1 2 libstdc++ Frequently Asked Questions 3 4 The latest version of this document is always available at 5 [1]http://gcc.gnu.org/onlinedocs/libstdc++/faq/. The main 6 documentation page is at 7 [2]http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html. 8 9 To the [3]libstdc++-v3 homepage. 10 _________________________________________________________________ 11 12 Questions 13 14 1. [4]General Information 15 1. [5]What is libstdc++-v3? 16 2. [6]Why should I use libstdc++? 17 3. [7]Who's in charge of it? 18 4. [8]How do I get libstdc++? 19 5. [9]When is libstdc++ going to be finished? 20 6. [10]How do I contribute to the effort? 21 7. [11]What happened to libg++? I need that! 22 8. [12]What if I have more questions? 23 9. [13]What are the license terms for libstdc++-v3? 24 2. [14]Installation 25 1. [15]How do I install libstdc++-v3? 26 2. [16][removed] 27 3. [17]What is this CVS thing that you keep mentioning? 28 4. [18]How do I know if it works? 29 5. [19]This library is HUGE! And what's libsupc++? 30 3. [20]Platform-Specific Issues 31 1. [21]Can libstdc++-v3 be used with <my favorite compiler>? 32 2. [22][removed] 33 3. [23][removed] 34 4. [24]I can't use 'long long' on Solaris 35 5. [25]_XOPEN_SOURCE / _GNU_SOURCE / etc is always defined 36 6. [26]OS X ctype.h is broken! How can I hack it? 37 7. [27]Threading is broken on i386 38 8. [28]Recent GNU/Linux glibc required? 39 9. [29]Can't use wchar_t/wstring on FreeBSD 40 10. [30]MIPS atomic operations 41 4. [31]Known Bugs and Non-Bugs 42 1. [32]What works already? 43 2. [33]Bugs in gcc/g++ (not libstdc++-v3) 44 3. [34]Bugs in the C++ language/lib specification 45 4. [35]Things in libstdc++ that only look like bugs 46 o [36]reopening a stream fails 47 o [37]-Weffc++ complains too much 48 o [38]"ambiguous overloads" after including an old-style 49 header 50 o [39]The g++-3 headers are not ours 51 o [40]compilation errors from streambuf.h 52 o [41]errors about *Concept and constraints in the STL... 53 o [42]program crashes when using library code in a 54 dynamically-loaded library 55 o [43]"memory leaks" in containers 56 5. [44]Aw, that's easy to fix! 57 5. [45]Miscellaneous 58 1. [46]string::iterator is not char*; vector<T>::iterator is not 59 T* 60 2. [47]What's next after libstdc++-v3? 61 3. [48]What about the STL from SGI? 62 4. [49]Extensions and Backward Compatibility 63 5. [50][removed] 64 6. [51]Is libstdc++-v3 thread-safe? 65 7. [52]How do I get a copy of the ISO C++ Standard? 66 8. [53]What's an ABI and why is it so messy? 67 _________________________________________________________________ 68 69 1.0 General Information 70 711.1 What is libstdc++-v3? 72 73 The GNU Standard C++ Library v3 is an ongoing project to implement the 74 ISO 14882 Standard C++ library as described in chapters 17 through 27 75 and annex D. As the library reaches stable plateaus, it is captured in 76 a snapshot and released. The latest release is [54]the fourteenth 77 snapshot but newer versions have been included in recent GCC releases. 78 For those who want to see exactly how far the project has come, or 79 just want the latest bleeding-edge code, the up-to-date source is 80 available over anonymous CVS, and can even be browsed over the Web 81 (see [55]1.4 below). 82 83 The older libstdc++-v2 project is no longer maintained; the code has 84 been completely replaced and rewritten. [56]If you are using V2, then 85 you need to report bugs to your system vendor, not to the V3 list. 86 87 A more formal description of the V3 goals can be found in the official 88 [57]design document. 89 _________________________________________________________________ 90 911.2 Why should I use libstdc++? 92 93 The completion of the ISO C++ standardization gave the C++ community a 94 powerful set of reuseable tools in the form of the C++ Standard 95 Library. However, all existing C++ implementations are (as the Draft 96 Standard used to say) "incomplet and incorrekt," and many suffer from 97 limitations of the compilers that use them. 98 99 The GNU C/C++/FORTRAN/<pick-a-language> compiler (gcc, g++, etc) is 100 widely considered to be one of the leading compilers in the world. Its 101 development has recently been taken over by the [58]GCC team. All of 102 the rapid development and near-legendary [59]portability that are the 103 hallmarks of an open-source project are being applied to libstdc++. 104 105 That means that all of the Standard classes and functions (such as 106 string, vector<>, iostreams, and algorithms) will be freely available 107 and fully compliant. Programmers will no longer need to "roll their 108 own" nor be worried about platform-specific incompatibilities. 109 _________________________________________________________________ 110 1111.3 Who's in charge of it? 112 113 The libstdc++ project is contributed to by several developers all over 114 the world, in the same way as GCC or Linux. Benjamin Kosnik, Gabriel 115 Dos Reis, Phil Edwards, Ulrich Drepper, Loren James Rittle, and Paolo 116 Carlini are the lead maintainers of the CVS archive. 117 118 Development and discussion is held on the libstdc++ mailing list. 119 Subscribing to the list, or searching the list archives, is open to 120 everyone. You can read instructions for doing so on the [60]homepage. 121 If you have questions, ideas, code, or are just curious, sign up! 122 _________________________________________________________________ 123 1241.4 How do I get libstdc++? 125 126 The [61]homepage has instructions for retrieving the latest CVS 127 sources, and for browsing the CVS sources over the web. 128 129 Stable versions of libstdc++-v3 are included with releases of [62]the 130 GCC compilers. 