1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<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 V1.75.2" /><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" title="Frequently Asked Questions"><div class="titlepage"><div><div><h2 class="title"><a id="faq"></a>Frequently Asked Questions</h2></div><div><p class="copyright">Copyright © 4 2008 5 6 <a class="ulink" href="http://www.fsf.org" target="_top">FSF</a> 7 </p></div></div><hr /></div><div class="qandaset" title="Frequently Asked Questions"><a id="id571249"></a><dl><dt>1. <a href="faq.html#faq.info">General Information</a></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what"> 8 What is libstdc++? 9 </a></dt><dt>1.2. <a href="faq.html#faq.why"> 10 Why should I use libstdc++? 11 </a></dt><dt>1.3. <a href="faq.html#faq.who"> 12 Who's in charge of it? 13 </a></dt><dt>1.4. <a href="faq.html#faq.when"> 14 When is libstdc++ going to be finished? 15 </a></dt><dt>1.5. <a href="faq.html#faq.how"> 16 How do I contribute to the effort? 17 </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old"> 18 What happened to the older libg++? I need that! 19 </a></dt><dt>1.7. <a href="faq.html#faq.more_questions"> 20 What if I have more questions? 21 </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"> 22 What are the license terms for libstdc++? 23 </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program"> 24 So any program which uses libstdc++ falls under the GPL? 25 </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl"> 26 How is that different from the GNU {Lesser,Library} GPL? 27 </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions"> 28 I see. So, what restrictions are there on programs that use the library? 29 </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++? 30 </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources? 31 </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works? 32 </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? 33 </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx"> 34 What's libsupc++? 35 </a></dt><dt>3.6. <a href="faq.html#faq.size"> 36 This library is HUGE! 37 </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"> 38 Can libstdc++ be used with non-GNU compilers? 39 </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long"> 40 No 'long long' type on Solaris? 41 </a></dt><dt>4.3. <a href="faq.html#faq.predefined"> 42 _XOPEN_SOURCE and _GNU_SOURCE are always defined? 43 </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype"> 44 Mac OS X ctype.h is broken! How can I fix it? 45 </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386"> 46 Threading is broken on i386? 47 </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips"> 48 MIPS atomic operations 49 </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc"> 50 Recent GNU/Linux glibc required? 51 </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar"> 52 Can't use wchar_t/wstring on FreeBSD 53 </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"> 54 What works already? 55 </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs"> 56 Bugs in the ISO C++ language or library specification 57 </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs"> 58 Bugs in the compiler (gcc/g++) and not libstdc++ 59 </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"> 60 Reopening a stream fails 61 </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose"> 62 -Weffc++ complains too much 63 </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads"> 64 Ambiguous overloads after including an old-style header 65 </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers"> 66 The g++-3 headers are not ours 67 </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks"> 68 Errors about *Concept and 69 constraints in the STL 70 </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash"> 71 Program crashes when using library code in a 72 dynamically-loaded library 73 </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks"> 74 “Memory leaks” in containers 75 </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on"> 76 list::size() is O(n)! 77 </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix"> 78 Aw, that's easy to fix! 79 </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"> 80 string::iterator is not char*; vector<T>::iterator is not T* 81 </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next"> 82 What's next after libstdc++? 83 </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl"> 84 What about the STL from SGI? 85 </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat"> 86 Extensions and Backward Compatibility 87 </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support"> 88 Does libstdc++ support TR1? 89 </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard? 90 </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi"> 91 What's an ABI and why is it so messy? 92 </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity"> 93 How do I make std::vector<T>::capacity() == std::vector<T>::size? 94 </a></dt></dl></dd></dl><table border="0" width="100%" summary="Q and A Set"><col align="left" width="1%" /><col /><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"> 95 What is libstdc++? 96 </a></dt><dt>1.2. <a href="faq.html#faq.why"> 97 Why should I use libstdc++? 98 </a></dt><dt>1.3. <a href="faq.html#faq.who"> 99 Who's in charge of it? 100 </a></dt><dt>1.4. <a href="faq.html#faq.when"> 101 When is libstdc++ going to be finished? 102 </a></dt><dt>1.5. <a href="faq.html#faq.how"> 103 How do I contribute to the effort? 104 </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old"> 105 What happened to the older libg++? I need that! 106 </a></dt><dt>1.7. <a href="faq.html#faq.more_questions"> 107 What if I have more questions? 108 </a></dt></dl></td></tr><tr class="question" title="1.1."><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> 109 What is libstdc++? 110 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p> 111 The GNU Standard C++ Library v3 is an ongoing project to 112 implement the ISO 14882 Standard C++ library as described in 113 chapters 17 through 27 and annex D. For those who want to see 114 exactly how far the project has come, or just want the latest 115 bleeding-edge code, the up-to-date source is available over 116 anonymous SVN, and can even be browsed over 117 the <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top">web</a>. 