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11 <title>libstdc++-v3 FAQ</title>
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14 ** Locations of "the most recent snapshot is the Nth" text are
15 ** answers 1_1, 1_4, 4_1.
20 <h1 class="centered">libstdc++ Frequently Asked Questions</h1>
22 <p>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>.
30 <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
33 <!-- ####################################################### -->
37 <li><a href="#1_0">General Information</a>
38 <!-- I suspect these will mostly be links to/into existing documents. -->
40 <li><a href="#1_1">What is libstdc++-v3?</a> </li>
41 <li><a href="#1_2">Why should I use libstdc++?</a> </li>
42 <li><a href="#1_3">Who's in charge of it?</a> </li>
43 <li><a href="#1_4">How do I get libstdc++?</a> </li>
44 <li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
45 <li><a href="#1_6">How do I contribute to the effort?</a> </li>
46 <li><a href="#1_7">What happened to libg++? I need that!</a> </li>
47 <li><a href="#1_8">What if I have more questions?</a> </li>
48 <li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
52 <li><a href="#2_0">Installation</a>
54 <li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
55 <li><a href="#2_2">[removed]</a> </li>
56 <li><a href="#2_3">What is this CVS thing that you keep
58 <li><a href="#2_4">How do I know if it works?</a> </li>
59 <li><a href="#2_5">This library is HUGE! And what's libsupc++?</a> </li>
63 <li><a href="#3_0">Platform-Specific Issues</a>
65 <li><a href="#3_1">Can libstdc++-v3 be used with <my
66 favorite compiler>?</a> </li>
67 <li><a href="#3_2">[removed]</a> </li>
68 <li><a href="#3_3">[removed]</a> </li>
69 <li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
70 <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
71 <code>_GNU_SOURCE</code> / etc is always defined</a>
73 <li><a href="#3_6">OS X ctype.h is broken! How can I hack it?</a></li>
74 <li><a href="#3_7">Threading is broken on i386</a></li>
75 <li><a href="#3_8">Recent GNU/Linux glibc required?</a></li>
76 <li><a href="#3_9">Can't use wchar_t/wstring on FreeBSD</a></li>
80 <li><a href="#4_0">Known Bugs and Non-Bugs</a>
82 <li><a href="#4_1">What works already?</a> </li>
83 <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
84 <li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
85 <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
86 <li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
87 <li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
88 <li><a href="#4_4_rel_ops">"ambiguous overloads"
89 after including an old-style header</a> </li>
90 <li><a href="#4_4_interface">The g++-3 headers are
91 <strong>not ours</strong></a> </li>
92 <li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
93 <li><a href="#4_4_checks">errors about <em>*Concept</em> and
94 <em>constraints</em> in the STL...</a> </li>
95 <li><a href="#4_4_dlsym">program crashes when using library code
96 in a dynamically-loaded library</a> </li>
99 <li><a href="#4_5">Aw, that's easy to fix!</a> </li>
103 <li><a href="#5_0">Miscellaneous</a>
105 <li><a href="#5_1">string::iterator is not char*;
106 vector<T>::iterator is not T*</a> </li>
107 <li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
108 <li><a href="#5_3">What about the STL from SGI?</a> </li>
109 <li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
110 <li><a href="#5_5">[removed]</a> </li>
111 <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
112 <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
113 <li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
121 <!-- ####################################################### -->
123 <h1><a name="1_0">1.0 General Information</a></h1>
124 <!-- I suspect these will mostly be links to/into existing documents. -->
125 <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
126 <p>The GNU Standard C++ Library v3 is an
127 ongoing project to implement the ISO 14882 Standard C++ library
128 as described in chapters 17 through 27 and annex D. As the
129 library reaches stable plateaus, it is captured in a snapshot
130 and released. The latest release is
131 <a href="http://gcc.gnu.org/libstdc++/index.html#download">the
132 fourteenth snapshot</a> but newer versions have been included
133 in recent GCC releases. For those who want to see exactly how
134 far the project has come, or just want the latest
135 bleeding-edge code, the up-to-date source is available over
136 anonymous CVS, and can even be browsed over the Web (see
137 <a href="#1_4">1.4</a> below).
139 <p>The older libstdc++-v2 project is no longer maintained; the code
140 has been completely replaced and rewritten.
141 <a href="#4_4_interface">If you are using V2</a>, then you need to
142 report bugs to your system vendor, not to the V3 list.
144 <p>A more formal description of the V3 goals can be found in the
145 official <a href="../17_intro/DESIGN">design document</a>.
149 <h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
150 <p>The completion of the ISO C++ standardization gave the
151 C++ community a powerful set of reuseable tools in the form
152 of the C++ Standard Library. However, all existing C++
153 implementations are (as the Draft Standard used to say)
154 "incomplet and incorrekt," and many suffer from
155 limitations of the compilers that use them.
