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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="id573102"></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">
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" 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">
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>
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
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">“<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
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
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.
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>.
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">
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.
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.
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">“<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.
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" 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.
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
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>.
319 Using LD_LIBRARY_PATH is not always the best solution, <a class="link" href="manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic" title="Finding Dynamic or Shared Libraries">Finding Dynamic or Shared
320 Libraries</a> in the manual gives some alternatives.
321 </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>
323 </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>
324 If the only functions from <code class="filename">libstdc++.a</code>
325 which you need are language support functions (those listed in
326 <a class="link" href="manual/support.html" title="Chapter 4. Support">clause 18</a> of the
327 standard, e.g., <code class="function">new</code> and
328 <code class="function">delete</code>), then try linking against
329 <code class="filename">libsupc++.a</code>, which is a subset of
330 <code class="filename">libstdc++.a</code>. (Using <span class="command"><strong>gcc</strong></span>
331 instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
332 <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
333 for the final link step will do it). This library contains only
334 those support routines, one per object file. But if you are
335 using anything from the rest of the library, such as IOStreams
336 or vectors, then you'll still need pieces from
337 <code class="filename">libstdc++.a</code>.
338 </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>
339 This library is HUGE!
340 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
341 Usually the size of libraries on disk isn't noticeable. When a
342 link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
343 static archive library, only the necessary object files are copied
344 into your executable, not the entire library. Unfortunately, even
345 if you only need a single function or variable from an object file,
346 the entire object file is extracted. (There's nothing unique to C++
347 or libstdc++ about this; it's just common behavior, given here
348 for background reasons.)
350 Some of the object files which make up libstdc++.a are rather large.
351 If you create a statically-linked executable with
352 <code class="literal">-static</code>, those large object files are suddenly part
353 of your executable. Historically the best way around this was to
354 only place a very few functions (often only a single one) in each
355 source/object file; then extracting a single function is the same
356 as extracting a single .o file. For libstdc++ this is only
357 possible to a certain extent; the object files in question contain
358 template classes and template functions, pre-instantiated, and
359 splitting those up causes severe maintenance headaches.
361 On supported platforms, libstdc++ takes advantage of garbage
362 collection in the GNU linker to get a result similar to separating
363 each symbol into a separate source and object files. On these platforms,
364 GNU ld can place each function and variable into its own
365 section in a .o file. The GNU linker can then perform garbage
366 collection on unused sections; this reduces the situation to only
367 copying needed functions into the executable, as before, but all
368 happens automatically.
369 </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">
370 Can libstdc++ be used with non-GNU compilers?
371 </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
372 No 'long long' type on Solaris?
373 </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
374 _XOPEN_SOURCE and _GNU_SOURCE are always defined?
375 </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
376 Mac OS X ctype.h is broken! How can I fix it?
377 </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
378 Threading is broken on i386?
379 </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
380 MIPS atomic operations
381 </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
382 Recent GNU/Linux glibc required?
383 </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
384 Can't use wchar_t/wstring on FreeBSD
385 </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>
386 Can libstdc++ be used with non-GNU compilers?
387 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
390 Since the goal of ISO Standardization is for all C++
391 implementations to be able to share code, libstdc++ should be
392 usable under any ISO-compliant compiler, at least in theory.
394 However, the reality is that libstdc++ is targeted and optimized
395 for GCC/g++. This means that often libstdc++ uses specific,
396 non-standard features of g++ that are not present in older
397 versions of proprietary compilers. It may take as much as a year or two
398 after an official release of GCC that contains these features for
399 proprietary tools support these constructs.
401 In the near past, specific released versions of libstdc++ have
402 been known to work with versions of the EDG C++ compiler, and
403 vendor-specific proprietary C++ compilers such as the Intel ICC
405 </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>
406 No 'long long' type on Solaris?
407 </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>
408 By default we try to support the C99 <span class="type">long long</span> type.
409 This requires that certain functions from your C library be present.
411 Up through release 3.0.2 the platform-specific tests performed by
412 libstdc++ were too general, resulting in a conservative approach
413 to enabling the <span class="type">long long</span> code paths. The most
414 commonly reported platform affected was Solaris.
416 This has been fixed for libstdc++ releases greater than 3.0.3.
417 </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>
418 <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
419 </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
420 macro <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
421 with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list;
422 other macros and other platforms are also affected.)