118 </p></td></tr><tr class="question" title="1.2."><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> 119 Why should I use libstdc++? 120 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p> 121 The completion of the ISO C++ standardization gave the C++ 122 community a powerful set of reuseable tools in the form of the C++ 123 Standard Library. However, all existing C++ implementations are 124 (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and 125 incorrekt</span>”</span>, and many suffer from limitations of the compilers 126 that use them. 127 </p><p> 128 The GNU compiler collection 129 (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely 130 considered to be one of the leading compilers in the world. Its 131 development is overseen by the 132 <a class="ulink" href="http://gcc.gnu.org/" target="_top">GCC team</a>. All of 133 the rapid development and near-legendary 134 <a class="ulink" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a> 135 that are the hallmarks of an open-source project are being 136 applied to libstdc++. 137 </p><p> 138 That means that all of the Standard classes and functions will be 139 freely available and fully compliant. (Such as 140 <code class="classname">string</code>, 141 <code class="classname">vector<></code>, iostreams, and algorithms.) 142 Programmers will no longer need to <span class="quote">“<span class="quote">roll their own</span>”</span> 143 nor be worried about platform-specific incompatibilities. 144 </p></td></tr><tr class="question" title="1.3."><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> 145 Who's in charge of it? 146 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p> 147 The libstdc++ project is contributed to by several developers 148 all over the world, in the same way as GCC or Linux. 149 Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper, 150 Loren James Rittle, and Paolo Carlini are the lead maintainers of 151 the SVN archive. 152 </p><p> 153 Development and discussion is held on the libstdc++ mailing 154 list. Subscribing to the list, or searching the list 155 archives, is open to everyone. You can read instructions for 156 doing so on the <a class="ulink" href="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>. 157 If you have questions, ideas, code, or are just curious, sign up! 158 </p></td></tr><tr class="question" title="1.4."><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> 159 When is libstdc++ going to be finished? 160 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p> 161 Nathan Myers gave the best of all possible answers, responding to 162 a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you 163 help.</em></span> 164 </p></td></tr><tr class="question" title="1.5."><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> 165 How do I contribute to the effort? 166 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p> 167 Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">a page devoted to 168 this topic</a>. Subscribing to the mailing list (see above, or 169 the homepage) is a very good idea if you have something to 170 contribute, or if you have spare time and want to 171 help. Contributions don't have to be in the form of source code; 172 anybody who is willing to help write documentation, for example, 173 or has found a bug in code that we all thought was working and is 174 willing to provide details, is more than welcome! 175 </p></td></tr><tr class="question" title="1.6."><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> 176 What happened to the older libg++? I need that! 177 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p> 178 The most recent libg++ README states that libg++ is no longer 179 being actively maintained. It should not be used for new 180 projects, and is only being kicked along to support older code. 181 </p><p> 182 More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a> 183 </p></td></tr><tr class="question" title="1.7."><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> 184 What if I have more questions? 185 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p> 186 If you have read the README file, and your question remains 187 unanswered, then just ask the mailing list. At present, you do not 188 need to be subscribed to the list to send a message to it. More 189 information is available on the homepage (including how to browse 190 the list archives); to send a message to the list, 191 use <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code>. 192 </p><p> 193 If you have a question that you think should be included 194 here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer 195 here, please send email to the libstdc++ mailing list, as above. 196 </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"> 197 What are the license terms for libstdc++? 198 </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program"> 199 So any program which uses libstdc++ falls under the GPL? 200 </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl"> 201 How is that different from the GNU {Lesser,Library} GPL? 202 </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions"> 203 I see. So, what restrictions are there on programs that use the library? 204 </a></dt></dl></td></tr><tr class="question" title="2.1."><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> 205 What are the license terms for libstdc++? 206 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p> 207 See <a class="link" href="manual/license.html" title="License">our license description</a> 208 for these and related questions. 209 </p></td></tr><tr class="question" title="2.2."><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> 210 So any program which uses libstdc++ falls under the GPL? 211 </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> 212 No. The special exception permits use of the library in 213 proprietary applications. 214 </p></td></tr><tr class="question" title="2.3."><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> 215 How is that different from the GNU {Lesser,Library} GPL? 216 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p> 217 The LGPL requires that users be able to replace the LGPL code with a 218 modified version; this is trivial if the library in question is a C 219 shared library. But there's no way to make that work with C++, where 220 much of the library consists of inline functions and templates, which 221 are expanded inside the code that uses the library. So to allow people 222 to replace the library code, someone using the library would have to 223 distribute their own source, rendering the LGPL equivalent to the GPL. 224 </p></td></tr><tr class="question" title="2.4."