157 <p>The GNU C/C++/FORTRAN/<pick-a-language> compiler
158 (<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
159 one of the leading compilers in the world. Its development
160 has recently been taken over by the
161 <a href="http://gcc.gnu.org/">GCC team</a>. All of
162 the rapid development and near-legendary
163 <a href="http://gcc.gnu.org/gcc-3.0/buildstat.html">portability</a>
164 that are the hallmarks of an open-source project are being
165 applied to libstdc++.
167 <p>That means that all of the Standard classes and functions
168 (such as <code>string</code>, <code>vector<></code>, iostreams,
169 and algorithms) will be freely available and fully compliant.
170 Programmers will no longer need to "roll their own"
171 nor be worried about platform-specific incompatibilities.
175 <h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
176 <p>The libstdc++ project is contributed to by several developers
177 all over the world, in the same way as GCC or Linux.
178 Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
179 Loren James Rittle, and Paolo Carlini are the lead maintainers of
182 <p>Development and discussion is held on the libstdc++ mailing
183 list. Subscribing to the list, or searching the list
184 archives, is open to everyone. You can read instructions for
185 doing so on the <a href="http://gcc.gnu.org/libstdc++/">homepage</a>.
186 If you have questions, ideas, code, or are just curious, sign up!
190 <h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
191 <p>The fourteenth (and latest) snapshot of libstdc++-v3 is
192 <a href="http://gcc.gnu.org/libstdc++/index.html#download">available
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>The subset commonly known as the Standard Template Library
200 (chapters 23 through 25, mostly) is adapted from the final release
205 <h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
206 <!-- <p>Nathan Myers gave the best of all possible answers in <a
207 href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
208 Usenet article</a>.</p>
209 which is no longer available, thanks deja...-->
210 <p>Nathan Myers gave the best of all possible answers, responding to a
211 Usenet article asking this question: <em>Sooner, if you help.</em>
215 <h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
216 <p>Here is <a href="../17_intro/contribute.html">a
217 page devoted to this topic</a>. Subscribing to the mailing
218 list (see above, or the homepage) is a very good idea if you
219 have something to contribute, or if you have spare time and
220 want to help. Contributions don't have to be in the form of
221 source code; anybody who is willing to help write
222 documentation, for example, or has found a bug in code that
223 we all thought was working, is more than welcome!
227 <h2><a name="1_7">1.7 What happened to libg++? I need that!</a></h2>
228 <p>The most recent libg++ README states that libg++ is no longer
229 being actively maintained. It should not be used for new
230 projects, and is only being kicked along to support older code.
232 <p>The libg++ was designed and created when there was no Standard
233 to provide guidance. Classes like linked lists are now provided
234 for by <code>list<T></code> and do not need to be created by
235 <code>genclass</code>. (For that matter, templates exist now and
236 are well-supported, whereas genclass (mostly) predates them.)
238 <p>There are other classes in libg++ that are not specified in the
239 ISO Standard (e.g., statistical analysis). While there are a
240 lot of really useful things that are used by a lot of people
241 (e.g., statistics :-), the Standards Committee couldn't include
242 everything, and so a lot of those "obvious" classes
245 <p>Since libstdc++ is an implementation of the Standard Library, we
246 have no plans at this time to include non-Standard utilities
247 in the implementation, however handy they are. (The extensions
248 provided in the SGI STL aren't maintained by us and don't get
249 a lot of our attention, because they don't require a lot of our
250 time.) It is entirely plausable that the "useful stuff"
251 from libg++ might be extracted into an updated utilities library,
252 but nobody has stated such a project yet.
254 <!-- The advertisement, so to speak, might have to go. Hmmmmm. -->
255 <p>(The <a href="http://www.boost.org/">Boost</a> site houses free
256 C++ libraries that do varying things, and happened to be started
257 by members of the Standards Committee. Certain "useful
258 stuff" classes will probably migrate there.)
260 <p>For the bold and/or desperate, the
261 <a href="http://gcc.gnu.org/extensions.html">GCC extensions page</a>
262 describes where to find the last libg++ source.
266 <h2><a name="1_8">1.8 What if I have more questions?</a></h2>
267 <p>If you have read the README and RELEASE-NOTES files, and your
268 question remains unanswered, then just ask the mailing list.
269 At present, you do not need to be subscribed to the list to
270 send a message to it. More information is available on the
271 homepage (including how to browse the list archives); to send
272 to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
273 <code>libstdc++@gcc.gnu.org</code></a>.
