path: root/libstdc++-v3/docs/html/faq/index.txt

                     libstdc++ Frequently Asked Questions
                                       
   The latest version of this document is always available at
   [1]http://gcc.gnu.org/onlinedocs/libstdc++/faq/.
   
   To the [2]libstdc++-v3 homepage.
     _________________________________________________________________
   
                                   Questions
                                       
    1. [3]General Information
         1. [4]What is libstdc++-v3?
         2. [5]Why should I use libstdc++?
         3. [6]Who's in charge of it?
         4. [7]How do I get libstdc++?
         5. [8]When is libstdc++ going to be finished?
         6. [9]How do I contribute to the effort?
         7. [10]What happened to libg++? I need that!
         8. [11]What if I have more questions?
    2. [12]Installation
         1. [13]How do I install libstdc++-v3?
         2. [14]Is this a drop-in replacement for the libstdc++ that's
            shipped with g++?
         3. [15]What is this CVS thing that you keep mentioning?
         4. [16]How do I know if it works?
    3. [17]Platform-Specific Issues
         1. [18]Can libstdc++-v3 be used with <my favorite compiler>?
         2. [19]Building under Cygwin hangs/explodes!?
    4. [20]Known Bugs and Non-Bugs
         1. [21]What works already?
         2. [22]Bugs in gcc/g++ (not libstdc++-v3)
         3. [23]Bugs in the C++ language/lib specification
         4. [24]Things in libstdc++ that look like bugs
            [25]The g++-3 headers are not ours
         5. [26]Aw, that's easy to fix!
    5. [27]Miscellaneous
         1. [28]string::iterator is not char*; vector<T>::iterator is not
            T*
         2. [29]What's next after libstdc++-v3?
         3. [30]What about the STL from SGI?
         4. [31]Extensions and Backward Compatibility
         5. [32]Compiling with "-fnew-abi"
         6. [33]Is libstdc++-v3 thread-safe?
         7. [34]How do I get a copy of the ISO C++ Standard?
     _________________________________________________________________
   
                            1.0 General Information
                                       
1.1 What is libstdc++-v3?

   The GNU Standard C++ Library v3, or libstdc++-2.90.x/2.9x, is an
   ongoing project to implement the ISO 14882 Standard C++ library as
   described in chapters 17 through 27 and annex D. As the library
   reaches stable plateaus, it is captured in a snapshot and released.
   The current release is [35]the tenth snapshot. For those who want to
   see exactly how far the project has come, or just want the latest
   bleeding-edge code, the up-to-date source is available over anonymous
   CVS, and can even be browsed over the Web (see below).
   
   A more formal description of the V3 goals can be found in the official
   [36]design document.
     _________________________________________________________________
   
1.2 Why should I use libstdc++?

   The completion of the ISO C++ standardization gave the C++ community a
   powerful set of reuseable tools in the form of the C++ Standard
   Library. However, all existing C++ implementations are (as the Draft
   Standard used to say) "incomplet and incorrekt," and many suffer from
   limitations of the compilers that use them.
   
   The GNU C/C++/FORTRAN/<pick-a-language> compiler (gcc, g++, etc) is
   widely considered to be one of the leading compilers in the world. Its
   development has recently been taken over by the [37]GCC team. All of
   the rapid development and near-legendary [38]portability that are the
   hallmarks of an open-source project are being applied to libstdc++.
   
   That means that all of the Standard classes and functions (such as
   string, vector<>, iostreams, and algorithms) will be freely available
   and fully compliant. Programmers will no longer need to "roll their
   own" nor be worried about platform-specific incompatabilities.
     _________________________________________________________________
   
1.3 Who's in charge of it?

   The libstdc++ project is contributed to by several developers all over
   the world, in the same way as GCC or Linux. Benjamin Kosnik, Gabriel
   Dos Reis, Phil Edwards, and Ulrich Drepper are the lead maintainers of
   the CVS archive.
   
   Development and discussion is held on the libstdc++ mailing list.
   Subscribing to the list, or searching the list archives, is open to
   everyone. You can read instructions for doing so on the [39]homepage.
   If you have questions, ideas, code, or are just curious, sign up!
     _________________________________________________________________
   
1.4 How do I get libstdc++?

   The tenth (and latest) snapshot of libstdc++-v3 is [40]available via
   ftp.
   