><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> 225 I see. So, what restrictions are there on programs that use the library? 226 </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> 227 None. We encourage such programs to be released as open source, 228 but we won't punish you or sue you if you choose otherwise. 229 </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++? 230 </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources? 231 </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works? 232 </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? 233 </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx"> 234 What's libsupc++? 235 </a></dt><dt>3.6. <a href="faq.html#faq.size"> 236 This library is HUGE! 237 </a></dt></dl></td></tr><tr class="question" title="3.1."><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++? 238 </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> 239 Often libstdc++ comes pre-installed as an integral part of many 240 existing Linux and Unix systems, as well as many embedded 241 development tools. It may be necessary to install extra 242 development packages to get the headers, or the documentation, or 243 the source: please consult your vendor for details. 244 </p><p> 245 To build and install from the GNU GCC sources, please consult the 246 <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup 247 documentation</a> for detailed 248 instructions. You may wish to browse those files ahead 249 of time to get a feel for what's required. 250 </p></td></tr><tr class="question" title="3.2."><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? 251 </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> 252 Libstdc++ sources for all official releases can be obtained as 253 part of the GCC sources, available from various sites and 254 mirrors. A full <a class="ulink" href="http://gcc.gnu.org/mirrors.html" target="_top">list of 255 download sites</a> is provided on the main GCC site. 256 </p><p> 257 Current libstdc++ sources can always be checked out of the main 258 GCC source repository using the appropriate version control 259 tool. At this time, that tool 260 is <span class="application">Subversion</span>. 261 </p><p> 262 <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is 263 one of several revision control packages. It was selected for GNU 264 projects because it's free (speech), free (beer), and very high 265 quality. The <a class="ulink" href="http://subversion.tigris.org" target="_top"> Subversion 266 home page</a> has a better description. 267 </p><p> 268 The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is 269 similar to anonymous FTP in that it allows anyone to retrieve 270 the latest libstdc++ sources. 271 </p><p> 272 For more information 273 see <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym> 274 details</a>. 275 </p></td></tr><tr class="question" title="3.3."><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? 276 </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> 277 Libstdc++ comes with its own validation testsuite, which includes 278 conformance testing, regression testing, ABI testing, and 279 performance testing. Please consult the 280 <a class="ulink" href="http://gcc.gnu.org/install/test.html" target="_top">testing 281 documentation</a> for more details. 282 </p><p> 283 If you find bugs in the testsuite programs themselves, or if you 284 think of a new test program that should be added to the suite, 285 <span class="emphasis"><em>please</em></span> write up your idea and send it to the list! 286 </p></td></tr><tr class="question" title="3.4."><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? 287 </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> 288 Depending on your platform and library version, the error message might 289 be similar to one of the following: 290 </p><pre class="screen"> 291 /a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory 292 293 /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found 294 </pre><p> 295 This doesn't mean that the shared library isn't installed, only 296 that the dynamic linker can't find it. When a dynamically-linked 297 executable is run the linker finds and loads the required shared 298 libraries by searching a pre-configured list of directories. If 299 the directory where you've installed libstdc++ is not in this list 300 then the libraries won't be found. The simplest way to fix this is 301 to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable, 302 which is a colon-separated list of directories in which the linker 303 will search for shared libraries: 304 </p><pre class="screen"> 305 LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH 306 export LD_LIBRARY_PATH 307 </pre><p> 308 The exact environment variable to use will depend on your 309 platform, e.g. DYLD_LIBRARY_PATH for Darwin, 310 LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit, 311 LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs and 312 SHLIB_PATH for HP-UX. 313 </p><p> 314 See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span> 315 and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic 316 linker has different names on different platforms but the man page 317 is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>. 318 </p></td></tr><tr class="question" title="3.5."><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> 319 What's libsupc++? 320 </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> 321 If the only functions from <code class="filename">libstdc++.a</code> 322 which you need are language support functions (those listed in 323 <a class="link" href="manual/support.html" title="Part II. Support">clause 18</a> of the 324 standard, e.g., <code class="function">new</code> and 325 <code class="function">delete</code>), then try linking against 326 <code class="filename">libsupc++.a</code>, which is a subset of 327 <code class="filename">libstdc++.a</code>. (Using <span class="command"><strong>gcc</strong></span> 328 instead of <span class="command"><strong>g++</strong></span> and explicitly linking in 329 <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code> 330 for the final link step will do it). This library contains only 331 those support routines, one per object file. But if you are 332 using anything from the rest of the library, such as IOStreams 333 or vectors, then you'll still need pieces from 334 <code class="filename">libstdc++.a</code>. 