131 132 The subset commonly known as the Standard Template Library (chapters 133 23 through 25, mostly) is adapted from the final release of the SGI 134 STL. 135 _________________________________________________________________ 136 1371.5 When is libstdc++ going to be finished? 138 139 Nathan Myers gave the best of all possible answers, responding to a 140 Usenet article asking this question: Sooner, if you help. 141 _________________________________________________________________ 142 1431.6 How do I contribute to the effort? 144 145 Here is [63]a page devoted to this topic. Subscribing to the mailing 146 list (see above, or the homepage) is a very good idea if you have 147 something to contribute, or if you have spare time and want to help. 148 Contributions don't have to be in the form of source code; anybody who 149 is willing to help write documentation, for example, or has found a 150 bug in code that we all thought was working, is more than welcome! 151 _________________________________________________________________ 152 1531.7 What happened to libg++? I need that! 154 155 The most recent libg++ README states that libg++ is no longer being 156 actively maintained. It should not be used for new projects, and is 157 only being kicked along to support older code. 158 159 The libg++ was designed and created when there was no Standard to 160 provide guidance. Classes like linked lists are now provided for by 161 list<T> and do not need to be created by genclass. (For that matter, 162 templates exist now and are well-supported, whereas genclass (mostly) 163 predates them.) 164 165 There are other classes in libg++ that are not specified in the ISO 166 Standard (e.g., statistical analysis). While there are a lot of really 167 useful things that are used by a lot of people (e.g., statistics :-), 168 the Standards Committee couldn't include everything, and so a lot of 169 those "obvious" classes didn't get included. 170 171 Since libstdc++ is an implementation of the Standard Library, we have 172 no plans at this time to include non-Standard utilities in the 173 implementation, however handy they are. (The extensions provided in 174 the SGI STL aren't maintained by us and don't get a lot of our 175 attention, because they don't require a lot of our time.) It is 176 entirely plausable that the "useful stuff" from libg++ might be 177 extracted into an updated utilities library, but nobody has started 178 such a project yet. 179 180 (The [64]Boost site houses free C++ libraries that do varying things, 181 and happened to be started by members of the Standards Committee. 182 Certain "useful stuff" classes will probably migrate there.) 183 184 For the bold and/or desperate, the [65]GCC extensions page describes 185 where to find the last libg++ source. 186 _________________________________________________________________ 187 1881.8 What if I have more questions? 189 190 If you have read the README and RELEASE-NOTES files, and your question 191 remains unanswered, then just ask the mailing list. At present, you do 192 not need to be subscribed to the list to send a message to it. More 193 information is available on the homepage (including how to browse the 194 list archives); to send to the list, use [66]libstdc++@gcc.gnu.org. 195 196 If you have a question that you think should be included here, or if 197 you have a question about a question/answer here, contact [67]Phil 198 Edwards or [68]Gabriel Dos Reis. 199 _________________________________________________________________ 200 2011.9 What are the license terms for libstdc++-v3? 202 203 See [69]our license description for these and related questions. 204 _________________________________________________________________ 205 206 2.0 Installation 207 2082.1 How do I install libstdc++-v3? 209 210 Complete instructions are not given here (this is a FAQ, not an 211 installation document), but the tools required are few: 212 * A 3.x release of GCC. Note that building GCC is much easier and 213 more automated than building the GCC 2.[78] series was. If you are 214 using GCC 2.95, you can still build earlier snapshots of 215 libstdc++. 216 * GNU Make is recommended, but should not be required. 217 * The GNU Autotools are needed if you are messing with the configury 218 or makefiles. 219 220 The file [70]documentation.html provides a good overview of the steps 221 necessary to build, install, and use the library. Instructions for 222 configuring the library with new flags such as --enable-threads are 223 there also, as well as patches and instructions for working with GCC 224 2.95. 225 226 The top-level install.html and [71]RELEASE-NOTES files contain the 227 exact build and installation instructions. You may wish to browse 228 those files over CVSweb ahead of time to get a feel for what's 229 required. RELEASE-NOTES is located in the ".../docs/17_intro/" 230 directory of the distribution. 231 _________________________________________________________________ 232 2332.2 [removed] 234 235 This question has become moot and has been removed. The stub is here 236 to preserve numbering (and hence links/bookmarks). 237 _________________________________________________________________ 238 2392.3 What is this CVS thing that you keep mentioning? 240 241 The Concurrent Versions System is one of several revision control 242 packages. It was selected for GNU projects because it's free (speech), 243 free (beer), and very high quality. The [72]CVS entry in the GNU 244 software catalogue has a better description as well as a [73]link to 245 the makers of CVS. 246 247 The "anonymous client checkout" feature of CVS is similar to anonymous 248 FTP in that it allows anyone to retrieve the latest libstdc++ sources. 249 250 After the first of April, American users will have a "/pharmacy" 251 command-line option... 