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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 V1.74.0" /><link rel="home" href="spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="bk03.html" title="" /><link rel="prev" href="bk03.html" title="" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frequently Asked Questions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><th width="60%" align="center"></th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="article" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="faq"></a>Frequently Asked Questions</h2></div><div><p class="copyright">Copyright ©
6 <a class="ulink" href="http://fsf.org" target="_top">FSF</a>
7 </p></div></div><hr /></div><div class="qandaset"><dl><dt>1. <a href="faq.html#faq.info">General Information</a></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
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">
35 </a></dt><dt>3.6. <a href="faq.html#faq.size">
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">
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">
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" summary="Q and A Set"><col align="left" width="1%" /><tbody><tr class="qandadiv"><td align="left" valign="top" colspan="2"><h3 class="title"><a id="faq.info"></a>1. General Information</h3></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
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"><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>
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"><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">incomplet and
125 incorrekt</span>”, and many suffer from limitations of the compilers
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++.
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">roll their own</span>”
143 nor be worried about platform-specific incompatibilities.
144 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><b>1.3.</b></p></td><td align="left" valign="top"><p>
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
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"><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
164 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><b>1.5.</b></p></td><td align="left" valign="top"><p>
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"><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.
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"><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>.
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"><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"><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"><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"><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">
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"><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.
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"><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.
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>.
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.
268 The “<span class="quote">anonymous client checkout</span>” feature of SVN is
269 similar to anonymous FTP in that it allows anyone to retrieve
270 the latest libstdc++ sources.
273 see <a class="ulink" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
275 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_test"></a><a id="q-how_to_test"></a><p><b>3.3.</b></p></td><td align="left" valign="top"><p>How do I know if it works?
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.
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"><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
293 /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
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
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.
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"><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>
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"><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">linker</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.)
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.
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"><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>
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.
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.
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
402 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.solaris_long_long"></a><a id="q-solaris_long_long"></a><p><b>4.2.</b></p></td><td align="left" valign="top"><p>
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.
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.
413 This has been fixed for libstdc++ releases greater than 3.0.3.
414 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><b>4.3.</b></p></td><td align="left" valign="top"><p>
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
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"><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"><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"><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.
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"><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"><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.
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">
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"><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>
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.
508 Long answer: See the implementation status pages for
509 <a class="link" href="manual/status.html#manual.intro.status.standard.1998" title="C++ 1998/2003">C++98</a>,
510 <a class="link" href="manual/status.html#manual.intro.status.standard.tr1" title="C++ TR1">TR1</a>, and
511 <a class="link" href="manual/status.html#manual.intro.status.standard.200x" title="C++ 200x">C++0x</a>.
512 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><b>5.2.</b></p></td><td align="left" valign="top"><p>
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.
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++.
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"><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
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.
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">g++</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"><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 />
569 std::fstream fs(“<span class="quote">a_file</span>”);<br />
571 // . do things with fs...<br />
574 fs.open(“<span class="quote">a_new_file</span>”);<br />
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"><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.
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"><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">using</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"><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
623 If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
624 if the installed library's name looks like
625 <code class="filename">libstdc++-2.10.a</code> or
626 <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
627 old libstdc++-v2 library, which is nonstandard and
628 unmaintained. Do not report problems with -v2 to the -v3
631 For GCC versions 3.0 and 3.1 the libstdc++ header files are
632 installed in <code class="filename">${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"><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).
649 More information, including how to optionally enable/disable the
651 <a class="link" href="manual/bk01pt03ch08.html" title="Chapter 8. Concept Checking">here</a>.
652 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><b>6.6.</b></p></td><td align="left" valign="top"><p>
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 />
664 g++ -fPIC -c z.cc<br />
666 // create your library<br />
667 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
669 // link the executable<br />
670 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
671 </p></div></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.memory_leaks"></a><a id="q-memory_leaks"></a><p><b>6.7.</b></p></td><td align="left" valign="top"><p>
672 “<span class="quote">Memory leaks</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>
684 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.list_size_on"></a><a id="q-list_size_on"></a><p><b>6.8.</b></p></td><td align="left" valign="top"><p>
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>
688 the <a class="link" href="manual/containers.html" title="Part VII. Containers">Containers</a>
690 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.easy_to_fix"></a><a id="q-easy_to_fix"></a><p><b>6.9.</b></p></td><td align="left" valign="top"><p>
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.
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"><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.
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
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"><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.
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"><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.
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.
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
773 and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
774 compatibility</a> documentation.
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"><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"><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>
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>.
792 The implementation status of TR1 in libstdc++ can be tracked <a class="link" href="manual/status.html#manual.intro.status.standard.tr1" title="C++ TR1">on the TR1 status
794 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.get_iso_cxx"></a><a id="q-get_iso_cxx"></a><p><b>7.6.</b></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard?
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/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003" target="_top">buy the standard on-line</a>.
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!
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"><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">Application Binary
817 Interface</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.
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">free-standing implementation</span>” that doesn't include (much
840 of) the standard library. It is a good basis for the work to come.
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.
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"><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 />
870 The copy will take O(n) time and the swap is constant time.
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>
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