275 <p>If you have a question that you think should be included here,
276 or if you have a question <em>about</em> a question/answer here,
277 contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
278 or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
282 <h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
283 <p>See <a href="../17_intro/license.html">our license description</a>
284 for these and related questions.
288 <h1><a name="2_0">2.0 Installation</a></h1>
289 <h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
290 <p>Complete instructions are not given here (this is a FAQ, not
291 an installation document), but the tools required are few:
294 <li> A 3.x release of GCC. Note that building GCC is much
295 easier and more automated than building the GCC 2.[78]
296 series was. If you are using GCC 2.95, you can still
297 build earlier snapshots of libstdc++.
299 <li> GNU Make is recommended, but should not be required.
301 <li> The GNU Autotools are needed if you are messing with
302 the configury or makefiles.
305 <p>The file <a href="../documentation.html">documentation.html</a>
306 provides a good overview of the steps necessary to build, install,
307 and use the library. Instructions for configuring the library
308 with new flags such as --enable-threads are there also, as well as
309 patches and instructions for working with GCC 2.95.
311 <p>The top-level install.html and
312 <a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
313 the exact build and installation instructions. You may wish to
314 browse those files over CVSweb ahead of time to get a feel for
315 what's required. RELEASE-NOTES is located in the
316 ".../docs/17_intro/" directory of the distribution.
320 <h2><a name="2_2">2.2 [removed]</a></h2>
321 <p>This question has become moot and has been removed. The stub
322 is here to preserve numbering (and hence links/bookmarks).
326 <h2><a name="2_3">2.3 What is this CVS thing that you
327 keep mentioning?</a></h2>
328 <p>The <em>Concurrent Versions System</em> is one of several revision
329 control packages. It was selected for GNU projects because it's
330 free (speech), free (beer), and very high quality. The <a
331 href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
332 the GNU software catalogue</a> has a better description as
334 <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
336 <p>The "anonymous client checkout" feature of CVS is
337 similar to anonymous FTP in that it allows anyone to retrieve
338 the latest libstdc++ sources.
340 <p>After the first of April, American users will have a
341 "/pharmacy" command-line option...
342 <!-- wonder how long that'll live -->
346 <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
347 <p>libstdc++-v3 comes with its own testsuite. You do not need
348 to actually install the library ("<code>make
349 install</code>") to run the testsuite.
351 <p>To run the testsuite on the library after building it, use
352 "make check" while in your build directory. To run
353 the testsuite on the library after building and installing it,
354 use "make check-install" instead.
356 <p>If you find bugs in the testsuite programs themselves, or if you
357 think of a new test program that should be added to the suite,
358 <strong>please</strong> write up your idea and send it to the list!
362 <h2><a name="2_5">2.4 This library is HUGE! And what's libsupc++?</a></h2>
363 <p>Usually the size of libraries on disk isn't noticeable. When a
364 link editor (or simply "linker") pulls things from a
365 static archive library, only the necessary object files are copied
366 into your executable, not the entire library. Unfortunately, even
367 if you only need a single function or variable from an object file,
368 the entire object file is extracted. (There's nothing unique to C++
369 or libstdc++-v3 about this; it's just common behavior, given here
370 for background reasons.)
372 <p>Some of the object files which make up libstdc++.a are rather large.
373 If you create a statically-linked executable with
374 <code> -static</code>, those large object files are suddenly part
375 of your executable. Historically the best way around this was to
376 only place a very few functions (often only a single one) in each
377 source/object file; then extracting a single function is the same
378 as extracting a single .o file. For libstdc++-v3 this is only
379 possible to a certain extent; the object files in question contain
380 template classes and template functions, pre-instantiated, and
381 splitting those up causes severe maintenance headaches.
383 <p>It's not a bug, and it's not really a problem. Nevertheless, some
384 people don't like it, so here are two pseudo-solutions:
386 <p>If the only functions from libstdc++.a which you need are language
387 support functions (those listed in
388 <a href="../18_support/howto.html">clause 18</a> of the standard,
389 e.g., <code>new</code> and <code>delete</code>), then try linking
390 against <code>libsupc++.a</code> (usually specifying
391 <code>-lsupc++</code> when calling g++ for the final link step will
392 do it). This library contains only those support routines, one per
393 object file. But if you are using anything from the rest of the
394 library, such as IOStreams or vectors, then you'll still need
395 pieces from <code>libstdc++.a</code>.
397 <p>The second method is one we hope to incorporate into the library
398 build process. Some platforms can place each function and variable
399 into its own section in a .o file. The GNU linker can then perform
400 garbage collection on unused sections; this reduces the situation
401 to only copying needed functions into the executable, as before,
402 but all happens automatically.
