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11 <title>libstdc++-v3 FAQ</title>
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19 <h1 class="centered">libstdc++ Frequently Asked Questions</h1>
21 <p class="fineprint"><em>
22 The latest version of this document is always available at
23 <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/">
24 http://gcc.gnu.org/onlinedocs/libstdc++/faq/</a>. The main documentation
26 <a href="http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html">
27 http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html</a>.
31 To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
34 <!-- ####################################################### -->
38 <li><a href="#1_0">General Information</a>
39 <!-- I suspect these will mostly be links to/into existing documents. -->
41 <li><a href="#1_1">What is libstdc++-v3?</a> </li>
42 <li><a href="#1_2">Why should I use libstdc++?</a> </li>
43 <li><a href="#1_3">Who's in charge of it?</a> </li>
44 <li><a href="#1_4">How do I get libstdc++?</a> </li>
45 <li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
46 <li><a href="#1_6">How do I contribute to the effort?</a> </li>
47 <li><a href="#1_7">What happened to libg++? I need that!</a> </li>
48 <li><a href="#1_8">What if I have more questions?</a> </li>
49 <li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
53 <li><a href="#2_0">Installation</a>
55 <li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
56 <li><a href="#2_2">[removed]</a> </li>
57 <li><a href="#2_3">What is this CVS thing that you keep
59 <li><a href="#2_4">How do I know if it works?</a> </li>
60 <li><a href="#2_5">This library is HUGE! And what's libsupc++?</a> </li>
61 <li><a href="#2_6">Why do I get an error saying
62 <code>libstdc++.so.X</code> is missing when I
63 run my program?</a> </li>
67 <li><a href="#3_0">Platform-Specific Issues</a>
69 <li><a href="#3_1">Can libstdc++-v3 be used with <my
70 favorite compiler>?</a> </li>
71 <li><a href="#3_2">[removed]</a> </li>
72 <li><a href="#3_3">[removed]</a> </li>
73 <li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
74 <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
75 <code>_GNU_SOURCE</code> / etc is always defined</a>
77 <li><a href="#3_6">OS X ctype.h is broken! How can I hack it?</a></li>
78 <li><a href="#3_7">Threading is broken on i386</a></li>
79 <li><a href="#3_8">Recent GNU/Linux glibc required?</a></li>
80 <li><a href="#3_9">Can't use wchar_t/wstring on FreeBSD</a></li>
81 <li><a href="#3_10">MIPS atomic operations</a></li>
85 <li><a href="#4_0">Known Bugs and Non-Bugs</a>
87 <li><a href="#4_1">What works already?</a> </li>
88 <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
89 <li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
90 <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
91 <li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
92 <li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
93 <li><a href="#4_4_rel_ops">"ambiguous overloads"
94 after including an old-style header</a> </li>
95 <li><a href="#4_4_interface">The g++-3 headers are
96 <strong>not ours</strong></a> </li>
97 <li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
98 <li><a href="#4_4_checks">errors about <em>*Concept</em> and
99 <em>constraints</em> in the STL...</a> </li>
100 <li><a href="#4_4_dlsym">program crashes when using library code
101 in a dynamically-loaded library</a> </li>
102 <li><a href="#4_4_leak">"memory leaks" in containers</a> </li>
105 <li><a href="#4_5">Aw, that's easy to fix!</a> </li>
109 <li><a href="#5_0">Miscellaneous</a>
111 <li><a href="#5_1">string::iterator is not char*;
112 vector<T>::iterator is not T*</a> </li>
113 <li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
114 <li><a href="#5_3">What about the STL from SGI?</a> </li>
115 <li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
116 <li><a href="#5_5">Does libstdc++ support TR1?</a> </li>
117 <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
118 <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
119 <li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
120 <li><a href="#5_9">How do I make std::vector<T>::capacity()
121 == std::vector<T>::size?</a> </li>
129 <!-- ####################################################### -->
131 <h1><a name="1_0">1.0 General Information</a></h1>
132 <!-- I suspect these will mostly be links to/into existing documents. -->
133 <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
134 <p>The GNU Standard C++ Library v3 is an
135 ongoing project to implement the ISO 14882 Standard C++ library
136 as described in chapters 17 through 27 and annex D.
137 For those who want to see exactly how
138 far the project has come, or just want the latest
139 bleeding-edge code, the up-to-date source is available over
140 anonymous CVS, and can even be browsed over the Web (see
141 <a href="#1_4">1.4</a> below).
143 <p>The older libstdc++-v2 project is no longer maintained; the code
144 has been completely replaced and rewritten.
145 <a href="#4_4_interface">If you are using V2</a>, then you need to
146 report bugs to your system vendor, not to the V3 list.
148 <p>A more formal description of the V3 goals can be found in the
149 official <a href="../17_intro/DESIGN">design document</a>.
153 <h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
154 <p>The completion of the ISO C++ standardization gave the
155 C++ community a powerful set of reuseable tools in the form
156 of the C++ Standard Library. However, all existing C++
157 implementations are (as the Draft Standard used to say)
158 "incomplet and incorrekt," and many suffer from
159 limitations of the compilers that use them.
161 <p>The GNU C/C++/FORTRAN/<pick-a-language> compiler
162 (<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
163 one of the leading compilers in the world. Its development
165 <a href="http://gcc.gnu.org/">GCC team</a>. All of
166 the rapid development and near-legendary
167 <a href="http://gcc.gnu.org/gcc-3.3/buildstat.html">portability</a>
168 that are the hallmarks of an open-source project are being
169 applied to libstdc++.
