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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE html
3 PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
4 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
5
6<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
7<head>
8 <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
9 <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++, libg++, STL" />
10 <meta name="DESCRIPTION" content="FAQ for the GNU libstdc++ effort." />
11 <title>libstdc++-v3 FAQ</title>
12<link rel="StyleSheet" href="../lib3styles.css" />
13<!--
14 ** Locations of "the most recent snapshot is the Nth" text are
15 ** answers 1_1, .
16-->
17</head>
18<body>
19
20<h1 class="centered">libstdc++ Frequently Asked Questions</h1>
21
22<p class="fineprint"><em>
23 The latest version of this document is always available at
24 <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/">
25 http://gcc.gnu.org/onlinedocs/libstdc++/faq/</a>. The main documentation
26 page is at
27 <a href="http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html">
28 http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html</a>.
29</em></p>
30
31<p><em>
32 To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
33</em></p>
34
35<!-- ####################################################### -->
36<hr />
37<h1>Questions</h1>
38<ol>
39 <li><a href="#1_0">General Information</a>
40 <!-- I suspect these will mostly be links to/into existing documents. -->
41 <ol>
42 <li><a href="#1_1">What is libstdc++-v3?</a> </li>
43 <li><a href="#1_2">Why should I use libstdc++?</a> </li>
44 <li><a href="#1_3">Who's in charge of it?</a> </li>
45 <li><a href="#1_4">How do I get libstdc++?</a> </li>
46 <li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
47 <li><a href="#1_6">How do I contribute to the effort?</a> </li>
48 <li><a href="#1_7">What happened to libg++? I need that!</a> </li>
49 <li><a href="#1_8">What if I have more questions?</a> </li>
50 <li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
51 </ol>
52 </li>
53
54 <li><a href="#2_0">Installation</a>
55 <ol>
56 <li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
57 <li><a href="#2_2">[removed]</a> </li>
58 <li><a href="#2_3">What is this CVS thing that you keep
59 mentioning?</a> </li>
60 <li><a href="#2_4">How do I know if it works?</a> </li>
61 <li><a href="#2_5">This library is HUGE! And what's libsupc++?</a> </li>
62 </ol>
63 </li>
64
65 <li><a href="#3_0">Platform-Specific Issues</a>
66 <ol>
67 <li><a href="#3_1">Can libstdc++-v3 be used with &lt;my
68 favorite compiler&gt;?</a> </li>
69 <li><a href="#3_2">[removed]</a> </li>
70 <li><a href="#3_3">[removed]</a> </li>
71 <li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
72 <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
73 <code>_GNU_SOURCE</code> / etc is always defined</a>
74 </li>
75 <li><a href="#3_6">OS X ctype.h is broken! How can I hack it?</a></li>
76 <li><a href="#3_7">Threading is broken on i386</a></li>
77 <li><a href="#3_8">Recent GNU/Linux glibc required?</a></li>
78 <li><a href="#3_9">Can't use wchar_t/wstring on FreeBSD</a></li>
79 <li><a href="#3_10">MIPS atomic operations</a></li>
80 </ol>
81 </li>
82
83 <li><a href="#4_0">Known Bugs and Non-Bugs</a>
84 <ol>
85 <li><a href="#4_1">What works already?</a> </li>
86 <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
87 <li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
88 <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
89 <li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
90 <li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
91 <li><a href="#4_4_rel_ops">&quot;ambiguous overloads&quot;
92 after including an old-style header</a> </li>
93 <li><a href="#4_4_interface">The g++-3 headers are
94 <strong>not ours</strong></a> </li>
95 <li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
96 <li><a href="#4_4_checks">errors about <em>*Concept</em> and
97 <em>constraints</em> in the STL...</a> </li>
98 <li><a href="#4_4_dlsym">program crashes when using library code
99 in a dynamically-loaded library</a> </li>
100 <li><a href="#4_4_leak">"memory leaks" in containers</a> </li>
101 </ul>
102 </li>
103 <li><a href="#4_5">Aw, that's easy to fix!</a> </li>
104 </ol>
105 </li>
106
107 <li><a href="#5_0">Miscellaneous</a>
108 <ol>
109 <li><a href="#5_1">string::iterator is not char*;
110 vector&lt;T&gt;::iterator is not T*</a> </li>
111 <li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
112 <li><a href="#5_3">What about the STL from SGI?</a> </li>
113 <li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
114 <li><a href="#5_5">[removed]</a> </li>
115 <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
116 <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
117 <li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
118 </ol>
119 </li>
120
121</ol>
122
123<hr />
124
125<!-- ####################################################### -->
126
127<h1><a name="1_0">1.0 General Information</a></h1>
128<!-- I suspect these will mostly be links to/into existing documents. -->
129 <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
130 <p>The GNU Standard C++ Library v3 is an
131 ongoing project to implement the ISO 14882 Standard C++ library
132 as described in chapters 17 through 27 and annex D. As the
133 library reaches stable plateaus, it is captured in a snapshot
134 and released. The latest release is
135 <a href="http://gcc.gnu.org/libstdc++/index.html#download">the
136 fourteenth snapshot</a> but newer versions have been included
137 in recent GCC releases. 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).