252 _________________________________________________________________ 253 2542.4 How do I know if it works? 255 256 libstdc++-v3 comes with its own testsuite. You do not need to actually 257 install the library ("make install") to run the testsuite, but you do 258 need DejaGNU, as described [74]here. 259 260 To run the testsuite on the library after building it, use "make 261 check" while in your build directory. To run the testsuite on the 262 library after building and installing it, use "make check-install" 263 instead. 264 265 If you find bugs in the testsuite programs themselves, or if you think 266 of a new test program that should be added to the suite, please write 267 up your idea and send it to the list! 268 _________________________________________________________________ 269 2702.5 This library is HUGE! And what's libsupc++? 271 272 Usually the size of libraries on disk isn't noticeable. When a link 273 editor (or simply "linker") pulls things from a static archive 274 library, only the necessary object files are copied into your 275 executable, not the entire library. Unfortunately, even if you only 276 need a single function or variable from an object file, the entire 277 object file is extracted. (There's nothing unique to C++ or 278 libstdc++-v3 about this; it's just common behavior, given here for 279 background reasons.) 280 281 Some of the object files which make up libstdc++.a are rather large. 282 If you create a statically-linked executable with -static, those large 283 object files are suddenly part of your executable. Historically the 284 best way around this was to only place a very few functions (often 285 only a single one) in each source/object file; then extracting a 286 single function is the same as extracting a single .o file. For 287 libstdc++-v3 this is only possible to a certain extent; the object 288 files in question contain template classes and template functions, 289 pre-instantiated, and splitting those up causes severe maintenance 290 headaches. 291 292 It's not a bug, and it's not really a problem. Nevertheless, some 293 people don't like it, so here are two pseudo-solutions: 294 295 If the only functions from libstdc++.a which you need are language 296 support functions (those listed in [75]clause 18 of the standard, 297 e.g., new and delete), then try linking against libsupc++.a (usually 298 specifying -lsupc++ when calling g++ for the final link step will do 299 it). This library contains only those support routines, one per object 300 file. But if you are using anything from the rest of the library, such 301 as IOStreams or vectors, then you'll still need pieces from 302 libstdc++.a. 303 304 The second method is one we hope to incorporate into the library build 305 process. Some platforms can place each function and variable into its 306 own section in a .o file. The GNU linker can then perform garbage 307 collection on unused sections; this reduces the situation to only 308 copying needed functions into the executable, as before, but all 309 happens automatically. 310 311 Unfortunately the garbage collection in GNU ld is buggy; sections 312 (corresponding to functions and variables) which are used are 313 mistakenly removed, leading to horrible crashes when your executable 314 starts up. For the time being, this feature is not used when building 315 the library. 316 _________________________________________________________________ 317 318 3.0 Platform-Specific Issues 319 3203.1 Can libstdc++-v3 be used with <my favorite compiler>? 321 322 Probably not. Yet. 323 324 Because GCC advances so rapidly, development and testing of libstdc++ 325 is being done almost entirely under that compiler. If you are curious 326 about whether other, lesser compilers (*grin*) support libstdc++, you 327 are more than welcome to try. Configuring and building the library 328 (see above) will still require certain tools, however. Also keep in 329 mind that building libstdc++ does not imply that your compiler will be 330 able to use all of the features found in the C++ Standard Library. 331 332 Since the goal of ISO Standardization is for all C++ implementations 333 to be able to share code, the final libstdc++ should, in theory, be 334 usable under any ISO-compliant compiler. It will still be targeted and 335 optimized for GCC/g++, however. 336 _________________________________________________________________ 337 3383.2 [removed] 339 340 This question has become moot and has been removed. The stub is here 341 to preserve numbering (and hence links/bookmarks). 342 _________________________________________________________________ 343 3443.3 [removed] 345 346 This question has become moot and has been removed. The stub is here 347 to preserve numbering (and hence links/bookmarks). 348 _________________________________________________________________ 349 3503.4 I can't use 'long long' on Solaris 351 352 By default we try to support the C99 long long type. This requires 353 that certain functions from your C library be present. 354 355 Up through release 3.0.2 the tests performed were too general, and 356 this feature was disabled when it did not need to be. The most 357 commonly reported platform affected was Solaris. 358 359 This has been fixed for 3.0.3 and onwards. 360 _________________________________________________________________ 361 3623.5 _XOPEN_SOURCE / _GNU_SOURCE / etc is always defined 363 364 On Solaris, g++ (but not gcc) always defines the preprocessor macro 365 _XOPEN_SOURCE. On GNU/Linux, the same happens with _GNU_SOURCE. (This 366 is not an exhaustive list; other macros and other platforms are also 367 affected.) 