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diff --git a/libstdc++-v3/doc/xml/faq.xml b/libstdc++-v3/doc/xml/faq.xml new file mode 100644 index 00000000000..629d1ec12a6 --- /dev/null +++ b/libstdc++-v3/doc/xml/faq.xml @@ -0,0 +1,1254 @@ +<?xml version='1.0'?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" +[ ]> + +<book> + +<article id="faq" xreflabel="Frequently Asked Questions"> +<?dbhtml filename="faq.html"?> + +<articleinfo> + <title>Frequently Asked Questions</title> + <copyright> + <year> + 2008 + </year> + <holder> + <ulink url="http://fsf.org">FSF</ulink> + </holder> + </copyright> +</articleinfo> + +<!-- FAQ starts here --> +<qandaset> + +<!-- General Information --> +<qandadiv id="faq.info" xreflabel="General Information"> +<title>General Information</title> + +<qandaentry id="faq.what"> + <question id="faq.what.q"> + <para> + What is libstdc++? + </para> + </question> + <answer id="faq.what.a"> + <para> + 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 <ulink url="http://gcc.gnu.org/svn.html">web</ulink>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.why"> + <question id="q-why"> + <para> + Why should I use libstdc++? + </para> + </question> + <answer id="a-why"> + <para> + 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) <quote>incomplet and + incorrekt</quote>, and many suffer from limitations of the compilers + that use them. + </para> + <para> + The GNU compiler collection + (<command>gcc</command>, <command>g++</command>, etc) is widely + considered to be one of the leading compilers in the world. Its + development is overseen by the + <ulink url="http://gcc.gnu.org/">GCC team</ulink>. All of + the rapid development and near-legendary + <ulink url="http://gcc.gnu.org/buildstat.html">portability</ulink> + that are the hallmarks of an open-source project are being + applied to libstdc++. + </para> + <para> + That means that all of the Standard classes and functions will be + freely available and fully compliant. (Such as + <classname>string</classname>, + <classname>vector<></classname>, iostreams, and algorithms.) + Programmers will no longer need to <quote>roll their own</quote> + nor be worried about platform-specific incompatibilities. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.who"> + <question id="q-who"> + <para> + Who's in charge of it? + </para> + </question> + <answer id="a-who"> + <para> + 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. + </para> + <para> + 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 <ulink url="http://gcc.gnu.org/libstdc++/">homepage</ulink>. + If you have questions, ideas, code, or are just curious, sign up! + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.when"> + <question id="q-when"> + <para> + When is libstdc++ going to be finished? + </para> + </question> + <answer id="a-when"> + <para> + Nathan Myers gave the best of all possible answers, responding to + a Usenet article asking this question: <emphasis>Sooner, if you + help.</emphasis> + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.how"> + <question id="q-how"> + <para> + How do I contribute to the effort? + </para> + </question> + <answer id="a-how"> + <para> + Here is <ulink url="../17_intro/contribute.html">a page devoted to + this topic</ulink>. 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! + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.whereis_old"> + <question id="q-whereis_old"> + <para> + What happened to the older libg++? I need that! + </para> + </question> + <answer id="a-whereis_old"> + <para> + 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. + </para> + <para> + More information in the <link linkend="manual.appendix.porting.backwards">backwards compatibility documentation</link> + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.more_questions"> + <question id="q-more_questions"> + <para> + What if I have more questions? + </para> + </question> + <answer id="a-more_questions"> + <para> + 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 <email>libstdc++@gcc.gnu.org</email>. + </para> + + <para> + If you have a question that you think should be included + here, or if you have a question <emphasis>about</emphasis> a question/answer + here, please send email to the libstdc++ mailing list, as above. + </para> + </answer> +</qandaentry> + +</qandadiv> + +<!-- License --> +<qandadiv id="faq.license" xreflabel="License QA"> +<title>License</title> + +<qandaentry id="faq.license.what"> + <question id="q-license.what"> + <para> + What are the license terms for libstdc++? + </para> + </question> + <answer id="a-license.what"> + <para> + See <link linkend="manual.intro.status.license">our license description</link> + for these and related questions. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.license.any_program"> + <question id="q-license.any_program"> + <para> + So any program which uses libstdc++ falls under the GPL? + </para> + </question> + <answer id="a-license.any_program"> + <para> + No. The special exception permits use of the library in + proprietary applications. + </para> + </answer> +</qandaentry> + + +<qandaentry id="faq.license.lgpl"> + <question id="q-license.lgpl"> + <para> + How is that different from the GNU {Lesser,Library} GPL? + </para> + </question> + <answer id="a-license.lgpl"> + <para> + 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. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.license.what_restrictions"> + <question id="q-license.what_restrictions"> + <para> + I see. So, what restrictions are there on programs that use the library? + </para> + </question> + <answer id="a-license.what_restrictions"> + <para> + None. We encourage such programs to be released as open source, + but we won't punish you or sue you if you choose otherwise. + </para> + </answer> +</qandaentry> + +</qandadiv> + +<!-- Installation --> +<qandadiv id="faq.installation" xreflabel="Installation"> +<title>Installation</title> + +<qandaentry id="faq.how_to_install"> + <question id="q-how_to_install"> + <para>How do I install libstdc++? + </para> + </question> + <answer id="a-how_to_install"> + <para> + 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. + </para> + <para> + To build and install from the GNU GCC sources, please consult the + <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/install.html">install + documentation</ulink> for detailed + instructions. You may wish to browse those files ahead + of time to get a feel for what's required. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.how_to_get_sources"> + <question id="q-how_to_get_sources"> + <para>How does one get current libstdc++ sources? + </para> + </question> + <answer id="a-how_to_get_sources"> + <para> + Libstdc++ sources for all official releases can be obtained as + part of the GCC sources, available from various sites and + mirrors. A full <ulink url="http://gcc.gnu.org/mirrors.html">list of + download sites</ulink> is provided on the main GCC site. + </para> + <para> + 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 <application>Subversion</application>. + </para> + <para> + <application>Subversion</application>, or <acronym>SVN</acronym>, 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 <ulink url="http://subversion.tigris.org"> Subversion + home page</ulink> has a better description. + </para> + <para> + The <quote>anonymous client checkout</quote> feature of SVN is + similar to anonymous FTP in that it allows anyone to retrieve + the latest libstdc++ sources. + </para> + <para> + For more information + see <ulink url="http://gcc.gnu.org/svn.html"><acronym>SVN</acronym> + details</ulink>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.how_to_test"> + <question id="q-how_to_test"> + <para>How do I know if it works? + </para> + </question> + <answer id="a-how_to_test"> + <para> + Libstdc++ comes with its own validation testsuite, which includes + conformance testing, regression testing, ABI testing, and + performance testing. Please consult the + <ulink url="http://gcc.gnu.org/install/test.html">testing + documentation</ulink> for more details. + </para> + <para> + 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, + <emphasis>please</emphasis> write up your idea and send it to the list! + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.how_to_set_paths"> + <question id="q-how_to_set_paths"> + <para>How do I insure that the dynamically linked library will be found? + </para> + </question> + <answer id="a-how_to_set_paths"> + <para> + Depending on your platform and library version, the error message might + be similar to one of the following: + </para> + + <screen> + ./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 + </screen> + + <para> + 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 <literal>LD_LIBRARY_PATH</literal> environment variable, + which is a colon-separated list of directories in which the linker + will search for shared libraries: + </para> + + <screen> + LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH + export LD_LIBRARY_PATH + </screen> + + <para> + 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. + </para> + <para> + See the man pages for <command>ld</command>, <command>ldd</command> + and <command>ldconfig</command> for more information. The dynamic + linker has different names on different platforms but the man page + is usually called something such as <filename>ld.so/rtld/dld.so</filename>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.what_is_libsupcxx"> + <question id="q-what_is_libsupcxx"> + <para> + What's libsupc++? + </para> + </question> + <answer id="a-what_is_libsupcxx"> + <para> + If the only functions from <filename>libstdc++.a</filename> + which you need are language support functions (those listed in + <ulink url="../18_support/howto.html">clause 18</ulink> of the + standard, e.g., <function>new</function> and + <function>delete</function>), then try linking against + <filename>libsupc++.a</filename>, which is a subset of + <filename>libstdc++.a</filename>. (Using <command>gcc</command> + instead of <command>g++</command> and explicitly linking in + <filename>libsupc++.a</filename> via <literal>-lsupc++</literal> + 