142 </p>
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.
147 </p>
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>.
150 </p>
151
152<hr />
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 &quot;incomplet and incorrekt,&quot; and many suffer from
159 limitations of the compilers that use them.
160 </p>
161 <p>The GNU C/C++/FORTRAN/&lt;pick-a-language&gt; 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
164 has recently been taken over by the
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-3.0/buildstat.html">portability</a>
168 that are the hallmarks of an open-source project are being
169 applied to libstdc++.
170 </p>
171 <p>That means that all of the Standard classes and functions
172 (such as <code>string</code>, <code>vector&lt;&gt;</code>, iostreams,
173 and algorithms) will be freely available and fully compliant.
174 Programmers will no longer need to &quot;roll their own&quot;
175 nor be worried about platform-specific incompatibilities.
176 </p>
177
178<hr />
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
184 the CVS archive.
185 </p>
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!
191 </p>
192
193<hr />
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.
198 </p>
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>.
201 </p>
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.
205 </p>
206
207<hr />
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>
212which 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>
215 </p>
216
217<hr />
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!
227 </p>
228
229<hr />
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.
234 </p>
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&lt;T&gt;</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.)
240 </p>
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 &quot;obvious&quot; classes
246 didn't get included.
247 </p>
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 &quot;useful stuff&quot;
254 from libg++ might be extracted into an updated utilities library,
255 but nobody has started such a project yet.
256 </p>
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 &quot;useful
260 stuff&quot; classes will probably migrate there.)
261 </p>
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.
265 </p>
266
267<hr />
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:[email protected]">
275 <code>[email protected]</code></a>.
276 </p>
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:[email protected]">Phil Edwards</a>
280 or <a href="mailto:[email protected]">Gabriel Dos Reis</a>.
281 </p>
282
283<hr />
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.
287 </p>
288
289<hr />
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:
294 </p>
295 <ul>
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++.
300 </li>
301 <li> GNU Make is recommended, but should not be required.
302 </li>
303 <li> The GNU Autotools are needed if you are messing with
304 the configury or makefiles.
305 </li>
306 </ul>
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.
312 </p>
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 &quot;.../docs/17_intro/&quot; directory of the distribution.
319 </p>
320
321<hr />
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).
325 </p>
326
327<hr />
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
335 well as a
336 <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
337 </p>
338 <p>The &quot;anonymous client checkout&quot; feature of CVS is
339 similar to anonymous FTP in that it allows anyone to retrieve
340 the latest libstdc++ sources.
341 </p>
342 <p>After the first of April, American users will have a
343 &quot;/pharmacy&quot; command-line option...
344 <!-- wonder how long that'll live -->
345 </p>
346
347<hr />
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 (&quot;<code>make
351 install</code>&quot;) to run the testsuite, but you do need
352 DejaGNU, as described
353 <a href="http://gcc.gnu.org/install/test.html">here</a>.
354 </p>
355 <p>To run the testsuite on the library after building it, use
356 &quot;make check&quot; while in your build directory. To run
357 the testsuite on the library after building and installing it,
358 use &quot;make check-install&quot; instead.
359 </p>
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!
363 </p>
364
365<hr />
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 &quot;linker&quot;) 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.)
375 </p>
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.
386 </p>
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:
389 </p>
390 <p>If the only functions from libstdc++.a which you need are language
391 support functions (those listed in
392 <a href="../18_support/howto.html">clause 18</a> of the standard,
393 e.g., <code>new</code> and <code>delete</code>), then try linking
394 against <code>libsupc++.a</code> (usually specifying
395 <code>-lsupc++</code> when calling g++ for the final link step will
396 do it). This library contains only those support routines, one per
397 object file. But if you are using anything from the rest of the
398 library, such as IOStreams or vectors, then you'll still need
399 pieces from <code>libstdc++.a</code>.
400 </p>
401 <p>The second method is one we hope to incorporate into the library
402 build process. Some platforms can place each function and variable
403 into its own section in a .o file. The GNU linker can then perform
404 garbage collection on unused sections; this reduces the situation
405 to only copying needed functions into the executable, as before,
406 but all happens automatically.
