libstdc++-v3/docs/html/faq/index.html

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  14
  15 <h1 class="centered">libstdc++ Frequently Asked Questions</h1>
  16
  17 <p>The latest version of this document is always available at
  18    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/">
  19    http://gcc.gnu.org/onlinedocs/libstdc++/faq/</a>.  The main documentation
  20    page is at
  21    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html">
  22    http://gcc.gnu.org/onlinedocs/libstdc++/documentation.html</a>.
  23 </p>
  24
  25 <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
  26
  27 <!-- ####################################################### -->
  28 <hr>
  29 <h1>Questions</h1>
  30 <ol>
  31    <li><a href="#1_0">General Information</a>
  32    <!-- I suspect these will mostly be links to/into existing documents. -->
  33    <ol>
  34       <li><a href="#1_1">What is libstdc++-v3?</a>
  35       <li><a href="#1_2">Why should I use libstdc++?</a>
  36       <li><a href="#1_3">Who's in charge of it?</a>
  37       <li><a href="#1_4">How do I get libstdc++?</a>
  38       <li><a href="#1_5">When is libstdc++ going to be finished?</a>
  39       <li><a href="#1_6">How do I contribute to the effort?</a>
  40       <li><a href="#1_7">What happened to libg++?  I need that!</a>
  41       <li><a href="#1_8">What if I have more questions?</a>
  42       <li><a href="#1_9">What are the license terms for libstdc++-v3?</a>
  43    </ol>
  44
  45    <li><a href="#2_0">Installation</a>
  46       <ol>
  47          <li><a href="#2_1">How do I install libstdc++-v3?</a>
  48          <li><a href="#2_2">[removed]</a>
  49          <li><a href="#2_3">What is this CVS thing that you keep
  50                             mentioning?</a>
  51          <li><a href="#2_4">How do I know if it works?</a>
  52          <li><a href="#2_5">This library is HUGE!  And what's libsupc++?</a>
  53       </ol>
  54
  55    <li><a href="#3_0">Platform-Specific Issues</a>
  56       <ol>
  57          <li><a href="#3_1">Can libstdc++-v3 be used with &lt;my
  58                             favorite compiler&gt;?</a>
  59          <li><a href="#3_2">[removed]</a>
  60          <li><a href="#3_3">[removed]</a>
  61          <li><a href="#3_4">I can't use 'long long' on Solaris</a>
  62          <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
  63                             <code>_GNU_SOURCE</code> / etc is always defined</a>
  64          <li><a href="#3_6">OS X ctype.h is broken!  How can I hack it?</a>
  65       </ol>
  66
  67    <li><a href="#4_0">Known Bugs and Non-Bugs</a>
  68       <ol>
  69          <li><a href="#4_1">What works already?</a>
  70          <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a>
  71          <li><a href="#4_3">Bugs in the C++ language/lib specification</a>
  72          <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
  73            <li><a href="#4_4_iostreamclear">reopening a stream fails</a>
  74            <li><a href="#4_4_Weff">-Weffc++ complains too much</a>
  75            <li><a href="#4_4_rel_ops">&quot;ambiguous overloads&quot;
  76                                after including an old-style header</a>
  77            <li><a href="#4_4_interface">The g++-3 headers are
  78                                <strong>not ours</strong></a>
  79            <li><a href="#4_4_glibc">compilation errors from streambuf.h</a>
  80            <li><a href="#4_4_checks">errors about <em>*Concept</em> and
  81                                <em>constraints</em> in the STL...</a>
  82            <li><a href="#4_4_dlsym">program crashes when using library code
  83                                in a dynamically-loaded library</a>
  84          </ul>
  85          <li><a href="#4_5">Aw, that's easy to fix!</a>
  86       </ol>
  87
  88    <li><a href="#5_0">Miscellaneous</a>
  89       <ol>
  90          <li><a href="#5_1">string::iterator is not char*;
  91                             vector&lt;T&gt;::iterator is not T*</a>
  92          <li><a href="#5_2">What's next after libstdc++-v3?</a>
  93          <li><a href="#5_3">What about the STL from SGI?</a>
  94          <li><a href="#5_4">Extensions and Backward Compatibility</a>
  95          <li><a href="#5_5">[removed]</a>
  96          <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a>
  97          <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a>
  98          <li><a href="#5_8">What's an ABI and why is it so messy?</a>
  99       </ol>
 100
 101 </ol>
 102
 103 <hr>
 104
 105 <!-- ####################################################### -->
 106
 107 <h1><a name="1_0">1.0 General Information</a></h1>
 108 <!-- I suspect these will mostly be links to/into existing documents. -->
 109    <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
 110       <p>The GNU Standard C++ Library v3 is an
 111          ongoing project to implement the ISO 14882 Standard C++ library
 112          as described in chapters 17 through 27 and annex D.  As the
 113          library reaches stable plateaus, it is captured in a snapshot
 114          and released.  The current release is
 115          <a href="http://gcc.gnu.org/libstdc++/download.html">the
 116          fourteenth snapshot</a>.  For those who want to see exactly how
 117          far the project has come, or just want the latest
 118          bleeding-edge code, the up-to-date source is available over
 119          anonymous CVS, and can even be browsed over the Web (see below).