368 369 These macros are typically used in C library headers, guarding new 370 versions of functions from their older versions. The C++ standard 371 library includes the C standard library, but it requires the C90 372 version, which for backwards-compatability reasons is often not the 373 default for many vendors. 374 375 More to the point, the C++ standard requires behavior which is only 376 available on certain platforms after certain symbols are defined. 377 Usually the issue involves I/O-related typedefs. In order to ensure 378 correctness, the compiler simply predefines those symbols. 379 380 Note that it's not enough to #define them only when the library is 381 being built (during installation). Since we don't have an 'export' 382 keyword, much of the library exists as headers, which means that the 383 symbols must also be defined as your programs are parsed and compiled. 384 385 To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in the 386 gcc config headers for your target (and try changing them to see what 387 happens when building complicated code). You can also run "g++ -E -dM 388 - < /dev/null" to display a list of predefined macros for any 389 particular installation. 390 391 This has been discussed on the mailing lists [76]quite a bit. 392 393 This method is something of a wart. We'd like to find a cleaner 394 solution, but nobody yet has contributed the time. 395 _________________________________________________________________ 396 3973.6 OS X ctype.h is broken! How can I hack it? 398 399 This is a long-standing bug in the OS X support. Fortunately, the 400 patch is quite simple, and well-known. [77]Here's a link to the 401 solution. 402 _________________________________________________________________ 403 4043.7 Threading is broken on i386 405 406 Support for atomic integer operations is/was broken on i386 platforms. 407 The assembly code accidentally used opcodes that are only available on 408 the i486 and later. So if you configured GCC to target, for example, 409 i386-linux, but actually used the programs on an i686, then you would 410 encounter no problems. Only when actually running the code on a i386 411 will the problem appear. 412 413 This is fixed in 3.2.2. 414 _________________________________________________________________ 415 4163.8 Recent GNU/Linux glibc required? 417 418 When running on GNU/Linux, libstdc++ 3.2.1 (shared library version 419 5.0.1) and later uses localization and formatting code from the system 420 C library (glibc) version 2.2.5. That version of glibc is over a year 421 old and contains necessary bugfixes. Many GNU/Linux distros make glibc 422 version 2.3.x available now. 423 424 The guideline is simple: the more recent the C++ library, the more 425 recent the C library. (This is also documented in the main GCC 426 installation instructions.) 427 _________________________________________________________________ 428 4293.9 Can't use wchar_t/wstring on FreeBSD 430 431 At the moment there are a few problems in FreeBSD's support for wide 432 character functions, and as a result the libstdc++ configury decides 433 that wchar_t support should be disabled. Once the underlying problems 434 are fixed in FreeBSD (soon), the library support will automatically 435 enable itself. 436 437 You can fix the problems yourself, and learn more about the situation, 438 by reading [78]this short thread ("_GLIBCPP_USE_WCHAR_T undefined in 439 FreeBSD's c++config.h?"). 440 _________________________________________________________________ 441 4423.10 MIPS atomic operations 443 444 The atomic locking routines for MIPS targets requires MIPS II and 445 later. A patch went in just after the 3.3 release to make mips* use 446 the generic implementation instead. You can also configure for 447 mipsel-elf as a workaround. 448 449 mips*-*-linux* continues to use the MIPS II routines, and more work in 450 this area is expected. 451 _________________________________________________________________ 452 453 4.0 Known Bugs and Non-Bugs 454 455 Note that this section can get rapdily outdated -- such is the nature 456 of an open-source project. For the latest information, join the 457 mailing list or look through recent archives. The RELEASE- NOTES and 458 BUGS files are generally kept up-to-date. 459 460 For 3.0.1, the most common "bug" is an apparently missing "../" in 461 include/Makefile, resulting in files like gthr.h and gthr-single.h not 462 being found. Please read [79]the configuration instructions for GCC, 463 specifically the part about configuring in a separate build directory, 464 and how strongly recommended it is. Building in the source directory 465 is fragile, is rarely tested, and tends to break, as in this case. 466 This was fixed for 3.0.2. 467 468 For 3.1, the most common "bug" is a parse error when using <fstream>, 469 ending with a message, "bits/basic_file.h:52: parse error before `{' 470 token." Please read [80]the installation instructions for GCC, 471 specifically the part about not installing newer versions on top of 472 older versions. If you install 3.1 over a 3.0.x release, then the 473 wrong basic_file.h header will be found (its location changed between 474 releases). 475 476 Please do not report these as bugs. We know about them. Reporting this 477 -- or any other problem that's already been fixed -- hinders the 478 development of GCC, because we have to take time to respond to your 479 report. Thank you. 480 4814.1 What works already? 482 483 Short answer: Pretty much everything works except for some corner 484 cases. Also, localization is incomplete. For whether it works well, or 485 as you expect it to work, see 5.2. 486 487 Long answer: See the docs/html/17_intro/CHECKLIST file, which is badly 488 outdated... 