335 </p></td></tr><tr class="question" title="3.6."><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> 336 This library is HUGE! 337 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p> 338 Usually the size of libraries on disk isn't noticeable. When a 339 link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a 340 static archive library, only the necessary object files are copied 341 into your executable, not the entire library. Unfortunately, even 342 if you only need a single function or variable from an object file, 343 the entire object file is extracted. (There's nothing unique to C++ 344 or libstdc++ about this; it's just common behavior, given here 345 for background reasons.) 346 </p><p> 347 Some of the object files which make up libstdc++.a are rather large. 348 If you create a statically-linked executable with 349 <code class="literal">-static</code>, those large object files are suddenly part 350 of your executable. Historically the best way around this was to 351 only place a very few functions (often only a single one) in each 352 source/object file; then extracting a single function is the same 353 as extracting a single .o file. For libstdc++ this is only 354 possible to a certain extent; the object files in question contain 355 template classes and template functions, pre-instantiated, and 356 splitting those up causes severe maintenance headaches. 357 </p><p> 358 On supported platforms, libstdc++ takes advantage of garbage 359 collection in the GNU linker to get a result similar to separating 360 each symbol into a separate source and object files. On these platforms, 361 GNU ld can place each function and variable into its own 362 section in a .o file. The GNU linker can then perform garbage 363 collection on unused sections; this reduces the situation to only 364 copying needed functions into the executable, as before, but all 365 happens automatically. 366 </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"> 367 Can libstdc++ be used with non-GNU compilers? 368 </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long"> 369 No 'long long' type on Solaris? 370 </a></dt><dt>4.3. <a href="faq.html#faq.predefined"> 371 _XOPEN_SOURCE and _GNU_SOURCE are always defined? 372 </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype"> 373 Mac OS X ctype.h is broken! How can I fix it? 374 </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386"> 375 Threading is broken on i386? 376 </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips"> 377 MIPS atomic operations 378 </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc"> 379 Recent GNU/Linux glibc required? 380 </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar"> 381 Can't use wchar_t/wstring on FreeBSD 382 </a></dt></dl></td></tr><tr class="question" title="4.1."><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> 383 Can libstdc++ be used with non-GNU compilers? 384 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p> 385 Perhaps. 386 </p><p> 387 Since the goal of ISO Standardization is for all C++ 388 implementations to be able to share code, libstdc++ should be 389 usable under any ISO-compliant compiler, at least in theory. 390 </p><p> 391 However, the reality is that libstdc++ is targeted and optimized 392 for GCC/g++. This means that often libstdc++ uses specific, 393 non-standard features of g++ that are not present in older 394 versions of proprietary compilers. It may take as much as a year or two 395 after an official release of GCC that contains these features for 396 proprietary tools support these constructs. 397 </p><p> 398 In the near past, specific released versions of libstdc++ have 399 been known to work with versions of the EDG C++ compiler, and 400 vendor-specific proprietary C++ compilers such as the Intel ICC 401 C++ compiler. 402 </p></td></tr><tr class="question" title="4.2."><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> 403 No 'long long' type on Solaris? 404 </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> 405 By default we try to support the C99 <span class="type">long long</span> type. 406 This requires that certain functions from your C library be present. 407 </p><p> 408 Up through release 3.0.2 the platform-specific tests performed by 409 libstdc++ were too general, resulting in a conservative approach 410 to enabling the <span class="type">long long</span> code paths. The most 411 commonly reported platform affected was Solaris. 412 </p><p> 413 This has been fixed for libstdc++ releases greater than 3.0.3. 414 </p></td></tr><tr class="question" title="4.3."><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> 415 <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined? 416 </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 417 macro <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens 418 with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list; 419 other macros and other platforms are also affected.) 420 </p><p>These macros are typically used in C library headers, guarding new 421 versions of functions from their older versions. The C++ standard 422 library includes the C standard library, but it requires the C90 423 version, which for backwards-compatibility reasons is often not the 424 default for many vendors. 425 </p><p>More to the point, the C++ standard requires behavior which is only 426 available on certain platforms after certain symbols are defined. 427 Usually the issue involves I/O-related typedefs. In order to 428 ensure correctness, the compiler simply predefines those symbols. 429 </p><p>Note that it's not enough to #define them only when the library is 430 being built (during installation). Since we don't have an 'export' 431 keyword, much of the library exists as headers, which means that 432 the symbols must also be defined as your programs are parsed and 433 compiled. 434 </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in 435 the gcc config headers for your target (and try changing them to 436 see what happens when building complicated code). You can also run 437 <span class="command"><strong>g++ -E -dM - < /dev/null"</strong></span> to display 438 a list of predefined macros for any particular installation. 