   The [41]homepage has instructions for retrieving the latest CVS
   sources, and for browsing the CVS sources over the web.
   
   The subset commonly known as the Standard Template Library (chapters
   23 through 25, mostly) is adapted from the SGI STL, which is also an
   ongoing work.
     _________________________________________________________________
   
1.5 When is libstdc++ going to be finished?

   Nathan Myers gave the best of all possible answers, responding to a
   Usenet article asking this question: Sooner, if you help.
     _________________________________________________________________
   
1.6 How do I contribute to the effort?

   Here is [42]a page devoted to this topic. Subscribing to the mailing
   list (see above, or the homepage) is a very good idea if you have
   something to contribute, or if you have spare time and want to help.
   Contributions don't have to be in the form of source code; anybody who
   is willing to help write documentation, for example, or has found a
   bug in code that we all thought was working, is more than welcome!
     _________________________________________________________________
   
1.7 What happened to libg++? I need that!

   The most recent libg++ README states that libg++ is no longer being
   actively maintained. It should not be used for new projects, and is
   only being kicked along to support older code.
   
   The libg++ was designed and created when there was no Standard to
   provide guidance. Classes like linked lists are now provided for by
   list<T> and do not need to be created by genclass. (For that matter,
   templates exist now and are well-supported, whereas genclass (mostly)
   predates them.)
   
   There are other classes in libg++ that are not specified in the ISO
   Standard (e.g., statistical analysis). While there are a lot of really
   useful things that are used by a lot of people (e.g., statistics :-),
   the Standards Committee couldn't include everything, and so a lot of
   those "obvious" classes didn't get included.
   
   Since libstdc++ is an implementation of the Standard Library, we have
   no plans at this time to include non-Standard utilities in the
   implementation, however handy they are. (The extensions provided in
   the SGI STL aren't maintained by us and don't get a lot of our
   attention, because they don't require a lot of our time.) It is
   entirely plausable that the "useful stuff" from libg++ might be
   extracted into an updated utilities library, but nobody has stated
   such a project yet.
   
   (The [43]Boost site houses free C++ libraries that do varying things,
   and happened to be started by members of the Standards Committee.
   Certain "useful stuff" classes will probably migrate there.)
   
   For the bold and/or desperate, the [44]GCC FAQ describes where to find
   the last libg++ source.
     _________________________________________________________________
   
1.8 What if I have more questions?

   If you have read the README and RELEASE-NOTES files, and your question
   remains unanswered, then just ask the mailing list. At present, you do
   not need to be subscribed to the list to send a message to it. More
   information is available on the homepage (including how to browse the
   list archives); to send to the list, use [45]libstdc++@gcc.gnu.org.
   
   If you have a question that you think should be included here, or if
   you have a question about a question/answer here, contact [46]Phil
   Edwards or [47]Gabriel Dos Reis.
     _________________________________________________________________
   
                               2.0 Installation
                                       
2.1 How do I install libstdc++-v3?

   Complete instructions are not given here (this is a FAQ, not an
   installation document), but the tools required are few:
     * A release of libstdc++.
     * A recent release of GCC (version 2.95 works). Note that building
       GCC is much easier and more automated than building the GCC 2.[78]
       series was.
     * If you plan on hacking around with the makefiles, you will need
       the tools [48]autoconfand [49]automake.
     * GNU Make is the only make that supports these makefiles.
       
   The file [50]documentation.html provides a good overview of the steps
   necessary to build, install, and use the library. Instructions for
   configuring the library with new flags such as --enable-threads are
   there also.
   
   The top-level install.html and [51]RELEASE-NOTES files contain the
   exact build and installation instructions. You may wish to browse
   those files over CVSweb ahead of time to get a feel for what's
   required. RELEASE-NOTES is located in the ".../docs/17_intro/"
   directory of the distribution.
     _________________________________________________________________
   
2.2 Is this a drop-in replacement for the libstdc++ that's shipped with g++?

   Yes, as of 2.90.8, it is intended as such. And as of 2.91,
   libstdc++-v3 is the library that's shipped with g++, so much of this
   answer has become moot.
     _________________________________________________________________
   
2.3 What is this CVS thing that you keep mentioning?

   The Concurrent Versions System is one of several revision control
   packages. It was selected for GNU projects because it's free (speech),
   free (beer), and very high quality. The [52]CVS entry in the GNU
   software catalogue has a better description as well as a [53]link to
   the makers of CVS.
   