407 </p>
408 <p>Unfortunately the garbage collection in GNU ld is buggy; sections
409 (corresponding to functions and variables) which <em>are</em> used
410 are mistakenly removed, leading to horrible crashes when your
411 executable starts up. For the time being, this feature is not used
412 when building the library.
413 </p>
414
415<hr />
416<h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
417 <h2><a name="3_1">3.1 Can libstdc++-v3 be used with &lt;my
418 favorite compiler&gt;?</a></h2>
419 <p>Probably not. Yet.</p>
420 <p>Because GCC advances so rapidly, development and testing of
421 libstdc++ is being done almost entirely under that compiler.
422 If you are curious about whether other, lesser compilers
423 (*grin*) support libstdc++, you are more than welcome to try.
424 Configuring and building the library (see above) will still
425 require certain tools, however. Also keep in mind that
426 <em>building</em> libstdc++ does not imply that your compiler
427 will be able to <em>use</em> all of the features found in the
428 C++ Standard Library.
429 </p>
430 <p>Since the goal of ISO Standardization is for all C++
431 implementations to be able to share code, the final libstdc++
432 should, in theory, be usable under any ISO-compliant
433 compiler. It will still be targeted and optimized for
434 GCC/g++, however.
435 </p>
436
437<hr />
438 <h2><a name="3_2">3.2 [removed]</a></h2>
439 <p>This question has become moot and has been removed. The stub
440 is here to preserve numbering (and hence links/bookmarks).
441 </p>
442
443<hr />
444 <h2><a name="3_3">3.3 [removed]</a></h2>
445 <p>This question has become moot and has been removed. The stub
446 is here to preserve numbering (and hence links/bookmarks).
447 </p>
448
449<hr />
450 <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
451 <p>By default we try to support the C99 <code>long long</code> type.
452 This requires that certain functions from your C library be present.
453 </p>
454 <p>Up through release 3.0.2 the tests performed were too general, and
455 this feature was disabled when it did not need to be. The most
456 commonly reported platform affected was Solaris.
457 </p>
458 <p>This has been fixed for 3.0.3 and onwards.
459 </p>
460
461<hr />
462 <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
463 / etc is always defined</a></h2>
464 <p>On Solaris, g++ (but not gcc) always defines the preprocessor
465 macro <code>_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
466 with <code>_GNU_SOURCE</code>. (This is not an exhaustive list;
467 other macros and other platforms are also affected.)
468 </p>
469 <p>These macros are typically used in C library headers, guarding new
470 versions of functions from their older versions. The C++ standard
471 library includes the C standard library, but it requires the C90
472 version, which for backwards-compatability reasons is often not the
473 default for many vendors.
474 </p>
475 <p>More to the point, the C++ standard requires behavior which is only
476 available on certain platforms after certain symbols are defined.
477 Usually the issue involves I/O-related typedefs. In order to
478 ensure correctness, the compiler simply predefines those symbols.
479 </p>
480 <p>Note that it's not enough to #define them only when the library is
481 being built (during installation). Since we don't have an 'export'
482 keyword, much of the library exists as headers, which means that
483 the symbols must also be defined as your programs are parsed and
484 compiled.
485 </p>
486 <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
487 the gcc config headers for your target (and try changing them to
488 see what happens when building complicated code). You can also run
489 <code>&quot;g++ -E -dM - &lt; /dev/null&quot;</code> to display
490 a list of predefined macros for any particular installation.
491 </p>
492 <p>This has been discussed on the mailing lists
493 <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&amp;format=builtin-long&amp;sort=score&amp;words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
494 </p>
495 <p>This method is something of a wart. We'd like to find a cleaner
496 solution, but nobody yet has contributed the time.
497 </p>
498
499<hr />
500 <h2><a name="3_6">3.6 OS X ctype.h is broken! How can I hack it?</a></h2>
501 <p>This is a long-standing bug in the OS X support. Fortunately,
502 the patch is quite simple, and well-known.
503 <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
504 link to the solution.</a>
505 </p>
506
507<hr />
508 <h2><a name="3_7">3.7 Threading is broken on i386</a></h2>
509 <p>Support for atomic integer operations is/was broken on i386
510 platforms. The assembly code accidentally used opcodes that are
511 only available on the i486 and later. So if you configured GCC
512 to target, for example, i386-linux, but actually used the programs
513 on an i686, then you would encounter no problems. Only when
514 actually running the code on a i386 will the problem appear.
515 </p>
516 <p>This is fixed in 3.2.2.