489 490 What follows is a verbatim clip from the "Status" section of the 491 RELEASE-NOTES for the latest snapshot. For a list of fixed bugs, see 492 that file. 493New: 494 _________________________________________________________________ 495 4964.2 Bugs in gcc/g++ (not libstdc++-v3) 497 498 This is by no means meant to be complete nor exhaustive, but mentions 499 some problems that users may encounter when building or using 500 libstdc++. If you are experiencing one of these problems, you can find 501 more information on the libstdc++ and the GCC mailing lists. 502 503 Before reporting a bug, examine the [81]bugs database with the 504 category set to "libstdc++". The BUGS file in the source tree also 505 tracks known serious problems. 506 * Debugging is problematic, due to bugs in line-number generation 507 (mostly fixed in the compiler) and gdb lagging behind the compiler 508 (lack of personnel). We recommend configuring the compiler using 509 --with-dwarf2 if the DWARF2 debugging format is not already the 510 default on your platform. Also, [82]changing your GDB settings can 511 have a profound effect on your C++ debugging experiences. :-) 512 _________________________________________________________________ 513 5144.3 Bugs in the C++ language/lib specification 515 516 Yes, unfortunately, there are some. In a [83]message to the list, 517 Nathan Myers announced that he has started a list of problems in the 518 ISO C++ Standard itself, especially with regard to the chapters that 519 concern the library. The list itself is [84]posted on his website. 520 Developers who are having problems interpreting the Standard may wish 521 to consult his notes. 522 523 For those people who are not part of the ISO Library Group (i.e., 524 nearly all of us needing to read this page in the first place :-), a 525 public list of the library defects is occasionally published [85]here. 526 Some of these have resulted in [86]code changes. 527 _________________________________________________________________ 528 5294.4 Things in libstdc++ that only look like bugs 530 531 There are things which are not bugs in the compiler (4.2) nor the 532 language specification (4.3), but aren't really bugs in libstdc++, 533 either. Really! Please do not report these as bugs. 534 535 -Weffc++ The biggest of these is the quadzillions of warnings about 536 the library headers emitted when -Weffc++ is used. Making libstdc++ 537 "-Weffc++-clean" is not a goal of the project, for a few reasons. 538 Mainly, that option tries to enforce object-oriented programming, 539 while the Standard Library isn't necessarily trying to be OO. 540 541 reopening a stream fails Did I just say that -Weffc++ was our biggest 542 false-bug report? I lied. (It used to be.) Today it seems to be 543 reports that after executing a sequence like 544 #include <fstream> 545 ... 546 std::fstream fs("a_file"); 547 // . 548 // . do things with fs... 549 // . 550 fs.close(); 551 fs.open("a_new_file"); 552 553 all operations on the re-opened fs will fail, or at least act very 554 strangely. Yes, they often will, especially if fs reached the EOF 555 state on the previous file. The reason is that the state flags are not 556 cleared on a successful call to open(). The standard unfortunately did 557 not specify behavior in this case, and to everybody's great sorrow, 558 the [87]proposed LWG resolution in DR #22 is to leave the flags 559 unchanged. You must insert a call to fs.clear() between the calls to 560 close() and open(), and then everything will work like we all expect 561 it to work. 562 563 rel_ops Another is the rel_ops namespace and the template comparison 564 operator functions contained therein. If they become visible in the 565 same namespace as other comparison functions (e.g., 'using' them and 566 the <iterator> header), then you will suddenly be faced with huge 567 numbers of ambiguity errors. This was discussed on the -v3 list; 568 Nathan Myers [88]sums things up here. The collisions with 569 vector/string iterator types have been fixed for 3.1. 570 571 The g++-3 headers are not ours 572 573 If you have found an extremely broken header file which is causing 574 problems for you, look carefully before submitting a "high" priority 575 bug report (which you probably shouldn't do anyhow; see the last 576 paragraph of the page describing [89]the GCC bug database). 577 578 If the headers are in ${prefix}/include/g++-3, or if the installed 579 library's name looks like libstdc++-2.10.a or libstdc++-libc6-2.10.so, 580 then you are using the old libstdc++-v2 library, which is nonstandard 581 and unmaintained. Do not report problems with -v2 to the -v3 mailing 582 list. 583 584 For GCC versions 3.0 and 3.1 the libstdc++-v3 header files are 585 installed in ${prefix}/include/g++-v3 (see the 'v'?). Starting with 586 version 3.2 the headers are installed in 587 ${prefix}/include/c++/${version} as this prevents headers from 588 previous versions being found by mistake. 589 590 glibc If you're on a GNU/Linux system and have just upgraded to glibc 591 2.2, but are still using gcc 2.95.2, then you should have read the 592 glibc FAQ, specifically 2.34: 5932.34. When compiling C++ programs, I get a compilation error in streambuf.h. 594 595{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to 596apply a patch to the include files in /usr/include/g++, because the fpos_t 597type has changed in glibc 2.2. The patch is at 598http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff 599 600 601 Note that 2.95.x shipped with the [90]old v2 library which is no 602 longer maintained. Also note that gcc 2.95.3 fixes this problem, but 603 requires a separate patch for libstdc++-v3. 