X-Git-Url: https://oss.titaniummirror.com/gitweb?a=blobdiff_plain;f=libstdc%2B%2B-v3%2Fdoc%2Fxml%2Ffaq.xml;fp=libstdc%2B%2B-v3%2Fdoc%2Fxml%2Ffaq.xml;h=c8907cabed8a109c835e19ef57ed5c09b066e877;hb=6fed43773c9b0ce596dca5686f37ac3fc0fa11c0;hp=0000000000000000000000000000000000000000;hpb=27b11d56b743098deb193d510b337ba22dc52e5c;p=msp430-gcc.git diff --git a/libstdc++-v3/doc/xml/faq.xml b/libstdc++-v3/doc/xml/faq.xml new file mode 100644 index 00000000..c8907cab --- /dev/null +++ b/libstdc++-v3/doc/xml/faq.xml @@ -0,0 +1,1255 @@ + + + + + +
+ + + + Frequently Asked Questions + + + 2008 + + + FSF + + + + + + + + + +General Information + + + + + What is libstdc++? + + + + + 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. 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 SVN, and can even be browsed over + the web. + + + + + + + + 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 compiler collection + (gcc, g++, etc) is widely + considered to be one of the leading compilers in the world. Its + development is overseen 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 will be + freely available and fully compliant. (Such as + string, + vector<>, iostreams, and algorithms.) + Programmers will no longer need to roll their own + nor be worried about platform-specific incompatibilities. + + + + + + + + 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 SVN 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! + + + + + + + + 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. + + + + + + + + How do I contribute to the effort? + + + + + 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 and is + willing to provide details, is more than welcome! + + + + + + + + What happened to the older 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. + + + More information in the backwards compatibility documentation + + + + + + + + What if I have more questions? + + + + + If you have read the README file, 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 a message 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, please send email to the libstdc++ mailing list, as above. + + + + + + + + +License + + + + + What are the license terms for libstdc++? + + + + + See our license description + for these and related questions. + + + + + + + + So any program which uses libstdc++ falls under the GPL? + + + + + No. The special exception permits use of the library in + proprietary applications. + + + + + + + + + How is that different from the GNU {Lesser,Library} GPL? + + + + + The LGPL requires that users be able to replace the LGPL code with a + modified version; this is trivial if the library in question is a C + shared library. But there's no way to make that work with C++, where + much of the library consists of inline functions and templates, which + are expanded inside the code that uses the library. So to allow people + to replace the library code, someone using the library would have to + distribute their own source, rendering the LGPL equivalent to the GPL. + + + + + + + + I see. So, what restrictions are there on programs that use the library? + + + + + None. We encourage such programs to be released as open source, + but we won't punish you or sue you if you choose otherwise. + + + + + + + + +Installation + + + + How do I install libstdc++? + + + + + Often libstdc++ comes pre-installed as an integral part of many + existing Linux and Unix systems, as well as many embedded + development tools. It may be necessary to install extra + development packages to get the headers, or the documentation, or + the source: please consult your vendor for details. + + + To build and install from the GNU GCC sources, please consult the + setup + documentation for detailed + instructions. You may wish to browse those files ahead + of time to get a feel for what's required. + + + + + + + How does one get current libstdc++ sources? + + + + + Libstdc++ sources for all official releases can be obtained as + part of the GCC sources, available from various sites and + mirrors. A full list of + download sites is provided on the main GCC site. + + + Current libstdc++ sources can always be checked out of the main + GCC source repository using the appropriate version control + tool. At this time, that tool + is Subversion. + + + Subversion, or SVN, 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 Subversion + home page has a better description. + + + The anonymous client checkout feature of SVN is + similar to anonymous FTP in that it allows anyone to retrieve + the latest libstdc++ sources. + + + For more information + see SVN + details. + + + + + + + How do I know if it works? + + + + + Libstdc++ comes with its own validation testsuite, which includes + conformance testing, regression testing, ABI testing, and + performance testing. Please consult the + testing + documentation for more details. + + + 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! + + + + + + + How do I insure that the dynamically linked library will be found? + + + + + Depending on your platform and library version, the error message might + be similar to one of the following: + + + + ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory + + /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found + + + + This doesn't mean that the shared library isn't installed, only + that the dynamic linker can't find it. When a dynamically-linked + executable is run the linker finds and loads the required shared + libraries by searching a pre-configured list of directories. If + the directory where you've installed libstdc++ is not in this list + then the libraries won't be found. The simplest way to fix this is + to use the LD_LIBRARY_PATH environment variable, + which is a