439 </p><p>This has been discussed on the mailing lists 440 <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>. 441 </p><p>This method is something of a wart. We'd like to find a cleaner 442 solution, but nobody yet has contributed the time. 443 </p></td></tr><tr class="question" title="4.4."><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> 444 Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it? 445 </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, 446 the patch is quite simple, and well-known. 447 <a class="ulink" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a 448 link to the solution</a>. 449 </p></td></tr><tr class="question" title="4.5."><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> 450 Threading is broken on i386? 451 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p> 452 </p><p>Support for atomic integer operations is/was broken on i386 453 platforms. The assembly code accidentally used opcodes that are 454 only available on the i486 and later. So if you configured GCC 455 to target, for example, i386-linux, but actually used the programs 456 on an i686, then you would encounter no problems. Only when 457 actually running the code on a i386 will the problem appear. 458 </p><p>This is fixed in 3.2.2. 459 </p></td></tr><tr class="question" title="4.6."><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> 460 MIPS atomic operations 461 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p> 462 The atomic locking routines for MIPS targets requires MIPS II 463 and later. A patch went in just after the 3.3 release to 464 make mips* use the generic implementation instead. You can also 465 configure for mipsel-elf as a workaround. 466 </p><p> 467 The mips*-*-linux* port continues to use the MIPS II routines, and more 468 work in this area is expected. 469 </p></td></tr><tr class="question" title="4.7."><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> 470 Recent GNU/Linux glibc required? 471 </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 472 5.0.1) and later uses localization and formatting code from the system 473 C library (glibc) version 2.2.5. That version of glibc is over a 474 year old and contains necessary bugfixes. Many GNU/Linux distros make 475 glibc version 2.3.x available now. 476 </p><p>The guideline is simple: the more recent the C++ library, the 477 more recent the C library. (This is also documented in the main 478 GCC installation instructions.) 479 </p></td></tr><tr class="question" title="4.8."><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> 480 Can't use wchar_t/wstring on FreeBSD 481 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p> 482 Older versions of FreeBSD's C library do not have sufficient 483 support for wide character functions, and as a result the 484 libstdc++ configury decides that wchar_t support should be 485 disabled. In addition, the libstdc++ platform checks that 486 enabled <span class="type">wchar_t</span> were quite strict, and not granular 487 enough to detect when the minimal support to 488 enable <span class="type">wchar_t</span> and C++ library structures 489 like <code class="classname">wstring</code> were present. This impacted Solaris, 490 Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0. 491 </p><p> 492 </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"> 493 What works already? 494 </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs"> 495 Bugs in the ISO C++ language or library specification 496 </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs"> 497 Bugs in the compiler (gcc/g++) and not libstdc++ 498 </a></dt></dl></td></tr><tr class="question" title="5.1."><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> 499 What works already? 500 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p> 501 Short answer: Pretty much everything <span class="emphasis"><em>works</em></span> 502 except for some corner cases. Support for localization 503 in <code class="classname">locale</code> may be incomplete on non-GNU 504 platforms. Also dependant on the underlying platform is support 505 for <span class="type">wchar_t</span> and <span class="type">long 506 long</span> specializations, and details of thread support. 507 </p><p> 508 Long answer: See the implementation status pages for 509 <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>, 510 <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and 511 <a class="link" href="manual/status.html#status.iso.200x" title="C++ 200x">C++0x</a>. 512 </p></td></tr><tr class="question" title="5.2."><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> 513 Bugs in the ISO C++ language or library specification 514 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p> 515 Unfortunately, there are some. 516 </p><p> 517 For those people who are not part of the ISO Library Group 518 (i.e., nearly all of us needing to read this page in the first 519 place), a public list of the library defects is occasionally 520 published <a class="ulink" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/" target="_top">here</a>. 521 Some of these issues have resulted in code changes in libstdc++. 522 </p><p> 523 If you think you've discovered a new bug that is not listed, 524 please post a message describing your problem 525 to <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code> or the Usenet group 526 comp.lang.c++.moderated. 527 </p></td></tr><tr class="question" title="5.3."><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> 528 Bugs in the compiler (gcc/g++) and not libstdc++ 529 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p> 530 On occasion, the compiler is wrong. Please be advised that this 531 happens much less often than one would think, and avoid jumping to 532 conclusions. 533 </p><p> 534 First, examine the ISO C++ standard. Second, try another compiler 535 or an older version of the GNU compilers. Third, you can find more 536 information on the libstdc++ and the GCC mailing lists: search 537 these lists with terms describing your issue. 538 </p><p> 539 Before reporting a bug, please examine the 540 <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the 541 category set to <span class="quote">“<span class="quote">g++</span>”</span>. 