604 605 concept checks If you see compilation errors containing messages about 606 fooConcept and a constraints member function, then most likely you 607 have violated one of the requirements for types used during 608 instantiation of template containers and functions. For example, 609 EqualityComparableConcept appears if your types must be comparable 610 with == and you have not provided this capability (a typo, or wrong 611 visibility, or you just plain forgot, etc). 612 613 More information, including how to optionally enable/disable the 614 checks, is available [91]here. 615 616 dlopen/dlsym If you are using the C++ library across 617 dynamically-loaded objects, make certain that you are passing the 618 correct options when compiling and linking: 619 // compile your library components 620 g++ -fPIC -c a.cc 621 g++ -fPIC -c b.cc 622 ... 623 g++ -fPIC -c z.cc 624 625 // create your library 626 g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o 627 628 // link the executable 629 g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl 630 631 "memory leaks" in containers A few people have reported that the 632 standard containers appear to leak memory when tested with memory 633 checkers such as [92]valgrind. The library's default allocators keep 634 free memory in a pool for later reuse, rather than returning it to the 635 OS. Although this memory is always reachable by the library and is 636 never lost, memory debugging tools can report it as a leak. If you 637 want to test the library for memory leaks please read [93]Tips for 638 memory leak hunting first. 639 _________________________________________________________________ 640 6414.5 Aw, that's easy to fix! 642 643 If you have found a bug in the library and you think you have a 644 working fix, then send it in! The main GCC site has a page on 645 [94]submitting patches that covers the procedure, but for libstdc++ 646 you should also send the patch to our mailing list in addition to the 647 GCC patches mailing list. The libstdc++ [95]contributors' page also 648 talks about how to submit patches. 649 650 In addition to the description, the patch, and the ChangeLog entry, it 651 is a Good Thing if you can additionally create a small test program to 652 test for the presence of the bug that your patch fixes. Bugs have a 653 way of being reintroduced; if an old bug creeps back in, it will be 654 caught immediately by the [96]testsuite -- but only if such a test 655 exists. 656 _________________________________________________________________ 657 658 5.0 Miscellaneous 659 6605.1 string::iterator is not char*; vector<T>::iterator is not T* 661 662 If you have code that depends on container<T> iterators being 663 implemented as pointer-to-T, your code is broken. 664 665 While there are arguments for iterators to be implemented in that 666 manner, A) they aren't very good ones in the long term, and B) they 667 were never guaranteed by the Standard anyway. The type-safety achieved 668 by making iterators a real class rather than a typedef for T* 669 outweighs nearly all opposing arguments. 670 671 Code which does assume that a vector iterator i is a pointer can often 672 be fixed by changing i in certain expressions to &*i . Future 673 revisions of the Standard are expected to bless this usage for 674 vector<> (but not for basic_string<>). 675 _________________________________________________________________ 676 6775.2 What's next after libstdc++-v3? 678 679 Hopefully, not much. The goal of libstdc++-v3 is to produce a 680 fully-compliant, fully-portable Standard Library. After that, we're 681 mostly done: there won't be any more compliance work to do. However: 682 1. The ISO Committee will meet periodically to review Defect Reports 683 in the C++ Standard. Undoubtedly some of these will result in 684 changes to the Standard, which will be reflected in patches to 685 libstdc++. Some of that is already happening, see 4.2. Some of 686 those changes are being predicted by the library maintainers, and 687 we add code to the library based on what the current proposed 688 resolution specifies. Those additions are listed in [97]the 689 extensions page. 690 2. Performance tuning. Lots of performance tuning. This too is 691 already underway for post-3.0 releases, starting with memory 692 expansion in container classes and buffer usage in synchronized 693 stream objects. 694 3. An ABI for libstdc++ is being developed, so that multiple 695 binary-incompatible copies of the library can be replaced with a 696 single backwards-compatible library, like libgcc_s.so is. 697 4. The current libstdc++ contains extensions to the Library which 698 must be explicitly requested by client code (for example, the hash 699 tables from SGI). Other extensions may be added to libstdc++-v3 if 700 they seem to be "standard" enough. (For example, the "long long" 701 type from C99.) Bugfixes and rewrites (to improve or fix thread 702 safety, for instance) will of course be a continuing task. 703 704 [98]This question about the next libstdc++ prompted some brief but 705 interesting [99]speculation. 706 _________________________________________________________________ 707 7085.3 What about the STL from SGI? 709 710 The [100]STL from SGI, version 3.3, was the most recent merge of the 711 STL codebase. The code in libstdc++ contains many fixes and changes, 712 and it is very likely that the SGI code is no longer under active 713 development. We expect that no future merges will take place. 714 715 In particular, string is not from SGI and makes no use of their "rope" 716 class (which is included as an optional extension), nor is valarray 717 and some others. Classes like vector<> are, however we have made 718 significant changes to them since then. 719 720 The FAQ for SGI's STL (one jump off of their main page) is recommended 721 reading. 