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 + <filename>libstdc++.a</filename>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.size"> + <question id="q-size"> + <para> + This library is HUGE! + </para> + </question> + <answer id="a-size"> + <para> + Usually the size of libraries on disk isn't noticeable. When a + link editor (or simply <quote>linker</quote>) 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.) + </para> + <para> + Some of the object files which make up libstdc++.a are rather large. + If you create a statically-linked executable with + <literal>-static</literal>, 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. + </para> + <para> + 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. + </para> + </answer> +</qandaentry> + +</qandadiv> + + +<!-- Platorm-Specific Issues --> +<qandadiv id="faq.platform-specific" xreflabel="Platform-Specific Issues"> +<title>Platform-Specific Issues</title> + +<qandaentry id="faq.other_compilers"> + <question id="q-other_compilers"> + <para> + Can libstdc++ be used with non-GNU compilers? + </para> + </question> + <answer id="a-other_compilers"> + <para> + Perhaps. + </para> + <para> + 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. + </para> + <para> + 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. + </para> + <para> + 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. + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.solaris_long_long"> + <question id="q-solaris_long_long"> + <para> + No 'long long' type on Solaris? + </para> + </question> + <answer id="a-solaris_long_long"> + <para> + By default we try to support the C99 <type>long long</type> type. + This requires that certain functions from your C library be present. + </para> + <para> + Up through release 3.0.2 the platform-specific tests performed by + libstdc++ were too general, resulting in a conservative approach + to enabling the <type>long long</type> code paths. The most + commonly reported platform affected was Solaris. + </para> + <para> + This has been fixed for libstdc++ releases greater than 3.0.3. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.predefined"> + <question id="q-predefined"> + <para> + <constant>_XOPEN_SOURCE</constant> and <constant>_GNU_SOURCE</constant> are always defined? + </para> + </question> + <answer id="a-predefined"> + <para>On Solaris, g++ (but not gcc) always defines the preprocessor + macro <constant>_XOPEN_SOURCE</constant>. On GNU/Linux, the same happens + with <constant>_GNU_SOURCE</constant>. (This is not an exhaustive list; + other macros and other platforms are also affected.) + </para> + <para>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. + </para> + <para>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. + </para> + <para>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. + </para> + <para>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 + <command>g++ -E -dM - < /dev/null"</command> to display + a list of predefined macros for any particular installation. + </para> + <para>This has been discussed on the mailing lists + <ulink url="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris">quite a bit</ulink>. + </para> + <para>This method is something of a wart. We'd like to find a cleaner + solution, but nobody yet has contributed the time. + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.darwin_ctype"> + <question id="q-darwin_ctype"> + <para> + Mac OS X <filename class="headerfile">ctype.h</filename> is broken! How can I fix it? + </para> + </question> + <answer id="a-darwin_ctype"> + <para>This is a long-standing bug in the OS X support. Fortunately, + the patch is quite simple, and well-known. + <ulink url="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a + link to the solution</ulink>. + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.threads_i386"> + <question id="q-threads_i386"> + <para> + Threading is broken on i386? + </para> + </question> + <answer id="a-threads_i386"> + <para> + </para> + <para>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. + </para> + <para>This is fixed in 3.2.2. + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.atomic_mips"> + <question id="q-atomic_mips"> + <para> + MIPS atomic operations + </para> + </question> + <answer id="a-atomic_mips"> + <para> + 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. + </para> + <para> + The mips*-*-linux* port continues to use the MIPS II routines, and more + work in this area is expected. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.linux_glibc"> + <question id="q-linux_glibc"> + <para> + Recent GNU/Linux glibc required? + </para> + </question> + <answer id="a-linux_glibc"> + <para>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. + </para> + <para>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.) + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.freebsd_wchar"> + <question id="q-freebsd_wchar"> + <para> + Can't use wchar_t/wstring on FreeBSD + </para> + </question> + <answer id="a-freebsd_wchar"> + <para> + 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 <type>wchar_t</type> were quite strict, and not granular + enough to detect when the minimal support to + enable <type>wchar_t</type> and C++ library structures + like <classname>wstring</classname> were present. This impacted Solaris, + Darwin, and BSD varients, and is fixed in libstdc++ versions post 4.1.0. + </para> + <para> + </para> + </answer> +</qandaentry> + +</qandadiv> + + +<!