colon-separated list of directories in which the linker + will search for shared libraries: + + + + LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH + export LD_LIBRARY_PATH + + + + The exact environment variable to use will depend on your + platform, e.g. DYLD_LIBRARY_PATH for Darwin, + LD_LIBRARY_PATH_32/LD_LIBRARY_PATH_64 for Solaris 32-/64-bit, + LD_LIBRARYN32_PATH/LD_LIBRARY64_PATH for Irix N32/64-bit ABIs and + SHLIB_PATH for HP-UX. + + + See the man pages for ld, ldd + and ldconfig for more information. The dynamic + linker has different names on different platforms but the man page + is usually called something such as ld.so/rtld/dld.so. + + + + + + + + What's libsupc++? + + + + + If the only functions from libstdc++.a + which you need are language support functions (those listed in + clause 18 of the + standard, e.g., new and + delete), then try linking against + libsupc++.a, which is a subset of + libstdc++.a. (Using gcc + instead of g++ and explicitly linking in + libsupc++.a via -lsupc++ + 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. + + + + + + + + This library is HUGE! + + + + + 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++ 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++ 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. + + + On supported platforms, libstdc++ takes advantage of garbage + collection in the GNU linker to get a result similar to separating + each symbol into a separate source and object files. On these platforms, + GNU ld 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. + + + + + + + + + +Platform-Specific Issues + + + + + Can libstdc++ be used with non-GNU compilers? + + + + + Perhaps. + + + Since the goal of ISO Standardization is for all C++ + implementations to be able to share code, libstdc++ should be + usable under any ISO-compliant compiler, at least in theory. + + + However, the reality is that libstdc++ is targeted and optimized + for GCC/g++. This means that often libstdc++ uses specific, + non-standard features of g++ that are not present in older + versions of proprietary compilers. It may take as much as a year or two + after an official release of GCC that contains these features for + proprietary tools support these constructs. + + + In the near past, specific released versions of libstdc++ have + been known to work with versions of the EDG C++ compiler, and + vendor-specific proprietary C++ compilers such as the Intel ICC + C++ compiler. + + + + + + + + + No 'long long' type 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 platform-specific tests performed by + libstdc++ were too general, resulting in a conservative approach + to enabling the long long code paths. The most + commonly reported platform affected was Solaris. + + + This has been fixed for libstdc++ releases greater than 3.0.3. + + + + + + + + _XOPEN_SOURCE and _GNU_SOURCE are 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-compatibility 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 + 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. + + + + + + + + + Mac OS X ctype.h is broken! How can I fix it? + + + + This is a long-standing bug in the OS X support. Fortunately, + the patch is quite simple, and well-known. + Here's a + link to the solution. + + + + + + + + + Threading is broken on i386? + + + + + + Support for atomic integer operations is/was broken on i386 + platforms. The assembly code accidentally used opcodes that are + only available on the i486 and later. So if you configured GCC + to target, for example, i386-linux, but actually used the programs + on an i686, then you would encounter no problems. Only when + actually running the code on a i386 will the problem appear. + + This is fixed in 3.2.2. + + + + + + + + + MIPS atomic operations + + + + + The atomic locking routines for MIPS targets requires MIPS II + and later. A patch went in just after the 3.3 release to + make mips* use the generic implementation instead. You can also + configure for mipsel-elf as a workaround. + + + The mips*-*-linux* port continues to use the MIPS II routines, and more + work in this area is expected. + + + + + + + + Recent GNU/Linux glibc required? + + + + When running on GNU/Linux, libstdc++ 3.2.1 (shared library version + 5.0.1) and later uses localization and formatting code from the system + C library (glibc) version 2.2.5. That version of glibc is over a + year old and contains necessary bugfixes. Many GNU/Linux distros make + glibc version 2.3.x available now. + + The guideline is simple: the more recent the C++ library, the + more recent the C library. (This is also documented in the main + GCC installation instructions.) + + + + + + + + + Can't use wchar_t/wstring on FreeBSD + + + + + Older versions of FreeBSD's C library do not have sufficient + support for wide character functions, and as a result the + libstdc++ configury decides that wchar_t support should be + disabled. In addition, the libstdc++ platform checks that + enabled wchar_t were quite strict, and not granular + enough to detect when the minimal support to + enable wchar_t and C++ library structures + like wstring were present. This impacted Solaris, + Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0. + + + + + + + + + + + +Known Bugs + + + + + What works already? + + + + + Short answer: Pretty much everything works + except for some corner cases. Support for localization + in locale may be incomplete on non-GNU + platforms. Also dependant on the underlying platform is support + for wchar_t and long + long specializations, and details of thread support. + + + Long answer: See the implementation status pages for + C++98, + TR1, and + C++0x. + + + + + + + + Bugs in the ISO C++ language or