404 <p>Unfortunately the garbage collection in GNU ld is buggy; sections
405 (corresponding to functions and variables) which <em>are</em> used
406 are mistakenly removed, leading to horrible crashes when your
407 executable starts up. For the time being, this feature is not used
408 when building the library.
412 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
413 <h2><a name="3_1">3.1 Can libstdc++-v3 be used with <my
414 favorite compiler>?</a></h2>
415 <p>Probably not. Yet.</p>
416 <p>Because GCC advances so rapidly, development and testing of
417 libstdc++ is being done almost entirely under that compiler.
418 If you are curious about whether other, lesser compilers
419 (*grin*) support libstdc++, you are more than welcome to try.
420 Configuring and building the library (see above) will still
421 require certain tools, however. Also keep in mind that
422 <em>building</em> libstdc++ does not imply that your compiler
423 will be able to <em>use</em> all of the features found in the
424 C++ Standard Library.
426 <p>Since the goal of ISO Standardization is for all C++
427 implementations to be able to share code, the final libstdc++
428 should, in theory, be usable under any ISO-compliant
429 compiler. It will still be targeted and optimized for
434 <h2><a name="3_2">3.2 [removed]</a></h2>
435 <p>This question has become moot and has been removed. The stub
436 is here to preserve numbering (and hence links/bookmarks).
440 <h2><a name="3_3">3.3 [removed]</a></h2>
441 <p>This question has become moot and has been removed. The stub
442 is here to preserve numbering (and hence links/bookmarks).
446 <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
447 <p>By default we try to support the C99 <code>long long</code> type.
448 This requires that certain functions from your C library be present.
450 <p>Up through release 3.0.2 the tests performed were too general, and
451 this feature was disabled when it did not need to be. The most
452 commonly reported platform affected was Solaris.
454 <p>This has been fixed for 3.0.3 and onwards.
458 <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
459 / etc is always defined</a></h2>
460 <p>On Solaris, g++ (but not gcc) always defines the preprocessor
461 macro <code>_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
462 with <code>_GNU_SOURCE</code>. (This is not an exhaustive list;
463 other macros and other platforms are also affected.)
465 <p>These macros are typically used in C library headers, guarding new
466 versions of functions from their older versions. The C++ standard
467 library includes the C standard library, but it requires the C90
468 version, which for backwards-compatability reasons is often not the
469 default for many vendors.
471 <p>More to the point, the C++ standard requires behavior which is only
472 available on certain platforms after certain symbols are defined.
473 Usually the issue involves I/O-related typedefs. In order to
474 ensure correctness, the compiler simply predefines those symbols.
476 <p>Note that it's not enough to #define them only when the library is
477 being built (during installation). Since we don't have an 'export'
478 keyword, much of the library exists as headers, which means that
479 the symbols must also be defined as your programs are parsed and
482 <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
483 the gcc config headers for your target (and try changing them to
484 see what happens when building complicated code). You can also run
485 <code>"g++ -E -dM - < /dev/null"</code> to display
486 a list of predefined macros for any particular installation.
488 <p>This has been discussed on the mailing lists
489 <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
491 <p>This method is something of a wart. We'd like to find a cleaner
492 solution, but nobody yet has contributed the time.
496 <h2><a name="3_6">3.6 OS X ctype.h is broken! How can I hack it?</a></h2>
497 <p>This is a long-standing bug in the OS X support. Fortunately,
498 the patch is quite simple, and well-known.
499 <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
500 link to the solution.</a>
504 <h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
505 <p>Support for atomic integer operations is/was broken on i386
506 platforms. The assembly code accidentally used opcodes that are
507 only available on the i486 and later. So if you configured GCC
508 to target, for example, i386-linux, but actually used the programs
509 on an i686, then you would encounter no problems. Only when
510 actually running the code on a i386 will the problem appear.
512 <p>This is fixed in 3.2.2.
516 <h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
517 <p>For 3.2.1 (shared library version 5.0.1) and later, the library
518 uses localization and formatting code from the system C library
519 (glibc) version 2.2.5. That version of glibc is over a year old
520 and contains necessary bugfixes. Many GNU/Linux distros make
521 glibc version 2.3.x available now.
523 <p>The guideline is simple: the more recent the C++ library, the
524 more recent the C library. (This is also documented in the main
525 GCC installation instructions.)
529 <h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
530 <p>At the moment there are a few problems in FreeBSD's support for
531 wide character functions, and as a result the libstdc++ configury
532 decides that wchar_t support should be disabled. Once the underlying
533 problems are fixed in FreeBSD (soon), the library support will
534 automatically enable itself.
