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5 <a class="link" href="http://www.fsf.org" target="_top">FSF</a>
6 </p></div></div><hr /></div><div class="qandaset"><a id="idp1581728"></a><dl><dt></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what">
8 </a></dt><dt>1.2. <a href="faq.html#faq.why">
9 Why should I use libstdc++?
10 </a></dt><dt>1.3. <a href="faq.html#faq.who">
11 Who's in charge of it?
12 </a></dt><dt>1.4. <a href="faq.html#faq.when">
13 When is libstdc++ going to be finished?
14 </a></dt><dt>1.5. <a href="faq.html#faq.how">
15 How do I contribute to the effort?
16 </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
17 What happened to the older libg++? I need that!
18 </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
19 What if I have more questions?
20 </a></dt></dl></dd><dt></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what">
21 What are the license terms for libstdc++?
22 </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
23 So any program which uses libstdc++ falls under the GPL?
24 </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
25 How is that different from the GNU {Lesser,Library} GPL?
26 </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
27 I see. So, what restrictions are there on programs that use the library?
28 </a></dt></dl></dd><dt></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++?
29 </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
30 </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
31 </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?
32 </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
34 </a></dt><dt>3.6. <a href="faq.html#faq.size">
36 </a></dt></dl></dd><dt></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
37 Can libstdc++ be used with non-GNU compilers?
38 </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
39 No 'long long' type on Solaris?
40 </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
41 _XOPEN_SOURCE and _GNU_SOURCE are always defined?
42 </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
43 Mac OS X ctype.h is broken! How can I fix it?
44 </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
45 Threading is broken on i386?
46 </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
47 MIPS atomic operations
48 </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
49 Recent GNU/Linux glibc required?
50 </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
51 Can't use wchar_t/wstring on FreeBSD
52 </a></dt></dl></dd><dt></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works">
54 </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
55 Bugs in the ISO C++ language or library specification
56 </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
57 Bugs in the compiler (gcc/g++) and not libstdc++
58 </a></dt></dl></dd><dt></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
59 Reopening a stream fails
60 </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
61 -Weffc++ complains too much
62 </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
63 Ambiguous overloads after including an old-style header
64 </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
65 The g++-3 headers are not ours
66 </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
67 Errors about *Concept and
68 constraints in the STL
69 </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
70 Program crashes when using library code in a
71 dynamically-loaded library
72 </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
73 “Memory leaks” in containers
74 </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
76 </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
77 Aw, that's easy to fix!
78 </a></dt></dl></dd><dt></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
79 string::iterator is not char*; vector<T>::iterator is not T*
80 </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
81 What's next after libstdc++?
82 </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
83 What about the STL from SGI?
84 </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
85 Extensions and Backward Compatibility
86 </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
87 Does libstdc++ support TR1?
88 </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
89 </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
90 What's an ABI and why is it so messy?
91 </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
92 How do I make std::vector<T>::capacity() == std::vector<T>::size?
93 </a></dt></dl></dd></dl><table border="0" style="width: 100%;"><colgroup><col align="left" width="1%" /><col /></colgroup><tbody><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what">
95 </a></dt><dt>1.2. <a href="faq.html#faq.why">
96 Why should I use libstdc++?
97 </a></dt><dt>1.3. <a href="faq.html#faq.who">
98 Who's in charge of it?
99 </a></dt><dt>1.4. <a href="faq.html#faq.when">
100 When is libstdc++ going to be finished?
101 </a></dt><dt>1.5. <a href="faq.html#faq.how">
102 How do I contribute to the effort?
103 </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old">
104 What happened to the older libg++? I need that!
105 </a></dt><dt>1.7. <a href="faq.html#faq.more_questions">
106 What if I have more questions?
107 </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><strong>1.1.</strong></p></td><td align="left" valign="top"><p>
109 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p>
110 The GNU Standard C++ Library v3 is an ongoing project to
111 implement the ISO 14882 Standard C++ library as described in
112 chapters 17 through 27 and annex D. For those who want to see
113 exactly how far the project has come, or just want the latest
114 bleeding-edge code, the up-to-date source is available over
115 anonymous SVN, and can even be browsed over
116 the <a class="link" href="http://gcc.gnu.org/svn.html" target="_top">web</a>.
117 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><strong>1.2.</strong></p></td><td align="left" valign="top"><p>
118 Why should I use libstdc++?
119 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p>
120 The completion of the ISO C++ standardization gave the C++
121 community a powerful set of reuseable tools in the form of the C++
122 Standard Library. However, all existing C++ implementations are
123 (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and
124 incorrekt</span>”</span>, and many suffer from limitations of the compilers
127 The GNU compiler collection
128 (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely
129 considered to be one of the leading compilers in the world. Its
130 development is overseen by the
131 <a class="link" href="http://gcc.gnu.org/" target="_top">GCC team</a>. All of
132 the rapid development and near-legendary
133 <a class="link" href="http://gcc.gnu.org/buildstat.html" target="_top">portability</a>
134 that are the hallmarks of an open-source project are being
135 applied to libstdc++.
