The latest version of this document is always available at http://gcc.gnu.org/onlinedocs/libstdc++/faq/.
To the libstdc++-v3 homepage.
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 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 design document.
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 GCC team. All of the rapid development and near-legendary 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.
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 homepage. If you have questions, ideas, code, or are just curious, sign up!
The eleventh (and latest) snapshot of libstdc++-v3 is available via ftp.
The 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.
Nathan Myers gave the best of all possible answers, responding to a Usenet article asking this question: Sooner, if you help.
Here is 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!
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 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 GCC FAQ describes where to find the last libg++ source.
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
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 Phil Edwards or Gabriel Dos Reis.
Complete instructions are not given here (this is a FAQ, not an installation document), but the tools required are few:
The file 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 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.
This question has become moot and has been removed. The stub is here to preserve numbering (and hence links/bookmarks).
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 CVS entry in the GNU software catalogue has a better description as well as a 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...
libstdc++-v3 comes with its own testsuite. You do not need to actually install the library ("gmake install") to run the testsuite.
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.
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!
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.
This question has become moot and has been removed. The stub is here to preserve numbering (and hence links/bookmarks).
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 knows the DEC assembler well enough to provide the equivalent of these two pseudos would win praise and accolades from many.
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++
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.
Yes, unfortunately, there are some. In a 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 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 here.
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 sums things up here.
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 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 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
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 here.
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 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++ 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 testsuite -- but only if such a test exists.
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.
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. 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.
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.
This question about the next libstdc++ prompted some brief but interesting speculation.
The STL from SGI is merged into libstdc++-v3 with changes as necessary. Currently release 3.3 is being used as an initial codebase, plus changes, fixes, and extensions.
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.
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 their own page.
This question has become moot and has been removed. The stub is here to preserve numbering (and hence links/bookmarks).
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 Library Introduction. Threadsafe containers are covered in more detail in the Received Wisdom section on containers.
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 here. (And if you've already registered with them, clicking this link will take you to directly to the place where you can buy the standard on-line.
Who is your country's member body? Visit the ISO homepage and find out!
Comments and suggestions are welcome, and may be sent to
the mailing list.
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