536 <p>You can fix the problems yourself, and learn more about the situation,
538 <a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
539 this short thread</a> ("_GLIBCPP_USE_WCHAR_T undefined in
540 FreeBSD's c++config.h?").
544 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
545 <em>Note that this section can get rapdily outdated -- such is the
546 nature of an open-source project. For the latest information, join
547 the mailing list or look through recent archives. The RELEASE-
548 NOTES and BUGS files are generally kept up-to-date.</em>
550 <p>For 3.0.1, the most common "bug" is an apparently missing
551 "<code>../</code>" in include/Makefile, resulting in files
552 like gthr.h and gthr-single.h not being found. Please read
553 <a href="http://gcc.gnu.org/install/configure.html">the configuration
554 instructions for GCC</a>,
555 specifically the part about configuring in a separate build directory,
556 and how strongly recommended it is. Building in the source directory
557 is fragile, is rarely tested, and tends to break, as in this case.
558 This was fixed for 3.0.2.
561 <p>For 3.1, the most common "bug" is a parse error when using
562 <code><fstream></code>, ending with a message,
563 "<code>bits/basic_file.h:52: parse error before `{'
564 token</code>." Please read
565 <a href="http://gcc.gnu.org/install/">the installation instructions for
566 GCC</a>, specifically the part about not installing newer versions on
567 top of older versions. If you install 3.1 over a 3.0.x release, then
568 the wrong basic_file.h header will be found (its location changed
572 <p><strong>Please do not report these as bugs. We know about them.</strong>
573 Reporting this -- or any other problem that's already been fixed --
574 hinders the development of GCC, because we have to take time to
575 respond to your report. Thank you.
578 <h2><a name="4_1">4.1 What works already?</a></h2>
579 <p>This is a verbatim clip from the "Status" section
580 of the RELEASE-NOTES for the latest snapshot. For a list of
581 fixed bugs, see that file.
584 <!-- Yeah, I meant that "verbatim clip" thing literally... :-) -->
590 - more doxygen documentation
591 - more named locale fixups
592 - stdio_filebuf that takes fd, FILE
593 - io performance tuning
594 - allocation tuning, valgrind fixups
595 - __cxa_demangle now supported
597 - more doxygen documentation.
598 - more named locale bug fixes
599 - support for symbol versioning when using GNU ld >= 2.12
601 - tuning for executable size
603 - more doxygen documentation.
604 - extensions moved out of namespace std
605 - HPUX long long support
606 - more string optimizations
607 - support for NetBSD cross compiles
608 - concept_check merge from boost
609 - header simplification
610 - named locale bug shakeout
613 - add S390, m68k, x86-64 support.
614 - doxygen documentation has been extended, including man pages.
615 - verbose terminate handling has been added.
616 - some libsupc++ tweaks
617 - warnings for deprecated headers now active.
618 - dejagnu testsuite preliminary documentation.
619 - dejagnu testsuite default.
620 - dejagnu testsuite cross compiler, multilib safe.
621 - long long iostreams on by default, rework of ISO C99 support.
622 - iterator re-write and testsuites.
623 - container testsuites.
624 - allocator revamp and testsuites.
625 - more concept-checking work.
626 - basic_string optimization and MT fixes.
627 - new limits implementation.
628 - update -fno-exceptions code, verify it works.
629 - full named locale support fpr all facets, choice of gnu,
630 ieee_1003.1-200x (POSIX 2), or generic models. Full support depends
631 on target OS and underlying "C" library support.
636 <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
637 <p>This is by no means meant to be complete nor exhaustive, but
638 mentions some problems that users may encounter when building
639 or using libstdc++. If you are experiencing one of these
640 problems, you can find more information on the libstdc++ and
641 the GCC mailing lists.
643 <p>Before reporting a bug, examine the
644 <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
645 category set to "libstdc++". The BUGS file in the source
646 tree also tracks known serious problems.
649 <li>Debugging is problematic, due to bugs in line-number generation
650 (mostly fixed in the compiler) and gdb lagging behind the
651 compiler (lack of personnel). We recommend configuring the
652 compiler using <code>--with-dwarf2</code> if the DWARF2
653 debugging format is not already the default on your platform.
655 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
656 GDB settings</a> can have a profound effect on your C++ debugging
657 experiences. :-)</li>
661 <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
662 <p>Yes, unfortunately, there are some. In a
663 <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
664 to the list</a>, Nathan Myers announced that he has started a list of
665 problems in the ISO C++ Standard itself, especially with
666 regard to the chapters that concern the library. The list
668 <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
669 website</a>. Developers who are having problems interpreting
670 the Standard may wish to consult his notes.
672 <p>For those people who are not part of the ISO Library Group
673 (i.e., nearly all of us needing to read this page in the first
674 place :-), a public list of the library defects is occasionally
675 published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
676 Some of these have resulted in <a href="#5_2">code changes</a>.
680 <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
681 <p>There are things which are not bugs in the compiler (4.2) nor
682 the language specification (4.3), but aren't really bugs in
683 libstdc++, either. Really! Please do not report these as bugs.