 120       </p>
 121       <p>The older libstdc++-v2 project is no longer maintained; the code
 122          has been completely replaced and rewritten.
 123          <a href="#4_4_interface">If you are using V2</a>, then you need to
 124          report bugs to your system vendor, not to the V3 list.
 125       </p>
 126       <p>A more formal description of the V3 goals can be found in the
 127          official <a href="../17_intro/DESIGN">design document</a>.
 128       </p>
 129
 130 <hr>
 131    <h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
 132       <p>The completion of the ISO C++ standardization gave the
 133          C++ community a powerful set of reuseable tools in the form
 134          of the C++ Standard Library.  However, all existing C++
 135          implementations are (as the Draft Standard used to say)
 136          &quot;incomplet and incorrekt,&quot; and many suffer from
 137          limitations of the compilers that use them.
 138       </p>
 139       <p>The GNU C/C++/FORTRAN/&lt;pick-a-language&gt; compiler
 140          (<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
 141          one of the leading compilers in the world.  Its development
 142          has recently been taken over by the
 143          <a href="http://gcc.gnu.org/">GCC team</a>.  All of
 144          the rapid development and near-legendary
 145          <a href="http://gcc.gnu.org/gcc-3.0/buildstat.html">portability</a>
 146          that are the hallmarks of an open-source project are being
 147          applied to libstdc++.
 148       </p>
 149       <p>That means that all of the Standard classes and functions
 150          (such as <code>string</code>, <code>vector&lt;&gt;</code>, iostreams,
 151          and algorithms) will be freely available and fully compliant.
 152          Programmers will no longer need to &quot;roll their own&quot;
 153          nor be worried about platform-specific incompatibilities.
 154       </p>
 155
 156 <hr>
 157    <h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
 158       <p>The libstdc++ project is contributed to by several developers
 159          all over the world, in the same way as GCC or Linux.
 160          Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, and Ulrich
 161          Drepper are the lead maintainers of the CVS archive.
 162       </p>
 163       <p>Development and discussion is held on the libstdc++ mailing
 164          list.  Subscribing to the list, or searching the list
 165          archives, is open to everyone.  You can read instructions for
 166          doing so on the <a href="http://gcc.gnu.org/libstdc++/">homepage</a>.
 167          If you have questions, ideas, code, or are just curious, sign up!
 168       </p>
 169
 170 <hr>
 171    <h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
 172       <p>The fourteenth (and latest) snapshot of libstdc++-v3 is
 173          <a href="http://gcc.gnu.org/libstdc++/download.html">available via
 174          ftp</a>.
 175       </p>
 176       <p>The <a href="http://gcc.gnu.org/libstdc++/">homepage</a>
 177          has instructions for retrieving the latest CVS sources, and for
 178          browsing the CVS sources over the web.
 179       </p>
 180       <p>The subset commonly known as the Standard Template Library
 181          (chapters 23 through 25, mostly) is adapted from the final release
 182          of the SGI STL.