137 That means that all of the Standard classes and functions will be
138 freely available and fully compliant. (Such as
139 <code class="classname">string</code>,
140 <code class="classname">vector<></code>, iostreams, and algorithms.)
141 Programmers will no longer need to <span class="quote">“<span class="quote">roll their own</span>”</span>
142 nor be worried about platform-specific incompatibilities.
143 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><strong>1.3.</strong></p></td><td align="left" valign="top"><p>
144 Who's in charge of it?
145 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p>
146 The libstdc++ project is contributed to by several developers
147 all over the world, in the same way as GCC or the Linux kernel.
148 Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
149 Loren James Rittle, and Paolo Carlini are the lead maintainers of
152 Development and discussion is held on the libstdc++ mailing
153 list. Subscribing to the list, or searching the list
154 archives, is open to everyone. You can read instructions for
155 doing so on the <a class="link" href="http://gcc.gnu.org/libstdc++/" target="_top">homepage</a>.
156 If you have questions, ideas, code, or are just curious, sign up!
157 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.when"></a><a id="q-when"></a><p><strong>1.4.</strong></p></td><td align="left" valign="top"><p>
158 When is libstdc++ going to be finished?
159 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p>
160 Nathan Myers gave the best of all possible answers, responding to
161 a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you
163 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><strong>1.5.</strong></p></td><td align="left" valign="top"><p>
164 How do I contribute to the effort?
165 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p>
166 Here is <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">a page devoted to
167 this topic</a>. Subscribing to the mailing list (see above, or
168 the homepage) is a very good idea if you have something to
169 contribute, or if you have spare time and want to
170 help. Contributions don't have to be in the form of source code;
171 anybody who is willing to help write documentation, for example,
172 or has found a bug in code that we all thought was working and is
173 willing to provide details, is more than welcome!
174 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.whereis_old"></a><a id="q-whereis_old"></a><p><strong>1.6.</strong></p></td><td align="left" valign="top"><p>
175 What happened to the older libg++? I need that!
176 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p>
177 The most recent libg++ README states that libg++ is no longer
178 being actively maintained. It should not be used for new
179 projects, and is only being kicked along to support older code.
181 More information in the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards compatibility documentation</a>
182 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.more_questions"></a><a id="q-more_questions"></a><p><strong>1.7.</strong></p></td><td align="left" valign="top"><p>
183 What if I have more questions?
184 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p>
185 If you have read the README file, and your question remains
186 unanswered, then just ask the mailing list. At present, you do not
187 need to be subscribed to the list to send a message to it. More
188 information is available on the homepage (including how to browse
189 the list archives); to send a message to the list,
190 use <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code>.
192 If you have a question that you think should be included
193 here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer
194 here, please send email to the libstdc++ mailing list, as above.
195 </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what">
196 What are the license terms for libstdc++?
197 </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program">
198 So any program which uses libstdc++ falls under the GPL?
199 </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl">
200 How is that different from the GNU {Lesser,Library} GPL?
201 </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions">
202 I see. So, what restrictions are there on programs that use the library?
203 </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><strong>2.1.</strong></p></td><td align="left" valign="top"><p>
204 What are the license terms for libstdc++?
205 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p>
206 See <a class="link" href="manual/license.html" title="License">our license description</a>
207 for these and related questions.
208 </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><strong>2.2.</strong></p></td><td align="left" valign="top"><p>
209 So any program which uses libstdc++ falls under the GPL?
210 </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>
211 No. The special exception permits use of the library in
212 proprietary applications.
213 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.lgpl"></a><a id="q-license.lgpl"></a><p><strong>2.3.</strong></p></td><td align="left" valign="top"><p>
214 How is that different from the GNU {Lesser,Library} GPL?
215 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p>
216 The LGPL requires that users be able to replace the LGPL code with a
217 modified version; this is trivial if the library in question is a C
218 shared library. But there's no way to make that work with C++, where
219 much of the library consists of inline functions and templates, which
220 are expanded inside the code that uses the library. So to allow people
221 to replace the library code, someone using the library would have to
222 distribute their own source, rendering the LGPL equivalent to the GPL.
223 </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><strong>2.4.</strong></p></td><td align="left" valign="top"><p>
224 I see. So, what restrictions are there on programs that use the library?
225 </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>
226 None. We encourage such programs to be released as open source,
227 but we won't punish you or sue you if you choose otherwise.
228 </p></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++?
229 </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources?
230 </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works?
231 </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?
232 </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx">
234 </a></dt><dt>3.6. <a href="faq.html#faq.size">
235 This library is HUGE!
236 </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><strong>3.1.</strong></p></td><td align="left" valign="top"><p>How do I install libstdc++?