685 <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
686 The biggest of these is the quadzillions of warnings about the
687 library headers emitted when <code>-Weffc++</code> is used. Making
688 libstdc++ "-Weffc++-clean" is not a goal of the project,
689 for a few reasons. Mainly, that option tries to enforce
690 object-oriented programming, while the Standard Library isn't
691 necessarily trying to be OO.
693 <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
694 </a> Did I just say that -Weffc++ was our biggest false-bug report?
695 I lied. (It used to be.) Today it seems to be reports that after
696 executing a sequence like
699 #include <fstream>
701 std::fstream fs("a_file");
703 // . do things with fs...
706 fs.open("a_new_file");</pre>
707 <p>all operations on the re-opened <code>fs</code> will fail, or at
708 least act very strangely. Yes, they often will, especially if
709 <code>fs</code> reached the EOF state on the previous file. The
710 reason is that the state flags are <strong>not</strong> cleared
711 on a successful call to open(). The standard unfortunately did
712 not specify behavior in this case, and to everybody's great sorrow,
713 the <a href="../ext/howto.html#5">proposed LWG resolution</a> (see
714 DR #22) is to leave the flags unchanged. You must insert a call
715 to <code>fs.clear()</code> between the calls to close() and open(),
716 and then everything will work like we all expect it to work.
718 <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
719 Another is the <code>rel_ops</code> namespace and the template
720 comparison operator functions contained therein. If they become
721 visible in the same namespace as other comparison functions
722 (e.g., '<code>using</code>' them and the <iterator> header),
723 then you will suddenly be faced with huge numbers of ambiguity
724 errors. This was discussed on the -v3 list; Nathan Myers
725 <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
726 things up here</a>. The collisions with vector/string iterator
727 types have been fixed for 3.1. <!-- more links to email here -->
729 <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
730 <p>If you have found an extremely broken header file which is
731 causing problems for you, look carefully before submitting a
732 "high" priority bug report (which you probably shouldn't
733 do anyhow; see the last paragraph of the page describing
734 <a href="http://gcc.gnu.org/gnatswrite.html">the GCC bug database</a>).
736 <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
737 the installed library's name looks like <code>libstdc++-2.10.a</code>
738 or <code>libstdc++-libc6-2.10.so</code>,
739 then you are using the old libstdc++-v2 library, which is nonstandard
740 and unmaintained. Do not report problems with -v2 to the -v3
743 <p>Currently our header files are installed in
744 <code>${prefix}/include/g++-v3</code> (see the 'v'?). This may
745 change with the next release of GCC, as it may be too confusing,
746 but <a href="http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html">the
747 question has not yet been decided</a>.
749 <p><a name="4_4_glibc"><strong>glibc</strong></a>
750 If you're on a GNU/Linux system and have just upgraded to
751 glibc 2.2, but are still using gcc 2.95.2, then you should have
752 read the glibc FAQ, specifically 2.34:
755 2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
757 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
758 apply a patch to the include files in /usr/include/g++, because the fpos_t
759 type has changed in glibc 2.2. The patch is at
760 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
762 <p>Note that 2.95.x shipped with the
763 <a href="#4_4_interface">old v2 library</a> which is no longer
764 maintained. Also note that gcc 2.95.3 fixes this problem, but
765 requires a separate patch for libstdc++-v3.
767 <p><a name="4_4_checks"><strong>concept checks</strong></a>
768 If you see compilation errors containing messages about
769 <code> <em>foo</em>Concept </code>and a<code> constraints </code>
770 member function, then most likely you have violated one of the
771 requirements for types used during instantiation of template
772 containers and functions. For example, EqualityComparableConcept
773 appears if your types must be comparable with == and you have not
774 provided this capability (a typo, or wrong visibility, or you
775 just plain forgot, etc).
777 <p>More information, including how to optionally enable/disable the
779 <a href="../19_diagnostics/howto.html#3">here</a>.
781 <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
782 If you are using the C++ library across dynamically-loaded
783 objects, make certain that you are passing the correct options
784 when compiling and linking:
787 // compile the library components
793 // create the library
794 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
796 // link the executable
797 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
800 <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
801 <p>If you have found a bug in the library and you think you have
802 a working fix, then send it in! The main GCC site has a page
803 on <a href="http://gcc.gnu.org/contribute.html">submitting
804 patches</a> that covers the procedure, but for libstdc++ you
805 should also send the patch to our mailing list in addition to
806 the GCC patches mailing list. The libstdc++
807 <a href="../17_intro/contribute.html">contributors' page</a>
808 also talks about how to submit patches.