423 </p><p>These macros are typically used in C library headers, guarding new
424 versions of functions from their older versions. The C++ standard
425 library includes the C standard library, but it requires the C90
426 version, which for backwards-compatibility reasons is often not the
427 default for many vendors.
428 </p><p>More to the point, the C++ standard requires behavior which is only
429 available on certain platforms after certain symbols are defined.
430 Usually the issue involves I/O-related typedefs. In order to
431 ensure correctness, the compiler simply predefines those symbols.
432 </p><p>Note that it's not enough to #define them only when the library is
433 being built (during installation). Since we don't have an 'export'
434 keyword, much of the library exists as headers, which means that
435 the symbols must also be defined as your programs are parsed and
437 </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
438 the gcc config headers for your target (and try changing them to
439 see what happens when building complicated code). You can also run
440 <span class="command"><strong>g++ -E -dM - < /dev/null"</strong></span> to display
441 a list of predefined macros for any particular installation.
442 </p><p>This has been discussed on the mailing lists
443 <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>.
444 </p><p>This method is something of a wart. We'd like to find a cleaner
445 solution, but nobody yet has contributed the time.
446 </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>
447 Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
448 </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,
449 the patch is quite simple, and well-known.
450 <a class="ulink" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
451 link to the solution</a>.
452 </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>
453 Threading is broken on i386?
454 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
455 </p><p>Support for atomic integer operations is/was broken on i386
456 platforms. The assembly code accidentally used opcodes that are
457 only available on the i486 and later. So if you configured GCC
458 to target, for example, i386-linux, but actually used the programs
459 on an i686, then you would encounter no problems. Only when
460 actually running the code on a i386 will the problem appear.
461 </p><p>This is fixed in 3.2.2.
462 </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>
463 MIPS atomic operations
464 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
465 The atomic locking routines for MIPS targets requires MIPS II
466 and later. A patch went in just after the 3.3 release to
467 make mips* use the generic implementation instead. You can also
468 configure for mipsel-elf as a workaround.
470 The mips*-*-linux* port continues to use the MIPS II routines, and more
471 work in this area is expected.
472 </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>
473 Recent GNU/Linux glibc required?
474 </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
475 5.0.1) and later uses localization and formatting code from the system
476 C library (glibc) version 2.2.5 which contains necessary bugfixes.
477 Most GNU/Linux distros make more recent versions available now.
478 libstdc++ 4.6.0 and later require glibc 2.3 or later for this
479 localization and formatting code.
480 </p><p>The guideline is simple: the more recent the C++ library, the
481 more recent the C library. (This is also documented in the main
482 GCC installation instructions.)
483 </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>
484 Can't use wchar_t/wstring on FreeBSD
485 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
486 Older versions of FreeBSD's C library do not have sufficient
487 support for wide character functions, and as a result the
488 libstdc++ configury decides that wchar_t support should be
489 disabled. In addition, the libstdc++ platform checks that
490 enabled <span class="type">wchar_t</span> were quite strict, and not granular
491 enough to detect when the minimal support to
492 enable <span class="type">wchar_t</span> and C++ library structures
493 like <code class="classname">wstring</code> were present. This impacted Solaris,
494 Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
496 </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">
498 </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
499 Bugs in the ISO C++ language or library specification
500 </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
501 Bugs in the compiler (gcc/g++) and not libstdc++
502 </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>
504 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
505 Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
506 except for some corner cases. Support for localization
507 in <code class="classname">locale</code> may be incomplete on non-GNU
508 platforms. Also dependant on the underlying platform is support
509 for <span class="type">wchar_t</span> and <span class="type">long
510 long</span> specializations, and details of thread support.
512 Long answer: See the implementation status pages for
513 <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
514 <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
515 <a class="link" href="manual/status.html#status.iso.200x" title="C++ 200x">C++0x</a>.
516 </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>
517 Bugs in the ISO C++ language or library specification
518 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
519 Unfortunately, there are some.
521 For those people who are not part of the ISO Library Group
522 (i.e., nearly all of us needing to read this page in the first
523 place), a public list of the library defects is occasionally
524 published <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">here</a>.
525 Some of these issues have resulted in code changes in libstdc++.
527 If you think you've discovered a new bug that is not listed,
528 please post a message describing your problem
529 to <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code> or the Usenet group
530 comp.lang.c++.moderated.