-- Known Bugs --> +<qandadiv id="faq.known_bugs" xreflabel="Known Bugs"> +<title>Known Bugs</title> + +<qandaentry id="faq.what_works"> + <question id="q-what_works"> + <para> + What works already? + </para> + </question> + <answer id="a-what_works"> + <para> + Short answer: Pretty much everything <emphasis>works</emphasis> + except for some corner cases. Support for localization + in <classname>locale</classname> may be incomplete on non-GNU + platforms. Also dependant on the underlying platform is support + for <type>wchar_t</type> and <type>long + long</type> specializations, and details of thread support. + </para> + <para> + Long answer: See the implementation status pages for + <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/c++1998_status.html">C++98</ulink>, + <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/tr1_status.html">TR1</ulink>, and <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/c++0x_status.html">C++0x</ulink>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.standard_bugs"> + <question id="q-standard_bugs"> + <para> + Bugs in the ISO C++ language or library specification + </para> + </question> + <answer id="a-standard_bugs"> + <para> + Unfortunately, there are some. + </para> + <para> + 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 <ulink url="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</ulink>. + Some of these issues have resulted in code changes in libstdc++. + </para> + <para> + If you think you've discovered a new bug that is not listed, + please post a message describing your problem + to <email>libstdc++@gcc.gnu.org</email> or the Usenet group + comp.lang.c++.moderated. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.compiler_bugs"> + <question id="q-compiler_bugs"> + <para> + Bugs in the compiler (gcc/g++) and not libstdc++ + </para> + </question> + <answer id="a-compiler_bugs"> + <para> + On occasion, the compiler is wrong. Please be advised that this + happens much less often than one would think, and avoid jumping to + conclusions. + </para> + <para> + 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. + </para> + <para> + Before reporting a bug, please examine the + <ulink url="http://gcc.gnu.org/bugs.html">bugs database</ulink> with the + category set to <quote>g++</quote>. + </para> + </answer> +</qandaentry> + +</qandadiv> + +<!-- Known Non-Bugs --> +<qandadiv id="faq.known_non-bugs" xreflabel="Known Non-Bugs"> +<title>Known Non-Bugs</title> + +<qandaentry id="faq.stream_reopening_fails"> + <question id="q-stream_reopening_fails"> + <para> + Reopening a stream fails + </para> + </question> + <answer id="a-stream_reopening_fails"> + <para> + One of the most-reported non-bug reports. Executing a sequence like: + </para> + + <literallayout> + #include <fstream> + ... + std::fstream fs(<quote>a_file</quote>); + // . + // . do things with fs... + // . + fs.close(); + fs.open(<quote>a_new_file</quote>); + </literallayout> + + <para> + All operations on the re-opened <varname>fs</varname> will fail, or at + least act very strangely. Yes, they often will, especially if + <varname>fs</varname> reached the EOF state on the previous file. The + reason is that the state flags are <emphasis>not</emphasis> cleared + on a successful call to open(). The standard unfortunately did + not specify behavior in this case, and to everybody's great sorrow, + the <ulink url="../ext/howto.html#5">proposed LWG resolution in + DR #22</ulink> is to leave the flags unchanged. You must insert a call + to <function>fs.clear()</function> between the calls to close() and open(), + and then everything will work like we all expect it to work. + <emphasis>Update:</emphasis> for GCC 4.0 we implemented the resolution + of <ulink url="../ext/howto.html#5">DR #409</ulink> and open() now calls + <function>clear()</function> on success! + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.wefcxx_verbose"> + <question id="q-wefcxx_verbose"> + <para> + -Weffc++ complains too much + </para> + </question> + <answer id="a-wefcxx_verbose"> + <para> + Many warnings are emitted when <literal>-Weffc++</literal> is used. Making + libstdc++ <literal>-Weffc++</literal>-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. + </para> + <para> + We do, however, try to have libstdc++ sources as clean as possible. If + you see some simple changes that pacify <literal>-Weffc++</literal> + without other drawbacks, send us a patch. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.ambiguous_overloads"> + <question id="q-ambiguous_overloads"> + <para> + Ambiguous overloads after including an old-style header + </para> + </question> + <answer id="a-ambiguous_overloads"> + <para> + Another problem is the <literal>rel_ops</literal> namespace and the template + comparison operator functions contained therein. If they become + visible in the same namespace as other comparison functions + (e.g., <quote>using</quote> 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 + <ulink url="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums + things up here</ulink>. The collisions with vector/string iterator + types have been fixed for 3.1. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.v2_headers"> + <question id="q-v2_headers"> + <para> + The g++-3 headers are <emphasis>not ours</emphasis> + </para> + </question> + <answer id="a-v2_headers"> + <para> + 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 <ulink url="http://gcc.gnu.org/bugs.html">the GCC + bug database</ulink>). + </para> + <para> + If the headers are in <filename>${prefix}/include/g++-3</filename>, or + if the installed library's name looks like + <filename>libstdc++-2.10.a</filename> or + <filename>libstdc++-libc6-2.10.so</filename>, then you are using the + old libstdc++-v2 library, which is nonstandard and + unmaintained. Do not report problems with -v2 to the -v3 + mailing list. + </para> + <para> + For GCC versions 3.0 and 3.1 the libstdc++ header files are + installed in <filename>${prefix}/include/g++-v3</filename> (see the + 'v'?). Starting with version 3.2 the headers are installed in + <filename>${prefix}/include/c++/${version}</filename> as this prevents + headers from previous versions being found by mistake. + </para> + + </answer> +</qandaentry> + +<qandaentry id="faq.boost_concept_checks"> + <question id="q-boost_concept_checks"> + <para> + Errors about <emphasis>*Concept</emphasis> and + <emphasis>constraints</emphasis> in the STL + </para> + </question> + <answer id="a-boost_concept_checks"> + <para> + If you see compilation errors containing messages about + <errortext>foo Concept </errortext>and something to do with a + <errortext>constraints</errortext> 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). + </para> + <para> + More information, including how to optionally enable/disable the + checks, is available + <ulink url="../19_diagnostics/howto.html#3">here</ulink>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.dlopen_crash"> + <question id="q-dlopen_crash"> + <para> + Program crashes when using library code in a + dynamically-loaded library + </para> + </question> + <answer id="a-dlopen_crash"> + <para> + If you are using the C++ library across dynamically-loaded + objects, make certain that you are passing the correct options + when compiling and linking: + </para> + + <literallayout> + // 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 + </literallayout> + </answer> +</qandaentry> + +<qandaentry id="faq.memory_leaks"> + <question id="q-memory_leaks"> + <para> + <quote>Memory leaks</quote> in containers + </para> + </question> + <answer id="a-memory_leaks"> + <para> + A few people have reported that the standard containers appear + to leak memory when tested with memory checkers such as + <ulink url="http://developer.kde.org/~sewardj/">valgrind</ulink>. + 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 + <ulink url="../debug.html#mem">Tips for memory leak hunting</ulink> + first. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.list_size_on"> + <question id="q-list_size_on"> + <para> + list::size() is O(n)! + </para> + </question> + <answer id="a-list_size_on"> + <para> + See + the <ulink url="../23_containers/howto.html#6">Containers</ulink> + chapter. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.easy_to_fix"> + <question id="q-easy_to_fix"> + <para> + Aw, that's easy to fix! + </para> + </question> + <answer id="a-easy_to_fix"> + <para> + 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 <ulink url="http://gcc.gnu.org/contribute.html">submitting + patches</ulink> 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++ + <ulink url="../17_intro/contribute.html">contributors' page</ulink> + also talks about how to submit patches. + </para> + <para> + 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 + <ulink url="#2_4">testsuite</ulink> -- but only if such a test exists. + </para> + </answer> +</qandaentry> + +</qandadiv> + + +<!-- Miscellaneous --> +<qandadiv id="faq.misc" xreflabel="Miscellaneous"> +<title>Miscellaneous</title> + +<qandaentry id="faq.iterator_as_pod"> + <question id="faq.iterator_as_pod_q"> + <para> + string::iterator is not char*; vector<T>::iterator is not T* + </para> + </question> + <answer id="faq.iterator_as_pod_a"> + <para> + 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. + </para> + <para> + 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 <type>T*</type> outweighs nearly all opposing + arguments. + </para> + <para> + Code which does assume that a vector iterator <varname>i</varname> + is a pointer can often be fixed by changing <varname>i</varname> in + certain expressions to <varname>&*i</varname>. Future revisions + of the Standard are expected to bless this usage for + vector<> (but not for