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2003-05-21 Jonathan Wakely <redi@gcc.gnu.org> * docs/html/faq/index.html: Fix typo. * docs/html/faq/index.txt: Regenerate. From-SVN: r67061
1068 lines
52 KiB
HTML
1068 lines
52 KiB
HTML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++, libg++, STL" />
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<meta name="DESCRIPTION" content="FAQ for the GNU libstdc++ effort." />
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<title>libstdc++-v3 FAQ</title>
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<link rel="StyleSheet" href="../lib3styles.css" />
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<!--
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** Locations of "the most recent snapshot is the Nth" text are
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** answers 1_1, .
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-->
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</head>
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<body>
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<h1 class="centered">libstdc++ Frequently Asked Questions</h1>
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<p class="fineprint"><em>
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The latest version of this document is always available at
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<a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/">
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http://gcc.gnu.org/onlinedocs/libstdc++/faq/</a>. The main documentation
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page is at
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<a href="http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html">
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http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html</a>.
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</em></p>
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<p><em>
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To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
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</em></p>
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<!-- ####################################################### -->
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<hr />
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<h1>Questions</h1>
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<ol>
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<li><a href="#1_0">General Information</a>
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<!-- I suspect these will mostly be links to/into existing documents. -->
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<ol>
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<li><a href="#1_1">What is libstdc++-v3?</a> </li>
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<li><a href="#1_2">Why should I use libstdc++?</a> </li>
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<li><a href="#1_3">Who's in charge of it?</a> </li>
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<li><a href="#1_4">How do I get libstdc++?</a> </li>
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<li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
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<li><a href="#1_6">How do I contribute to the effort?</a> </li>
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<li><a href="#1_7">What happened to libg++? I need that!</a> </li>
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<li><a href="#1_8">What if I have more questions?</a> </li>
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<li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
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</ol>
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</li>
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<li><a href="#2_0">Installation</a>
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<ol>
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<li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
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<li><a href="#2_2">[removed]</a> </li>
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<li><a href="#2_3">What is this CVS thing that you keep
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mentioning?</a> </li>
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<li><a href="#2_4">How do I know if it works?</a> </li>
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<li><a href="#2_5">This library is HUGE! And what's libsupc++?</a> </li>
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</ol>
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</li>
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<li><a href="#3_0">Platform-Specific Issues</a>
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<ol>
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<li><a href="#3_1">Can libstdc++-v3 be used with <my
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favorite compiler>?</a> </li>
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<li><a href="#3_2">[removed]</a> </li>
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<li><a href="#3_3">[removed]</a> </li>
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<li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
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<li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
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<code>_GNU_SOURCE</code> / etc is always defined</a>
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</li>
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<li><a href="#3_6">OS X ctype.h is broken! How can I hack it?</a></li>
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<li><a href="#3_7">Threading is broken on i386</a></li>
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<li><a href="#3_8">Recent GNU/Linux glibc required?</a></li>
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<li><a href="#3_9">Can't use wchar_t/wstring on FreeBSD</a></li>
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<li><a href="#3_10">MIPS atomic operations</a></li>
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</ol>
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</li>
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<li><a href="#4_0">Known Bugs and Non-Bugs</a>
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<ol>
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<li><a href="#4_1">What works already?</a> </li>
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<li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
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<li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
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<li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
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<li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
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<li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
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<li><a href="#4_4_rel_ops">"ambiguous overloads"
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after including an old-style header</a> </li>
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<li><a href="#4_4_interface">The g++-3 headers are
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<strong>not ours</strong></a> </li>
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<li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
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<li><a href="#4_4_checks">errors about <em>*Concept</em> and
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<em>constraints</em> in the STL...</a> </li>
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<li><a href="#4_4_dlsym">program crashes when using library code
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in a dynamically-loaded library</a> </li>
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<li><a href="#4_4_leak">"memory leaks" in containers</a> </li>
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</ul>
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</li>
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<li><a href="#4_5">Aw, that's easy to fix!</a> </li>
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</ol>
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</li>
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<li><a href="#5_0">Miscellaneous</a>
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<ol>
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<li><a href="#5_1">string::iterator is not char*;
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vector<T>::iterator is not T*</a> </li>
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<li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
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<li><a href="#5_3">What about the STL from SGI?</a> </li>
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<li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
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<li><a href="#5_5">[removed]</a> </li>
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<li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
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<li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
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<li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
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</ol>
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</li>
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</ol>
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<hr />
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<!-- ####################################################### -->
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<h1><a name="1_0">1.0 General Information</a></h1>
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<!-- I suspect these will mostly be links to/into existing documents. -->
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<h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
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<p>The GNU Standard C++ Library v3 is an
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ongoing project to implement the ISO 14882 Standard C++ library
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as described in chapters 17 through 27 and annex D. As the
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library reaches stable plateaus, it is captured in a snapshot
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and released. The latest release is
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<a href="http://gcc.gnu.org/libstdc++/index.html#download">the
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fourteenth snapshot</a> but newer versions have been included
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in recent GCC releases. For those who want to see exactly how
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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 CVS, and can even be browsed over the Web (see
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<a href="#1_4">1.4</a> below).
