
                     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][removed]
         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][removed]
         3. [20]Building under DEC OSF kills the assembler
    4. [21]Known Bugs and Non-Bugs
         1. [22]What works already?
         2. [23]Bugs in gcc/g++ (not libstdc++-v3)
         3. [24]Bugs in the C++ language/lib specification
         4. [25]Things in libstdc++ that look like bugs
               o [26]-Weffc++ complains too much
               o [27]"ambiguous overloads" after including an old-style
                 header
               o [28]The g++-3 headers are not ours
               o [29]compilation errors from streambuf.h
               o [30]errors about *Cconcept and constraints in the STL...
         5. [31]Aw, that's easy to fix!
    5. [32]Miscellaneous
         1. [33]string::iterator is not char*; vector<T>::iterator is not
            T*
         2. [34]What's next after libstdc++-v3?
         3. [35]What about the STL from SGI?
         4. [36]Extensions and Backward Compatibility
         5. [37][removed]
         6. [38]Is libstdc++-v3 thread-safe?
         7. [39]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++-2.9x, 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 [40]the eleventh 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
   [41]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 [42]GCC team. All of
   the rapid development and near-legendary [43]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 [44]homepage.
   If you have questions, ideas, code, or are just curious, sign up!
     _________________________________________________________________

1.4 How do I get libstdc++?

   The eleventh (and latest) snapshot of libstdc++-v3 is [45]available
   via ftp.

   The [46]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 [47]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 [48]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 [49]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 [50]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 [51]Phil
   Edwards or [52]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 3.x release of GCC. Note that building GCC is much easier and
       more automated than building the GCC 2.[78] series was. If you are
       using GCC 2.95, you can still build earlier snapshots of
       libstdc++.
     * GNU Make is recommended, but should not be required.
     * The GNU Autotools are needed if you are messing with the configury
       or makefiles.

   The file [53]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, as well as patches and instructions for working with GCC
   2.95.

   The top-level install.html and [54]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 [removed]

   This question has become moot and has been removed. The stub is here
   to preserve numbering (and hence links/bookmarks).
     _________________________________________________________________

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 [55]CVS entry in the GNU
   software catalogue has a better description as well as a [56]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 ("make install") to run the testsuite.

   To run the testsuite on the library after building it, use "make
   check" while in your build directory. To run the testsuite on the
   library after building and installing it, use "make check-install"
   instead.

   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 [removed]

   This question has become moot and has been removed. The stub is here
   to preserve numbering (and hence links/bookmarks).
     _________________________________________________________________

3.3 Building DEC OSF kills the assembler

   The atomicity.h header for the Alpha processor currently uses
   pseudo-operators which the DEC assembler doesn't understand (in
   particular, .subsection and .previous). The simple solution is to
   install GNU as and arrange for the GCC build to use it (or merge the
   sources and build it during the bootstrap).

   Anyone who [57]knows the DEC assembler well enough to provide the
   equivalent of these two pseudos would win praise and accolades from
   many.
     _________________________________________________________________

                          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:
---
- preliminary doxygen documentation has been added. Running "make
  doxygen" in the libstdc++-v3 build directory will generate HTML
  documentation that can be used to cross-reference names and files in
  the library.
- a dejagnu based testing framework has been added
- a new implementation of the concept checking code has been ported
  from the boost libraries.
- support for -fno-exceptions has been added
- stdexcept was re-written
- using deprecated or antiquated headers now gives a warning
- the stdio interface to iostreams has been tweaked, and now works
  with synchronized c/c++ io
- new libsupc++ routines implementing the IA-64 C++ ABI.
- HPUX configuration files
- support for AIX added
- a lot of bugs were fixed.
- preliminary named locales implemented
- portability improvements made to generation of <limits>
- speedups to improve configuration time.
- DJGPP support added.
- support for dlopening shared libstdc++
     _________________________________________________________________

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 [58]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 [59]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 [60]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! Please do not report these as bugs.

   -Weffc++ 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.

   rel_ops Another is the rel_ops namespace and the template comparison
   operator functions contained therein. If they become visible in the
   same namespace as other comparison functions (e.g., 'using' them and
   the <iterator> header), then you will suddenly be faced with huge
   numbers of ambiguity errors. This was discussed on the -v3 list;
   Nathan Myers [61]sums things up here.

  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 [62]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 [63]the question has not yet been decided.

   glibc If you're on a GNU/Linux system and have just upgraded to glibc
   2.2, but are still using gcc 2.95.2, then you should have read the
   glibc FAQ, specifically 2.34:
2.34.   When compiling C++ programs, I get a compilation error in streambuf.h.

{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
apply a patch to the include files in /usr/include/g++, because the fpos_t
type has changed in glibc 2.2.  The patch is at
http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff


   Note that 2.95.x shipped with the [64]old v2 library which is no
   longer maintained. Also note that gcc 2.95.3 fixes this problem, but
   requires a separate patch for libstdc++-v3.

   concept checks If you see compilation errors containing messages about
   fooConcept and a constraints member function, then most likely you
   have violated one of the requirements for types used during
   instantiation of template containers and functions. For example,
   EqualityComparableConcept appears if your types must be comparable
   with == and you have not provided this capability (a typo, or wrong
   visibility, or you just plain forgot, etc).