810 <p>In addition to the description, the patch, and the ChangeLog
811 entry, it is a Good Thing if you can additionally create a small
812 test program to test for the presence of the bug that your
813 patch fixes. Bugs have a way of being reintroduced; if an old
814 bug creeps back in, it will be caught immediately by the
815 <a href="#2_4">testsuite</a> -- but only if such a test exists.
819 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
820 <h2><a name="5_1">5.1 string::iterator is not char*;
821 vector<T>::iterator is not T*</a></h2>
822 <p>If you have code that depends on container<T> iterators
823 being implemented as pointer-to-T, your code is broken.
825 <p>While there are arguments for iterators to be implemented in
826 that manner, A) they aren't very good ones in the long term,
827 and B) they were never guaranteed by the Standard anyway. The
828 type-safety achieved by making iterators a real class rather
829 than a typedef for <code>T*</code> outweighs nearly all opposing
832 <p>Code which does assume that a vector iterator <code> i </code>
833 is a pointer can often be fixed by changing <code> i </code> in
834 certain expressions to <code> &*i </code>. Future revisions
835 of the Standard are expected to bless this usage for
836 vector<> (but not for basic_string<>).
840 <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
841 <p>Hopefully, not much. The goal of libstdc++-v3 is to produce
842 a fully-compliant, fully-portable Standard Library. After that,
843 we're mostly done: there won't <em>be</em> any more compliance
847 <li><p>The ISO Committee will meet periodically to review Defect Reports
848 in the C++ Standard. Undoubtedly some of these will result in
849 changes to the Standard, which will be reflected in patches to
850 libstdc++. Some of that is already happening, see 4.2. Some of
851 those changes are being predicted by the library maintainers, and
852 we add code to the library based on what the current proposed
853 resolution specifies. Those additions are listed in
854 <a href="../ext/howto.html#5">the extensions page</a>.
856 <li><p>Performance tuning. Lots of performance tuning. This too is
857 already underway for post-3.0 releases, starting with memory
858 expansion in container classes and buffer usage in synchronized
861 <li><p>An ABI for libstdc++ is being developed, so that
862 multiple binary-incompatible copies of the library can be replaced
863 with a single backwards-compatible library, like libgcc_s.so is.
865 <li><p>The current libstdc++ contains extensions to the Library which
866 must be explicitly requested by client code (for example, the
867 hash tables from SGI). Other extensions may be added to
868 libstdc++-v3 if they seem to be "standard" enough.
869 (For example, the "long long" type from C99.)
870 Bugfixes and rewrites (to improve or fix thread safety, for
871 instance) will of course be a continuing task.
874 <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
875 question</a> about the next libstdc++ prompted some brief but
877 <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
881 <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
882 <p>The <a href="http://www.sgi.com/Technology/STL/">STL from SGI</a>,
883 version 3.3, was the most recent merge of the STL codebase. The
884 code in libstdc++ contains many fixes and changes, and it is
885 very likely that the SGI code is no longer under active
886 development. We expect that no future merges will take place.
888 <p>In particular, <code>string</code> is not from SGI and makes no
889 use of their "rope" class (which is included as an
890 optional extension), nor is <code>valarray</code> and some others.
891 Classes like <code>vector<></code> are, however.
893 <p>The FAQ for SGI's STL (one jump off of their main page) is
898 <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
899 <p>Headers in the <code>ext</code> and <code>backward</code>
900 subdirectories should be referred to by their relative paths:
901 <!-- Careful, the leading spaces in PRE show up directly. -->
904 #include <ext/hash_map> </pre>
905 <p>rather than using <code>-I</code> or other options. This is more
906 portable and forward-compatible. (The situation is the same as
907 that of other headers whose directories are not searched directly,
908 e.g., <code><sys/stat.h></code>, <code><X11/Xlib.h></code>.
911 <p>The extensions are no longer in the global or <code>std</code>
912 namespaces, instead they are declared in the <code>__gnu_cxx</code>
913 namespace. For maximum portability, consider defining a namespace
914 alias to use to talk about extensions, e.g.:
919 #include <hash_map.h>
920 namespace Sgi { using ::hash_map; }; // inherit globals
922 #include <ext/hash_map>
923 #if __GNUC_MINOR__ == 0
924 namespace Sgi = std; // GCC 3.0
926 namespace Sgi = ::__gnu_cxx; // GCC 3.1 and later
929 #else // ... there are other compilers, right?
933 Sgi::hash_map<int,int> my_map; </pre>
934 <p>This is a bit cleaner than defining typedefs for all the
935 instantiations you might need.
938 <p>Extensions to the library have
939 <a href="../ext/howto.html">their own page</a>.