542 </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"> 543 Reopening a stream fails 544 </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose"> 545 -Weffc++ complains too much 546 </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads"> 547 Ambiguous overloads after including an old-style header 548 </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers"> 549 The g++-3 headers are not ours 550 </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks"> 551 Errors about *Concept and 552 constraints in the STL 553 </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash"> 554 Program crashes when using library code in a 555 dynamically-loaded library 556 </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks"> 557 “Memory leaks” in containers 558 </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on"> 559 list::size() is O(n)! 560 </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix"> 561 Aw, that's easy to fix! 562 </a></dt></dl></td></tr><tr class="question" title="6.1."><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> 563 Reopening a stream fails 564 </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> 565 One of the most-reported non-bug reports. Executing a sequence like: 566 </p><div class="literallayout"><p><br /> 567 #include <fstream><br /> 568 ...<br /> 569 std::fstream fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br /> 570 // .<br /> 571 // . do things with fs...<br /> 572 // .<br /> 573 fs.close();<br /> 574 fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br /> 575 </p></div><p> 576 All operations on the re-opened <code class="varname">fs</code> will fail, or at 577 least act very strangely. Yes, they often will, especially if 578 <code class="varname">fs</code> reached the EOF state on the previous file. The 579 reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared 580 on a successful call to open(). The standard unfortunately did 581 not specify behavior in this case, and to everybody's great sorrow, 582 the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in 583 DR #22</a> is to leave the flags unchanged. You must insert a call 584 to <code class="function">fs.clear()</code> between the calls to close() and open(), 585 and then everything will work like we all expect it to work. 586 <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution 587 of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open() 588 now calls <code class="function">clear()</code> on success! 589 </p></td></tr><tr class="question" title="6.2."><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> 590 -Weffc++ complains too much 591 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p> 592 Many warnings are emitted when <code class="literal">-Weffc++</code> is used. Making 593 libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project, 594 for a few reasons. Mainly, that option tries to enforce 595 object-oriented programming, while the Standard Library isn't 596 necessarily trying to be OO. 597 </p><p> 598 We do, however, try to have libstdc++ sources as clean as possible. If 599 you see some simple changes that pacify <code class="literal">-Weffc++</code> 600 without other drawbacks, send us a patch. 601 </p></td></tr><tr class="question" title="6.3."><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> 602 Ambiguous overloads after including an old-style header 603 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p> 604 Another problem is the <code class="literal">rel_ops</code> namespace and the template 605 comparison operator functions contained therein. If they become 606 visible in the same namespace as other comparison functions 607 (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the <iterator> header), 608 then you will suddenly be faced with huge numbers of ambiguity 609 errors. This was discussed on the -v3 list; Nathan Myers 610 <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums 611 things up here</a>. The collisions with vector/string iterator 612 types have been fixed for 3.1. 613 </p></td></tr><tr class="question" title="6.4."><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> 614 The g++-3 headers are <span class="emphasis"><em>not ours</em></span> 615 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p> 616 If you have found an extremely broken header file which is 617 causing problems for you, look carefully before submitting a 618 "high" priority bug report (which you probably 619 shouldn't do anyhow; see the last paragraph of the page 620 describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC 621 bug database</a>). 622 </p><p> 623 If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or 624 if the installed library's name looks like 625 <code class="filename">libstdc++-2.10.a</code> or 626 <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the 627 old libstdc++-v2 library, which is nonstandard and 628 unmaintained. Do not report problems with -v2 to the -v3 629 mailing list. 630 </p><p> 631 For GCC versions 3.0 and 3.1 the libstdc++ header files are 632 installed in <code class="filename">${prefix}/include/g++-v3</code> (see the 633 'v'?). Starting with version 3.2 the headers are installed in 634 <code class="filename">${prefix}/include/c++/${version}</code> as this prevents 635 headers from previous versions being found by mistake. 636 </p></td></tr><tr class="question" title="6.5."><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> 637 Errors about <span class="emphasis"><em>*Concept</em></span> and 638 <span class="emphasis"><em>constraints</em></span> in the STL 639 </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> 640 If you see compilation errors containing messages about 641 <span class="errortext">foo Concept </span>and something to do with a 642 <span class="errortext">constraints</span> member function, then most 643 likely you have violated one of the requirements for types used 644 during instantiation of template containers and functions. For 645 example, EqualityComparableConcept appears if your types must be 646 comparable with == and you have not provided this capability (a 647 typo, or wrong visibility, or you just plain forgot, etc). 648 </p><p> 649 More information, including how to optionally enable/disable the 650 checks, is available 651 <a class="link" href="manual/bk01pt03ch08.html" title="Chapter 8. Concept Checking">here</a>. 652 </p></td></tr><tr class="question" title="6.6."