517 </p>
518
519<hr />
520 <h2><a name="3_8">3.8 Recent GNU/Linux glibc required?</a></h2>
521 <p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version
522 5.0.1) and later uses localization and formatting code from the system
523 C library (glibc) version 2.2.5. That version of glibc is over a
524 year old and contains necessary bugfixes. Many GNU/Linux distros make
525 glibc version 2.3.x available now.
526 </p>
527 <p>The guideline is simple: the more recent the C++ library, the
528 more recent the C library. (This is also documented in the main
529 GCC installation instructions.)
530 </p>
531
532<hr />
533 <h2><a name="3_9">3.9 Can't use wchar_t/wstring on FreeBSD</a></h2>
534 <p>At the moment there are a few problems in FreeBSD's support for
535 wide character functions, and as a result the libstdc++ configury
536 decides that wchar_t support should be disabled. Once the underlying
537 problems are fixed in FreeBSD (soon), the library support will
538 automatically enable itself.
539 </p>
540 <p>You can fix the problems yourself, and learn more about the situation,
541 by reading
542 <a href="http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286">
543 this short thread</a> (&quot;_GLIBCPP_USE_WCHAR_T undefined in
544 FreeBSD's c++config.h?&quot;).
545 </p>
546
547<hr />
548 <h2><a name="3_10">3.10 MIPS atomic operations</a></h2>
549 <p>The atomic locking routines for MIPS targets requires MIPS II
550 and later. A patch went in just after the 3.3 release to
551 make mips* use the generic implementation instead. You can also
552 configure for mipsel-elf as a workaround.
553 </p>
554 <p>mips*-*-linux* continues to use the MIPS II routines, and more
555 work in this area is expected.
556 </p>
557
558<hr />
559<h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
560 <em>Note that this section can get rapdily outdated -- such is the
561 nature of an open-source project. For the latest information, join
562 the mailing list or look through recent archives. The RELEASE-
563 NOTES and BUGS files are generally kept up-to-date.</em>
564
565 <p>For 3.0.1, the most common &quot;bug&quot; is an apparently missing
566 &quot;<code>../</code>&quot; in include/Makefile, resulting in files
567 like gthr.h and gthr-single.h not being found. Please read
568 <a href="http://gcc.gnu.org/install/configure.html">the configuration
569 instructions for GCC</a>,
570 specifically the part about configuring in a separate build directory,
571 and how strongly recommended it is. Building in the source directory
572 is fragile, is rarely tested, and tends to break, as in this case.
573 This was fixed for 3.0.2.
574 </p>
575
576 <p>For 3.1, the most common &quot;bug&quot; is a parse error when using
577 <code>&lt;fstream&gt;</code>, ending with a message,
578 &quot;<code>bits/basic_file.h:52: parse error before `{'
579 token</code>.&quot; Please read
580 <a href="http://gcc.gnu.org/install/">the installation instructions for
581 GCC</a>, specifically the part about not installing newer versions on
582 top of older versions. If you install 3.1 over a 3.0.x release, then
583 the wrong basic_file.h header will be found (its location changed
584 between releases).
585 </p>
586
587 <p><strong>Please do not report these as bugs. We know about them.</strong>
588 Reporting this -- or any other problem that's already been fixed --
589 hinders the development of GCC, because we have to take time to
590 respond to your report. Thank you.
591 </p>
592
593 <h2><a name="4_1">4.1 What works already?</a></h2>
594 <p>Short answer: Pretty much everything <em>works</em> except for some
595 corner cases. Also, localization is incomplete. For whether it works
596 well, or as you expect it to work, see 5.2.
597 </p>
598 <p>Long answer: See the docs/html/17_intro/CHECKLIST file, which is
599 badly outdated...
600 </p>
601 <p>What follows is a verbatim clip from the &quot;Status&quot; section
602 of the RELEASE-NOTES for the latest snapshot. For a list of
603 fixed bugs, see that file.
604 </p>
605
606<!-- Yeah, I meant that "verbatim clip" thing literally... :-) -->
607
608<pre>
609New:
610</pre>
611
612
613<hr />
614 <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
615 <p>This is by no means meant to be complete nor exhaustive, but
616 mentions some problems that users may encounter when building
617 or using libstdc++. If you are experiencing one of these
618 problems, you can find more information on the libstdc++ and
619 the GCC mailing lists.
620 </p>
621 <p>Before reporting a bug, examine the
622 <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
623 category set to &quot;libstdc++&quot;. The BUGS file in the source
624 tree also tracks known serious problems.
625 </p>
626 <ul>
627 <li>Debugging is problematic, due to bugs in line-number generation
628 (mostly fixed in the compiler) and gdb lagging behind the
629 compiler (lack of personnel). We recommend configuring the
630 compiler using <code>--with-dwarf2</code> if the DWARF2
631 debugging format is not already the default on your platform.