722 _________________________________________________________________ 723 7245.4 Extensions and Backward Compatibility 725 726 Headers in the ext and backward subdirectories should be referred to 727 by their relative paths: 728 #include <ext/hash_map> 729 730 rather than using -I or other options. This is more portable and 731 forward-compatible. (The situation is the same as that of other 732 headers whose directories are not searched directly, e.g., 733 <sys/stat.h>, <X11/Xlib.h>. 734 735 The extensions are no longer in the global or std namespaces, instead 736 they are declared in the __gnu_cxx namespace. For maximum portability, 737 consider defining a namespace alias to use to talk about extensions, 738 e.g.: 739 #ifdef __GNUC__ 740 #if __GNUC__ < 3 741 #include <hash_map.h> 742 namespace Sgi { using ::hash_map; }; // inherit globals 743 #else 744 #include <ext/hash_map> 745 #if __GNUC_MINOR__ == 0 746 namespace Sgi = std; // GCC 3.0 747 #else 748 namespace Sgi = ::__gnu_cxx; // GCC 3.1 and later 749 #endif 750 #endif 751 #else // ... there are other compilers, right? 752 namespace Sgi = std; 753 #endif 754 755 Sgi::hash_map<int,int> my_map; 756 757 This is a bit cleaner than defining typedefs for all the 758 instantiations you might need. 759 760 Extensions to the library have [101]their own page. 761 _________________________________________________________________ 762 7635.5 [removed] 764 765 This question has become moot and has been removed. The stub is here 766 to preserve numbering (and hence links/bookmarks). 767 _________________________________________________________________ 768 7695.6 Is libstdc++-v3 thread-safe? 770 771 libstdc++-v3 strives to be thread-safe when all of the following 772 conditions are met: 773 * The system's libc is itself thread-safe, 774 * gcc -v reports a thread model other than 'single', 775 * [pre-3.3 only] a non-generic implementation of atomicity.h exists 776 for the architecture in question. 777 778 The user-code must guard against concurrent method calls which may 779 access any particular library object's state. Typically, the 780 application programmer may infer what object locks must be held based 781 on the objects referenced in a method call. Without getting into great 782 detail, here is an example which requires user-level locks: 783 library_class_a shared_object_a; 784 785 thread_main () { 786 library_class_b *object_b = new library_class_b; 787 shared_object_a.add_b (object_b); // must hold lock for shared_object_ 788a 789 shared_object_a.mutate (); // must hold lock for shared_object_ 790a 791 } 792 793 // Multiple copies of thread_main() are started in independent threads. 794 795 Under the assumption that object_a and object_b are never exposed to 796 another thread, here is an example that should not require any 797 user-level locks: 798 thread_main () { 799 library_class_a object_a; 800 library_class_b *object_b = new library_class_b; 801 object_a.add_b (object_b); 802 object_a.mutate (); 803 } 804 805 All library objects are safe to use in a multithreaded program as long 806 as each thread carefully locks out access by any other thread while it 807 uses any object visible to another thread, i.e., treat library objects 808 like any other shared resource. In general, this requirement includes 809 both read and write access to objects; unless otherwise documented as 810 safe, do not assume that two threads may access a shared standard 811 library object at the same time. 812 813 See chapters [102]17 (library introduction), [103]23 (containers), and 814 [104]27 (I/O) for more information. 815 _________________________________________________________________ 816 8175.7 How do I get a copy of the ISO C++ Standard? 818 819 Copies of the full ISO 14882 standard are available on line via the 820 ISO mirror site for committee members. Non-members, or those who have 821 not paid for the privilege of sitting on the committee and sustained 822 their two-meeting commitment for voting rights, may get a copy of the 823 standard from their respective national standards organization. In the 824 USA, this national standards organization is ANSI and their website is 825 right [105]here. (And if you've already registered with them, clicking 826 this link will take you to directly to the place where you can 827 [106]buy the standard on-line. 828 829 Who is your country's member body? Visit the [107]ISO homepage and 830 find out! 831 _________________________________________________________________ 832 8335.8 What's an ABI and why is it so messy? 834 835 "ABI" stands for "Application Binary Interface." Conventionally, it 836 refers to a great mass of details about how arguments are arranged on 837 the call stack and/or in registers, and how various types are arranged 838 and padded in structs. A single CPU design may suffer multiple ABIs 839 designed by different development tool vendors who made different 840 choices, or even by the same vendor for different target applications 841 or compiler versions. In ideal circumstances the CPU designer presents 842 one ABI and all the OSes and compilers use it. In practice every ABI 843 omits details that compiler implementers (consciously or accidentally) 844 must choose for themselves. 845 846 That ABI definition suffices for compilers to generate code so a 847 program can interact safely with an OS and its lowest-level libraries. 