><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> 653 Program crashes when using library code in a 654 dynamically-loaded library 655 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p> 656 If you are using the C++ library across dynamically-loaded 657 objects, make certain that you are passing the correct options 658 when compiling and linking: 659 </p><div class="literallayout"><p><br /> 660 // compile your library components<br /> 661 g++ -fPIC -c a.cc<br /> 662 g++ -fPIC -c b.cc<br /> 663 ...<br /> 664 g++ -fPIC -c z.cc<br /> 665<br /> 666 // create your library<br /> 667 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br /> 668<br /> 669 // link the executable<br /> 670 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br /> 671 </p></div></td></tr><tr class="question" title="6.7."><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> 672 <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers 673 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p> 674 A few people have reported that the standard containers appear 675 to leak memory when tested with memory checkers such as 676 <a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>. 677 The library's default allocators keep free memory in a pool 678 for later reuse, rather than returning it to the OS. Although 679 this memory is always reachable by the library and is never 680 lost, memory debugging tools can report it as a leak. If you 681 want to test the library for memory leaks please read 682 <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a> 683 first. 684 </p></td></tr><tr class="question" title="6.8."><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> 685 list::size() is O(n)! 686 </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> 687 See 688 the <a class="link" href="manual/containers.html" title="Part VII. Containers">Containers</a> 689 chapter. 690 </p></td></tr><tr class="question" title="6.9."><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> 691 Aw, that's easy to fix! 692 </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> 693 If you have found a bug in the library and you think you have 694 a working fix, then send it in! The main GCC site has a page 695 on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting 696 patches</a> that covers the procedure, but for libstdc++ you 697 should also send the patch to our mailing list in addition to 698 the GCC patches mailing list. The libstdc++ 699 <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">contributors' page</a> 700 also talks about how to submit patches. 701 </p><p> 702 In addition to the description, the patch, and the ChangeLog 703 entry, it is a Good Thing if you can additionally create a small 704 test program to test for the presence of the bug that your 705 patch fixes. Bugs have a way of being reintroduced; if an old 706 bug creeps back in, it will be caught immediately by the 707 <a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists. 708 </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"> 709 string::iterator is not char*; vector<T>::iterator is not T* 710 </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next"> 711 What's next after libstdc++? 712 </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl"> 713 What about the STL from SGI? 714 </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat"> 715 Extensions and Backward Compatibility 716 </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support"> 717 Does libstdc++ support TR1? 718 </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard? 719 </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi"> 720 What's an ABI and why is it so messy? 721 </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity"> 722 How do I make std::vector<T>::capacity() == std::vector<T>::size? 723 </a></dt></dl></td></tr><tr class="question" title="7.1."><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> 724 string::iterator is not char*; vector<T>::iterator is not T* 725 </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> 726 If you have code that depends on container<T> iterators 727 being implemented as pointer-to-T, your code is broken. It's 728 considered a feature, not a bug, that libstdc++ points this out. 729 </p><p> 730 While there are arguments for iterators to be implemented in 731 that manner, A) they aren't very good ones in the long term, 732 and B) they were never guaranteed by the Standard anyway. The 733 type-safety achieved by making iterators a real class rather 734 than a typedef for <span class="type">T*</span> outweighs nearly all opposing 735 arguments. 736 </p><p> 737 Code which does assume that a vector iterator <code class="varname">i</code> 738 is a pointer can often be fixed by changing <code class="varname">i</code> in 739 certain expressions to <code class="varname">&*i</code>. Future revisions 740 of the Standard are expected to bless this usage for 741 vector<> (but not for basic_string<>). 742 </p></td></tr><tr class="question" title="7.2."><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> 743 What's next after libstdc++? 744 </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> 745 Hopefully, not much. The goal of libstdc++ is to produce a 746 fully-compliant, fully-portable Standard Library. After that, 747 we're mostly done: there won't <span class="emphasis"><em>be</em></span> any 748 more compliance work to do. 749 </p><p> 750 There is an effort underway to add significant extensions to 751 the standard library specification. The latest version of 752 this effort is described in 753 <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top"> 754 The C++ Library Technical Report 1</a>. 755 </p></td></tr><tr class="question" title="7.3."><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> 756 What about the STL from SGI? 757 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p> 758 The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>, 759 version 3.3, was the final merge of the STL codebase. The 760 code in libstdc++ contains many fixes and changes, and 761 the SGI code is no longer under active 762 development. We expect that no future merges will take place. 763 </p><p> 764 In particular, <code class="classname">string</code> is not from SGI and makes no 765 use of their "rope" class (which is included as an 766 optional extension), nor is <code class="classname">valarray</code> and some others. 767 Classes like <code class="classname">vector<></code> are, but have been 768 extensively modified. 