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</p>
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<p>The older libstdc++-v2 project is no longer maintained; the code
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has been completely replaced and rewritten.
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<a href="#4_4_interface">If you are using V2</a>, then you need to
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report bugs to your system vendor, not to the V3 list.
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</p>
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<p>A more formal description of the V3 goals can be found in the
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official <a href="../17_intro/DESIGN">design document</a>.
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</p>
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<hr />
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<h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
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<p>The completion of the ISO C++ standardization gave the
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C++ community a powerful set of reuseable tools in the form
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of the C++ Standard Library. However, all existing C++
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implementations are (as the Draft Standard used to say)
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"incomplet and incorrekt," and many suffer from
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limitations of the compilers that use them.
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</p>
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<p>The GNU C/C++/FORTRAN/<pick-a-language> compiler
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(<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
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one of the leading compilers in the world. Its development
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has recently been taken over by the
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<a href="http://gcc.gnu.org/">GCC team</a>. All of
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the rapid development and near-legendary
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<a href="http://gcc.gnu.org/gcc-3.0/buildstat.html">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>
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<p>That means that all of the Standard classes and functions
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(such as <code>string</code>, <code>vector<></code>, iostreams,
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and algorithms) will be freely available and fully compliant.
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Programmers will no longer need to "roll their own"
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nor be worried about platform-specific incompatibilities.
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</p>
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<hr />
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<h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
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<p>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 CVS archive.
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</p>
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<p>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 href="http://gcc.gnu.org/libstdc++/">homepage</a>.
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If you have questions, ideas, code, or are just curious, sign up!
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</p>
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<hr />
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<h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
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<p>The <a href="http://gcc.gnu.org/libstdc++/">homepage</a>
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has instructions for retrieving the latest CVS sources, and for
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browsing the CVS sources over the web.
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</p>
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<p>Stable versions of libstdc++-v3 are included with releases of
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<a href="http://gcc.gnu.org/releases.html">the GCC compilers</a>.
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</p>
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<p>The subset commonly known as the Standard Template Library
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(chapters 23 through 25, mostly) is adapted from the final release
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of the SGI STL.
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</p>
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<hr />
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<h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
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<!-- <p>Nathan Myers gave the best of all possible answers in <a
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href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
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Usenet article</a>.</p>
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which is no longer available, thanks deja...-->
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<p>Nathan Myers gave the best of all possible answers, responding to a
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Usenet article asking this question: <em>Sooner, if you help.</em>
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</p>
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<hr />
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<h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
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<p>Here is <a href="../17_intro/contribute.html">a
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page devoted to this topic</a>. Subscribing to the mailing
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list (see above, or the homepage) is a very good idea if you
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have something to contribute, or if you have spare time and
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want to help. Contributions don't have to be in the form of
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source code; anybody who is willing to help write
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documentation, for example, or has found a bug in code that
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we all thought was working, is more than welcome!
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</p>
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<hr />
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<h2><a name="1_7">1.7 What happened to libg++? I need that!</a></h2>
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<p>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>
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<p>The libg++ was designed and created when there was no Standard
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to provide guidance. Classes like linked lists are now provided
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for by <code>list<T></code> and do not need to be created by
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<code>genclass</code>. (For that matter, templates exist now and
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are well-supported, whereas genclass (mostly) predates them.)
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</p>
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<p>There are other classes in libg++ that are not specified in the
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ISO Standard (e.g., statistical analysis). While there are a
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lot of really useful things that are used by a lot of people
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(e.g., statistics :-), the Standards Committee couldn't include
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everything, and so a lot of those "obvious" classes
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didn't get included.