531 </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>
532 Bugs in the compiler (gcc/g++) and not libstdc++
533 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
534 On occasion, the compiler is wrong. Please be advised that this
535 happens much less often than one would think, and avoid jumping to
538 First, examine the ISO C++ standard. Second, try another compiler
539 or an older version of the GNU compilers. Third, you can find more
540 information on the libstdc++ and the GCC mailing lists: search
541 these lists with terms describing your issue.
543 Before reporting a bug, please examine the
544 <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">bugs database</a> with the
545 category set to <span class="quote">“<span class="quote">g++</span>”</span>.
546 </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">
547 Reopening a stream fails
548 </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
549 -Weffc++ complains too much
550 </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
551 Ambiguous overloads after including an old-style header
552 </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
553 The g++-3 headers are not ours
554 </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
555 Errors about *Concept and
556 constraints in the STL
557 </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
558 Program crashes when using library code in a
559 dynamically-loaded library
560 </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
561 “Memory leaks” in containers
562 </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
563 list::size() is O(n)!
564 </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
565 Aw, that's easy to fix!
566 </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>
567 Reopening a stream fails
568 </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>
569 One of the most-reported non-bug reports. Executing a sequence like:
570 </p><div class="literallayout"><p><br />
571 #include <fstream><br />
573 std::fstream fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
575 // . do things with fs...<br />
578 fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
580 All operations on the re-opened <code class="varname">fs</code> will fail, or at
581 least act very strangely. Yes, they often will, especially if
582 <code class="varname">fs</code> reached the EOF state on the previous file. The
583 reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
584 on a successful call to open(). The standard unfortunately did
585 not specify behavior in this case, and to everybody's great sorrow,
586 the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
587 DR #22</a> is to leave the flags unchanged. You must insert a call
588 to <code class="function">fs.clear()</code> between the calls to close() and open(),
589 and then everything will work like we all expect it to work.
590 <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
591 of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
592 now calls <code class="function">clear()</code> on success!
593 </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>
594 -Weffc++ complains too much
595 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
596 Many warnings are emitted when <code class="literal">-Weffc++</code> is used. Making
597 libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
598 for a few reasons. Mainly, that option tries to enforce
599 object-oriented programming, while the Standard Library isn't
600 necessarily trying to be OO.
602 We do, however, try to have libstdc++ sources as clean as possible. If
603 you see some simple changes that pacify <code class="literal">-Weffc++</code>
604 without other drawbacks, send us a patch.
605 </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>
606 Ambiguous overloads after including an old-style header
607 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
608 Another problem is the <code class="literal">rel_ops</code> namespace and the template
609 comparison operator functions contained therein. If they become
610 visible in the same namespace as other comparison functions
611 (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the <iterator> header),
612 then you will suddenly be faced with huge numbers of ambiguity
613 errors. This was discussed on the -v3 list; Nathan Myers
614 <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
615 things up here</a>. The collisions with vector/string iterator
616 types have been fixed for 3.1.
617 </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>
618 The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
619 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
620 If you have found an extremely broken header file which is
621 causing problems for you, look carefully before submitting a
622 "high" priority bug report (which you probably
623 shouldn't do anyhow; see the last paragraph of the page
624 describing <a class="ulink" href="http://gcc.gnu.org/bugs.html" target="_top">the GCC
627 If the headers are in <code class="filename">${prefix}/include/g++-3</code>, or
628 if the installed library's name looks like
629 <code class="filename">libstdc++-2.10.a</code> or
630 <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
631 old libstdc++-v2 library, which is nonstandard and
632 unmaintained. Do not report problems with -v2 to the -v3
635 For GCC versions 3.0 and 3.1 the libstdc++ header files are
636 installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
637 'v'?). Starting with version 3.2 the headers are installed in
638 <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
639 headers from previous versions being found by mistake.
640 </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>
641 Errors about <span class="emphasis"><em>*Concept</em></span> and
642 <span class="emphasis"><em>constraints</em></span> in the STL
643 </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>
644 If you see compilation errors containing messages about
645 <span class="errortext">foo Concept </span>and something to do with a
646 <span class="errortext">constraints</span> member function, then most
647 likely you have violated one of the requirements for types used
648 during instantiation of template containers and functions. For
649 example, EqualityComparableConcept appears if your types must be
650 comparable with == and you have not provided this capability (a
651 typo, or wrong visibility, or you just plain forgot, etc).