769 </p><p> 770 More information on the evolution of libstdc++ can be found at the 771 <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API 772 evolution</a> 773 and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards 774 compatibility</a> documentation. 775 </p><p> 776 The FAQ for SGI's STL (one jump off of their main page) is 777 still recommended reading. 778 </p></td></tr><tr class="question" title="7.4."><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> 779 Extensions and Backward Compatibility 780 </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> 781 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. 782 </p></td></tr><tr class="question" title="7.5."><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> 783 Does libstdc++ support TR1? 784 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p> 785 Yes. 786 </p><p> 787 The C++ Standard Library Technical Report adds many new features to 788 the library. The latest version of this effort is described in 789 <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top"> 790 Technical Report 1</a>. 791 </p><p> 792 The implementation status of TR1 in libstdc++ can be tracked <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status 793 page</a>. 794 </p></td></tr><tr class="question" title="7.6."><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? 795 </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> 796 Copies of the full ISO 14882 standard are available on line via 797 the ISO mirror site for committee members. Non-members, or those 798 who have not paid for the privilege of sitting on the committee 799 and sustained their two-meeting commitment for voting rights, may 800 get a copy of the standard from their respective national 801 standards organization. In the USA, this national standards 802 organization is ANSI and their website is 803 right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>. (And if 804 you've already registered with them, clicking this link will take 805 you to directly to the place where you can 806 <a class="ulink" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>. 807 </p><p> 808 Who is your country's member body? Visit the 809 <a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out! 810 </p><p> 811 The 2003 version of the standard (the 1998 version plus TC1) is 812 available in print, ISBN 0-470-84674-7. 813 </p></td></tr><tr class="question" title="7.7."><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> 814 What's an ABI and why is it so messy? 815 </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> 816 <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary 817 Interface</span>”</span>. Conventionally, it refers to a great 818 mass of details about how arguments are arranged on the call 819 stack and/or in registers, and how various types are arranged 820 and padded in structs. A single CPU design may suffer 821 multiple ABIs designed by different development tool vendors 822 who made different choices, or even by the same vendor for 823 different target applications or compiler versions. In ideal 824 circumstances the CPU designer presents one ABI and all the 825 OSes and compilers use it. In practice every ABI omits 826 details that compiler implementers (consciously or 827 accidentally) must choose for themselves. 828 </p><p> 829 That ABI definition suffices for compilers to generate code so a 830 program can interact safely with an OS and its lowest-level libraries. 831 Users usually want an ABI to encompass more detail, allowing libraries 832 built with different compilers (or different releases of the same 833 compiler!) to be linked together. For C++, this includes many more 834 details than for C, and CPU designers (for good reasons elaborated 835 below) have not stepped up to publish C++ ABIs. The details include 836 virtual function implementation, struct inheritance layout, name 837 mangling, and exception handling. Such an ABI has been defined for 838 GNU C++, and is immediately useful for embedded work relying only on 839 a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much 840 of) the standard library. It is a good basis for the work to come. 841 </p><p> 842 A useful C++ ABI must also incorporate many details of the standard 843 library implementation. For a C ABI, the layouts of a few structs 844 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice. 845 For C++, the details include the complete set of names of functions 846 and types used, the offsets of class members and virtual functions, 847 and the actual definitions of all inlines. C++ exposes many more 848 library details to the caller than C does. It makes defining 849 a complete ABI a much bigger undertaking, and requires not just 850 documenting library implementation details, but carefully designing 851 those details so that future bug fixes and optimizations don't 852 force breaking the ABI. 853 </p><p> 854 There are ways to help isolate library implementation details from the 855 ABI, but they trade off against speed. Library details used in 856 inner loops (e.g., getchar) must be exposed and frozen for all 857 time, but many others may reasonably be kept hidden from user code, 858 so they may later be changed. Deciding which, and implementing 859 the decisions, must happen before you can reasonably document a 860 candidate C++ ABI that encompasses the standard library. 861 </p></td></tr><tr class="question" title="7.8."><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> 862 How do I make std::vector<T>::capacity() == std::vector<T>::size? 863 </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> 864 The standard idiom for deallocating a <code class="classname">vector<T></code>'s 865 unused memory is to create a temporary copy of the vector and swap their 866 contents, e.g. for <code class="classname">vector<T> v</code> 867 </p><div class="literallayout"><p><br /> 868 std::vector<T>(v).swap(v);<br /> 869 </p></div><p> 870 The copy will take O(n) time and the swap is constant time. 871 </p><p> 872 See <a class="link" href="manual/bk01pt05ch13s05.html" title="Shrink to Fit">Shrink-to-fit 873 strings</a> for a similar solution for strings. 874 </p></td></tr></tbody></table></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk03.html">Up</a></td><td width="40%" align="right"> </td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="spine.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html> 875