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</p>
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<p>Since libstdc++ is an implementation of the Standard Library, we
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have no plans at this time to include non-Standard utilities
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in the implementation, however handy they are. (The extensions
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provided in the SGI STL aren't maintained by us and don't get
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a lot of our attention, because they don't require a lot of our
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time.) It is entirely plausable that the "useful stuff"
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from libg++ might be extracted into an updated utilities library,
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but nobody has started such a project yet.
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</p>
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<p>(The <a href="http://www.boost.org/">Boost</a> site houses free
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C++ libraries that do varying things, and happened to be started
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by members of the Standards Committee. Certain "useful
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stuff" classes will probably migrate there.)
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</p>
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<p>For the bold and/or desperate, the
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<a href="http://gcc.gnu.org/extensions.html">GCC extensions page</a>
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describes where to find the last libg++ source.
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</p>
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<hr />
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<h2><a name="1_8">1.8 What if I have more questions?</a></h2>
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<p>If you have read the README and RELEASE-NOTES files, and your
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question remains unanswered, then just ask the mailing list.
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At present, you do not need to be subscribed to the list to
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send a message to it. More information is available on the
|
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homepage (including how to browse the list archives); to send
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to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
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<code>libstdc++@gcc.gnu.org</code></a>.
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</p>
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<p>If you have a question that you think should be included here,
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or if you have a question <em>about</em> a question/answer here,
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contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
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or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
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</p>
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<hr />
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<h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
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<p>See <a href="../17_intro/license.html">our license description</a>
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for these and related questions.
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</p>
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<hr />
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<h1><a name="2_0">2.0 Installation</a></h1>
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<h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
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<p>Complete instructions are not given here (this is a FAQ, not
|
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an installation document), but the tools required are few:
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</p>
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<ul>
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<li> A 3.x release of GCC. Note that building GCC is much
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easier and more automated than building the GCC 2.[78]
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series was. If you are using GCC 2.95, you can still
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build earlier snapshots of libstdc++.
|
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</li>
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<li> GNU Make is recommended, but should not be required.
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</li>
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<li> The GNU Autotools are needed if you are messing with
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the configury or makefiles.
|
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</li>
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</ul>
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<p>The file <a href="../documentation.html">documentation.html</a>
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provides a good overview of the steps necessary to build, install,
|
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and use the library. Instructions for configuring the library
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with new flags such as --enable-threads are there also, as well as
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patches and instructions for working with GCC 2.95.
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</p>
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<p>The top-level install.html and
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<a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
|
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the exact build and installation instructions. You may wish to
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browse those files over CVSweb ahead of time to get a feel for
|
|
what's required. RELEASE-NOTES is located in the
|
|
".../docs/17_intro/" directory of the distribution.
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</p>
|
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|
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<hr />
|
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<h2><a name="2_2">2.2 [removed]</a></h2>
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<p>This question has become moot and has been removed. The stub
|
|
is here to preserve numbering (and hence links/bookmarks).
|
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</p>
|
|
|
|
<hr />
|
|
<h2><a name="2_3">2.3 What is this CVS thing that you
|
|
keep mentioning?</a></h2>
|
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<p>The <em>Concurrent Versions System</em> is one of several revision
|
|
control packages. It was selected for GNU projects because it's
|
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free (speech), free (beer), and very high quality. The <a
|
|
href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
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the GNU software catalogue</a> has a better description as
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well as a
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<a href="http://www.cvshome.org/">link to the makers of CVS</a>.
|
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</p>
|
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<p>The "anonymous client checkout" feature of CVS is
|
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similar to anonymous FTP in that it allows anyone to retrieve
|
|
the latest libstdc++ sources.
|
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</p>
|
|
<p>After the first of April, American users will have a
|
|
"/pharmacy" command-line option...
|
|
<!-- wonder how long that'll live -->
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="2_4">2.4 How do I know if it works?</a></h2>
|
|
<p>libstdc++-v3 comes with its own testsuite. You do not need
|
|
to actually install the library ("<code>make
|
|
install</code>") to run the testsuite, but you do need
|
|
DejaGNU, as described
|
|
<a href="http://gcc.gnu.org/install/test.html">here</a>.
|
|
</p>
|
|
<p>To run the testsuite on the library after building it, use
|
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"make check" while in your build directory. To run
|
|
the testsuite on the library after building and installing it,
|
|
use "make check-install" instead.
|
|
</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,
|
|
<strong>please</strong> write up your idea and send it to the list!