basic_string<>). + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.what_is_next"> + <question id="q-what_is_next"> + <para> + What's next after libstdc++? + </para> + </question> + <answer id="a-what_is_next"> + <para> + 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 <emphasis>be</emphasis> any + more compliance work to do. + </para> + <para> + There is an effort underway to add significant extensions to + the standard library specification. The latest version of + this effort is described in + <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf"> + The C++ Library Technical Report 1</ulink>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.sgi_stl"> + <question id="q-sgi_stl"> + <para> + What about the STL from SGI? + </para> + </question> + <answer id="a-sgi_stl"> + <para> + The <ulink url="http://www.sgi.com/tech/stl/">STL from SGI</ulink>, + 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. + </para> + <para> + In particular, <classname>string</classname> is not from SGI and makes no + use of their "rope" class (which is included as an + optional extension), nor is <classname>valarray</classname> and some others. + Classes like <classname>vector<></classname> are, but have been + extensively modified. + </para> + <para> + More information on the evolution of libstdc++ can be found at the + <link linkend="appendix.porting.api">API + evolution</link> + and <link linkend="manual.appendix.porting.backwards">backwards + compatibility</link> documentation. + </para> + <para> + The FAQ for SGI's STL (one jump off of their main page) is + still recommended reading. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.extensions_and_backwards_compat"> + <question id="q-extensions_and_backwards_compat"> + <para> + Extensions and Backward Compatibility + </para> + </question> + <answer id="a-extensions_and_backwards_compat"> + <para> + See the <link linkend="manual.appendix.porting.backwards">link</link> on backwards compatiblity and <link linkend="appendix.porting.api">link</link> on evolution. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.tr1_support"> + <question id="q-tr1_support"> + <para> + Does libstdc++ support TR1? + </para> + </question> + <answer id="a-tr1_support"> + <para> + Yes. + </para> + <para> + The C++ Standard Library Technical Report adds many new features to + the library. The latest version of this effort is described in + <ulink url= + "http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf"> + Technical Report 1</ulink>. + </para> + <para> + The implementation status of TR1 in libstdc++ can be tracked <link + linkend="manual.intro.status.standard.tr1">on the TR1 status + page</link>. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.get_iso_cxx"> + <question id="q-get_iso_cxx"> + <para>How do I get a copy of the ISO C++ Standard? + </para> + </question> + <answer id="a-get_iso_cxx"> + <para> + 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 <ulink url="http://www.ansi.org">here</ulink>. (And if + you've already registered with them, clicking this link will take + you to directly to the place where you can + <ulink url="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%3A2003">buy the standard on-line</ulink>. + </para> + <para> + Who is your country's member body? Visit the + <ulink url="http://www.iso.ch/">ISO homepage</ulink> and find out! + </para> + <para> + The 2003 version of the standard (the 1998 version plus TC1) is + available in print, ISBN 0-470-84674-7. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.what_is_abi"> + <question id="q-what_is_abi"> + <para> + What's an ABI and why is it so messy? + </para> + </question> + <answer id="a-what_is_abi"> + <para> + <acronym>ABI</acronym> stands for <quote>Application Binary + Interface</quote>. 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. + </para> + <para> + 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 <quote>free-standing implementation</quote> that doesn't include (much + of) the standard library. It is a good basis for the work to come. + </para> + <para> + 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. + </para> + <para> + 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. + </para> + </answer> +</qandaentry> + +<qandaentry id="faq.size_equals_capacity"> + <question id="q-size_equals_capacity"> + <para> + How do I make std::vector<T>::capacity() == std::vector<T>::size? + </para> + </question> + <answer id="a-size_equals_capacity"> + <para> + The standard idiom for deallocating a <classname>vector<T></classname>'s + unused memory is to create a temporary copy of the vector and swap their + contents, e.g. for <classname>vector<T> v</classname> + </para> + <literallayout> + std::vector<T>(v).swap(v); + </literallayout> + <para> + The copy will take O(n) time and the swap is constant time. + </para> + <para> + See <ulink url="../21_strings/howto.html#6">Shrink-to-fit + strings</ulink> for a similar solution for strings. + </para> + </answer> +</qandaentry> + +</qandadiv> + + +<!-- FAQ ends here --> +</qandaset> + +</article> + +</book>
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