171 <p>That means that all of the Standard classes and functions
172 (such as <code>string</code>, <code>vector<></code>, iostreams,
173 and algorithms) will be freely available and fully compliant.
174 Programmers will no longer need to "roll their own"
175 nor be worried about platform-specific incompatibilities.
179 <h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
180 <p>The libstdc++ project is contributed to by several developers
181 all over the world, in the same way as GCC or Linux.
182 Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
183 Loren James Rittle, and Paolo Carlini are the lead maintainers of
186 <p>Development and discussion is held on the libstdc++ mailing
187 list. Subscribing to the list, or searching the list
188 archives, is open to everyone. You can read instructions for
189 doing so on the <a href="http://gcc.gnu.org/libstdc++/">homepage</a>.
190 If you have questions, ideas, code, or are just curious, sign up!
194 <h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
195 <p>The <a href="http://gcc.gnu.org/libstdc++/">homepage</a>
196 has instructions for retrieving the latest CVS sources, and for
197 browsing the CVS sources over the web.
199 <p>Stable versions of libstdc++-v3 are included with releases of
200 <a href="http://gcc.gnu.org/releases.html">the GCC compilers</a>.
202 <p>The subset commonly known as the Standard Template Library
203 (chapters 23 through 25, mostly) is adapted from the final release
204 of the SGI STL, with extensive changes.
208 <h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
209 <!-- <p>Nathan Myers gave the best of all possible answers in <a
210 href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
211 Usenet article</a>.</p>
212 which is no longer available, thanks deja...-->
213 <p>Nathan Myers gave the best of all possible answers, responding to a
214 Usenet article asking this question: <em>Sooner, if you help.</em>
218 <h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
219 <p>Here is <a href="../17_intro/contribute.html">a
220 page devoted to this topic</a>. Subscribing to the mailing
221 list (see above, or the homepage) is a very good idea if you
222 have something to contribute, or if you have spare time and
223 want to help. Contributions don't have to be in the form of
224 source code; anybody who is willing to help write
225 documentation, for example, or has found a bug in code that
226 we all thought was working, is more than welcome!
230 <h2><a name="1_7">1.7 What happened to libg++? I need that!</a></h2>
231 <p>The most recent libg++ README states that libg++ is no longer
232 being actively maintained. It should not be used for new
233 projects, and is only being kicked along to support older code.
235 <p>The libg++ was designed and created when there was no Standard
236 to provide guidance. Classes like linked lists are now provided
237 for by <code>list<T></code> and do not need to be created by
238 <code>genclass</code>. (For that matter, templates exist now and
239 are well-supported, whereas genclass (mostly) predates them.)
241 <p>There are other classes in libg++ that are not specified in the
242 ISO Standard (e.g., statistical analysis). While there are a
243 lot of really useful things that are used by a lot of people
244 (e.g., statistics :-), the Standards Committee couldn't include
245 everything, and so a lot of those "obvious" classes
248 <p>Since libstdc++ is an implementation of the Standard Library, we
249 have no plans at this time to include non-Standard utilities
250 in the implementation, however handy they are. (The extensions
251 provided in the SGI STL aren't maintained by us and don't get
252 a lot of our attention, because they don't require a lot of our
253 time.) It is entirely plausable that the "useful stuff"
254 from libg++ might be extracted into an updated utilities library,
255 but nobody has started such a project yet.
257 <p>(The <a href="http://www.boost.org/">Boost</a> site houses free
258 C++ libraries that do varying things, and happened to be started
259 by members of the Standards Committee. Certain "useful
260 stuff" classes will probably migrate there.)
262 <p>For the bold and/or desperate, the
263 <a href="http://gcc.gnu.org/extensions.html">GCC extensions page</a>
264 describes where to find the last libg++ source.
268 <h2><a name="1_8">1.8 What if I have more questions?</a></h2>
269 <p>If you have read the README and RELEASE-NOTES files, and your
270 question remains unanswered, then just ask the mailing list.
271 At present, you do not need to be subscribed to the list to
272 send a message to it. More information is available on the
273 homepage (including how to browse the list archives); to send
274 to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
275 <code>libstdc++@gcc.gnu.org</code></a>.
277 <p>If you have a question that you think should be included here,
278 or if you have a question <em>about</em> a question/answer here,
279 contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
280 or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
284 <h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
285 <p>See <a href="../17_intro/license.html">our license description</a>
286 for these and related questions.
290 <h1><a name="2_0">2.0 Installation</a></h1>
291 <h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
292 <p>Complete instructions are not given here (this is a FAQ, not
293 an installation document), but the tools required are few:
296 <li> A 3.x release of GCC. Note that building GCC is much
297 easier and more automated than building the GCC 2.[78]
298 series was. If you are using GCC 2.95, you can still
299 build earlier snapshots of libstdc++.
301 <li> GNU Make is required for GCC 3.4 and later.
303 <li> The GNU Autotools are needed if you are messing with
304 the configury or makefiles.
307 <p>The file <a href="../documentation.html">documentation.html</a>
308 provides a good overview of the steps necessary to build, install,
309 and use the library. Instructions for configuring the library
310 with new flags such as --enable-threads are there also, as well as
311 patches and instructions for working with GCC 2.95.