632 Also,
633<a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
634 GDB settings</a> can have a profound effect on your C++ debugging
635 experiences. :-)</li>
636 </ul>
637
638<hr />
639 <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
640 <p>Yes, unfortunately, there are some. In a
641 <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
642 to the list</a>, Nathan Myers announced that he has started a list of
643 problems in the ISO C++ Standard itself, especially with
644 regard to the chapters that concern the library. The list
645 itself is
646 <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
647 website</a>. Developers who are having problems interpreting
648 the Standard may wish to consult his notes.
649 </p>
650 <p>For those people who are not part of the ISO Library Group
651 (i.e., nearly all of us needing to read this page in the first
652 place :-), a public list of the library defects is occasionally
653 published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
654 Some of these have resulted in <a href="#5_2">code changes</a>.
655 </p>
656
657<hr />
658 <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
659 <p>There are things which are not bugs in the compiler (4.2) nor
660 the language specification (4.3), but aren't really bugs in
661 libstdc++, either. Really! Please do not report these as bugs.
662 </p>
663 <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
664 The biggest of these is the quadzillions of warnings about the
665 library headers emitted when <code>-Weffc++</code> is used. Making
666 libstdc++ &quot;-Weffc++-clean&quot; is not a goal of the project,
667 for a few reasons. Mainly, that option tries to enforce
668 object-oriented programming, while the Standard Library isn't
669 necessarily trying to be OO.
670 </p>
671 <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
672 </a> Did I just say that -Weffc++ was our biggest false-bug report?
673 I lied. (It used to be.) Today it seems to be reports that after
674 executing a sequence like
675 </p>
676 <pre>
677 #include &lt;fstream&gt;
678 ...
679 std::fstream fs(&quot;a_file&quot;);
680 // .
681 // . do things with fs...
682 // .
683 fs.close();
684 fs.open(&quot;a_new_file&quot;);</pre>
685 <p>all operations on the re-opened <code>fs</code> will fail, or at
686 least act very strangely. Yes, they often will, especially if
687 <code>fs</code> reached the EOF state on the previous file. The
688 reason is that the state flags are <strong>not</strong> cleared
689 on a successful call to open(). The standard unfortunately did
690 not specify behavior in this case, and to everybody's great sorrow,
691 the <a href="../ext/howto.html#5">proposed LWG resolution in
692 DR #22</a> is to leave the flags unchanged. You must insert a call
693 to <code>fs.clear()</code> between the calls to close() and open(),
694 and then everything will work like we all expect it to work.
695 </p>
696 <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
697 Another is the <code>rel_ops</code> namespace and the template
698 comparison operator functions contained therein. If they become
699 visible in the same namespace as other comparison functions
700 (e.g., '<code>using</code>' them and the &lt;iterator&gt; header),
701 then you will suddenly be faced with huge numbers of ambiguity
702 errors. This was discussed on the -v3 list; Nathan Myers
703 <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
704 things up here</a>. The collisions with vector/string iterator
705 types have been fixed for 3.1. <!-- more links to email here -->
706 </p>
707 <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
708 <p>If you have found an extremely broken header file which is
709 causing problems for you, look carefully before submitting a
710 &quot;high&quot; priority bug report (which you probably shouldn't
711 do anyhow; see the last paragraph of the page describing
712 <a href="http://gcc.gnu.org/gnatswrite.html">the GCC bug database</a>).
713 </p>
714 <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
715 the installed library's name looks like <code>libstdc++-2.10.a</code>
716 or <code>libstdc++-libc6-2.10.so</code>, then you are using the old
717 libstdc++-v2 library, which is nonstandard and unmaintained. Do not
718 report problems with -v2 to the -v3 mailing list.
719 </p>
720 <p>For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are
721 installed in <code>${prefix}/include/g++-v3</code> (see the 'v'?).
722 Starting with version 3.2 the headers are installed in
723 <code>${prefix}/include/c++/${version}</code> as this prevents
724 headers from previous versions being found by mistake.
725 </p>
726 <p><a name="4_4_glibc"><strong>glibc</strong></a>
727 If you're on a GNU/Linux system and have just upgraded to
728 glibc 2.2, but are still using gcc 2.95.2, then you should have
729 read the glibc FAQ, specifically 2.34:
730 </p>
731 <pre>
7322.34. When compiling C++ programs, I get a compilation error in streambuf.h.
733
734{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
735apply a patch to the include files in /usr/include/g++, because the fpos_t
736type has changed in glibc 2.2. The patch is at
737http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
738 </pre>
739 <p>Note that 2.95.x shipped with the
740 <a href="#4_4_interface">old v2 library</a> which is no longer
741 maintained. Also note that gcc 2.95.3 fixes this problem, but
742 requires a separate patch for libstdc++-v3.