237 </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>
238 Often libstdc++ comes pre-installed as an integral part of many
239 existing GNU/Linux and Unix systems, as well as many embedded
240 development tools. It may be necessary to install extra
241 development packages to get the headers, or the documentation, or
242 the source: please consult your vendor for details.
244 To build and install from the GNU GCC sources, please consult the
245 <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup
246 documentation</a> for detailed
247 instructions. You may wish to browse those files ahead
248 of time to get a feel for what's required.
249 </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><strong>3.2.</strong></p></td><td align="left" valign="top"><p>How does one get current libstdc++ sources?
250 </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>
251 Libstdc++ sources for all official releases can be obtained as
252 part of the GCC sources, available from various sites and
253 mirrors. A full <a class="link" href="http://gcc.gnu.org/mirrors.html" target="_top">list of
254 download sites</a> is provided on the main GCC site.
256 Current libstdc++ sources can always be checked out of the main
257 GCC source repository using the appropriate version control
258 tool. At this time, that tool
259 is <span class="application">Subversion</span>.
261 <span class="application">Subversion</span>, or <acronym class="acronym">SVN</acronym>, is
262 one of several revision control packages. It was selected for GNU
263 projects because it's free (speech), free (beer), and very high
264 quality. The <a class="link" href="http://subversion.tigris.org" target="_top"> Subversion
265 home page</a> has a better description.
267 The <span class="quote">“<span class="quote">anonymous client checkout</span>”</span> feature of SVN is
268 similar to anonymous FTP in that it allows anyone to retrieve
269 the latest libstdc++ sources.
272 see <a class="link" href="http://gcc.gnu.org/svn.html" target="_top"><acronym class="acronym">SVN</acronym>
274 </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><strong>3.3.</strong></p></td><td align="left" valign="top"><p>How do I know if it works?
275 </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>
276 Libstdc++ comes with its own validation testsuite, which includes
277 conformance testing, regression testing, ABI testing, and
278 performance testing. Please consult the
279 <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing
280 documentation</a> for more details.
282 If you find bugs in the testsuite programs themselves, or if you
283 think of a new test program that should be added to the suite,
284 <span class="emphasis"><em>please</em></span> write up your idea and send it to the list!
285 </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><strong>3.4.</strong></p></td><td align="left" valign="top"><p>How do I insure that the dynamically linked library will be found?
286 </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>
287 Depending on your platform and library version, the error message might
288 be similar to one of the following:
289 </p><pre class="screen">
290 ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
292 /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found
294 This doesn't mean that the shared library isn't installed, only
295 that the dynamic linker can't find it. When a dynamically-linked
296 executable is run the linker finds and loads the required shared
297 libraries by searching a pre-configured list of directories. If
298 the directory where you've installed libstdc++ is not in this list
299 then the libraries won't be found. The simplest way to fix this is
300 to use the <code class="literal">LD_LIBRARY_PATH</code> environment variable,
301 which is a colon-separated list of directories in which the linker
302 will search for shared libraries:
303 </p><pre class="screen">
304 LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
305 export LD_LIBRARY_PATH
307 The exact environment variable to use will depend on your
308 platform, e.g. DYLD_LIBRARY_PATH for Darwin,
309 LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit
310 and SHLIB_PATH for HP-UX.
312 See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span>
313 and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic
314 linker has different names on different platforms but the man page
315 is usually called something such as <code class="filename">ld.so/rtld/dld.so</code>.
317 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
318 Libraries</a> in the manual gives some alternatives.
319 </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><strong>3.5.</strong></p></td><td align="left" valign="top"><p>
321 </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>
322 If the only functions from <code class="filename">libstdc++.a</code>
323 which you need are language support functions (those listed in
324 <a class="link" href="manual/support.html" title="Chapter 4. Support">clause 18</a> of the
325 standard, e.g., <code class="function">new</code> and
326 <code class="function">delete</code>), then try linking against
327 <code class="filename">libsupc++.a</code>, which is a subset of
328 <code class="filename">libstdc++.a</code>. (Using <span class="command"><strong>gcc</strong></span>
329 instead of <span class="command"><strong>g++</strong></span> and explicitly linking in
330 <code class="filename">libsupc++.a</code> via <code class="literal">-lsupc++</code>
331 for the final link step will do it). This library contains only
332 those support routines, one per object file. But if you are
333 using anything from the rest of the library, such as IOStreams
334 or vectors, then you'll still need pieces from
335 <code class="filename">libstdc++.a</code>.