943 <h2><a name="5_5">5.5 [removed]</a></h2>
944 <p>This question has become moot and has been removed. The stub
945 is here to preserve numbering (and hence links/bookmarks).
949 <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
950 <p>When the system's libc is itself thread-safe, a non-generic
951 implementation of atomicity.h exists for the architecture, and gcc
952 itself reports a thread model other than single; libstdc++-v3
953 strives to be thread-safe. The user-code must guard against
954 concurrent method calls which may access any particular library
955 object's state. Typically, the application programmer may infer
956 what object locks must be held based on the objects referenced in
957 a method call. Without getting into great detail, here is an
958 example which requires user-level locks:
961 library_class_a shared_object_a;
964 library_class_b *object_b = new library_class_b;
965 shared_object_a.add_b (object_b); // must hold lock for shared_object_a
966 shared_object_a.mutate (); // must hold lock for shared_object_a
969 // Multiple copies of thread_main() are started in independent threads.</pre>
970 <p>Under the assumption that object_a and object_b are never exposed to
971 another thread, here is an example that should not require any
976 library_class_a object_a;
977 library_class_b *object_b = new library_class_b;
978 object_a.add_b (object_b);
981 <p>All library objects are safe to use in a multithreaded program as
982 long as each thread carefully locks out access by any other thread
983 while it uses any object visible to another thread. In general,
984 this requirement includes both read and write access to objects;
985 unless otherwise documented as safe, do not assume that two
986 threads may access a shared standard library object at the
989 <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
990 introduction), <a href="../23_containers/howto.html#3">23</a>
991 (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
996 <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
997 <p>Copies of the full ISO 14882 standard are available on line via the
998 ISO mirror site for committee members. Non-members, or those who
999 have not paid for the privilege of sitting on the committee and
1000 sustained their two-meeting commitment for voting rights, may get a
1001 copy of the standard from their respective national standards
1002 organization. In the USA, this national standards organization is
1003 ANSI and their website is right <a href="http://www.ansi.org">here</a>.
1004 (And if you've already registered with them, clicking this link will
1005 take you to directly to the place where you can
1006 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998">buy
1007 the standard on-line</a>.
1009 <p>Who is your country's member body? Visit the
1010 <a href="http://www.iso.ch/">ISO homepage</a> and find out!
1014 <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
1015 <p>"ABI" stands for "Application Binary Interface."
1016 Conventionally, it refers to a great mass of details about how
1017 arguments are arranged on the call stack and/or in registers, and
1018 how various types are arranged and padded in structs. A single CPU
1019 design may suffer multiple ABIs designed by different development
1020 tool vendors who made different choices, or even by the same vendor
1021 for different target applications or compiler versions. In ideal
1022 circumstances the CPU designer presents one ABI and all the OSes and
1023 compilers use it. In practice every ABI omits details that compiler
1024 implementers (consciously or accidentally) must choose for themselves.
1026 <p>That ABI definition suffices for compilers to generate code so a
1027 program can interact safely with an OS and its lowest-level libraries.
1028 Users usually want an ABI to encompass more detail, allowing libraries
1029 built with different compilers (or different releases of the same
1030 compiler!) to be linked together. For C++, this includes many more
1031 details than for C, and CPU designers (for good reasons elaborated
1032 below) have not stepped up to publish C++ ABIs. The details include
1033 virtual function implementation, struct inheritance layout, name
1034 mangling, and exception handling. Such an ABI has been defined for
1035 GNU C++, and is immediately useful for embedded work relying only on
1036 a "free-standing implementation" that doesn't include (much
1037 of) the standard library. It is a good basis for the work to come.
1039 <p>A useful C++ ABI must also incorporate many details of the standard
1040 library implementation. For a C ABI, the layouts of a few structs
1041 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
1042 For C++, the details include the complete set of names of functions
1043 and types used, the offsets of class members and virtual functions,
1044 and the actual definitions of all inlines. C++ exposes many more
1045 library details to the caller than C does. It makes defining
1046 a complete ABI a much bigger undertaking, and requires not just
1047 documenting library implementation details, but carefully designing
1048 those details so that future bug fixes and optimizations don't
1049 force breaking the ABI.
1051 <p>There are ways to help isolate library implementation details from the
1052 ABI, but they trade off against speed. Library details used in
1053 inner loops (e.g., getchar) must be exposed and frozen for all
1054 time, but many others may reasonably be kept hidden from user code,
1055 so they may later be changed. Deciding which, and implementing
1056 the decisions, must happen before you can reasonably document a
1057 candidate C++ ABI that encompasses the standard library.
1060 <!-- ####################################################### -->
1063 <p class="fineprint"><em>
1064 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
1065 Comments and suggestions are welcome, and may be sent to
1066 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.