   More information, including how to optionally enable/disable the
   checks, is available [65]here.
     _________________________________________________________________

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
   [66]submitting patches that covers the procedure, but for libstdc++
   you should also send the patch to our mailing list in addition to the
   GCC patches mailing list. The libstdc++ [67]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 [68]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.

   Code which does assume that a vector iterator i is a pointer can often
   be fixed by changing i in certain expressions to &*i . Future
   revisions of the Standard are expected to bless this usage for
   vector<> (but not for basic_string<>).
     _________________________________________________________________

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. However:
    1. The ISO Committee will meet periodically to review Defect Reports
       in the C++ Standard. Undoubtedly 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.
    2. Performance tuning. Lots of performance tuning. This too is
       already underway for post-3.0 releases, starting with memory
       expansion in container classes and buffer usage in synchronized
       stream objects.
    3. An ABI for libstdc++ will eventually be developed, so that
       multiple binary-incompatible copies of the library can be replaced
       with a single backwards-compatible library, like libgcc_s.so is.
    4. 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.

   [69]This question about the next libstdc++ prompted some brief but
   interesting [70]speculation.
     _________________________________________________________________

5.3 What about the STL from SGI?

   The [71]STL from SGI, version 3.3, was the most recent merge of the
   STL codebase. The code in libstdc++ contains many fixes and changes,
   and it is very likely that the SGI code is no longer under active
   development. We expect that no future merges will take place.

   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 [72]their own page.
     _________________________________________________________________

5.5 [removed]

   This question has become moot and has been removed. The stub is here
   to preserve numbering (and hence links/bookmarks).
     _________________________________________________________________

5.6 Is libstdc++-v3 thread-safe?

   Quick answer: no, as of 2.92 (eleventh 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 [73]Library Introduction.
   Threadsafe containers are covered in more detail in [74]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 [75]here. (And if you've already registered with them, clicking
   this link will take you to directly to the place where you can [76]buy
   the standard on-line.

   Who is your country's member body? Visit the [77]ISO homepage and find
   out!
     _________________________________________________________________

   Comments and suggestions are welcome, and may be sent to [78]the
   mailing list.
   $Id: index.txt,v 1.2.4.5 2001/07/18 21:39:58 pme 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#3_3
  21. ../faq/index.html#4_0
  22. ../faq/index.html#4_1
  23. ../faq/index.html#4_2
  24. ../faq/index.html#4_3
  25. ../faq/index.html#4_4
  26. ../faq/index.html#4_4_Weff
  27. ../faq/index.html#4_4_rel_ops
  28. ../faq/index.html#4_4_interface
  29. ../faq/index.html#4_4_glibc
  30. ../faq/index.html#4_4_checks
  31. ../faq/index.html#4_5
  32. ../faq/index.html#5_0
  33. ../faq/index.html#5_1
  34. ../faq/index.html#5_2
  35. ../faq/index.html#5_3
  36. ../faq/index.html#5_4
  37. ../faq/index.html#5_5
  38. ../faq/index.html#5_6
  39. ../faq/index.html#5_7
  40. ftp://gcc.gnu.org/pub/libstdc++/libstdc++-2.92.tar.gz
  41. ../17_intro/DESIGN
  42. http://gcc.gnu.org/
  43. http://gcc.gnu.org/gcc-2.95/buildstat.html
  44. http://gcc.gnu.org/libstdc++/
  45. ftp://gcc.gnu.org/pub/libstdc++/libstdc++-2.92.tar.gz
  46. http://gcc.gnu.org/libstdc++/
  47. ../17_intro/contribute.html
  48. http://www.boost.org/
  49. http://gcc.gnu.org/fom_serv/cache/33.html
  50. mailto:libstdc++@gcc.gnu.org
  51. mailto:pme@gcc.gnu.org
  52. mailto:gdr@gcc.gnu.org
  53. ../documentation.html
  54. ../17_intro/RELEASE-NOTES
  55. http://www.gnu.org/software/cvs/cvs.html
  56. http://www.cvshome.org/
  57. http://gcc.gnu.org/ml/libstdc++/2000-12/msg00279.html
  58. http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html
  59. http://www.cantrip.org/draft-bugs.txt
  60. http://anubis.dkuug.dk/jtc1/sc22/wg21/
  61. http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html
  62. http://gcc.gnu.org/gnatswrite.html
  63. http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html
  64. ../faq/index.html#4_4_interface
  65. ../19_diagnostics/howto.html#3
  66. http://gcc.gnu.org/contribute.html
  67. ../17_intro/contribute.html
  68. ../faq/index.html#2_4
  69. http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html
  70. http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html
  71. http://www.sgi.com/Technology/STL/
  72. ../ext/howto.html
  73. http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/howto.html#3
  74. http://gcc.gnu.org/onlinedocs/libstdc++/23_containers/howto.html
  75. http://www.ansi.org/
  76. http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998
  77. http://www.iso.ch/
  78. mailto:libstdc++@gcc.gnu.org