   The "anonymous client checkout" feature of CVS is similar to anonymous
   FTP in that it allows anyone to retrieve the latest libstdc++ sources.
   
   After the first of April, American users will have a "/pharmacy"
   command-line option...
     _________________________________________________________________
   
2.4 How do I know if it works?

   libstdc++-v3 comes with its own testsuite. You do not need to actually
   install the library ("gmake install") to run the testsuite. Note that
   2.91 does not use DejaGNU yet.
   
   To run the testsuite on the library after building it, use "gmake
   check" while in your build directory. To run the testsuite on the
   library after building and installing it, use "gmake check-install"
   instead.
   
   The testsuite subdirectory in your build directory will then contain
   three files of the form YYYYMMDD-mkcheck*.txt. One of them
   (-mkcheck.txt itself) contains the results of the tests; this can be
   mailed to the list. The other files (-mkchecklog.txt and
   -mkcheckfiles.txt) contain messages from the compiler while building
   the test programs, and a list of the tests to be run, respectively.
   
   If you find bugs in the testsuite programs themselves, or if you think
   of a new test program that should be added to the suite, please write
   up your idea and send it to the list!
     _________________________________________________________________
   
                         3.0 Platform-Specific Issues
                                       
3.1 Can libstdc++-v3 be used with <my favorite compiler>?

   Probably not. Yet.
   
   Because GCC advances so rapidly, development and testing of libstdc++
   is being done almost entirely under that compiler. If you are curious
   about whether other, lesser compilers (*grin*) support libstdc++, you
   are more than welcome to try. Configuring and building the library
   (see above) will still require certain tools, however. Also keep in
   mind that building libstdc++ does not imply that your compiler will be
   able to use all of the features found in the C++ Standard Library.
   
   Since the goal of ISO Standardization is for all C++ implementations
   to be able to share code, the final libstdc++ should, in theory, be
   useable under any ISO-compliant compiler. It will still be targeted
   and optimized for GCC/g++, however.
     _________________________________________________________________
   
3.2 Building under Cygwin hangs/explodes!?

   Sometimes, yes. You're probably in the middle of generating the
   numeric_limits specializations when it hangs, right? Thought so...
   
   The <limits> header and its associated library code are
   platform-specific. These files get generated from scratch during
   installation, and it is this generator that is hanging. More
   specifically, the only sure way to determine what the
   numeric_limits<T>::traps boolean should be is to actually divide by
   zero and see if it is trapped or not.
   
   Under NT, this will occasionally just hang. On those occasions when
   the test does not hang, the zero-division is in fact trapped. That
   doesn't prevent hanging elsewhere.
   
   You have two options. You can get a newer cygwin1.dll (see the Cygwin
   paragraph in the [54]installation instructions). Or you can get a
   prebuilt set of bits/std_limits.h and src/limitsMEMBERS.cc files from
   Mumit Khan's [55]Cygwin-related website.
     _________________________________________________________________
   
                          4.0 Known Bugs and Non-Bugs
                                       
   Note that this section can get rapdily outdated -- such is the nature
   of an open-source project. For the latest information, join the
   mailing list or look through recent archives. The RELEASE- NOTES and
   BUGS files are generally kept up-to-date.
   