743 </p>
744 <p><a name="4_4_checks"><strong>concept checks</strong></a>
745 If you see compilation errors containing messages about
746 <code> <em>foo</em>Concept </code>and a<code> constraints </code>
747 member function, then most likely you have violated one of the
748 requirements for types used during instantiation of template
749 containers and functions. For example, EqualityComparableConcept
750 appears if your types must be comparable with == and you have not
751 provided this capability (a typo, or wrong visibility, or you
752 just plain forgot, etc).
753 </p>
754 <p>More information, including how to optionally enable/disable the
755 checks, is available
756 <a href="../19_diagnostics/howto.html#3">here</a>.
757 </p>
758 <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
759 If you are using the C++ library across dynamically-loaded
760 objects, make certain that you are passing the correct options
761 when compiling and linking:
762 </p>
763 <pre>
764 // compile your library components
765 g++ -fPIC -c a.cc
766 g++ -fPIC -c b.cc
767 ...
768 g++ -fPIC -c z.cc
769
770 // create your library
771 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
772
773 // link the executable
774 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
775 <p><a name="4_4_leak"><strong>"memory leaks" in containers</strong></a>
776 A few people have reported that the standard containers appear
777 to leak memory when tested with memory checkers such as
778 <a href="http://developer.kde.org/~sewardj/">valgrind</a>.
779 The library's default allocators keep free memory in a pool
780 for later reuse, rather than returning it to the OS. Although
781 this memory is always reachable by the library and is never
782 lost, memory debugging tools can report it as a leak. If you
783 want to test the library for memory leaks please read
784 <a href="../debug.html#mem">Tips for memory leak hunting</a>
785 first.
786 </p>
787
788<hr />
789 <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
790 <p>If you have found a bug in the library and you think you have
791 a working fix, then send it in! The main GCC site has a page
792 on <a href="http://gcc.gnu.org/contribute.html">submitting
793 patches</a> that covers the procedure, but for libstdc++ you
794 should also send the patch to our mailing list in addition to
795 the GCC patches mailing list. The libstdc++
796 <a href="../17_intro/contribute.html">contributors' page</a>
797 also talks about how to submit patches.
798 </p>
799 <p>In addition to the description, the patch, and the ChangeLog
800 entry, it is a Good Thing if you can additionally create a small
801 test program to test for the presence of the bug that your
802 patch fixes. Bugs have a way of being reintroduced; if an old
803 bug creeps back in, it will be caught immediately by the
804 <a href="#2_4">testsuite</a> -- but only if such a test exists.
805 </p>
806
807<hr />
808<h1><a name="5_0">5.0 Miscellaneous</a></h1>
809 <h2><a name="5_1">5.1 string::iterator is not char*;
810 vector&lt;T&gt;::iterator is not T*</a></h2>
811 <p>If you have code that depends on container&lt;T&gt; iterators
812 being implemented as pointer-to-T, your code is broken.
813 </p>
814 <p>While there are arguments for iterators to be implemented in
815 that manner, A) they aren't very good ones in the long term,
816 and B) they were never guaranteed by the Standard anyway. The
817 type-safety achieved by making iterators a real class rather
818 than a typedef for <code>T*</code> outweighs nearly all opposing
819 arguments.
820 </p>
821 <p>Code which does assume that a vector iterator <code> i </code>
822 is a pointer can often be fixed by changing <code> i </code> in
823 certain expressions to <code> &amp;*i </code>. Future revisions
824 of the Standard are expected to bless this usage for
825 vector&lt;&gt; (but not for basic_string&lt;&gt;).
826 </p>
827
828<hr />
829 <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
830 <p>Hopefully, not much. The goal of libstdc++-v3 is to produce
831 a fully-compliant, fully-portable Standard Library. After that,
832 we're mostly done: there won't <em>be</em> any more compliance
833 work to do. However:
834 </p>
835 <ol>
836 <li><p>The ISO Committee will meet periodically to review Defect Reports
837 in the C++ Standard. Undoubtedly some of these will result in
838 changes to the Standard, which will be reflected in patches to
839 libstdc++. Some of that is already happening, see 4.2. Some of
840 those changes are being predicted by the library maintainers, and
841 we add code to the library based on what the current proposed
842 resolution specifies. Those additions are listed in
843 <a href="../ext/howto.html#5">the extensions page</a>.