 183       </p>
 184
 185 <hr>
 186    <h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
 187 <!--      <p>Nathan Myers gave the best of all possible answers in <A
 188          href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
 189          Usenet article</a>.</p>
 190 which is no longer available, thanks deja...-->
 191       <p>Nathan Myers gave the best of all possible answers, responding to a
 192          Usenet article asking this question:  <em>Sooner, if you help.</em>
 193       </p>
 194
 195 <hr>
 196    <h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
 197       <p>Here is <a href="../17_intro/contribute.html">a
 198          page devoted to this topic</a>.  Subscribing to the mailing
 199          list (see above, or the homepage) is a very good idea if you
 200          have something to contribute, or if you have spare time and
 201          want to help.  Contributions don't have to be in the form of
 202          source code; anybody who is willing to help write
 203          documentation, for example, or has found a bug in code that
 204          we all thought was working, is more than welcome!
 205       </p>
 206
 207 <hr>
 208    <h2><a name="1_7">1.7 What happened to libg++?  I need that!</a></h2>
 209       <p>The most recent libg++ README states that libg++ is no longer
 210          being actively maintained.  It should not be used for new
 211          projects, and is only being kicked along to support older code.
 212       </p>
 213       <p>The libg++ was designed and created when there was no Standard
 214          to provide guidance.  Classes like linked lists are now provided
 215          for by <code>list&lt;T&gt;</code> and do not need to be created by
 216          <code>genclass</code>.  (For that matter, templates exist now and
 217          are well-supported, whereas genclass (mostly) predates them.)
 218       </p>
 219       <p>There are other classes in libg++ that are not specified in the
 220          ISO Standard (e.g., statistical analysis).  While there are a
 221          lot of really useful things that are used by a lot of people
 222          (e.g., statistics :-), the Standards Committee couldn't include
 223          everything, and so a lot of those &quot;obvious&quot; classes
 224          didn't get included.
 225       </p>
 226       <p>Since libstdc++ is an implementation of the Standard Library, we
 227          have no plans at this time to include non-Standard utilities
 228          in the implementation, however handy they are.  (The extensions
 229          provided in the SGI STL aren't maintained by us and don't get
 230          a lot of our attention, because they don't require a lot of our
 231          time.)  It is entirely plausable that the &quot;useful stuff&quot;
 232          from libg++ might be extracted into an updated utilities library,
 233          but nobody has stated such a project yet.
 234       </p>
 235       <!-- The advertisement, so to speak, might have to go.  Hmmmmm.  -->
 236       <p>(The <a href="http://www.boost.org/">Boost</a> site houses free
 237          C++ libraries that do varying things, and happened to be started
 238          by members of the Standards Committee.  Certain &quot;useful
 239          stuff&quot; classes will probably migrate there.)
 240       </p>
 241       <p>For the bold and/or desperate, the
 242          <a href="http://gcc.gnu.org/fom_serv/cache/33.html">GCC FAQ</a>
 243          describes where to find the last libg++ source.
 244       </p>
 245
 246 <hr>
 247    <h2><a name="1_8">1.8 What if I have more questions?</a></h2>
 248       <p>If you have read the README and RELEASE-NOTES files, and your
 249          question remains unanswered, then just ask the mailing list.
 250          At present, you do not need to be subscribed to the list to
 251          send a message to it.  More information is available on the
 252          homepage (including how to browse the list archives); to send
 253          to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
 254          <code>libstdc++@gcc.gnu.org</code></a>.
 255       </p>
 256       <p>If you have a question that you think should be included here,
 257          or if you have a question <em>about</em> a question/answer here,
 258          contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
 259          or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
 260       </p>
 261
 262 <hr>
 263    <h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
 264       <p>See <a href="../17_intro/license.html">our license description</a>
 265          for these and related questions.
 266       </p>
 267
 268 <hr>
 269 <h1><a name="2_0">2.0 Installation</a></h1>
 270    <h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
 271       <p>Complete instructions are not given here (this is a FAQ, not
 272          an installation document), but the tools required are few:
 273       </p>
 274          <ul>
 275             <li> A 3.x release of GCC.  Note that building GCC is much
 276                  easier and more automated than building the GCC 2.[78]
 277                  series was.  If you are using GCC 2.95, you can still
 278                  build earlier snapshots of libstdc++.
 279             <li> GNU Make is recommended, but should not be required.
 280             <li> The GNU Autotools are needed if you are messing with
 281                  the configury or makefiles.
