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/.        The       main
   documentation page is at
   [2]http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html.

   To the [3]libstdc++-v3 homepage.
     _________________________________________________________________

                                   Questions

    1. [4]General Information
         1. [5]What is libstdc++-v3?
         2. [6]Why should I use libstdc++?
         3. [7]Who's in charge of it?
         4. [8]How do I get libstdc++?
         5. [9]When is libstdc++ going to be finished?
         6. [10]How do I contribute to the effort?
         7. [11]What happened to libg++? I need that!
         8. [12]What if I have more questions?
         9. [13]What are the license terms for libstdc++-v3?
    2. [14]Installation
         1. [15]How do I install libstdc++-v3?
         2. [16][removed]
         3. [17]What is this CVS thing that you keep mentioning?
         4. [18]How do I know if it works?
         5. [19]This library is HUGE! And what's libsupc++?
    3. [20]Platform-Specific Issues
         1. [21]Can libstdc++-v3 be used with <my favorite compiler>?
         2. [22][removed]
         3. [23][removed]
         4. [24]I can't use 'long long' on Solaris
         5. [25]_XOPEN_SOURCE / _GNU_SOURCE / etc is always defined
         6. [26]OS X ctype.h is broken! How can I hack it?
    4. [27]Known Bugs and Non-Bugs
         1. [28]What works already?
         2. [29]Bugs in gcc/g++ (not libstdc++-v3)
         3. [30]Bugs in the C++ language/lib specification
         4. [31]Things in libstdc++ that only look like bugs
               o [32]reopening a stream fails
               o [33]-Weffc++ complains too much
               o [34]"ambiguous  overloads"  after including an old-style
                 header
               o [35]The g++-3 headers are not ours
               o [36]compilation errors from streambuf.h
               o [37]errors about *Concept and constraints in the STL...
               o [38]program   crashes  when  using  library  code  in  a
                 dynamically-loaded library
         5. [39]Aw, that's easy to fix!
    5. [40]Miscellaneous
         1. [41]string::iterator is not char*; vector<T>::iterator is not
            T*
         2. [42]What's next after libstdc++-v3?
         3. [43]What about the STL from SGI?
         4. [44]Extensions and Backward Compatibility
         5. [45][removed]
         6. [46]Is libstdc++-v3 thread-safe?
         7. [47]How do I get a copy of the ISO C++ Standard?
         8. [48]What's an ABI and why is it so messy?
     _________________________________________________________________

                            1.0 General Information

1.1 What is libstdc++-v3?

   The GNU Standard C++ Library v3 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  latest release is [49]the fourteenth
   snapshot but newer versions have been included in recent GCC releases.
   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 [50]1.4 below).

   The  older  libstdc++-v2 project is no longer maintained; the code has
   been  completely replaced and rewritten. [51]If you are using V2, then
   you need to report bugs to your system vendor, not to the V3 list.

   A more formal description of the V3 goals can be found in the official
   [52]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 [53]GCC team. All of
   the  rapid development and near-legendary [54]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 incompatibilities.
     _________________________________________________________________

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, Ulrich Drepper, Loren James Rittle, and Paolo
   Carlini 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 [55]homepage.
   If you have questions, ideas, code, or are just curious, sign up!
     _________________________________________________________________

1.4 How do I get libstdc++?

   The  fourteenth (and latest) snapshot of libstdc++-v3 is [56]available
   via ftp.

   The  [57]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 final release of the SGI
   STL.
     _________________________________________________________________

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  [58]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  [59]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 [60]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 [61]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 [62]Phil
   Edwards or [63]Gabriel Dos Reis.
     _________________________________________________________________

1.9 What are the license terms for libstdc++-v3?

   See [64]our license description for these and related questions.
     _________________________________________________________________

                               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 [65]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  [66]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 [67]CVS entry in the GNU
   software  catalogue  has a better description as well as a [68]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!
     _________________________________________________________________

2.4 This library is HUGE! And what's libsupc++?

   Usually  the  size  of libraries on disk isn't noticeable. When a link
   editor  (or  simply  "linker")  pulls  things  from  a  static archive
   library,  only  the  necessary  object  files  are  copied  into  your
   executable,  not  the  entire library. Unfortunately, even if you only
   need  a  single  function  or variable from an object file, the entire
   object   file   is  extracted.  (There's  nothing  unique  to  C++  or
   libstdc++-v3  about  this;  it's  just common behavior, given here for
   background reasons.)