844 </p></li>
845 <li><p>Performance tuning. Lots of performance tuning. This too is
846 already underway for post-3.0 releases, starting with memory
847 expansion in container classes and buffer usage in synchronized
848 stream objects.
849 </p></li>
850 <li><p>An ABI for libstdc++ is being developed, so that
851 multiple binary-incompatible copies of the library can be replaced
852 with a single backwards-compatible library, like libgcc_s.so is.
853 </p></li>
854 <li><p>The current libstdc++ contains extensions to the Library which
855 must be explicitly requested by client code (for example, the
856 hash tables from SGI). Other extensions may be added to
857 libstdc++-v3 if they seem to be &quot;standard&quot; enough.
858 (For example, the &quot;long long&quot; type from C99.)
859 Bugfixes and rewrites (to improve or fix thread safety, for
860 instance) will of course be a continuing task.
861 </p></li>
862 </ol>
863 <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
864 question</a> about the next libstdc++ prompted some brief but
865 interesting
866 <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
867 </p>
868
869<hr />
870 <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
871 <p>The <a href="http://www.sgi.com/Technology/STL/">STL from SGI</a>,
872 version 3.3, was the most recent merge of the STL codebase. The
873 code in libstdc++ contains many fixes and changes, and it is
874 very likely that the SGI code is no longer under active
875 development. We expect that no future merges will take place.
876 </p>
877 <p>In particular, <code>string</code> is not from SGI and makes no
878 use of their &quot;rope&quot; class (which is included as an
879 optional extension), nor is <code>valarray</code> and some others.
880 Classes like <code>vector&lt;&gt;</code> are, however we have
881 made significant changes to them since then.
882 </p>
883 <p>The FAQ for SGI's STL (one jump off of their main page) is
884 recommended reading.
885 </p>
886
887<hr />
888 <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
889 <p>Headers in the <code>ext</code> and <code>backward</code>
890 subdirectories should be referred to by their relative paths:
891 <!-- Careful, the leading spaces in PRE show up directly. -->
892 </p>
893 <pre>
894 #include &lt;ext/hash_map&gt; </pre>
895 <p>rather than using <code>-I</code> or other options. This is more
896 portable and forward-compatible. (The situation is the same as
897 that of other headers whose directories are not searched directly,
898 e.g., <code>&lt;sys/stat.h&gt;</code>, <code>&lt;X11/Xlib.h&gt;</code>.
899 </p>
900
901 <p>The extensions are no longer in the global or <code>std</code>
902 namespaces, instead they are declared in the <code>__gnu_cxx</code>
903 namespace. For maximum portability, consider defining a namespace
904 alias to use to talk about extensions, e.g.:
905 </p>
906 <pre>
907 #ifdef __GNUC__
908 #if __GNUC__ &lt; 3
909 #include &lt;hash_map.h&gt;
910 namespace Sgi { using ::hash_map; }; // inherit globals
911 #else
912 #include &lt;ext/hash_map&gt;
913 #if __GNUC_MINOR__ == 0
914 namespace Sgi = std; // GCC 3.0
915 #else
916 namespace Sgi = ::__gnu_cxx; // GCC 3.1 and later
917 #endif
918 #endif
919 #else // ... there are other compilers, right?
920 namespace Sgi = std;
921 #endif
922
923 Sgi::hash_map&lt;int,int&gt; my_map; </pre>
924 <p>This is a bit cleaner than defining typedefs for all the
925 instantiations you might need.
926 </p>
927 <p>Extensions to the library have
928 <a href="../ext/howto.html">their own page</a>.
929 </p>
930
931<hr />
932 <h2><a name="5_5">5.5 [removed]</a></h2>
933 <p>This question has become moot and has been removed. The stub
934 is here to preserve numbering (and hence links/bookmarks).