313 <p>The top-level install.html and
314 <a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
315 the exact build and installation instructions. You may wish to
316 browse those files over CVSweb ahead of time to get a feel for
317 what's required. RELEASE-NOTES is located in the
318 ".../docs/17_intro/" directory of the distribution.
322 <h2><a name="2_2">2.2 [removed]</a></h2>
323 <p>This question has become moot and has been removed. The stub
324 is here to preserve numbering (and hence links/bookmarks).
328 <h2><a name="2_3">2.3 What is this CVS thing that you
329 keep mentioning?</a></h2>
330 <p>The <em>Concurrent Versions System</em> is one of several revision
331 control packages. It was selected for GNU projects because it's
332 free (speech), free (beer), and very high quality. The <a
333 href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
334 the GNU software catalogue</a> has a better description as
336 <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
338 <p>The "anonymous client checkout" feature of CVS is
339 similar to anonymous FTP in that it allows anyone to retrieve
340 the latest libstdc++ sources.
342 <p>After the first of April, American users will have a
343 "/pharmacy" command-line option...
344 <!-- wonder how long that'll live -->
348 <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
349 <p>libstdc++-v3 comes with its own testsuite. You do not need
350 to actually install the library ("<code>make
351 install</code>") to run the testsuite, but you do need
352 DejaGNU, as described
353 <a href="http://gcc.gnu.org/install/test.html">here</a>.
355 <p>To run the testsuite on the library after building it, use
356 "make check" while in your build directory. To run
357 the testsuite on the library after building and installing it,
358 use "make check-install" instead.
360 <p>If you find bugs in the testsuite programs themselves, or if you
361 think of a new test program that should be added to the suite,
362 <strong>please</strong> write up your idea and send it to the list!
366 <h2><a name="2_5">2.5 This library is HUGE! And what's libsupc++?</a></h2>
367 <p>Usually the size of libraries on disk isn't noticeable. When a
368 link editor (or simply "linker") pulls things from a
369 static archive library, only the necessary object files are copied
370 into your executable, not the entire library. Unfortunately, even
371 if you only need a single function or variable from an object file,
372 the entire object file is extracted. (There's nothing unique to C++
373 or libstdc++-v3 about this; it's just common behavior, given here
374 for background reasons.)
376 <p>Some of the object files which make up libstdc++.a are rather large.
377 If you create a statically-linked executable with
378 <code> -static</code>, those large object files are suddenly part
379 of your executable. Historically the best way around this was to
380 only place a very few functions (often only a single one) in each
381 source/object file; then extracting a single function is the same
382 as extracting a single .o file. For libstdc++-v3 this is only
383 possible to a certain extent; the object files in question contain
384 template classes and template functions, pre-instantiated, and
385 splitting those up causes severe maintenance headaches.
387 <p>It's not a bug, and it's not really a problem. Nevertheless, some
388 people don't like it, so here are two pseudo-solutions:
390 <p>If the only functions from libstdc++.a which you need are
391 language support functions (those listed in <a
392 href="../18_support/howto.html">clause 18</a> of the
393 standard, e.g., <code>new</code> and <code>delete</code>),
394 then try linking against <code>libsupc++.a</code> (Using
395 <code>gcc</code> instead of <code>g++</code> and explicitly
396 linking in <code>-lsupc++</code> for the final link step will
397 do it). This library contains only those support routines,
398 one per object file. But if you are using anything from the
399 rest of the library, such as IOStreams or vectors, then
400 you'll still need pieces from <code>libstdc++.a</code>.
402 <p>The second method is one we hope to incorporate into the library
403 build process. Some platforms can place each function and variable
404 into its own section in a .o file. The GNU linker can then perform
405 garbage collection on unused sections; this reduces the situation
406 to only copying needed functions into the executable, as before,
407 but all happens automatically.
409 <p>Unfortunately the garbage collection in GNU ld is buggy; sections
410 (corresponding to functions and variables) which <em>are</em> used
411 are mistakenly removed, leading to horrible crashes when your
412 executable starts up. For the time being, this feature is not used
413 when building the library.
417 <h2><a name="2_6">2.6 Why do I get an error saying
418 <code>libstdc++.so.X</code> is missing when I run
420 <p>Depending on your platform and library version, the message might
421 be similar to one of the following:
424 ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
426 /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found </pre>
428 <p>This doesn't mean that the shared library isn't installed, only
429 that the dynamic linker can't find it. When a dynamically-linked
430 executable is run the linker finds and loads the required shared
431 libraries by searching a pre-configured list of directories. If
432 the directory where you've installed libstdc++ is not in this
433 list then the libraries won't be found. The simplest way to fix
434 this is to use the <code>LD_LIBRARY_PATH</code> environment
435 variable, which is a colon-separated list of directories in which
436 the linker will search for shared libraries:
439 LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH
440 export LD_LIBRARY_PATH </pre>
441 <p>The exact environment variable to use will depend on your platform,
442 e.g. DYLD_LIBRARY_PATH for Darwin,
443 LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit,
444 LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs
445 and SHLIB_PATH for HP-UX.
447 <p>See the man pages for <code>ld(1)</code>, <code>ldd(1)</code> and
448 <code>ldconfig(8)</code> for more information. The dynamic linker
449 has different names on different platforms but the man page is
450 usually called something such as <code>ld.so / rtld / dld.so</code>.