   Some  of  the object files which make up libstdc++.a are rather large.
   If you create a statically-linked executable with -static, those large
   object  files  are  suddenly part of your executable. Historically the
   best  way  around  this  was to only place a very few functions (often
   only  a  single  one)  in  each  source/object file; then extracting a
   single  function  is  the  same  as  extracting  a single .o file. For
   libstdc++-v3  this  is  only  possible to a certain extent; the object
   files  in  question  contain  template classes and template functions,
   pre-instantiated,  and  splitting  those  up causes severe maintenance
   headaches.

   It's  not  a  bug,  and  it's not really a problem. Nevertheless, some
   people don't like it, so here are two pseudo-solutions:

   If  the  only  functions  from libstdc++.a which you need are language
   support  functions  (those  listed  in  [69]clause 18 of the standard,
   e.g.,  new  and delete), then try linking against libsupc++.a (usually
   specifying  -lsupc++  when calling g++ for the final link step will do
   it). This library contains only those support routines, one per object
   file. But if you are using anything from the rest of the library, such
   as   IOStreams   or  vectors,  then  you'll  still  need  pieces  from
   libstdc++.a.

   The second method is one we hope to incorporate into the library build
   process.  Some platforms can place each function and variable into its
   own  section  in  a  .o  file. The GNU linker can then perform garbage
   collection  on  unused  sections;  this  reduces the situation to only
   copying  needed  functions  into  the  executable,  as before, but all
   happens automatically.

   Unfortunately  the  garbage  collection  in  GNU ld is buggy; sections
   (corresponding   to  functions  and  variables)  which  are  used  are
   mistakenly  removed,  leading to horrible crashes when your executable
   starts  up. For the time being, this feature is not used when building
   the library.
     _________________________________________________________________

                         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
   usable 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 [removed]

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

3.4 I can't use 'long long' on Solaris

   By  default  we  try  to support the C99 long long type. This requires
   that certain functions from your C library be present.

   Up  through  release  3.0.2  the tests performed were too general, and
   this  feature  was  disabled  when  it  did  not  need to be. The most
   commonly reported platform affected was Solaris.

   This has been fixed for 3.0.3 and onwards.
     _________________________________________________________________

3.5 _XOPEN_SOURCE / _GNU_SOURCE / etc is always defined

   On  Solaris,  g++  (but not gcc) always defines the preprocessor macro
   _XOPEN_SOURCE.  On GNU/Linux, the same happens with _GNU_SOURCE. (This
   is  not  an exhaustive list; other macros and other platforms are also
   affected.)

   These  macros  are  typically  used in C library headers, guarding new
   versions  of  functions  from  their  older versions. The C++ standard
   library  includes  the  C  standard  library,  but it requires the C90
   version,  which  for  backwards-compatability reasons is often not the
   default for many vendors.

   More  to  the  point, the C++ standard requires behavior which is only
   available  on  certain  platforms  after  certain symbols are defined.
   Usually  the  issue  involves I/O-related typedefs. In order to ensure
   correctness, the compiler simply predefines those symbols.

   Note  that  it's  not  enough to #define them only when the library is
   being  built  (during  installation).  Since we don't have an 'export'
   keyword,  much  of the library exists as headers, which means that the
   symbols must also be defined as your programs are parsed and compiled.

   To  see  which symbols are defined, look for CPLUSPLUS_CPP_SPEC in the
   gcc  config headers for your target (and try changing them to see what
   happens  when building complicated code). You can also run "g++ -E -dM
   -  <  /dev/null"  to  display  a  list  of  predefined  macros for any
   particular installation.

   This has been discussed on the mailing lists [70]quite a bit.

   This  method  is  something  of  a  wart.  We'd like to find a cleaner
   solution, but nobody yet has contributed the time.
     _________________________________________________________________

3.6 OS X ctype.h is broken! How can I hack it?

   This  is  a  long-standing  bug  in the OS X support. Fortunately, the
   patch  is  quite  simple,  and  well-known.  [71]Here's  a link to the
   solution.
     _________________________________________________________________

                          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.

   For  3.0.1,  the  most  common "bug" is an apparently missing "../" in
   include/Makefile, resulting in files like gthr.h and gthr-single.h not
   being  found.  Please read [72]the configuration instructions for GCC,
   specifically the part about configuring in a separate build directory,
   and  how  strongly recommended it is. Building in the source directory
   is  fragile,  is  rarely  tested, and tends to break, as in this case.
   This was fixed for 3.0.2.