 282          </ul>
 283       <p>The file <a href="../documentation.html">documentation.html</a>
 284          provides a good overview of the steps necessary to build, install,
 285          and use the library.  Instructions for configuring the library
 286          with new flags such as --enable-threads are there also, as well as
 287          patches and instructions for working with GCC 2.95.
 288       </p>
 289       <p>The top-level install.html and
 290          <a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
 291          the exact build and installation instructions.  You may wish to
 292          browse those files over CVSweb ahead of time to get a feel for
 293          what's required.  RELEASE-NOTES is located in the
 294          &quot;.../docs/17_intro/&quot; directory of the distribution.
 295       </p>
 296
 297 <hr>
 298    <h2><a name="2_2">2.2 [removed]</a></h2>
 299       <p>This question has become moot and has been removed.  The stub
 300          is here to preserve numbering (and hence links/bookmarks).
 301       </p>
 302
 303 <hr>
 304    <h2><a name="2_3">2.3 What is this CVS thing that you
 305                          keep mentioning?</a></h2>
 306       <p>The <em>Concurrent Versions System</em> is one of several revision
 307          control packages.  It was selected for GNU projects because it's
 308          free (speech), free (beer), and very high quality.  The <A
 309          href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
 310          the GNU software catalogue</a> has a better description as
 311          well as a
 312          <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
 313       </p>
 314       <p>The &quot;anonymous client checkout&quot; feature of CVS is
 315          similar to anonymous FTP in that it allows anyone to retrieve
 316          the latest libstdc++ sources.
 317       </p>
 318       <p>After the first of April, American users will have a
 319          &quot;/pharmacy&quot; command-line option...
 320          <!-- wonder how long that'll live -->
 321       </p>
 322
 323 <hr>
 324    <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
 325       <p>libstdc++-v3 comes with its own testsuite.  You do not need
 326          to actually install the library (&quot;<code>make
 327          install</code>&quot;) to run the testsuite.
 328       </p>
 329       <p>To run the testsuite on the library after building it, use
 330          &quot;make check&quot; while in your build directory.  To run
 331          the testsuite on the library after building and installing it,
 332          use &quot;make check-install&quot; instead.
 333       </p>
 334       <p>If you find bugs in the testsuite programs themselves, or if you
 335          think of a new test program that should be added to the suite,
 336          <strong>please</strong> write up your idea and send it to the list!
 337       </p>
 338
 339 <hr>
 340    <h2><a name="2_5">2.4 This library is HUGE!  And what's libsupc++?</a></h2>
 341       <p>Usually the size of libraries on disk isn't noticeable.  When a
 342          link editor (or simply &quot;linker&quot;) pulls things from a
 343          static archive library, only the necessary object files are copied
 344          into your executable, not the entire library.  Unfortunately, even
 345          if you only need a single function or variable from an object file,
 346          the entire object file is extracted.  (There's nothing unique to C++
 347          or libstdc++-v3 about this; it's just common behavior, given here
 348          for background reasons.)
 349       </p>
 350       <p>Some of the object files which make up libstdc++.a are rather large.
 351          If you create a statically-linked executable with
 352          <code> -static</code>, those large object files are suddenly part
 353          of your executable.  Historically the best way around this was to
 354          only place a very few functions (often only a single one) in each
 355          source/object file; then extracting a single function is the same
 356          as extracting a single .o file.  For libstdc++-v3 this is only
 357          possible to a certain extent; the object files in question contain
 358          template classes and template functions, pre-instantiated, and
 359          splitting those up causes severe maintenance headaches.
 360       </p>
 361       <p>It's not a bug, and it's not really a problem.  Nevertheless, some
 362          people don't like it, so here are two pseudo-solutions:
 363       </p>
 364       <p>If the only functions from libstdc++.a which you need are language
 365          support functions (those listed in
 366          <a href="../18_support/howto.html">clause 18</a> of the standard,
 367          e.g., <code>new</code> and <code>delete</code>), then try linking
 368          against <code>libsupc++.a</code> (usually specifying
 369          <code>-lsupc++</code> when calling g++ for the final link step will
 370          do it).  This library contains only those support routines, one per
 371          object file.  But if you are using anything from the rest of the
 372          library, such as IOStreams or vectors, then you'll still need
 373          pieces from <code>libstdc++.a</code>.