454 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
455 <h2><a name="3_1">3.1 Can libstdc++-v3 be used with <my
456 favorite compiler>?</a></h2>
457 <p>Probably not. Yet.</p>
458 <p>Because GCC advances so rapidly, development and testing of
459 libstdc++ is being done almost entirely under that compiler.
460 If you are curious about whether other, lesser compilers
461 (*grin*) support libstdc++, you are more than welcome to try.
462 Configuring and building the library (see above) will still
463 require certain tools, however. Also keep in mind that
464 <em>building</em> libstdc++ does not imply that your compiler
465 will be able to <em>use</em> all of the features found in the
466 C++ Standard Library.
468 <p>Since the goal of ISO Standardization is for all C++
469 implementations to be able to share code, the final libstdc++
470 should, in theory, be usable under any ISO-compliant
471 compiler. It will still be targeted and optimized for
476 <h2><a name="3_2">3.2 [removed]</a></h2>
477 <p>This question has become moot and has been removed. The stub
478 is here to preserve numbering (and hence links/bookmarks).
482 <h2><a name="3_3">3.3 [removed]</a></h2>
483 <p>This question has become moot and has been removed. The stub
484 is here to preserve numbering (and hence links/bookmarks).
488 <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
489 <p>By default we try to support the C99 <code>long long</code> type.
490 This requires that certain functions from your C library be present.
492 <p>Up through release 3.0.2 the tests performed were too general, and
493 this feature was disabled when it did not need to be. The most
494 commonly reported platform affected was Solaris.
496 <p>This has been fixed for 3.0.3 and onwards.
500 <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
501 / etc is always defined</a></h2>
502 <p>On Solaris, g++ (but not gcc) always defines the preprocessor
503 macro <code>_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
504 with <code>_GNU_SOURCE</code>. (This is not an exhaustive list;
505 other macros and other platforms are also affected.)
507 <p>These macros are typically used in C library headers, guarding new
508 versions of functions from their older versions. The C++ standard
509 library includes the C standard library, but it requires the C90
510 version, which for backwards-compatability reasons is often not the
511 default for many vendors.
513 <p>More to the point, the C++ standard requires behavior which is only
514 available on certain platforms after certain symbols are defined.
515 Usually the issue involves I/O-related typedefs. In order to
516 ensure correctness, the compiler simply predefines those symbols.
518 <p>Note that it's not enough to #define them only when the library is
519 being built (during installation). Since we don't have an 'export'
520 keyword, much of the library exists as headers, which means that
521 the symbols must also be defined as your programs are parsed and
524 <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
525 the gcc config headers for your target (and try changing them to
526 see what happens when building complicated code). You can also run
527 <code>"g++ -E -dM - < /dev/null"</code> to display
528 a list of predefined macros for any particular installation.
530 <p>This has been discussed on the mailing lists
531 <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
533 <p>This method is something of a wart. We'd like to find a cleaner
534 solution, but nobody yet has contributed the time.
538 <h2><a name="3_6">3.6 OS X ctype.h is broken! How can I hack it?</a></h2>
539 <p>This is a long-standing bug in the OS X support. Fortunately,
540 the patch is quite simple, and well-known.
541 <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
542 link to the solution.</a>
546 <h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
547 <p>Support for atomic integer operations is/was broken on i386
548 platforms. The assembly code accidentally used opcodes that are
549 only available on the i486 and later. So if you configured GCC
550 to target, for example, i386-linux, but actually used the programs
551 on an i686, then you would encounter no problems. Only when
552 actually running the code on a i386 will the problem appear.
554 <p>This is fixed in 3.2.2.
558 <h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
559 <p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version
560 5.0.1) and later uses localization and formatting code from the system
561 C library (glibc) version 2.2.5. That version of glibc is over a
562 year old and contains necessary bugfixes. Many GNU/Linux distros make
563 glibc version 2.3.x available now.
565 <p>The guideline is simple: the more recent the C++ library, the
566 more recent the C library. (This is also documented in the main
567 GCC installation instructions.)
571 <h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
572 <p>At the moment there are a few problems in FreeBSD's support for
573 wide character functions, and as a result the libstdc++ configury
574 decides that wchar_t support should be disabled. Once the underlying
575 problems are fixed in FreeBSD (soon), the library support will
576 automatically enable itself.
578 <p>You can fix the problems yourself, and learn more about the situation,
580 <a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
581 this short thread</a> ("_GLIBCPP_USE_WCHAR_T undefined in
582 FreeBSD's c++config.h?").
586 <h2><a name="3_10">3.10 MIPS atomic operations</a></h2>
587 <p>The atomic locking routines for MIPS targets requires MIPS II
588 and later. A patch went in just after the 3.3 release to
589 make mips* use the generic implementation instead. You can also
590 configure for mipsel-elf as a workaround.
592 <p>mips*-*-linux* continues to use the MIPS II routines, and more
593 work in this area is expected.
597 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
598 <em>Note that this section can get rapdily outdated -- such is the
599 nature of an open-source project. For the latest information, join
600 the mailing list or look through recent archives. The RELEASE-
601 NOTES and BUGS files are generally kept up-to-date.</em>
603 <p>For 3.0.1, the most common "bug" is an apparently missing
604 "<code>../</code>" in include/Makefile, resulting in files
605 like gthr.h and gthr-single.h not being found. Please read
606 <a href="http://gcc.gnu.org/install/configure.html">the configuration
607 instructions for GCC</a>,
608 specifically the part about configuring in a separate build directory,
609 and how strongly recommended it is. Building in the source directory
610 is fragile, is rarely tested, and tends to break, as in this case.