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="2_5">2.5 This library is HUGE! And what's libsupc++?</a></h2>
|
|
<p>Usually the size of libraries on disk isn't noticeable. When a
|
|
link editor (or simply "linker") 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++-v3 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> -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++-v3 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>It's not a bug, and it's not really a problem. Nevertheless, some
|
|
people don't like it, so here are two pseudo-solutions:
|
|
</p>
|
|
<p>If the only functions from libstdc++.a which you need are language
|
|
support functions (those listed in
|
|
<a href="../18_support/howto.html">clause 18</a> of the standard,
|
|
e.g., <code>new</code> and <code>delete</code>), then try linking
|
|
against <code>libsupc++.a</code> (usually specifying
|
|
<code>-lsupc++</code> when calling g++ 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>libstdc++.a</code>.
|
|
</p>
|
|
<p>The second method is one we hope to incorporate into the library
|
|
build process. Some platforms 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>
|
|
<p>Unfortunately the garbage collection in GNU ld is buggy; sections
|
|
(corresponding to functions and variables) which <em>are</em> used
|
|
are mistakenly removed, leading to horrible crashes when your
|
|
executable starts up. For the time being, this feature is not used
|
|
when building the library.
|
|
</p>
|
|
|
|
<hr />
|
|
<h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
|
|
<h2><a name="3_1">3.1 Can libstdc++-v3 be used with <my
|
|
favorite compiler>?</a></h2>
|
|
<p>Probably not. Yet.</p>
|
|
<p>Because GCC advances so rapidly, development and testing of
|
|
libstdc++ is being done almost entirely under that compiler.
|
|
If you are curious about whether other, lesser compilers
|
|
(*grin*) support libstdc++, you are more than welcome to try.
|
|
Configuring and building the library (see above) will still
|
|
require certain tools, however. Also keep in mind that
|
|
<em>building</em> libstdc++ does not imply that your compiler
|
|
will be able to <em>use</em> all of the features found in the
|
|
C++ Standard Library.
|
|
</p>
|
|
<p>Since the goal of ISO Standardization is for all C++
|
|
implementations to be able to share code, the final libstdc++
|
|
should, in theory, be usable under any ISO-compliant
|
|
compiler. It will still be targeted and optimized for
|
|
GCC/g++, however.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_2">3.2 [removed]</a></h2>
|
|
<p>This question has become moot and has been removed. The stub
|
|
is here to preserve numbering (and hence links/bookmarks).
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_3">3.3 [removed]</a></h2>
|
|
<p>This question has become moot and has been removed. The stub
|
|
is here to preserve numbering (and hence links/bookmarks).
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
|
|
<p>By default we try to support the C99 <code>long long</code> type.
|
|
This requires that certain functions from your C library be present.
|
|
</p>
|
|
<p>Up through release 3.0.2 the tests performed were too general, and
|
|
this feature was disabled when it did not need to be. The most
|
|
commonly reported platform affected was Solaris.
|
|
</p>
|
|
<p>This has been fixed for 3.0.3 and onwards.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
|
|
/ etc is always defined</a></h2>
|
|
<p>On Solaris, g++ (but not gcc) always defines the preprocessor
|
|
macro <code>_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
|
|
with <code>_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-compatability 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
|
|
<code>"g++ -E -dM - < /dev/null"</code> to display
|
|
a list of predefined macros for any particular installation.
|
|
</p>
|
|
<p>This has been discussed on the mailing lists
|
|
<a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris">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>
|
|
|
|
<hr />
|
|
<h2><a name="3_6">3.6 OS X ctype.h is broken! How can I hack it?</a></h2>
|
|
<p>This is a long-standing bug in the OS X support. Fortunately,
|
|
the patch is quite simple, and well-known.
|
|
<a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
|
|
link to the solution.</a>
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
|
|
<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>
|
|
|
|
<hr />
|
|
<h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
|
|
<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>
|
|
|
|
<hr />
|
|
<h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
|
|
<p>At the moment there are a few problems in FreeBSD's support for
|
|
wide character functions, and as a result the libstdc++ configury
|
|
decides that wchar_t support should be disabled. Once the underlying
|
|
problems are fixed in FreeBSD (soon), the library support will
|
|
automatically enable itself.
|
|
</p>
|
|
<p>You can fix the problems yourself, and learn more about the situation,
|
|
by reading
|
|
<a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
|
|
this short thread</a> ("_GLIBCPP_USE_WCHAR_T undefined in
|
|
FreeBSD's c++config.h?").
