e.g. for <code class="classname">vector<T> v</code>
|
||
</p><div class="literallayout"><p><br />
|
||
std::vector<T>(v).swap(v);<br />
|
||
</p></div><p>
|
||
The copy will take O(n) time and the swap is constant time.
|
||
</p><p>
|
||
See <a class="link" href="manual/bk01pt05ch13s05.html" title="Shrink to Fit">Shrink-to-fit
|
||
strings</a> for a similar solution for strings.
|
||
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