4.1 What works already?

   This is a verbatim clip from the "Status" section of the RELEASE-NOTES
   for the latest snapshot.
New:
- namespace std:: is now on by default.
- choice of "C" include strategies, including the shadow header work,
  or generic global to std mapping of required "C" types.
- cpu/atomicity.h tweaks, additions of ia64 and arm support.
- abstraction of atomicity.h header to support notion of os/atomicity.h files.
- addition of backward header bits
- use of system_header pragma
- Conditional use of -Werror
- preliminary support for new g++ diagnostics capabilities, including
  -fdiagnostics-show-location=once
- pedantic and shadow argument warning fixes
- Ugly, yet correct mechanism for dealing with "C" math adopted,
  including the use of builtins.
- updates and configure/build work to support new libtool
- addition of strstream
- valarray work
- complex work
- update to SGI STL 3.3
- libio sync between glibc/libstdc++-v3. Some divergence since initial
  merge, but sources remain quite close.
- IO fixes for alpha
- wide character work for IO when using libio
- addition of c_io_stdio and "C" IO abstraction layer.
- auto_ptr fixes, testsuite additions
- Attempts to use -ffunction-sections -fdata-sections and
  --gc-sections, depending on use of GNU ld and specific features. As of
  late, --gc-sections has been disabled due to problems with it throwing
  away initialization sections. This work is ongoing.
- long double support
- sub directory removal, coherent organization of cpu and os-specific
  files, consolidation of include directories, integration of the C++
  support bits for operator new/delete,exceptions, etc. All includes
  are now either in the include/* hierarchy or in libsupc++'s sub directory.
- Support for more platforms, including irix and bsd variants.
- filebuf tweaks to deal with variable-size buffers.
- filebuf implementation for putbackc, etc. al.
- ctype rewritten. Includes ctype, ctype, and others.
- codecvt rewritten. Includes codecvt,
  codecvt. In addition,
  implementation-defined conversions using iconv are now supported with
  the __enc_traits partial-specialization of the State template
  parameter of the codecvt class. In this manner, conversions between
  encodings such as UCS4, USC2, UNICODE, UNICODEBIG, UNICODELITTLE, etc
  can be performed.
- preliminary work on named locales
- preliminary documentation for locale implementation has been established.
- Many, many bug fixes.
- Many, many testsuite additions and consistent VERIFY usage.
- work on mkcheck to make it more flexible, use libtool, etc.
     _________________________________________________________________
   
4.2 Bugs in gcc/g++ (not libstdc++-v3)

   This is by no means meant to be complete nor exhaustive, but mentions
   some problems that users may encounter when building or using
   libstdc++. If you are experiencing one of these problems, you can find
   more information on the libstdc++ and the GCC mailing lists.
     * As of 2.91, these bugs have all been fixed. We look forward to new
       ones, well, not exactly...
     _________________________________________________________________
   
4.3 Bugs in the C++ language/lib specification

   Yes, unfortunately, there are some. In a [56]message to the list,
   Nathan Myers announced that he has started a list of problems in the
   ISO C++ Standard itself, especially with regard to the chapters that
   concern the library. The list itself is [57]posted on his website.
   Developers who are having problems interpreting the Standard may wish
   to consult his notes.
   
   For those people who are not part of the ISO Library Group (i.e.,
   nearly all of us needing to read this page in the first place :-), a
   public list of the library defects is occasionally published [58]here.
     _________________________________________________________________
   
4.4 Things in libstdc++ that look like bugs

   There are things which are not bugs in the compiler (4.2) nor the
   language specification (4.3), but aren't really bugs in libstdc++,
   either. Really!
   
   The biggest of these is the quadzillions of warnings about the library
   headers emitted when -Weffc++ is used. Making libstdc++
   "-Weffc++-clean" is not a goal of the project, for a few reasons.
   Mainly, that option tries to enforce object-oriented programming,
   while the Standard Library isn't necessarily trying to be OO. There
   are multiple solutions under discussion.
   
  The g++-3 headers are not ours
  
   If you have found an extremely broken header file which is causing
   problems for you, look carefully before submitting a "high" priority
   bug report (which you probably shouldn't do anyhow; see the last
   paragraph of the page describing [59]the GCC bug database).
   
   If the headers are in ${prefix}/include/g++-3, then you are using the
   old libstdc++-v2 library, which is nonstandard and unmaintained. Do
   not report problems with -v2 to the -v3 mailing list.
   