611 This was fixed for 3.0.2.
614 <p>For 3.1, the most common "bug" is a parse error when using
615 <code><fstream></code>, ending with a message,
616 "<code>bits/basic_file.h:52: parse error before `{'
617 token</code>." Please read
618 <a href="http://gcc.gnu.org/install/">the installation instructions for
619 GCC</a>, specifically the part about not installing newer versions on
620 top of older versions. If you install 3.1 over a 3.0.x release, then
621 the wrong basic_file.h header will be found (its location changed
625 <p><strong>Please do not report these as bugs. We know about them.</strong>
626 Reporting this -- or any other problem that's already been fixed --
627 hinders the development of GCC, because we have to take time to
628 respond to your report. Thank you.
632 <h2><a name="4_1">4.1 What works already?</a></h2>
633 <p>Short answer: Pretty much everything <em>works</em> except for some
634 corner cases. Also, localization is incomplete. For whether it works
635 well, or as you expect it to work, see 5.2.
637 <p>Long answer: See the docs/html/17_intro/CHECKLIST file, which is
638 badly outdated... Also see the RELEASE-NOTES file, which is kept
643 <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
644 <p>This is by no means meant to be complete nor exhaustive, but
645 mentions some problems that users may encounter when building
646 or using libstdc++. If you are experiencing one of these
647 problems, you can find more information on the libstdc++ and
648 the GCC mailing lists.
650 <p>Before reporting a bug, examine the
651 <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
652 category set to "libstdc++". The BUGS file in the source
653 tree also tracks known serious problems.
656 <li>Debugging is problematic, due to bugs in line-number generation
657 (mostly fixed in the compiler) and gdb lagging behind the
658 compiler (lack of personnel). We recommend configuring the
659 compiler using <code>--with-dwarf2</code> if the DWARF2
660 debugging format is not already the default on your platform.
662 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
663 GDB settings</a> can have a profound effect on your C++ debugging
664 experiences. :-)</li>
668 <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
669 <p>Yes, unfortunately, there are some. In a
670 <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
671 to the list</a>, Nathan Myers announced that he has started a list of
672 problems in the ISO C++ Standard itself, especially with
673 regard to the chapters that concern the library. The list
675 <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
676 website</a>. Developers who are having problems interpreting
677 the Standard may wish to consult his notes.
679 <p>For those people who are not part of the ISO Library Group
680 (i.e., nearly all of us needing to read this page in the first
681 place :-), a public list of the library defects is occasionally
682 published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
683 Some of these have resulted in <a href="#5_2">code changes</a>.
687 <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
688 <p>There are things which are not bugs in the compiler (4.2) nor
689 the language specification (4.3), but aren't really bugs in
690 libstdc++, either. Really! Please do not report these as bugs.
692 <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
693 The biggest of these is the quadzillions of warnings about the
694 library headers emitted when <code>-Weffc++</code> is used. Making
695 libstdc++ "-Weffc++-clean" is not a goal of the project,
696 for a few reasons. Mainly, that option tries to enforce
697 object-oriented programming, while the Standard Library isn't
698 necessarily trying to be OO.
700 <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
701 </a> Did I just say that -Weffc++ was our biggest false-bug report?
702 I lied. (It used to be.) Today it seems to be reports that after
703 executing a sequence like
706 #include <fstream>
708 std::fstream fs("a_file");
710 // . do things with fs...
713 fs.open("a_new_file");</pre>
714 <p>all operations on the re-opened <code>fs</code> will fail, or at
715 least act very strangely. Yes, they often will, especially if
716 <code>fs</code> reached the EOF state on the previous file. The
717 reason is that the state flags are <strong>not</strong> cleared
718 on a successful call to open(). The standard unfortunately did
719 not specify behavior in this case, and to everybody's great sorrow,
720 the <a href="../ext/howto.html#5">proposed LWG resolution in
721 DR #22</a> is to leave the flags unchanged. You must insert a call
722 to <code>fs.clear()</code> between the calls to close() and open(),
723 and then everything will work like we all expect it to work.
724 <strong>Update:</strong> for GCC 4.0 we implemented the resolution
725 of <a href="../ext/howto.html#5">DR #409</a> and open() now calls
726 <code>clear()</code> on success!
728 <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
729 Another is the <code>rel_ops</code> namespace and the template
730 comparison operator functions contained therein. If they become
731 visible in the same namespace as other comparison functions
732 (e.g., '<code>using</code>' them and the <iterator> header),
733 then you will suddenly be faced with huge numbers of ambiguity
734 errors. This was discussed on the -v3 list; Nathan Myers
735 <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
736 things up here</a>. The collisions with vector/string iterator
737 types have been fixed for 3.1. <!-- more links to email here -->
739 <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
740 <p>If you have found an extremely broken header file which is
741 causing problems for you, look carefully before submitting a
742 "high" priority bug report (which you probably shouldn't
743 do anyhow; see the last paragraph of the page describing
744 <a href="http://gcc.gnu.org/bugs.html">the GCC bug database</a>).