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="3_10">3.10 MIPS atomic operations</a></h2>
|
|
<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>mips*-*-linux* continues to use the MIPS II routines, and more
|
|
work in this area is expected.
|
|
</p>
|
|
|
|
<hr />
|
|
<h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
|
|
<em>Note that this section can get rapdily outdated -- such is the
|
|
nature of an open-source project. For the latest information, join
|
|
the mailing list or look through recent archives. The RELEASE-
|
|
NOTES and BUGS files are generally kept up-to-date.</em>
|
|
|
|
<p>For 3.0.1, the most common "bug" is an apparently missing
|
|
"<code>../</code>" in include/Makefile, resulting in files
|
|
like gthr.h and gthr-single.h not being found. Please read
|
|
<a href="http://gcc.gnu.org/install/configure.html">the configuration
|
|
instructions for GCC</a>,
|
|
specifically the part about configuring in a separate build directory,
|
|
and how strongly recommended it is. Building in the source directory
|
|
is fragile, is rarely tested, and tends to break, as in this case.
|
|
This was fixed for 3.0.2.
|
|
</p>
|
|
|
|
<p>For 3.1, the most common "bug" is a parse error when using
|
|
<code><fstream></code>, ending with a message,
|
|
"<code>bits/basic_file.h:52: parse error before `{'
|
|
token</code>." Please read
|
|
<a href="http://gcc.gnu.org/install/">the installation instructions for
|
|
GCC</a>, specifically the part about not installing newer versions on
|
|
top of older versions. If you install 3.1 over a 3.0.x release, then
|
|
the wrong basic_file.h header will be found (its location changed
|
|
between releases).
|
|
</p>
|
|
|
|
<p><strong>Please do not report these as bugs. We know about them.</strong>
|
|
Reporting this -- or any other problem that's already been fixed --
|
|
hinders the development of GCC, because we have to take time to
|
|
respond to your report. Thank you.
|
|
</p>
|
|
|
|
<h2><a name="4_1">4.1 What works already?</a></h2>
|
|
<p>Short answer: Pretty much everything <em>works</em> except for some
|
|
corner cases. Also, localization is incomplete. For whether it works
|
|
well, or as you expect it to work, see 5.2.
|
|
</p>
|
|
<p>Long answer: See the docs/html/17_intro/CHECKLIST file, which is
|
|
badly outdated...
|
|
</p>
|
|
<p>What follows is a verbatim clip from the "Status" section
|
|
of the RELEASE-NOTES for the latest snapshot. For a list of
|
|
fixed bugs, see that file.
|
|
</p>
|
|
|
|
<!-- Yeah, I meant that "verbatim clip" thing literally... :-) -->
|
|
|
|
<pre>
|
|
New:
|
|
</pre>
|
|
|
|
|
|
<hr />
|
|
<h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
|
|
<p>This is by no means meant to be complete nor exhaustive, but
|
|
mentions some problems that users may encounter when building
|
|
or using libstdc++. If you are experiencing one of these
|
|
problems, you can find more information on the libstdc++ and
|
|
the GCC mailing lists.
|
|
</p>
|
|
<p>Before reporting a bug, examine the
|
|
<a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
|
|
category set to "libstdc++". The BUGS file in the source
|
|
tree also tracks known serious problems.
|
|
</p>
|
|
<ul>
|
|
<li>Debugging is problematic, due to bugs in line-number generation
|
|
(mostly fixed in the compiler) and gdb lagging behind the
|
|
compiler (lack of personnel). We recommend configuring the
|
|
compiler using <code>--with-dwarf2</code> if the DWARF2
|
|
debugging format is not already the default on your platform.
|
|
Also,
|
|
<a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
|
|
GDB settings</a> can have a profound effect on your C++ debugging
|
|
experiences. :-)</li>
|
|
</ul>
|
|
|
|
<hr />
|
|
<h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
|
|
<p>Yes, unfortunately, there are some. In a
|
|
<a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
|
|
to the list</a>, Nathan Myers announced that he has started a list of
|
|
problems in the ISO C++ Standard itself, especially with
|
|
regard to the chapters that concern the library. The list
|
|
itself is
|
|
<a href="http://www.cantrip.org/draft-bugs.txt">posted on his
|
|
website</a>. Developers who are having problems interpreting
|
|
the Standard may wish to consult his notes.