336 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size"></a><a id="q-size"></a><p><strong>3.6.</strong></p></td><td align="left" valign="top"><p>
337 This library is HUGE!
338 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p>
339 Usually the size of libraries on disk isn't noticeable. When a
340 link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a
341 static archive library, only the necessary object files are copied
342 into your executable, not the entire library. Unfortunately, even
343 if you only need a single function or variable from an object file,
344 the entire object file is extracted. (There's nothing unique to C++
345 or libstdc++ about this; it's just common behavior, given here
346 for background reasons.)
348 Some of the object files which make up libstdc++.a are rather large.
349 If you create a statically-linked executable with
350 <code class="literal">-static</code>, those large object files are suddenly part
351 of your executable. Historically the best way around this was to
352 only place a very few functions (often only a single one) in each
353 source/object file; then extracting a single function is the same
354 as extracting a single .o file. For libstdc++ this is only
355 possible to a certain extent; the object files in question contain
356 template classes and template functions, pre-instantiated, and
357 splitting those up causes severe maintenance headaches.
359 On supported platforms, libstdc++ takes advantage of garbage
360 collection in the GNU linker to get a result similar to separating
361 each symbol into a separate source and object files. On these platforms,
362 GNU ld can place each function and variable into its own
363 section in a .o file. The GNU linker can then perform garbage
364 collection on unused sections; this reduces the situation to only
365 copying needed functions into the executable, as before, but all
366 happens automatically.
367 </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers">
368 Can libstdc++ be used with non-GNU compilers?
369 </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long">
370 No 'long long' type on Solaris?
371 </a></dt><dt>4.3. <a href="faq.html#faq.predefined">
372 _XOPEN_SOURCE and _GNU_SOURCE are always defined?
373 </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype">
374 Mac OS X ctype.h is broken! How can I fix it?
375 </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386">
376 Threading is broken on i386?
377 </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips">
378 MIPS atomic operations
379 </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc">
380 Recent GNU/Linux glibc required?
381 </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar">
382 Can't use wchar_t/wstring on FreeBSD
383 </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><strong>4.1.</strong></p></td><td align="left" valign="top"><p>
384 Can libstdc++ be used with non-GNU compilers?
385 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p>
388 Since the goal of ISO Standardization is for all C++
389 implementations to be able to share code, libstdc++ should be
390 usable under any ISO-compliant compiler, at least in theory.
392 However, the reality is that libstdc++ is targeted and optimized
393 for GCC/g++. This means that often libstdc++ uses specific,
394 non-standard features of g++ that are not present in older
395 versions of proprietary compilers. It may take as much as a year or two
396 after an official release of GCC that contains these features for
397 proprietary tools to support these constructs.
399 In the near past, specific released versions of libstdc++ have
400 been known to work with versions of the EDG C++ compiler, and
401 vendor-specific proprietary C++ compilers such as the Intel ICC
403 </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><strong>4.2.</strong></p></td><td align="left" valign="top"><p>
404 No 'long long' type on Solaris?
405 </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>
406 By default we try to support the C99 <span class="type">long long</span> type.
407 This requires that certain functions from your C library be present.
409 Up through release 3.0.2 the platform-specific tests performed by
410 libstdc++ were too general, resulting in a conservative approach
411 to enabling the <span class="type">long long</span> code paths. The most
412 commonly reported platform affected was Solaris.
414 This has been fixed for libstdc++ releases greater than 3.0.3.
415 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><strong>4.3.</strong></p></td><td align="left" valign="top"><p>
416 <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
417 </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
418 macro <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
419 with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list;
420 other macros and other platforms are also affected.)
421 </p><p>These macros are typically used in C library headers, guarding new
422 versions of functions from their older versions. The C++ standard
423 library includes the C standard library, but it requires the C90
424 version, which for backwards-compatibility reasons is often not the
425 default for many vendors.
426 </p><p>More to the point, the C++ standard requires behavior which is only
427 available on certain platforms after certain symbols are defined.
428 Usually the issue involves I/O-related typedefs. In order to
429 ensure correctness, the compiler simply predefines those symbols.
430 </p><p>Note that it's not enough to #define them only when the library is
431 being built (during installation). Since we don't have an 'export'
432 keyword, much of the library exists as headers, which means that
433 the symbols must also be defined as your programs are parsed and
435 </p><p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
436 the gcc config headers for your target (and try changing them to
437 see what happens when building complicated code). You can also run
438 <span class="command"><strong>g++ -E -dM - < /dev/null"</strong></span> to display
439 a list of predefined macros for any particular installation.
440 </p><p>This has been discussed on the mailing lists
441 <a class="link" 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>.
442 </p><p>This method is something of a wart. We'd like to find a cleaner
443 solution, but nobody yet has contributed the time.
444 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.darwin_ctype"></a><a id="q-darwin_ctype"></a><p><strong>4.4.</strong></p></td><td align="left" valign="top"><p>
445 Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it?
446 </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,
447 the patch is quite simple, and well-known.
448 <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top"> Here's a
449 link to the solution</a>.