935 </p>
936
937<hr />
938 <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
939 <p>libstdc++-v3 strives to be thread-safe when all of the following
940 conditions are met:
941 </p>
942 <ul>
943 <li>The system's libc is itself thread-safe,</li>
944 <li><code>gcc -v</code> reports a thread model other than 'single',</li>
945 <li>[pre-3.3 only] a non-generic implementation of atomicity.h
946 exists for the architecture in question.</li>
947 </ul>
948 <p>The user-code must guard against concurrent method calls which may
949 access any particular library object's state. Typically, the
950 application programmer may infer what object locks must be held
951 based on the objects referenced in a method call. Without getting
952 into great detail, here is an example which requires user-level
953 locks:
954 </p>
955 <pre>
956 library_class_a shared_object_a;
957
958 thread_main () {
959 library_class_b *object_b = new library_class_b;
960 shared_object_a.add_b (object_b); // must hold lock for shared_object_a
961 shared_object_a.mutate (); // must hold lock for shared_object_a
962 }
963
964 // Multiple copies of thread_main() are started in independent threads.</pre>
965 <p>Under the assumption that object_a and object_b are never exposed to
966 another thread, here is an example that should not require any
967 user-level locks:
968 </p>
969 <pre>
970 thread_main () {
971 library_class_a object_a;
972 library_class_b *object_b = new library_class_b;
973 object_a.add_b (object_b);
974 object_a.mutate ();
975 } </pre>
976 <p>All library objects are safe to use in a multithreaded program as
977 long as each thread carefully locks out access by any other
978 thread while it uses any object visible to another thread, i.e.,
979 treat library objects like any other shared resource. In general,
980 this requirement includes both read and write access to objects;
981 unless otherwise documented as safe, do not assume that two threads
982 may access a shared standard library object at the same time.
983 </p>
984 <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
985 introduction), <a href="../23_containers/howto.html#3">23</a>
986 (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
987 more information.
988 </p>
989
990<hr />
991 <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
992 <p>Copies of the full ISO 14882 standard are available on line via the
993 ISO mirror site for committee members. Non-members, or those who
994 have not paid for the privilege of sitting on the committee and
995 sustained their two-meeting commitment for voting rights, may get a
996 copy of the standard from their respective national standards
997 organization. In the USA, this national standards organization is
998 ANSI and their website is right <a href="http://www.ansi.org">here</a>.
999 (And if you've already registered with them, clicking this link will
1000 take you to directly to the place where you can
1001<a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998">buy
1002 the standard on-line</a>.
1003 </p>
1004 <p>Who is your country's member body? Visit the
1005 <a href="http://www.iso.ch/">ISO homepage</a> and find out!
1006 </p>
1007
1008<hr />
1009 <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
1010 <p>&quot;ABI&quot; stands for &quot;Application Binary Interface.&quot;
1011 Conventionally, it refers to a great mass of details about how
1012 arguments are arranged on the call stack and/or in registers, and
1013 how various types are arranged and padded in structs. A single CPU
1014 design may suffer multiple ABIs designed by different development
1015 tool vendors who made different choices, or even by the same vendor
1016 for different target applications or compiler versions. In ideal
1017 circumstances the CPU designer presents one ABI and all the OSes and
1018 compilers use it. In practice every ABI omits details that compiler
1019 implementers (consciously or accidentally) must choose for themselves.
1020 </p>
1021 <p>That ABI definition suffices for compilers to generate code so a
1022 program can interact safely with an OS and its lowest-level libraries.
1023 Users usually want an ABI to encompass more detail, allowing libraries
1024 built with different compilers (or different releases of the same
1025 compiler!) to be linked together. For C++, this includes many more
1026 details than for C, and CPU designers (for good reasons elaborated
1027 below) have not stepped up to publish C++ ABIs. The details include
1028 virtual function implementation, struct inheritance layout, name
1029 mangling, and exception handling. Such an ABI has been defined for
1030 GNU C++, and is immediately useful for embedded work relying only on
1031 a &quot;free-standing implementation&quot; that doesn't include (much
1032 of) the standard library. It is a good basis for the work to come.
1033 </p>
1034 <p>A useful C++ ABI must also incorporate many details of the standard
1035 library implementation. For a C ABI, the layouts of a few structs
1036 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
1037 For C++, the details include the complete set of names of functions
1038 and types used, the offsets of class members and virtual functions,
1039 and the actual definitions of all inlines. C++ exposes many more
1040 library details to the caller than C does. It makes defining
1041 a complete ABI a much bigger undertaking, and requires not just
1042 documenting library implementation details, but carefully designing
1043 those details so that future bug fixes and optimizations don't
1044 force breaking the ABI.
1045 </p>
1046 <p>There are ways to help isolate library implementation details from the
1047 ABI, but they trade off against speed. Library details used in
1048 inner loops (e.g., getchar) must be exposed and frozen for all
1049 time, but many others may reasonably be kept hidden from user code,
1050 so they may later be changed. Deciding which, and implementing
1051 the decisions, must happen before you can reasonably document a
1052 candidate C++ ABI that encompasses the standard library.
1053 </p>
1054
1055<!-- ####################################################### -->
1056
1057<hr />
1058<p class="fineprint"><em>
1059See <a href="../17_intro/license.html">license.html</a> for copying conditions.
1060Comments and suggestions are welcome, and may be sent to
1061<a href="mailto:[email protected]">the libstdc++ mailing list</a>.
1062</em></p>
1063
1064
1065</body>
1066</html>
1067
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