848 Users usually want an ABI to encompass more detail, allowing libraries 849 built with different compilers (or different releases of the same 850 compiler!) to be linked together. For C++, this includes many more 851 details than for C, and CPU designers (for good reasons elaborated 852 below) have not stepped up to publish C++ ABIs. The details include 853 virtual function implementation, struct inheritance layout, name 854 mangling, and exception handling. Such an ABI has been defined for GNU 855 C++, and is immediately useful for embedded work relying only on a 856 "free-standing implementation" that doesn't include (much of) the 857 standard library. It is a good basis for the work to come. 858 859 A useful C++ ABI must also incorporate many details of the standard 860 library implementation. For a C ABI, the layouts of a few structs 861 (such as FILE, stat, jmpbuf, and the like) and a few macros suffice. 862 For C++, the details include the complete set of names of functions 863 and types used, the offsets of class members and virtual functions, 864 and the actual definitions of all inlines. C++ exposes many more 865 library details to the caller than C does. It makes defining a 866 complete ABI a much bigger undertaking, and requires not just 867 documenting library implementation details, but carefully designing 868 those details so that future bug fixes and optimizations don't force 869 breaking the ABI. 870 871 There are ways to help isolate library implementation details from the 872 ABI, but they trade off against speed. Library details used in inner 873 loops (e.g., getchar) must be exposed and frozen for all time, but 874 many others may reasonably be kept hidden from user code, so they may 875 later be changed. Deciding which, and implementing the decisions, must 876 happen before you can reasonably document a candidate C++ ABI that 877 encompasses the standard library. 878 _________________________________________________________________ 879 880 See [108]license.html for copying conditions. Comments and suggestions 881 are welcome, and may be sent to [109]the libstdc++ mailing list. 882 883References 884 885 1. http://gcc.gnu.org/onlinedocs/libstdc++/faq/ 886 2. http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html 887 3. http://gcc.gnu.org/libstdc++/ 888 4. ../faq/index.html#1_0 889 5. ../faq/index.html#1_1 890 6. ../faq/index.html#1_2 891 7. ../faq/index.html#1_3 892 8. ../faq/index.html#1_4 893 9. ../faq/index.html#1_5 894 10. ../faq/index.html#1_6 895 11. ../faq/index.html#1_7 896 12. ../faq/index.html#1_8 897 13. ../faq/index.html#1_9 898 14. ../faq/index.html#2_0 899 15. ../faq/index.html#2_1 900 16. ../faq/index.html#2_2 901 17. ../faq/index.html#2_3 902 18. ../faq/index.html#2_4 903 19. ../faq/index.html#2_5 904 20. ../faq/index.html#3_0 905 21. ../faq/index.html#3_1 906 22. ../faq/index.html#3_2 907 23. ../faq/index.html#3_3 908 24. ../faq/index.html#3_4 909 25. ../faq/index.html#3_5 910 26. ../faq/index.html#3_6 911 27. ../faq/index.html#3_7 912 28. ../faq/index.html#3_8 913 29. ../faq/index.html#3_9 914 30. ../faq/index.html#3_10 915 31. ../faq/index.html#4_0 916 32. ../faq/index.html#4_1 917 33. ../faq/index.html#4_2 918 34. ../faq/index.html#4_3 919 35. ../faq/index.html#4_4 920 36. ../faq/index.html#4_4_iostreamclear 921 37. ../faq/index.html#4_4_Weff 922 38. ../faq/index.html#4_4_rel_ops 923 39. ../faq/index.html#4_4_interface 924 40. ../faq/index.html#4_4_glibc 925 41. ../faq/index.html#4_4_checks 926 42. ../faq/index.html#4_4_dlsym 927 43. ../faq/index.html#4_4_leak 928 44. ../faq/index.html#4_5 929 45. ../faq/index.html#5_0 930 46. ../faq/index.html#5_1 931 47. ../faq/index.html#5_2 932 48. ../faq/index.html#5_3 933 49. ../faq/index.html#5_4 934 50. ../faq/index.html#5_5 935 51. ../faq/index.html#5_6 936 52. ../faq/index.html#5_7 937 53. ../faq/index.html#5_8 938 54. http://gcc.gnu.org/libstdc++/index.html#download 939 55. ../faq/index.html#1_4 940 56. ../faq/index.html#4_4_interface 941 57. ../17_intro/DESIGN 942 58. http://gcc.gnu.org/ 943 59. http://gcc.gnu.org/gcc-3.0/buildstat.html 944 60. http://gcc.gnu.org/libstdc++/ 945 61. http://gcc.gnu.org/libstdc++/ 946 62. http://gcc.gnu.org/releases.html 947 63. ../17_intro/contribute.html 948 64. http://www.boost.org/ 949 65. http://gcc.gnu.org/extensions.html 950 66. mailto:libstdc++@gcc.gnu.org 951 67. mailto:pme@gcc.gnu.org 952 68. mailto:gdr@gcc.gnu.org 953 69. ../17_intro/license.html 954 70. ../documentation.html 955 71. ../17_intro/RELEASE-NOTES 956 72. http://www.gnu.org/software/cvs/cvs.html 957 73. http://www.cvshome.org/ 958 74. http://gcc.gnu.org/install/test.html 959 75. ../18_support/howto.html 960 76. http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris 961 77. http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html 962 78. http://gcc.gnu.org/ml/libstdc++/2003-02/subjects.html#00286 963 79. http://gcc.gnu.org/install/configure.html 964 80. http://gcc.gnu.org/install/ 965 81. http://gcc.gnu.org/bugs.html 966 82. http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html 967 83. http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html 968 84. http://www.cantrip.org/draft-bugs.txt 969 85. http://anubis.dkuug.dk/jtc1/sc22/wg21/ 970 86. ../faq/index.html#5_2 971 87. ../ext/howto.html#5 972 88. http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html 973 89. http://gcc.gnu.org/gnatswrite.html 974 90. ../faq/index.html#4_4_interface 975 91. ../19_diagnostics/howto.html#3 976 92. http://developer.kde.org/~sewardj/ 977 93. ../debug.html#mem 978 94. http://gcc.gnu.org/contribute.html 979 95. ../17_intro/contribute.html 980 96. ../faq/index.html#2_4 981 97. ../ext/howto.html#5 982 98. http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html 983 99. http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html 984 100. http://www.sgi.com/Technology/STL/ 985 101. ../ext/howto.html 986 102. ../17_intro/howto.html#3 987 103. ../23_containers/howto.html#3 988 104. ../27_io/howto.html#9 989 105. http://www.ansi.org/ 990 106. http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998 991 107. http://www.iso.ch/ 992 108. ../17_intro/license.html 993 109. mailto:libstdc++@gcc.gnu.org 994