   Currently our header files are installed in ${prefix}/include/g++-v3
   (see the 'v'?). This may change with the next release of GCC, as it
   may be too confusing, but [60]the question has not yet been decided.
     _________________________________________________________________
   
4.5 Aw, that's easy to fix!

   If you have found a bug in the library and you think you have a
   working fix, then send it in! The main GCC site has a page on
   [61]submitting patches that covers the procedure, but for libstdc++
   you should of course send the patch to our mailing list, not the GCC
   mailing list. The libstdc++ [62]contributors' page also talks about
   how to submit patches.
   
   In addition to the description, the patch, and the ChangeLog entry, it
   is a Good Thing if you can additionally create a small test program to
   test for the presence of the bug that your patch fixes. Bugs have a
   way of being reintroduced; if an old bug creeps back in, it will be
   caught immediately by the [63]testsuite -- but only if such a test
   exists.
     _________________________________________________________________
   
                               5.0 Miscellaneous
                                       
5.1 string::iterator is not char*; vector<T>::iterator is not T*

   If you have code that depends on container<T> iterators being
   implemented as pointer-to-T, your code is broken.
   
   While there are arguments for iterators to be implemented in that
   manner, A) they aren't very good ones in the long term, and B) they
   were never guaranteed by the Standard anyway. The type-safety achieved
   by making iterators a real class rather than a typedef for T*
   outweighs nearly all opposing arguments.
     _________________________________________________________________
   
5.2 What's next after libstdc++-v3?

   Hopefully, not much. The goal of libstdc++-v3 is to produce a
   fully-compliant, fully-portable Standard Library. After that, we're
   mostly done: there won't be any more compliance work to do.
   
   The ISO Committee will meet periodically to review Defect Reports in
   the C++ Standard. Undoubtably some of these will result in changes to
   the Standard, which will be reflected in patches to libstdc++. Some of
   that is already happening, see 4.2. Some of those changes are being
   predicted by the library maintainers, and we add code to the library
   based on what the current proposed resolution specifies.
   
   The current libstdc++ contains extensions to the Library which must be
   explicitly requested by client code (for example, the hash tables from
   SGI). Other extensions may be added to libstdc++-v3 if they seem to be
   "standard" enough. (For example, the "long long" type from C99.)
   Bugfixes and rewrites (to improve or fix thread safety, for instance)
   will of course be a continuing task.
   
   [64]This question about the next libstdc++ prompted some brief but
   interesting [65]speculation.
     _________________________________________________________________
   
5.3 What about the STL from SGI?

   The [66]STL from SGI is merged into libstdc++-v3 with changes as
   necessary. Currently release 3.3 is being used. Changes in the STL
   usually produce some weird bugs and lots of changes in the rest of the
   libstd++ source as we scramble to keep up. :-)
   
   In particular, string is not from SGI and makes no use of their "rope"
   class (which is included as an optional extension), nor is valarray
   and some others. Classes like vector<> are, however.
   
   The FAQ for SGI's STL (one jump off of their main page) is recommended
   reading.
     _________________________________________________________________
   
5.4 Extensions and Backward Compatibility

   Although you can specify -I options to make the preprocessor search
   the g++-v3/ext and /backward directories, it is better to refer to
   files there by their path, as in:
       #include <ext/hash_map>


   Extensions to the library have [67]their own page.
     _________________________________________________________________
   
5.5 Compiling with "-fnew-abi"

   Towards the end of July 1999, this subject was brought up again on the
   mailing list under a different name. The related [68]thread (by the
   name HOWTO-honor-std) is very instructive. More info is at the end of
   RELEASE-NOTES.
   
   This functionality is now automated and turned on by default.
     _________________________________________________________________
   
5.6 Is libstdc++-v3 thread-safe?

   Quick answer: no, as of 2.91 (tenth snapshot), the library is not
   appropriate for multithreaded access. The string class is MT-safe.
   
   This is assuming that your idea of "multithreaded" is the same as
   ours... The general question of multithreading and libstdc++-v3 is
   addressed in the chapter-specific advice for [69]Library Introduction.
   Threadsafe containers are covered in more detail in [70]the Received
   Wisdom section on containers.
     _________________________________________________________________
   
5.7 How do I get a copy of the ISO C++ Standard?

   Copies of the full ISO 14882 standard are available on line via the
   ISO mirror site for committee members. Non-members, or those who have
   not paid for the privilege of sitting on the committee and sustained
   their two-meeting commitment for voting rights, may get a copy of the
   standard from their respective national standards organization. In the
   USA, this national standards organization is ANSI and their website is
   right [71]here. (And if you've already registered with them, clicking
   this link will take you to directly to the place where you can [72]buy
   the standard on-line.
   