|
|
</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 href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
|
|
Some of these have resulted in <a href="#5_2">code changes</a>.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
|
|
<p>There are things which are not bugs in the compiler (4.2) nor
|
|
the language specification (4.3), but aren't really bugs in
|
|
libstdc++, either. Really! Please do not report these as bugs.
|
|
</p>
|
|
<p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
|
|
The biggest of these is the quadzillions of warnings about the
|
|
library headers emitted when <code>-Weffc++</code> is used. Making
|
|
libstdc++ "-Weffc++-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><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
|
|
</a> Did I just say that -Weffc++ was our biggest false-bug report?
|
|
I lied. (It used to be.) Today it seems to be reports that after
|
|
executing a sequence like
|
|
</p>
|
|
<pre>
|
|
#include <fstream>
|
|
...
|
|
std::fstream fs("a_file");
|
|
// .
|
|
// . do things with fs...
|
|
// .
|
|
fs.close();
|
|
fs.open("a_new_file");</pre>
|
|
<p>all operations on the re-opened <code>fs</code> will fail, or at
|
|
least act very strangely. Yes, they often will, especially if
|
|
<code>fs</code> reached the EOF state on the previous file. The
|
|
reason is that the state flags are <strong>not</strong> 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 href="../ext/howto.html#5">proposed LWG resolution in
|
|
DR #22</a> is to leave the flags unchanged. You must insert a call
|
|
to <code>fs.clear()</code> between the calls to close() and open(),
|
|
and then everything will work like we all expect it to work.
|
|
</p>
|
|
<p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
|
|
Another is the <code>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., '<code>using</code>' 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 href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
|
|
things up here</a>. The collisions with vector/string iterator
|
|
types have been fixed for 3.1. <!-- more links to email here -->
|
|
</p>
|
|
<h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
|
|
<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 href="http://gcc.gnu.org/gnatswrite.html">the GCC bug database</a>).
|
|
</p>
|
|
<p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
|
|
the installed library's name looks like <code>libstdc++-2.10.a</code>
|
|
or <code>libstdc++-libc6-2.10.so</code>, then you are using the old
|
|
libstdc++-v2 library, which is nonstandard and unmaintained. Do not
|
|
report problems with -v2 to the -v3 mailing list.
|
|
</p>
|
|
<p>For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are
|
|
installed in <code>${prefix}/include/g++-v3</code> (see the 'v'?).
|
|
Starting with version 3.2 the headers are installed in
|
|
<code>${prefix}/include/c++/${version}</code> as this prevents
|
|
headers from previous versions being found by mistake.
|
|
</p>
|
|
<p><a name="4_4_glibc"><strong>glibc</strong></a>
|
|
If you're on a GNU/Linux system and have just upgraded to
|
|
glibc 2.2, but are still using gcc 2.95.2, then you should have
|
|
read the glibc FAQ, specifically 2.34:
|
|
</p>
|
|
<pre>
|
|
2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
|
|
|
|
{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
|
|
apply a patch to the include files in /usr/include/g++, because the fpos_t
|
|
type has changed in glibc 2.2. The patch is at
|
|
http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
|
|
</pre>
|
|
<p>Note that 2.95.x shipped with the
|
|
<a href="#4_4_interface">old v2 library</a> which is no longer
|
|
maintained. Also note that gcc 2.95.3 fixes this problem, but
|
|
requires a separate patch for libstdc++-v3.
|
|
</p>
|
|
<p><a name="4_4_checks"><strong>concept checks</strong></a>
|
|
If you see compilation errors containing messages about
|
|
<code> <em>foo</em>Concept </code>and a<code> constraints </code>
|
|
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 href="../19_diagnostics/howto.html#3">here</a>.
|
|
</p>
|
|
<p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
|
|
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>
|
|
<pre>
|
|
// compile your library components
|
|
g++ -fPIC -c a.cc
|
|
g++ -fPIC -c b.cc
|
|
...