746 <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
747 the installed library's name looks like <code>libstdc++-2.10.a</code>
748 or <code>libstdc++-libc6-2.10.so</code>, then you are using the old
749 libstdc++-v2 library, which is nonstandard and unmaintained. Do not
750 report problems with -v2 to the -v3 mailing list.
752 <p>For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are
753 installed in <code>${prefix}/include/g++-v3</code> (see the 'v'?).
754 Starting with version 3.2 the headers are installed in
755 <code>${prefix}/include/c++/${version}</code> as this prevents
756 headers from previous versions being found by mistake.
758 <p><a name="4_4_glibc"><strong>glibc</strong></a>
759 If you're on a GNU/Linux system and have just upgraded to
760 glibc 2.2, but are still using gcc 2.95.2, then you should have
761 read the glibc FAQ, specifically 2.34:
764 2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
766 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
767 apply a patch to the include files in /usr/include/g++, because the fpos_t
768 type has changed in glibc 2.2. The patch is at
769 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
771 <p>Note that 2.95.x shipped with the
772 <a href="#4_4_interface">old v2 library</a> which is no longer
773 maintained. Also note that gcc 2.95.3 fixes this problem, but
774 requires a separate patch for libstdc++-v3.
776 <p><a name="4_4_checks"><strong>concept checks</strong></a>
777 If you see compilation errors containing messages about
778 <code> <em>foo</em>Concept </code>and a<code> constraints </code>
779 member function, then most likely you have violated one of the
780 requirements for types used during instantiation of template
781 containers and functions. For example, EqualityComparableConcept
782 appears if your types must be comparable with == and you have not
783 provided this capability (a typo, or wrong visibility, or you
784 just plain forgot, etc).
786 <p>More information, including how to optionally enable/disable the
788 <a href="../19_diagnostics/howto.html#3">here</a>.
790 <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
791 If you are using the C++ library across dynamically-loaded
792 objects, make certain that you are passing the correct options
793 when compiling and linking:
796 // compile your library components
802 // create your library
803 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
805 // link the executable
806 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
807 <p><a name="4_4_leak"><strong>"memory leaks" in containers</strong></a>
808 A few people have reported that the standard containers appear
809 to leak memory when tested with memory checkers such as
810 <a href="http://developer.kde.org/~sewardj/">valgrind</a>.
811 The library's default allocators keep free memory in a pool
812 for later reuse, rather than returning it to the OS. Although
813 this memory is always reachable by the library and is never
814 lost, memory debugging tools can report it as a leak. If you
815 want to test the library for memory leaks please read
816 <a href="../debug.html#mem">Tips for memory leak hunting</a>
821 <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
822 <p>If you have found a bug in the library and you think you have
823 a working fix, then send it in! The main GCC site has a page
824 on <a href="http://gcc.gnu.org/contribute.html">submitting
825 patches</a> that covers the procedure, but for libstdc++ you
826 should also send the patch to our mailing list in addition to
827 the GCC patches mailing list. The libstdc++
828 <a href="../17_intro/contribute.html">contributors' page</a>
829 also talks about how to submit patches.
831 <p>In addition to the description, the patch, and the ChangeLog
832 entry, it is a Good Thing if you can additionally create a small
833 test program to test for the presence of the bug that your
834 patch fixes. Bugs have a way of being reintroduced; if an old
835 bug creeps back in, it will be caught immediately by the
836 <a href="#2_4">testsuite</a> -- but only if such a test exists.
840 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
841 <h2><a name="5_1">5.1 string::iterator is not char*;
842 vector<T>::iterator is not T*</a></h2>
843 <p>If you have code that depends on container<T> iterators
844 being implemented as pointer-to-T, your code is broken.
846 <p>While there are arguments for iterators to be implemented in
847 that manner, A) they aren't very good ones in the long term,
848 and B) they were never guaranteed by the Standard anyway. The
849 type-safety achieved by making iterators a real class rather
850 than a typedef for <code>T*</code> outweighs nearly all opposing
853 <p>Code which does assume that a vector iterator <code> i </code>
854 is a pointer can often be fixed by changing <code> i </code> in
855 certain expressions to <code> &*i </code>. Future revisions
856 of the Standard are expected to bless this usage for
857 vector<> (but not for basic_string<>).
861 <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
862 <p>Hopefully, not much. The goal of libstdc++-v3 is to produce
863 a fully-compliant, fully-portable Standard Library. After that,
864 we're mostly done: there won't <em>be</em> any more compliance
868 <li><p>The ISO Committee will meet periodically to review Defect Reports
869 in the C++ Standard. Undoubtedly some of these will result in
870 changes to the Standard, which will be reflected in patches to
871 libstdc++. Some of that is already happening, see <a href="#4_3">4.3</a>. Some of
872 those changes are being predicted by the library maintainers, and
873 we add code to the library based on what the current proposed
874 resolution specifies. Those additions are listed in
875 <a href="../ext/howto.html#5">the extensions page</a>.
877 <li><p>Performance tuning. Lots of performance tuning. This too is
878 already underway for post-3.0 releases, starting with memory
879 expansion in container classes and buffer usage in synchronized
882 <li><p>An ABI for libstdc++ is being developed, so that
883 multiple binary-incompatible copies of the library can be replaced
884 with a single backwards-compatible library, like libgcc_s.so is.
886 <li><p>The current libstdc++ contains extensions to the Library which
887 must be explicitly requested by client code (for example, the
888 hash tables from SGI). Other extensions may be added to
889 libstdc++-v3 if they seem to be "standard" enough.