653 More information, including how to optionally enable/disable the
654 checks, is available in the
655 <a class="link" href="manual/bk01pt02ch05s02.html" title="Concept Checking">Diagnostics</a>.
656 chapter of the manual.
657 </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>
658 Program crashes when using library code in a
659 dynamically-loaded library
660 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
661 If you are using the C++ library across dynamically-loaded
662 objects, make certain that you are passing the correct options
663 when compiling and linking:
664 </p><div class="literallayout"><p><br />
665 // compile your library components<br />
666 g++ -fPIC -c a.cc<br />
667 g++ -fPIC -c b.cc<br />
669 g++ -fPIC -c z.cc<br />
671 // create your library<br />
672 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
674 // link the executable<br />
675 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
676 </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>
677 <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
678 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
679 A few people have reported that the standard containers appear
680 to leak memory when tested with memory checkers such as
681 <a class="ulink" href="http://valgrind.org/" target="_top">valgrind</a>.
682 The library's default allocators keep free memory in a pool
683 for later reuse, rather than returning it to the OS. Although
684 this memory is always reachable by the library and is never
685 lost, memory debugging tools can report it as a leak. If you
686 want to test the library for memory leaks please read
687 <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
689 </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>
690 list::size() is O(n)!
691 </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>
693 the <a class="link" href="manual/containers.html" title="Chapter 9. Containers">Containers</a>
695 </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>
696 Aw, that's easy to fix!
697 </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>
698 If you have found a bug in the library and you think you have
699 a working fix, then send it in! The main GCC site has a page
700 on <a class="ulink" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
701 patches</a> that covers the procedure, but for libstdc++ you
702 should also send the patch to our mailing list in addition to
703 the GCC patches mailing list. The libstdc++
704 <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">contributors' page</a>
705 also talks about how to submit patches.
707 In addition to the description, the patch, and the ChangeLog
708 entry, it is a Good Thing if you can additionally create a small
709 test program to test for the presence of the bug that your
710 patch fixes. Bugs have a way of being reintroduced; if an old
711 bug creeps back in, it will be caught immediately by the
712 <a class="ulink" href="#2_4" target="_top">testsuite</a> -- but only if such a test exists.
713 </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">
714 string::iterator is not char*; vector<T>::iterator is not T*
715 </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
716 What's next after libstdc++?
717 </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
718 What about the STL from SGI?
719 </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
720 Extensions and Backward Compatibility
721 </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
722 Does libstdc++ support TR1?
723 </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
724 </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
725 What's an ABI and why is it so messy?
726 </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
727 How do I make std::vector<T>::capacity() == std::vector<T>::size?
728 </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>
729 string::iterator is not char*; vector<T>::iterator is not T*
730 </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>
731 If you have code that depends on container<T> iterators
732 being implemented as pointer-to-T, your code is broken. It's
733 considered a feature, not a bug, that libstdc++ points this out.
735 While there are arguments for iterators to be implemented in
736 that manner, A) they aren't very good ones in the long term,
737 and B) they were never guaranteed by the Standard anyway. The
738 type-safety achieved by making iterators a real class rather
739 than a typedef for <span class="type">T*</span> outweighs nearly all opposing
742 Code which does assume that a vector iterator <code class="varname">i</code>
743 is a pointer can often be fixed by changing <code class="varname">i</code> in
744 certain expressions to <code class="varname">&*i</code>. Future revisions
745 of the Standard are expected to bless this usage for
746 vector<> (but not for basic_string<>).
747 </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>
748 What's next after libstdc++?
749 </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>
750 Hopefully, not much. The goal of libstdc++ is to produce a
751 fully-compliant, fully-portable Standard Library. After that,
752 we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
753 more compliance work to do.
755 There is an effort underway to add significant extensions to
756 the standard library specification. The latest version of
757 this effort is described in
758 <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
759 The C++ Library Technical Report 1</a>.
760 </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>
761 What about the STL from SGI?
762 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
763 The <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
764 version 3.3, was the final merge of the STL codebase. The
765 code in libstdc++ contains many fixes and changes, and
766 the SGI code is no longer under active
767 development. We expect that no future merges will take place.