   For  3.1, the most common "bug" is a parse error when using <fstream>,
   ending  with  a message, "bits/basic_file.h:52: parse error before `{'
   token."   Please  read  [73]the  installation  instructions  for  GCC,
   specifically  the  part  about not installing newer versions on top of
   older  versions.  If  you  install  3.1 over a 3.0.x release, then the
   wrong  basic_file.h header will be found (its location changed between
   releases).

   Please do not report these as bugs. We know about them. Reporting this
   --  or  any  other  problem  that's  already been fixed -- hinders the
   development  of  GCC,  because we have to take time to respond to your
   report. Thank you.

4.1 What works already?

   This is a verbatim clip from the "Status" section of the RELEASE-NOTES
   for the latest snapshot. For a list of fixed bugs, see that file.
New:
---
(post 3.0.97)
- more doxygen documentation
- more named locale fixups
- stdio_filebuf that takes fd, FILE
- io performance tuning
- allocation tuning, valgrind fixups
- __cxa_demangle now supported
(3.0.97)
- more doxygen documentation.
- more named locale bug fixes
- support for symbol versioning when using GNU ld >= 2.12
- wide-io
- tuning for executable size
(3.0.96)
- more doxygen documentation.
- extensions moved out of namespace std
- HPUX long long support
- more string optimizations
- support for NetBSD cross compiles
- concept_check merge from boost
- header simplification
- named locale bug shakeout
- thread testsuite
(3.0.95)
- add S390, m68k, x86-64 support.
- doxygen documentation has been extended, including man pages.
- verbose terminate handling has been added.
- some libsupc++ tweaks
- warnings for deprecated headers now active.
- dejagnu testsuite preliminary documentation.
- dejagnu testsuite default.
- dejagnu testsuite cross compiler, multilib safe.
- long long iostreams on by default, rework of ISO C99 support.
- iterator re-write and testsuites.
- container testsuites.
- allocator revamp and testsuites.
- more concept-checking work.
- basic_string optimization and MT fixes.
- new limits implementation.
- update -fno-exceptions code, verify it works.
- full named locale support fpr all facets, choice of gnu,
  ieee_1003.1-200x (POSIX 2), or generic models. Full support depends
  on target OS and underlying "C" library support.
     _________________________________________________________________

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.

   Before  reporting  a  bug,  examine  the  [74]bugs  database  with the
   category  set  to  "libstdc++".  The BUGS file in the source tree also
   tracks known serious problems.
     * Debugging  is  problematic,  due to bugs in line-number generation
       (mostly fixed in the compiler) and gdb lagging behind the compiler
       (lack  of  personnel). We recommend configuring the compiler using
       --with-dwarf2  if  the  DWARF2 debugging format is not already the
       default on your platform. Also, [75]changing your GDB settings can
       have a profound effect on your C++ debugging experiences. :-)
     _________________________________________________________________

4.3 Bugs in the C++ language/lib specification

   Yes,  unfortunately,  there  are  some.  In a [76]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 [77]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 [78]here.
   Some of these have resulted in [79]code changes.
     _________________________________________________________________

4.4 Things in libstdc++ that only 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.

   reopening  a stream fails Did I just say that -Weffc++ was our biggest
   false-bug  report?  I  lied.  (It  used  to  be.) Today it seems to be
   reports that after executing a sequence like
    #include <fstream>
    ...
    std::fstream  fs("a_file");
    // .
    // . do things with fs...
    // .
    fs.close();
    fs.open("a_new_file");

   all  operations  on  the  re-opened fs will fail, or at least act very
   strangely.  Yes,  they  often  will,  especially if fs reached the EOF
   state on the previous file. The reason is that the state flags are not
   cleared on a successful call to open(). The standard unfortunately did
   not  specify  behavior  in this case, and to everybody's great sorrow,
   the  [80]proposed  LWG  resolution  (see DR #22) is to leave the flags
   unchanged.  You  must insert a call to fs.clear() between the calls to
   close()  and  open(), and then everything will work like we all expect
   it to work.

   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   [81]sums   things   up   here.  The  collisions  with
   vector/string iterator types have been fixed for 3.1.

  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 [82]the GCC bug database).