890 (For example, the "long long" type from C99.)
891 Bugfixes and rewrites (to improve or fix thread safety, for
892 instance) will of course be a continuing task.
894 <li><p>There is an effort underway to add significant extensions to
895 the standard library specification. The latest version of this effort is
897 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
898 The C++ Library Technical Report 1</a>.
899 See <a href="#5_5">5.5</a>.
902 <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
903 question</a> about the next libstdc++ prompted some brief but
905 <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
909 <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
910 <p>The <a href="http://www.sgi.com/tech/stl/">STL from SGI</a>,
911 version 3.3, was the final merge of the STL codebase. The
912 code in libstdc++ contains many fixes and changes, and
913 the SGI code is no longer under active
914 development. We expect that no future merges will take place.
916 <p>In particular, <code>string</code> is not from SGI and makes no
917 use of their "rope" class (which is included as an
918 optional extension), nor is <code>valarray</code> and some others.
919 Classes like <code>vector<></code> are, however we have
920 made significant changes to them since then.
922 <p>The FAQ for SGI's STL (one jump off of their main page) is
927 <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
928 <p>Headers in the <code>ext</code> and <code>backward</code>
929 subdirectories should be referred to by their relative paths:
930 <!-- Careful, the leading spaces in PRE show up directly. -->
933 #include <ext/hash_map> </pre>
934 <p>rather than using <code>-I</code> or other options. This is more
935 portable and forward-compatible. (The situation is the same as
936 that of other headers whose directories are not searched directly,
937 e.g., <code><sys/stat.h></code>, <code><X11/Xlib.h></code>.
940 <p>At this time most of the features of the SGI STL extension have been
941 replaced by standardized libraries.
942 In particular, the unordered_map and unordered_set containers of TR1
943 are suitable replacement for the non-standard hash_map and hash_set
944 containers in the SGI STL. See <a href="#5_5">5.5</a> for more details.
947 <p>The extensions are no longer in the global or <code>std</code>
948 namespaces, instead they are declared in the <code>__gnu_cxx</code>
949 namespace. For maximum portability, consider defining a namespace
950 alias to use to talk about extensions, e.g.:
955 #include <hash_map.h>
956 namespace Sgi { using ::hash_map; }; // inherit globals
958 #include <ext/hash_map>
959 #if __GNUC_MINOR__ == 0
960 namespace Sgi = std; // GCC 3.0
962 namespace Sgi = ::__gnu_cxx; // GCC 3.1 and later
965 #else // ... there are other compilers, right?
969 Sgi::hash_map<int,int> my_map; </pre>
970 <p>This is a bit cleaner than defining typedefs for all the
971 instantiations you might need.
973 <p><strong>Note:</strong> explicit template specializations must
974 be declared in the same namespace as the original template.
975 This means you cannot use a namespace alias when declaring
976 an explicit specialization.
978 <p>Extensions to the library have
979 <a href="../ext/howto.html">their own page</a>.
983 <h2><a name="5_5">5.5 Does libstdc++ support TR1?</a></h2>
985 <p>The C++ Standard Library Technical Report adds many new features to
986 the library. The latest version of this effort is described in
988 "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
989 Technical Report 1</a>.
992 <p>libstdc++ strives to implement all of TR1.
993 An <a href="../ext/tr1.html">overview</a> of the implementation status
997 <p>Briefly, the features of TR1 and the current status are:
1000 <p><strong>Unordered containers - Complete -</strong>
1001 The unordered_set, unordered_map, unordered_multiset, and
1002 unordered_multimap containers are hashed versions of the map, set,
1003 multimap, and multiset containers respectively. These classes are
1004 suitable replacements for the SGI STL hash_map and hash_set
1008 <p><strong>Reference-counted smart pointers - Complete -</strong>
1009 The shared_ptr and weak_ptr allow several object to know about a
1010 pointer and whether it is valid. When the last reference to the
1011 pointer is destroyed the pointer is freed.
1014 <p><strong>Type traits - Complete -</strong>
1015 The type_traits class gives templates the ability to probe
1016 information about the input type and enable type-dependent logic
1017 to be performed without the need of template specializations.
1020 <p><strong>Fixed-size arrays - Complete -</strong>
1021 The array class implements small fixed-sized arrays with container
1025 <p><strong>Tuples - Complete -</strong>
1026 The tuple class implements small heterogeneous arrays. This is an
1027 enhanced pair. In fact, the standard pair is enhanced with a tuple
1031 <p><strong>A regular expression engine</strong>
1032 This library provides for regular expression objects with traversal
1033 of text with return of subexpressions.
1036 <p><strong>A random number engine</strong>
1037 This library contains randow number generators with several different
1038 choices of distribution.
1041 <p><strong>Special functions - Under construction - </strong>
1042 Twenty-three mathematical functions familiar to physicists and
1043 engineers are included: cylindrical and spherical Bessel and Neumann
1044 functions, hypergeometric functions, Laguerre polynomials, Legendre
1045 functions, elliptic integrals, exponential integrals and the Riemann
1046 zeta function all for your computing pleasure.
1049 <p><strong>C99 compatibility - Under construction - </strong>
1050 There are many features designed to minimize the divergence of the C
1051 and the C++ languages.