library specification + + + + + Unfortunately, there are some. + + + 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. + Some of these issues have resulted in code changes in libstdc++. + + + If you think you've discovered a new bug that is not listed, + please post a message describing your problem + to libstdc++@gcc.gnu.org or the Usenet group + comp.lang.c++.moderated. + + + + + + + + Bugs in the compiler (gcc/g++) and not libstdc++ + + + + + On occasion, the compiler is wrong. Please be advised that this + happens much less often than one would think, and avoid jumping to + conclusions. + + + First, examine the ISO C++ standard. Second, try another compiler + or an older version of the GNU compilers. Third, you can find more + information on the libstdc++ and the GCC mailing lists: search + these lists with terms describing your issue. + + + Before reporting a bug, please examine the + bugs database with the + category set to g++. + + + + + + + + +Known Non-Bugs + + + + + Reopening a stream fails + + + + + One of the most-reported non-bug reports. 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 proposed LWG resolution in + 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. + Update: for GCC 4.0 we implemented the resolution + of DR #409 and open() + now calls clear() on success! + + + + + + + + -Weffc++ complains too much + + + + + Many warnings are 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. + + + We do, however, try to have libstdc++ sources as clean as possible. If + you see some simple changes that pacify -Weffc++ + without other drawbacks, send us a patch. + + + + + + + + Ambiguous overloads after including an old-style header + + + + + Another problem 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. 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 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. + + + For GCC versions 3.0 and 3.1 the libstdc++ header files are + installed in ${prefix}/include/g++-v3 (see the + 'v'?). Starting with version 3.2 the headers are installed in + ${prefix}/include/c++/${version} as this prevents + headers from previous versions being found by mistake. + + + + + + + + + Errors about *Concept and + constraints in the STL + + + + + If you see compilation errors containing messages about + foo Concept and something to do with 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. + + + + + + + + Program crashes when using library code in a + dynamically-loaded library + + + + + 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 your library components + g++ -fPIC -c a.cc + g++ -fPIC -c b.cc + ... + g++ -fPIC -c z.cc + + // create your 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 + + + + + + + + Memory leaks in containers + + + + + A few people have reported that the standard containers appear + to leak memory when tested with memory checkers such as + valgrind. + The library's default allocators keep free memory in a pool + for later reuse, rather than returning it to the OS. Although + this memory is always reachable by the library and is never + lost, memory debugging tools can report it as a leak. If you + want to test the library for memory leaks please read + Tips for memory leak hunting + first. + + + + + + + + list::size() is O(n)! + + + + + See + the Containers + chapter. + + + + + + + + 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 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. + + + + + + + + + +Miscellaneous + + + + + 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. It's + considered a feature, not a bug, that libstdc++ points this out. + + + 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<>). + + + + + + + + What's next after libstdc++? + + + + + Hopefully, not much. The goal of libstdc++ 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. + + + There is an effort underway to add significant extensions to + the standard library specification. The latest version of + this effort is described in + + The C++ Library Technical Report 1. + + + + + + + + What about the STL from SGI? + + + + + The STL from SGI, + version 3.3, was the final merge of the STL codebase. The + code in libstdc++ contains many fixes and changes, and + 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, but have been + extensively modified. + + + More information on the evolution of libstdc++ can be found at the + API + evolution + and backwards + compatibility documentation. + + + The FAQ for SGI's STL (one jump off of their main page) is + still recommended reading. + + + + + + + + Extensions and Backward Compatibility + + + + + See the link on backwards compatibility and link on evolution. + + + + + + + + Does libstdc++ support TR1? + + + + + Yes. + + + The C++ Standard Library Technical Report adds many new features to + the library. The latest version of this effort is described in + + Technical Report 1. + + + The implementation status of TR1 in libstdc++ can be tracked on the TR1 status + page. + + + + + + + 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 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! + + + The 2003 version of the standard (the 1998 version plus TC1) is + available in print, ISBN 0-470-84674-7. + + + + + + + + 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. + + + + + + + + How do I make std::vector<T>::capacity() == std::vector<T>::size? + + + + + The standard idiom for deallocating a vector<T>'s + unused memory is to create a temporary copy of the vector and swap their + contents, e.g. for vector<T> v + + + std::vector<T>(v).swap(v); + + + The copy will take O(n) time and the swap is constant time. + + + See Shrink-to-fit + strings for a similar solution for strings. + + + + + + + + + + +
+ +