450 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.threads_i386"></a><a id="q-threads_i386"></a><p><strong>4.5.</strong></p></td><td align="left" valign="top"><p>
451 Threading is broken on i386?
452 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><p>
453 </p><p>Support for atomic integer operations is/was broken on i386
454 platforms. The assembly code accidentally used opcodes that are
455 only available on the i486 and later. So if you configured GCC
456 to target, for example, i386-linux, but actually used the programs
457 on an i686, then you would encounter no problems. Only when
458 actually running the code on a i386 will the problem appear.
459 </p><p>This is fixed in 3.2.2.
460 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.atomic_mips"></a><a id="q-atomic_mips"></a><p><strong>4.6.</strong></p></td><td align="left" valign="top"><p>
461 MIPS atomic operations
462 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><p>
463 The atomic locking routines for MIPS targets requires MIPS II
464 and later. A patch went in just after the 3.3 release to
465 make mips* use the generic implementation instead. You can also
466 configure for mipsel-elf as a workaround.
468 The mips*-*-linux* port continues to use the MIPS II routines, and more
469 work in this area is expected.
470 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.linux_glibc"></a><a id="q-linux_glibc"></a><p><strong>4.7.</strong></p></td><td align="left" valign="top"><p>
471 Recent GNU/Linux glibc required?
472 </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
473 5.0.1) and later uses localization and formatting code from the system
474 C library (glibc) version 2.2.5 which contains necessary bugfixes.
475 Most GNU/Linux distros make more recent versions available now.
476 libstdc++ 4.6.0 and later require glibc 2.3 or later for this
477 localization and formatting code.
478 </p><p>The guideline is simple: the more recent the C++ library, the
479 more recent the C library. (This is also documented in the main
480 GCC installation instructions.)
481 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.freebsd_wchar"></a><a id="q-freebsd_wchar"></a><p><strong>4.8.</strong></p></td><td align="left" valign="top"><p>
482 Can't use wchar_t/wstring on FreeBSD
483 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><p>
484 Older versions of FreeBSD's C library do not have sufficient
485 support for wide character functions, and as a result the
486 libstdc++ configury decides that wchar_t support should be
487 disabled. In addition, the libstdc++ platform checks that
488 enabled <span class="type">wchar_t</span> were quite strict, and not granular
489 enough to detect when the minimal support to
490 enable <span class="type">wchar_t</span> and C++ library structures
491 like <code class="classname">wstring</code> were present. This impacted Solaris,
492 Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0.
494 </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works">
496 </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs">
497 Bugs in the ISO C++ language or library specification
498 </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs">
499 Bugs in the compiler (gcc/g++) and not libstdc++
500 </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><strong>5.1.</strong></p></td><td align="left" valign="top"><p>
502 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p>
503 Short answer: Pretty much everything <span class="emphasis"><em>works</em></span>
504 except for some corner cases. Support for localization
505 in <code class="classname">locale</code> may be incomplete on non-GNU
506 platforms. Also dependent on the underlying platform is support
507 for <span class="type">wchar_t</span> and <span class="type">long
508 long</span> specializations, and details of thread support.
510 Long answer: See the implementation status pages for
511 <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>,
512 <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, and
513 <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>.
514 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><strong>5.2.</strong></p></td><td align="left" valign="top"><p>
515 Bugs in the ISO C++ language or library specification
516 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p>
517 Unfortunately, there are some.
519 For those people who are not part of the ISO Library Group
520 (i.e., nearly all of us needing to read this page in the first
521 place), a public list of the library defects is occasionally
522 published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21
524 Some of these issues have resulted in code changes in libstdc++.
526 If you think you've discovered a new bug that is not listed,
527 please post a message describing your problem to the author of
528 the library issues list or the Usenet group comp.lang.c++.moderated.
529 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.compiler_bugs"></a><a id="q-compiler_bugs"></a><p><strong>5.3.</strong></p></td><td align="left" valign="top"><p>
530 Bugs in the compiler (gcc/g++) and not libstdc++
531 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p>
532 On occasion, the compiler is wrong. Please be advised that this
533 happens much less often than one would think, and avoid jumping to
536 First, examine the ISO C++ standard. Second, try another compiler
537 or an older version of the GNU compilers. Third, you can find more
538 information on the libstdc++ and the GCC mailing lists: search
539 these lists with terms describing your issue.
541 Before reporting a bug, please examine the
542 <a class="link" href="http://gcc.gnu.org/bugs/" target="_top">bugs database</a> with the
543 category set to <span class="quote">“<span class="quote">g++</span>”</span>.
544 </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails">
545 Reopening a stream fails
546 </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose">
547 -Weffc++ complains too much
548 </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads">
549 Ambiguous overloads after including an old-style header
550 </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers">
551 The g++-3 headers are not ours
552 </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks">
553 Errors about *Concept and
554 constraints in the STL
555 </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash">
556 Program crashes when using library code in a
557 dynamically-loaded library
558 </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks">
559 “Memory leaks” in containers
560 </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on">
561 list::size() is O(n)!