|
|
g++ -fPIC -c z.cc
|
|
|
|
// create your library
|
|
g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
|
|
|
|
// link the executable
|
|
g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
|
|
<p><a name="4_4_leak"><strong>"memory leaks" in containers</strong></a>
|
|
A few people have reported that the standard containers appear
|
|
to leak memory when tested with memory checkers such as
|
|
<a href="http://developer.kde.org/~sewardj/">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 href="../debug.html#mem">Tips for memory leak hunting</a>
|
|
first.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
|
|
<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 href="http://gcc.gnu.org/contribute.html">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 href="../17_intro/contribute.html">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 href="#2_4">testsuite</a> -- but only if such a test exists.
|
|
</p>
|
|
|
|
<hr />
|
|
<h1><a name="5_0">5.0 Miscellaneous</a></h1>
|
|
<h2><a name="5_1">5.1 string::iterator is not char*;
|
|
vector<T>::iterator is not T*</a></h2>
|
|
<p>If you have code that depends on container<T> iterators
|
|
being implemented as pointer-to-T, your code is broken.
|
|
</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 <code>T*</code> outweighs nearly all opposing
|
|
arguments.
|
|
</p>
|
|
<p>Code which does assume that a vector iterator <code> i </code>
|
|
is a pointer can often be fixed by changing <code> i </code> in
|
|
certain expressions to <code> &*i </code>. Future revisions
|
|
of the Standard are expected to bless this usage for
|
|
vector<> (but not for basic_string<>).
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
|
|
<p>Hopefully, not much. The goal of libstdc++-v3 is to produce
|
|
a fully-compliant, fully-portable Standard Library. After that,
|
|
we're mostly done: there won't <em>be</em> any more compliance
|
|
work to do. However:
|
|
</p>
|
|
<ol>
|
|
<li><p>The ISO Committee will meet periodically to review Defect Reports
|
|
in the C++ Standard. Undoubtedly some of these will result in
|
|
changes to the Standard, which will be reflected in patches to
|
|
libstdc++. Some of that is already happening, see 4.2. Some of
|
|
those changes are being predicted by the library maintainers, and
|
|
we add code to the library based on what the current proposed
|
|
resolution specifies. Those additions are listed in
|
|
<a href="../ext/howto.html#5">the extensions page</a>.
|
|
</p></li>
|
|
<li><p>Performance tuning. Lots of performance tuning. This too is
|
|
already underway for post-3.0 releases, starting with memory
|
|
expansion in container classes and buffer usage in synchronized
|
|
stream objects.
|
|
</p></li>
|
|
<li><p>An ABI for libstdc++ is being developed, so that
|
|
multiple binary-incompatible copies of the library can be replaced
|
|
with a single backwards-compatible library, like libgcc_s.so is.
|
|
</p></li>
|
|
<li><p>The current libstdc++ contains extensions to the Library which
|
|
must be explicitly requested by client code (for example, the
|
|
hash tables from SGI). Other extensions may be added to
|
|
libstdc++-v3 if they seem to be "standard" enough.
|
|
(For example, the "long long" type from C99.)
|
|
Bugfixes and rewrites (to improve or fix thread safety, for
|
|
instance) will of course be a continuing task.
|
|
</p></li>
|
|
</ol>
|
|
<p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
|
|
question</a> about the next libstdc++ prompted some brief but
|
|
interesting
|
|
<a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
|
|
<p>The <a href="http://www.sgi.com/Technology/STL/">STL from SGI</a>,
|
|
version 3.3, was the most recent merge of the STL codebase. The
|
|
code in libstdc++ contains many fixes and changes, and it is
|
|
very likely that the SGI code is no longer under active
|
|
development. We expect that no future merges will take place.
|
|
</p>
|
|
<p>In particular, <code>string</code> is not from SGI and makes no
|
|
use of their "rope" class (which is included as an
|
|
optional extension), nor is <code>valarray</code> and some others.
|
|
Classes like <code>vector<></code> are, however we have
|
|
made significant changes to them since then.
|
|
</p>
|
|
<p>The FAQ for SGI's STL (one jump off of their main page) is
|
|
recommended reading.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
|
|
<p>Headers in the <code>ext</code> and <code>backward</code>
|
|
subdirectories should be referred to by their relative paths:
|
|
<!-- Careful, the leading spaces in PRE show up directly. -->
|
|
</p>
|
|
<pre>
|
|
#include <ext/hash_map> </pre>
|
|
<p>rather than using <code>-I</code> or other options. This is more
|
|
portable and forward-compatible. (The situation is the same as
|
|
that of other headers whose directories are not searched directly,
|
|
e.g., <code><sys/stat.h></code>, <code><X11/Xlib.h></code>.