   If  the  headers  are  in ${prefix}/include/g++-3, or if the installed
   library's name looks like libstdc++-2.10.a or libstdc++-libc6-2.10.so,
   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 [83]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  [84]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 [85]here.

   dlopen/dlsym    If    you   are   using   the   C++   library   across
   dynamically-loaded  objects,  make  certain  that  you are passing the
   correct options when compiling and linking:
    // compile the library components
    g++ -fPIC -c a.cc
    g++ -fPIC -c b.cc
    ...
    g++ -fPIC -c z.cc

    // create the library
    g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o

    // link the executable
    g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl
     _________________________________________________________________

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
   [86]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++ [87]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  [88]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.  Those  additions  are  listed  in  [89]the
       extensions page.
    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++  is  being  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.

   [90]This  question  about  the  next libstdc++ prompted some brief but
   interesting [91]speculation.
     _________________________________________________________________

5.3 What about the STL from SGI?

   The  [92]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

   Headers  in  the ext and backward subdirectories should be referred to
   by their relative paths:
      #include <ext/hash_map>

   rather  than  using  -I  or  other  options. This is more portable and
   forward-compatible.  (The  situation  is  the  same  as  that of other
   headers   whose   directories   are   not   searched  directly,  e.g.,
   <sys/stat.h>, <X11/Xlib.h>.

   Extensions to the library have [93]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?

   When   the   system's   libc  is  itself  thread-safe,  a  non-generic
   implementation  of  atomicity.h  exists  for the architecture, and gcc
   itself  reports a thread model other than single; libstdc++-v3 strives
   to  be thread-safe. The user-code must guard against concurrent method
   calls   which  may  access  any  particular  library  object's  state.
   Typically, the application programmer may infer what object locks must
   be  held  based  on  the  objects referenced in a method call. Without
   getting   into  great  detail,  here  is  an  example  which  requires
   user-level locks:
     library_class_a shared_object_a;

     thread_main () {
       library_class_b *object_b = new library_class_b;
       shared_object_a.add_b (object_b);   // must hold lock for shared_object_
a
       shared_object_a.mutate ();          // must hold lock for shared_object_
a
     }

     // Multiple copies of thread_main() are started in independent threads.

   Under  the  assumption that object_a and object_b are never exposed to
   another  thread,  here  is  an  example  that  should  not require any
   user-level locks:
     thread_main () {
       library_class_a object_a;
       library_class_b *object_b = new library_class_b;
       object_a.add_b (object_b);
       object_a.mutate ();
     }

   All library objects are safe to use in a multithreaded program as long
   as each thread carefully locks out access by any other thread while it
   uses   any   object  visible  to  another  thread.  In  general,  this
   requirement  includes  both  read  and write access to objects; unless
   otherwise  documented  as  safe,  do  not  assume that two threads may
   access a shared standard library object at the same time.

   See  chapters  [94]17 (library introduction), [95]23 (containers), and
   [96]27 (I/O) for more information.
     _________________________________________________________________

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  [97]here. (And if you've already registered with them, clicking
   this link will take you to directly to the place where you can [98]buy
   the standard on-line.

   Who is your country's member body? Visit the [99]ISO homepage and find
   out!
     _________________________________________________________________

5.8 What's an ABI and why is it so messy?

   "ABI"  stands  for  "Application Binary Interface." Conventionally, it
   refers  to a great mass of details about how arguments are arranged on
   the call stack and/or in registers, and how various types are arranged
   and  padded  in  structs. A single CPU design may suffer multiple ABIs
   designed  by  different  development  tool  vendors who made different
   choices,  or even by the same vendor for different target applications
   or compiler versions. In ideal circumstances the CPU designer presents
   one  ABI  and all the OSes and compilers use it. In practice every ABI
   omits details that compiler implementers (consciously or accidentally)
   must choose for themselves.

   That  ABI  definition  suffices  for  compilers  to generate code so a
   program can interact safely with an OS and its lowest-level libraries.
   Users usually want an ABI to encompass more detail, allowing libraries
   built  with  different  compilers  (or  different releases of the same
   compiler!)  to  be  linked  together. For C++, this includes many more
   details  than  for  C,  and CPU designers (for good reasons elaborated
   below)  have  not  stepped up to publish C++ ABIs. The details include
   virtual  function  implementation,  struct  inheritance  layout,  name
   mangling, and exception handling. Such an ABI has been defined for GNU
   C++,  and  is  immediately  useful for embedded work relying only on a
   "free-standing  implementation"  that  doesn't  include  (much of) the
   standard library. It is a good basis for the work to come.