562 </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix">
563 Aw, that's easy to fix!
564 </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><strong>6.1.</strong></p></td><td align="left" valign="top"><p>
565 Reopening a stream fails
566 </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>
567 One of the most-reported non-bug reports. Executing a sequence like:
568 </p><div class="literallayout"><p><br />
569 #include <fstream><br />
571 std::fstream fs(<span class="quote">“<span class="quote">a_file</span>”</span>);<br />
573 // . do things with fs...<br />
576 fs.open(<span class="quote">“<span class="quote">a_new_file</span>”</span>);<br />
578 All operations on the re-opened <code class="varname">fs</code> will fail, or at
579 least act very strangely. Yes, they often will, especially if
580 <code class="varname">fs</code> reached the EOF state on the previous file. The
581 reason is that the state flags are <span class="emphasis"><em>not</em></span> cleared
582 on a successful call to open(). The standard unfortunately did
583 not specify behavior in this case, and to everybody's great sorrow,
584 the <a class="link" href="manual/bugs.html" title="Bugs">proposed LWG resolution in
585 DR #22</a> is to leave the flags unchanged. You must insert a call
586 to <code class="function">fs.clear()</code> between the calls to close() and open(),
587 and then everything will work like we all expect it to work.
588 <span class="emphasis"><em>Update:</em></span> for GCC 4.0 we implemented the resolution
589 of <a class="link" href="manual/bugs.html" title="Bugs">DR #409</a> and open()
590 now calls <code class="function">clear()</code> on success!
591 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.wefcxx_verbose"></a><a id="q-wefcxx_verbose"></a><p><strong>6.2.</strong></p></td><td align="left" valign="top"><p>
592 -Weffc++ complains too much
593 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p>
594 Many warnings are emitted when <code class="literal">-Weffc++</code> is used. Making
595 libstdc++ <code class="literal">-Weffc++</code>-clean is not a goal of the project,
596 for a few reasons. Mainly, that option tries to enforce
597 object-oriented programming, while the Standard Library isn't
598 necessarily trying to be OO.
600 We do, however, try to have libstdc++ sources as clean as possible. If
601 you see some simple changes that pacify <code class="literal">-Weffc++</code>
602 without other drawbacks, send us a patch.
603 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.ambiguous_overloads"></a><a id="q-ambiguous_overloads"></a><p><strong>6.3.</strong></p></td><td align="left" valign="top"><p>
604 Ambiguous overloads after including an old-style header
605 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><p>
606 Another problem is the <code class="literal">rel_ops</code> namespace and the template
607 comparison operator functions contained therein. If they become
608 visible in the same namespace as other comparison functions
609 (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the <iterator> header),
610 then you will suddenly be faced with huge numbers of ambiguity
611 errors. This was discussed on the -v3 list; Nathan Myers
612 <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums
613 things up here</a>. The collisions with vector/string iterator
614 types have been fixed for 3.1.
615 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.v2_headers"></a><a id="q-v2_headers"></a><p><strong>6.4.</strong></p></td><td align="left" valign="top"><p>
616 The g++-3 headers are <span class="emphasis"><em>not ours</em></span>
617 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><p>
618 If you are using headers in
619 <code class="filename">${prefix}/include/g++-3</code>, or if the installed
620 library's name looks like <code class="filename">libstdc++-2.10.a</code> or
621 <code class="filename">libstdc++-libc6-2.10.so</code>, then you are using the
622 old libstdc++-v2 library, which is nonstandard and
623 unmaintained. Do not report problems with -v2 to the -v3
626 For GCC versions 3.0 and 3.1 the libstdc++ header files are
627 installed in <code class="filename">${prefix}/include/g++-v3</code> (see the
628 'v'?). Starting with version 3.2 the headers are installed in
629 <code class="filename">${prefix}/include/c++/${version}</code> as this prevents
630 headers from previous versions being found by mistake.
631 </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><strong>6.5.</strong></p></td><td align="left" valign="top"><p>
632 Errors about <span class="emphasis"><em>*Concept</em></span> and
633 <span class="emphasis"><em>constraints</em></span> in the STL
634 </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>
635 If you see compilation errors containing messages about
636 <span class="errortext">foo Concept </span>and something to do with a
637 <span class="errortext">constraints</span> member function, then most
638 likely you have violated one of the requirements for types used
639 during instantiation of template containers and functions. For
640 example, EqualityComparableConcept appears if your types must be
641 comparable with == and you have not provided this capability (a
642 typo, or wrong visibility, or you just plain forgot, etc).