|
|
</p>
|
|
|
|
<p>The extensions are no longer in the global or <code>std</code>
|
|
namespaces, instead they are declared in the <code>__gnu_cxx</code>
|
|
namespace. For maximum portability, consider defining a namespace
|
|
alias to use to talk about extensions, e.g.:
|
|
</p>
|
|
<pre>
|
|
#ifdef __GNUC__
|
|
#if __GNUC__ < 3
|
|
#include <hash_map.h>
|
|
namespace Sgi { using ::hash_map; }; // inherit globals
|
|
#else
|
|
#include <ext/hash_map>
|
|
#if __GNUC_MINOR__ == 0
|
|
namespace Sgi = std; // GCC 3.0
|
|
#else
|
|
namespace Sgi = ::__gnu_cxx; // GCC 3.1 and later
|
|
#endif
|
|
#endif
|
|
#else // ... there are other compilers, right?
|
|
namespace Sgi = std;
|
|
#endif
|
|
|
|
Sgi::hash_map<int,int> my_map; </pre>
|
|
<p>This is a bit cleaner than defining typedefs for all the
|
|
instantiations you might need.
|
|
</p>
|
|
<p>Extensions to the library have
|
|
<a href="../ext/howto.html">their own page</a>.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_5">5.5 [removed]</a></h2>
|
|
<p>This question has become moot and has been removed. The stub
|
|
is here to preserve numbering (and hence links/bookmarks).
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
|
|
<p>libstdc++-v3 strives to be thread-safe when all of the following
|
|
conditions are met:
|
|
</p>
|
|
<ul>
|
|
<li>The system's libc is itself thread-safe,</li>
|
|
<li><code>gcc -v</code> reports a thread model other than 'single',</li>
|
|
<li>[pre-3.3 only] a non-generic implementation of atomicity.h
|
|
exists for the architecture in question.</li>
|
|
</ul>
|
|
<p>The user-code must guard against concurrent method calls which may
|
|
access any particular library object's state. Typically, the
|
|
application programmer may infer what object locks must be held
|
|
based on the objects referenced in a method call. Without getting
|
|
into great detail, here is an example which requires user-level
|
|
locks:
|
|
</p>
|
|
<pre>
|
|
library_class_a shared_object_a;
|
|
|
|
thread_main () {
|
|
library_class_b *object_b = new library_class_b;
|
|
shared_object_a.add_b (object_b); // must hold lock for shared_object_a
|
|
shared_object_a.mutate (); // must hold lock for shared_object_a
|
|
}
|
|
|
|
// Multiple copies of thread_main() are started in independent threads.</pre>
|
|
<p>Under the assumption that object_a and object_b are never exposed to
|
|
another thread, here is an example that should not require any
|
|
user-level locks:
|
|
</p>
|
|
<pre>
|
|
thread_main () {
|
|
library_class_a object_a;
|
|
library_class_b *object_b = new library_class_b;
|
|
object_a.add_b (object_b);
|
|
object_a.mutate ();
|
|
} </pre>
|
|
<p>All library objects are safe to use in a multithreaded program as
|
|
long as each thread carefully locks out access by any other
|
|
thread while it uses any object visible to another thread, i.e.,
|
|
treat library objects like any other shared resource. In general,
|
|
this requirement includes both read and write access to objects;
|
|
unless otherwise documented as safe, do not assume that two threads
|
|
may access a shared standard library object at the same time.
|
|
</p>
|
|
<p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
|
|
introduction), <a href="../23_containers/howto.html#3">23</a>
|
|
(containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
|
|
more information.
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
|
|
<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 href="http://www.ansi.org">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 href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998">buy
|
|
the standard on-line</a>.
|
|
</p>
|
|
<p>Who is your country's member body? Visit the
|
|
<a href="http://www.iso.ch/">ISO homepage</a> and find out!
|
|
</p>
|
|
|
|
<hr />
|
|
<h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
|
|
<p>"ABI" stands for "Application Binary Interface."
|
|
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 "free-standing implementation" 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>
|
|
|
|
<!-- ####################################################### -->
|
|
|
|
<hr />
|
|
<p class="fineprint"><em>
|
|
See <a href="../17_intro/license.html">license.html</a> for copying conditions.
|
|
Comments and suggestions are welcome, and may be sent to
|
|
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
|
|
</em></p>
|
|
|
|
|
|
</body>
|
|
</html>
|
|
|