1055 <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
1056 <p>libstdc++-v3 strives to be thread-safe when all of the following
1060 <li>The system's libc is itself thread-safe,</li>
1061 <li><code>gcc -v</code> reports a thread model other than 'single',</li>
1062 <li>[pre-3.3 only] a non-generic implementation of atomicity.h
1063 exists for the architecture in question.</li>
1065 <p>The user-code must guard against concurrent method calls which may
1066 access any particular library object's state. Typically, the
1067 application programmer may infer what object locks must be held
1068 based on the objects referenced in a method call. Without getting
1069 into great detail, here is an example which requires user-level
1073 library_class_a shared_object_a;
1076 library_class_b *object_b = new library_class_b;
1077 shared_object_a.add_b (object_b); // must hold lock for shared_object_a
1078 shared_object_a.mutate (); // must hold lock for shared_object_a
1081 // Multiple copies of thread_main() are started in independent threads.</pre>
1082 <p>Under the assumption that object_a and object_b are never exposed to
1083 another thread, here is an example that should not require any
1088 library_class_a object_a;
1089 library_class_b *object_b = new library_class_b;
1090 object_a.add_b (object_b);
1093 <p>All library objects are safe to use in a multithreaded program as
1094 long as each thread carefully locks out access by any other
1095 thread while it uses any object visible to another thread, i.e.,
1096 treat library objects like any other shared resource. In general,
1097 this requirement includes both read and write access to objects;
1098 unless otherwise documented as safe, do not assume that two threads
1099 may access a shared standard library object at the same time.
1101 <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
1102 introduction), <a href="../23_containers/howto.html#3">23</a>
1103 (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
1108 <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
1109 <p>Copies of the full ISO 14882 standard are available on line via the
1110 ISO mirror site for committee members. Non-members, or those who
1111 have not paid for the privilege of sitting on the committee and
1112 sustained their two-meeting commitment for voting rights, may get a
1113 copy of the standard from their respective national standards
1114 organization. In the USA, this national standards organization is
1115 ANSI and their website is right <a href="http://www.ansi.org">here</a>.
1116 (And if you've already registered with them, clicking this link will
1117 take you to directly to the place where you can
1118 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003">buy
1119 the standard on-line</a>.
1121 <p>Who is your country's member body? Visit the
1122 <a href="http://www.iso.ch/">ISO homepage</a> and find out!
1126 <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
1127 <p>"ABI" stands for "Application Binary Interface."
1128 Conventionally, it refers to a great mass of details about how
1129 arguments are arranged on the call stack and/or in registers, and
1130 how various types are arranged and padded in structs. A single CPU
1131 design may suffer multiple ABIs designed by different development
1132 tool vendors who made different choices, or even by the same vendor
1133 for different target applications or compiler versions. In ideal
1134 circumstances the CPU designer presents one ABI and all the OSes and
1135 compilers use it. In practice every ABI omits details that compiler
1136 implementers (consciously or accidentally) must choose for themselves.
1138 <p>That ABI definition suffices for compilers to generate code so a
1139 program can interact safely with an OS and its lowest-level libraries.
1140 Users usually want an ABI to encompass more detail, allowing libraries
1141 built with different compilers (or different releases of the same
1142 compiler!) to be linked together. For C++, this includes many more
1143 details than for C, and CPU designers (for good reasons elaborated
1144 below) have not stepped up to publish C++ ABIs. The details include
1145 virtual function implementation, struct inheritance layout, name
1146 mangling, and exception handling. Such an ABI has been defined for
1147 GNU C++, and is immediately useful for embedded work relying only on
1148 a "free-standing implementation" that doesn't include (much
1149 of) the standard library. It is a good basis for the work to come.
1151 <p>A useful C++ ABI must also incorporate many details of the standard
1152 library implementation. For a C ABI, the layouts of a few structs
1153 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
1154 For C++, the details include the complete set of names of functions
1155 and types used, the offsets of class members and virtual functions,
1156 and the actual definitions of all inlines. C++ exposes many more
1157 library details to the caller than C does. It makes defining
1158 a complete ABI a much bigger undertaking, and requires not just
1159 documenting library implementation details, but carefully designing
1160 those details so that future bug fixes and optimizations don't
1161 force breaking the ABI.
1163 <p>There are ways to help isolate library implementation details from the
1164 ABI, but they trade off against speed. Library details used in
1165 inner loops (e.g., getchar) must be exposed and frozen for all
1166 time, but many others may reasonably be kept hidden from user code,
1167 so they may later be changed. Deciding which, and implementing
1168 the decisions, must happen before you can reasonably document a
1169 candidate C++ ABI that encompasses the standard library.
1173 <h2><a name="5_9">5.9 How do I make std::vector<T>::capacity()
1174 == std::vector<T>::size()?</a> </h2>
1175 <!-- referenced by 21_strings/howto.html#6 -->
1176 <p>The standard idiom for deallocating a <code>std::vector<T></code>'s
1177 unused memory is to create a temporary copy of the vector and swap their
1178 contents, e.g. for <code>std::vector<T> v</code>
1181 std::vector<T>(v).swap(v);
1183 <p>The copy will take O(n) time and the swap is constant time.
1185 <p>See <a href='../21_strings/howto.html#6'>Shrink-to-fit strings</a> for
1186 a similar solution for strings.
1189 <!-- ####################################################### -->
1192 <p class="fineprint"><em>
1193 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
1194 Comments and suggestions are welcome, and may be sent to
1195 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
projects / l4.git / blob