644 More information, including how to optionally enable/disable the
645 checks, is available in the
646 <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>.
647 chapter of the manual.
648 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><strong>6.6.</strong></p></td><td align="left" valign="top"><p>
649 Program crashes when using library code in a
650 dynamically-loaded library
651 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p>
652 If you are using the C++ library across dynamically-loaded
653 objects, make certain that you are passing the correct options
654 when compiling and linking:
655 </p><div class="literallayout"><p><br />
656 // compile your library components<br />
657 g++ -fPIC -c a.cc<br />
658 g++ -fPIC -c b.cc<br />
660 g++ -fPIC -c z.cc<br />
662 // create your library<br />
663 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o<br />
665 // link the executable<br />
666 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl<br />
667 </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><strong>6.7.</strong></p></td><td align="left" valign="top"><p>
668 <span class="quote">“<span class="quote">Memory leaks</span>”</span> in containers
669 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p>
670 A few people have reported that the standard containers appear
671 to leak memory when tested with memory checkers such as
672 <a class="link" href="http://valgrind.org/" target="_top">valgrind</a>.
673 Under some configurations the library's allocators keep free memory in a
674 pool for later reuse, rather than returning it to the OS. Although
675 this memory is always reachable by the library and is never
676 lost, memory debugging tools can report it as a leak. If you
677 want to test the library for memory leaks please read
678 <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a>
680 </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><strong>6.8.</strong></p></td><td align="left" valign="top"><p>
681 list::size() is O(n)!
682 </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>
684 the <a class="link" href="manual/containers.html" title="Chapter 9. Containers">Containers</a>
686 </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><strong>6.9.</strong></p></td><td align="left" valign="top"><p>
687 Aw, that's easy to fix!
688 </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>
689 If you have found a bug in the library and you think you have
690 a working fix, then send it in! The main GCC site has a page
691 on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting
692 patches</a> that covers the procedure, but for libstdc++ you
693 should also send the patch to our mailing list in addition to
694 the GCC patches mailing list. The libstdc++
695 <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">contributors' page</a>
696 also talks about how to submit patches.
698 In addition to the description, the patch, and the ChangeLog
699 entry, it is a Good Thing if you can additionally create a small
700 test program to test for the presence of the bug that your patch
701 fixes. Bugs have a way of being reintroduced; if an old bug
702 creeps back in, it will be caught immediately by the testsuite -
703 but only if such a test exists.
704 </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod">
705 string::iterator is not char*; vector<T>::iterator is not T*
706 </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next">
707 What's next after libstdc++?
708 </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl">
709 What about the STL from SGI?
710 </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat">
711 Extensions and Backward Compatibility
712 </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support">
713 Does libstdc++ support TR1?
714 </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard?
715 </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi">
716 What's an ABI and why is it so messy?
717 </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity">
718 How do I make std::vector<T>::capacity() == std::vector<T>::size?
719 </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><strong>7.1.</strong></p></td><td align="left" valign="top"><p>
720 string::iterator is not char*; vector<T>::iterator is not T*
721 </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>
722 If you have code that depends on container<T> iterators
723 being implemented as pointer-to-T, your code is broken. It's
724 considered a feature, not a bug, that libstdc++ points this out.
726 While there are arguments for iterators to be implemented in
727 that manner, A) they aren't very good ones in the long term,
728 and B) they were never guaranteed by the Standard anyway. The
729 type-safety achieved by making iterators a real class rather
730 than a typedef for <span class="type">T*</span> outweighs nearly all opposing
733 Code which does assume that a vector iterator <code class="varname">i</code>
734 is a pointer can often be fixed by changing <code class="varname">i</code> in
735 certain expressions to <code class="varname">&*i</code>. Future revisions
736 of the Standard are expected to bless this usage for
737 vector<> (but not for basic_string<>).
738 </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><strong>7.2.</strong></p></td><td align="left" valign="top"><p>
739 What's next after libstdc++?
740 </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>
741 Hopefully, not much. The goal of libstdc++ is to produce a
742 fully-compliant, fully-portable Standard Library. After that,
743 we're mostly done: there won't <span class="emphasis"><em>be</em></span> any
744 more compliance work to do.
746 There is an effort underway to add significant extensions to
747 the standard library specification. The latest version of
748 this effort is described in
749 <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
750 The C++ Library Technical Report 1</a>.
751 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.sgi_stl"></a><a id="q-sgi_stl"></a><p><strong>7.3.</strong></p></td><td align="left" valign="top"><p>
752 What about the STL from SGI?
753 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p>
754 The <a class="link" href="http://www.sgi.com/tech/stl/" target="_top">STL from SGI</a>,
755 version 3.3, was the final merge of the STL codebase. The
756 code in libstdc++ contains many fixes and changes, and
757 the SGI code is no longer under active
758 development. We expect that no future merges will take place.