   Who is your country's member body? Visit the [73]ISO homepage and find
   out!
     _________________________________________________________________
   
   Comments and suggestions are welcome, and may be sent to [74]Phil
   Edwards or [75]Gabriel Dos Reis.
   $Id: index.html,v 1.10 2000/12/03 23:47:49 jsm28 Exp $ 

References

   1. http://gcc.gnu.org/onlinedocs/libstdc++/faq/
   2. http://gcc.gnu.org/libstdc++/
   3. ../faq/index.html#1_0
   4. ../faq/index.html#1_1
   5. ../faq/index.html#1_2
   6. ../faq/index.html#1_3
   7. ../faq/index.html#1_4
   8. ../faq/index.html#1_5
   9. ../faq/index.html#1_6
  10. ../faq/index.html#1_7
  11. ../faq/index.html#1_8
  12. ../faq/index.html#2_0
  13. ../faq/index.html#2_1
  14. ../faq/index.html#2_2
  15. ../faq/index.html#2_3
  16. ../faq/index.html#2_4
  17. ../faq/index.html#3_0
  18. ../faq/index.html#3_1
  19. ../faq/index.html#3_2
  20. ../faq/index.html#4_0
  21. ../faq/index.html#4_1
  22. ../faq/index.html#4_2
  23. ../faq/index.html#4_3
  24. ../faq/index.html#4_4
  25. ../faq/index.html#4_4_interface
  26. ../faq/index.html#4_5
  27. ../faq/index.html#5_0
  28. ../faq/index.html#5_1
  29. ../faq/index.html#5_2
  30. ../faq/index.html#5_3
  31. ../faq/index.html#5_4
  32. ../faq/index.html#5_5
  33. ../faq/index.html#5_6
  34. ../faq/index.html#5_7
  35. ftp://gcc.gnu.org/pub/libstdc++/libstdc++-2.91.tar.gz
  36. ../17_intro/DESIGN
  37. http://gcc.gnu.org/
  38. http://gcc.gnu.org/gcc-2.95/buildstat.html
  39. http://gcc.gnu.org/libstdc++/
  40. ftp://gcc.gnu.org/pub/libstdc++/libstdc++-2.91.tar.gz
  41. http://gcc.gnu.org/libstdc++/
  42. ../17_intro/contribute.html
  43. http://www.boost.org/
  44. http://gcc.gnu.org/fom_serv/cache/33.html
  45. mailto:libstdc++@gcc.gnu.org
  46. mailto:pme@sources.redhat.com
  47. mailto:gdr@gcc.gnu.org
  48. http://sources.redhat.com/autoconf/
  49. http://sources.redhat.com/automake/
  50. ../documentation.html
  51. ../17_intro/RELEASE-NOTES
  52. http://www.gnu.org/software/cvs/cvs.html
  53. http://www.cyclic.com/
  54. ../install.html
  55. http://www.xraylith.wisc.edu/~khan/software/gnu-win32/libstdc++-v3.html
  56. http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html
  57. http://www.cantrip.org/draft-bugs.txt
  58. http://anubis.dkuug.dk/jtc1/sc22/wg21/
  59. http://gcc.gnu.org/gnatswrite.html
  60. http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html
  61. http://gcc.gnu.org/contribute.html
  62. ../17_intro/contribute.html
  63. ../faq/index.html#2_4
  64. http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html
  65. http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html
  66. http://www.sgi.com/Technology/STL/
  67. ../ext/howto.html
  68. http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00066.html
  69. http://gcc.gnu.org/libstdc++/17_intro/howto.html#3
  70. http://gcc.gnu.org/libstdc++/23_containers/howto.html
  71. http://www.ansi.org/
  72. http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998
  73. http://www.iso.ch/
  74. mailto:pme@sources.redhat.com
  75. mailto:gdr@gcc.gnu.org