769 In particular, <code class="classname">string</code> is not from SGI and makes no
770 use of their "rope" class (which is included as an
771 optional extension), nor is <code class="classname">valarray</code> and some others.
772 Classes like <code class="classname">vector<></code> are, but have been
773 extensively modified.
775 More information on the evolution of libstdc++ can be found at the
776 <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
778 and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
779 compatibility</a> documentation.
781 The FAQ for SGI's STL (one jump off of their main page) is
782 still recommended reading.
783 </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>
784 Extensions and Backward Compatibility
785 </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>
786 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.
787 </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>
788 Does libstdc++ support TR1?
789 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
792 The C++ Standard Library Technical Report adds many new features to
793 the library. The latest version of this effort is described in
794 <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
795 Technical Report 1</a>.
797 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
799 </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?
800 </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>
801 Copies of the full ISO 14882 standard are available on line via
802 the ISO mirror site for committee members. Non-members, or those
803 who have not paid for the privilege of sitting on the committee
804 and sustained their two-meeting commitment for voting rights, may
805 get a copy of the standard from their respective national
806 standards organization. In the USA, this national standards
807 organization is ANSI and their website is
808 right <a class="ulink" href="http://www.ansi.org" target="_top">here</a>. (And if
809 you've already registered with them, clicking this link will take
810 you to directly to the place where you can
811 <a class="ulink" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
813 Who is your country's member body? Visit the
814 <a class="ulink" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
816 The 2003 version of the standard (the 1998 version plus TC1) is
817 available in print, ISBN 0-470-84674-7.
818 </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>
819 What's an ABI and why is it so messy?
820 </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>
821 <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
822 Interface</span>”</span>. Conventionally, it refers to a great
823 mass of details about how arguments are arranged on the call
824 stack and/or in registers, and how various types are arranged
825 and padded in structs. A single CPU design may suffer
826 multiple ABIs designed by different development tool vendors
827 who made different choices, or even by the same vendor for
828 different target applications or compiler versions. In ideal
829 circumstances the CPU designer presents one ABI and all the
830 OSes and compilers use it. In practice every ABI omits
831 details that compiler implementers (consciously or
832 accidentally) must choose for themselves.
834 That ABI definition suffices for compilers to generate code so a
835 program can interact safely with an OS and its lowest-level libraries.
836 Users usually want an ABI to encompass more detail, allowing libraries
837 built with different compilers (or different releases of the same
838 compiler!) to be linked together. For C++, this includes many more
839 details than for C, and CPU designers (for good reasons elaborated
840 below) have not stepped up to publish C++ ABIs. The details include
841 virtual function implementation, struct inheritance layout, name
842 mangling, and exception handling. Such an ABI has been defined for
843 GNU C++, and is immediately useful for embedded work relying only on
844 a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
845 of) the standard library. It is a good basis for the work to come.
847 A useful C++ ABI must also incorporate many details of the standard
848 library implementation. For a C ABI, the layouts of a few structs
849 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
850 For C++, the details include the complete set of names of functions
851 and types used, the offsets of class members and virtual functions,
852 and the actual definitions of all inlines. C++ exposes many more
853 library details to the caller than C does. It makes defining
854 a complete ABI a much bigger undertaking, and requires not just
855 documenting library implementation details, but carefully designing
856 those details so that future bug fixes and optimizations don't
857 force breaking the ABI.
859 There are ways to help isolate library implementation details from the
860 ABI, but they trade off against speed. Library details used in
861 inner loops (e.g., getchar) must be exposed and frozen for all
862 time, but many others may reasonably be kept hidden from user code,
863 so they may later be changed. Deciding which, and implementing
864 the decisions, must happen before you can reasonably document a
865 candidate C++ ABI that encompasses the standard library.
866 </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>
867 How do I make std::vector<T>::capacity() == std::vector<T>::size?
868 </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>
869 The standard idiom for deallocating a <code class="classname">vector<T></code>'s
870 unused memory is to create a temporary copy of the vector and swap their
871 contents, e.g. for <code class="classname">vector<T> v</code>
872 </p><div class="literallayout"><p><br />
873 std::vector<T>(v).swap(v);<br />
875 The copy will take O(n) time and the swap is constant time.
877 See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
878 strings</a> for a similar solution for strings.
879 </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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