760 In particular, <code class="classname">string</code> is not from SGI and makes no
761 use of their "rope" class (which is included as an
762 optional extension), nor is <code class="classname">valarray</code> and some others.
763 Classes like <code class="classname">vector<></code> are, but have been
764 extensively modified.
766 More information on the evolution of libstdc++ can be found at the
767 <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API
769 and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards
770 compatibility</a> documentation.
772 The FAQ for SGI's STL (one jump off of their main page) is
773 still recommended reading.
774 </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><strong>7.4.</strong></p></td><td align="left" valign="top"><p>
775 Extensions and Backward Compatibility
776 </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>
777 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.
778 </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.tr1_support"></a><a id="q-tr1_support"></a><p><strong>7.5.</strong></p></td><td align="left" valign="top"><p>
779 Does libstdc++ support TR1?
780 </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p>
783 The C++ Standard Library Technical Report adds many new features to
784 the library. The latest version of this effort is described in
785 <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">
786 Technical Report 1</a>.
788 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
790 </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><strong>7.6.</strong></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard?
791 </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>
792 Copies of the full ISO 14882 standard are available on line via
793 the ISO mirror site for committee members. Non-members, or those
794 who have not paid for the privilege of sitting on the committee
795 and sustained their two-meeting commitment for voting rights, may
796 get a copy of the standard from their respective national
797 standards organization. In the USA, this national standards
798 organization is ANSI and their website is
799 right <a class="link" href="http://www.ansi.org" target="_top">here</a>. (And if
800 you've already registered with them, clicking this link will take
801 you to directly to the place where you can
802 <a class="link" href="http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+14882:2003" target="_top">buy the standard on-line</a>.
804 Who is your country's member body? Visit the
805 <a class="link" href="http://www.iso.ch/" target="_top">ISO homepage</a> and find out!
807 The 2003 version of the standard (the 1998 version plus TC1) is
808 available in print, ISBN 0-470-84674-7.
809 </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><strong>7.7.</strong></p></td><td align="left" valign="top"><p>
810 What's an ABI and why is it so messy?
811 </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>
812 <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary
813 Interface</span>”</span>. Conventionally, it refers to a great
814 mass of details about how arguments are arranged on the call
815 stack and/or in registers, and how various types are arranged
816 and padded in structs. A single CPU design may suffer
817 multiple ABIs designed by different development tool vendors
818 who made different choices, or even by the same vendor for
819 different target applications or compiler versions. In ideal
820 circumstances the CPU designer presents one ABI and all the
821 OSes and compilers use it. In practice every ABI omits
822 details that compiler implementers (consciously or
823 accidentally) must choose for themselves.
825 That ABI definition suffices for compilers to generate code so a
826 program can interact safely with an OS and its lowest-level libraries.
827 Users usually want an ABI to encompass more detail, allowing libraries
828 built with different compilers (or different releases of the same
829 compiler!) to be linked together. For C++, this includes many more
830 details than for C, and CPU designers (for good reasons elaborated
831 below) have not stepped up to publish C++ ABIs. The details include
832 virtual function implementation, struct inheritance layout, name
833 mangling, and exception handling. Such an ABI has been defined for
834 GNU C++, and is immediately useful for embedded work relying only on
835 a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that doesn't include (much
836 of) the standard library. It is a good basis for the work to come.
838 A useful C++ ABI must also incorporate many details of the standard
839 library implementation. For a C ABI, the layouts of a few structs
840 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
841 For C++, the details include the complete set of names of functions
842 and types used, the offsets of class members and virtual functions,
843 and the actual definitions of all inlines. C++ exposes many more
844 library details to the caller than C does. It makes defining
845 a complete ABI a much bigger undertaking, and requires not just
846 documenting library implementation details, but carefully designing
847 those details so that future bug fixes and optimizations don't
848 force breaking the ABI.
850 There are ways to help isolate library implementation details from the
851 ABI, but they trade off against speed. Library details used in
852 inner loops (e.g., getchar) must be exposed and frozen for all
853 time, but many others may reasonably be kept hidden from user code,
854 so they may later be changed. Deciding which, and implementing
855 the decisions, must happen before you can reasonably document a
856 candidate C++ ABI that encompasses the standard library.
857 </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><strong>7.8.</strong></p></td><td align="left" valign="top"><p>
858 How do I make std::vector<T>::capacity() == std::vector<T>::size?
859 </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>
860 The standard idiom for deallocating a <code class="classname">vector<T></code>'s
861 unused memory is to create a temporary copy of the vector and swap their
862 contents, e.g. for <code class="classname">vector<T> v</code>
863 </p><div class="literallayout"><p><br />
864 std::vector<T>(v).swap(v);<br />
866 The copy will take O(n) time and the swap is constant time.
868 See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit
869 strings</a> for a similar solution for strings.
870 </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="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html>