   A  useful  C++  ABI must also incorporate many details of the standard
   library  implementation.  For  a  C  ABI, the layouts of a few structs
   (such  as  FILE, stat, jmpbuf, and the like) and a few macros suffice.
   For  C++,  the  details include the complete set of names of functions
   and  types  used,  the offsets of class members and virtual functions,
   and  the  actual  definitions  of  all  inlines. C++ exposes many more
   library  details  to  the  caller  than  C  does.  It makes defining a
   complete  ABI  a  much  bigger  undertaking,  and  requires  not  just
   documenting  library  implementation  details, but carefully designing
   those  details  so that future bug fixes and optimizations don't force
   breaking the ABI.

   There are ways to help isolate library implementation details from the
   ABI,  but  they trade off against speed. Library details used in inner
   loops  (e.g.,  getchar)  must  be exposed and frozen for all time, but
   many  others may reasonably be kept hidden from user code, so they may
   later be changed. Deciding which, and implementing the decisions, must
   happen  before  you  can  reasonably document a candidate C++ ABI that
   encompasses the standard library.
     _________________________________________________________________

   See [100]license.html for copying conditions. Comments and suggestions
   are welcome, and may be sent to [101]the libstdc++ mailing list. 

References

   1. http://gcc.gnu.org/onlinedocs/libstdc++/faq/
   2. http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html
   3. http://gcc.gnu.org/libstdc++/
   4. ../faq/index.html#1_0
   5. ../faq/index.html#1_1
   6. ../faq/index.html#1_2
   7. ../faq/index.html#1_3
   8. ../faq/index.html#1_4
   9. ../faq/index.html#1_5
  10. ../faq/index.html#1_6
  11. ../faq/index.html#1_7
  12. ../faq/index.html#1_8
  13. ../faq/index.html#1_9
  14. ../faq/index.html#2_0
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  16. ../faq/index.html#2_2
  17. ../faq/index.html#2_3
  18. ../faq/index.html#2_4
  19. ../faq/index.html#2_5
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  22. ../faq/index.html#3_2
  23. ../faq/index.html#3_3
  24. ../faq/index.html#3_4
  25. ../faq/index.html#3_5
  26. ../faq/index.html#3_6
  27. ../faq/index.html#4_0
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  29. ../faq/index.html#4_2
  30. ../faq/index.html#4_3
  31. ../faq/index.html#4_4
  32. ../faq/index.html#4_4_iostreamclear
  33. ../faq/index.html#4_4_Weff
  34. ../faq/index.html#4_4_rel_ops
  35. ../faq/index.html#4_4_interface
  36. ../faq/index.html#4_4_glibc
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  38. ../faq/index.html#4_4_dlsym
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  42. ../faq/index.html#5_2
  43. ../faq/index.html#5_3
  44. ../faq/index.html#5_4
  45. ../faq/index.html#5_5
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  58. ../17_intro/contribute.html
  59. http://www.boost.org/
  60. http://gcc.gnu.org/fom_serv/cache/33.html
  61. mailto:libstdc++@gcc.gnu.org
  62. mailto:pme@gcc.gnu.org
  63. mailto:gdr@gcc.gnu.org
  64. ../17_intro/license.html
  65. ../documentation.html
  66. ../17_intro/RELEASE-NOTES
  67. http://www.gnu.org/software/cvs/cvs.html
  68. http://www.cvshome.org/
  69. ../18_support/howto.html
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  76. http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html
  77. http://www.cantrip.org/draft-bugs.txt
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  82. http://gcc.gnu.org/gnatswrite.html
  83. http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html
  84. ../faq/index.html#4_4_interface
  85. ../19_diagnostics/howto.html#3
  86. http://gcc.gnu.org/contribute.html
  87. ../17_intro/contribute.html
  88. ../faq/index.html#2_4
  89. ../ext/howto.html#5
  90. http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html
  91. http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html
  92. http://www.sgi.com/Technology/STL/
  93. ../ext/howto.html
  94. ../17_intro/howto.html#3
  95. ../23_containers/howto.html#3
  96. ../27_io/howto.html#9
  97. http://www.ansi.org/
  98. http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998
  99. http://www.iso.ch/
 100. ../17_intro/license.html
 101. mailto:libstdc++@gcc.gnu.org