 374       </p>
 375       <p>The second method is one we hope to incorporate into the library
 376          build process.  Some platforms can place each function and variable
 377          into its own section in a .o file.  The GNU linker can then perform
 378          garbage collection on unused sections; this reduces the situation
 379          to only copying needed functions into the executable, as before,
 380          but all happens automatically.
 381       </p>
 382       <p>Unfortunately the garbage collection in GNU ld is buggy; sections
 383          (corresponding to functions and variables) which <em>are</em> used
 384          are mistakenly removed, leading to horrible crashes when your
 385          executable starts up.  For the time being, this feature is not used
 386          when building the library.
 387       </p>
 388
 389 <hr>
 390 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
 391    <h2><a name="3_1">3.1 Can libstdc++-v3 be used with &lt;my
 392                          favorite compiler&gt;?</a></h2>
 393       <p>Probably not.  Yet.</p>
 394       <p>Because GCC advances so rapidly, development and testing of
 395          libstdc++ is being done almost entirely under that compiler.
 396          If you are curious about whether other, lesser compilers
 397          (*grin*) support libstdc++, you are more than welcome to try.
 398          Configuring and building the library (see above) will still
 399          require certain tools, however.  Also keep in mind that
 400          <em>building</em> libstdc++ does not imply that your compiler
 401          will be able to <em>use</em> all of the features found in the
 402          C++ Standard Library.
 403       </p>
 404       <p>Since the goal of ISO Standardization is for all C++
 405          implementations to be able to share code, the final libstdc++
 406          should, in theory, be usable under any ISO-compliant
 407          compiler.  It will still be targeted and optimized for
 408          GCC/g++, however.
 409       </p>
 410
 411 <hr>
 412    <h2><a name="3_2">3.2 [removed]</a></h2>
 413       <p>This question has become moot and has been removed.  The stub
 414          is here to preserve numbering (and hence links/bookmarks).
 415       </p>
 416
 417 <hr>
 418    <h2><a name="3_3">3.3 [removed]</a></h2>
 419       <p>This question has become moot and has been removed.  The stub
 420          is here to preserve numbering (and hence links/bookmarks).
 421       </p>
 422
 423 <hr>
 424    <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
 425       <p>By default we try to support the C99 <code>long long</code> type.
 426          This requires that certain functions from your C library be present.
 427       </p>
 428       <p>Up through release 3.0.2 the tests performed were too general, and
 429          this feature was disabled when it did not need to be.  The most
 430          commonly reported platform affected was Solaris.
 431       </p>
 432       <p>This has been fixed for 3.0.3 and onwards.
 433       </p>
 434
 435 <hr>
 436    <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
 437                          / etc is always defined</a></h2>
 438       <p>On Solaris, g++ (but not gcc) always defines the preprocessor
 439          macro <code>_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 440          with <code>_GNU_SOURCE</code>.  (This is not an exhaustive list;
 441          other macros and other platforms are also affected.)
 442       </p>
 443       <p>These macros are typically used in C library headers, guarding new
 444          versions of functions from their older versions.  The C++ standard
 445          library includes the C standard library, but it requires the C90
 446          version, which for backwards-compatability reasons is often not the
 447          default for many vendors.
 448       </p>
 449       <p>More to the point, the C++ standard requires behavior which is only
 450          available on certain platforms after certain symbols are defined.
 451          Usually the issue involves I/O-related typedefs.  In order to
 452          ensure correctness, the compiler simply predefines those symbols.
 453       </p>
 454       <p>Note that it's not enough to #define them only when the library is
 455          being built (during installation).  Since we don't have an 'export'
 456          keyword, much of the library exists as headers, which means that
 457          the symbols must also be defined as your programs are parsed and
 458          compiled.
 459       </p>
 460       <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 461          the gcc config headers for your target (and try changing them to
 462          see what happens when building complicated code).  You can also run
 463          <code>&quot;g++ -E -dM - &lt; /dev/null&quot;</code> to display
 464          a list of predefined macros for any particular installation.
 465       </p>
 466       <p>This has been discussed on the mailing lists
 467          <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
 468       </p>
 469       <p>This method is something of a wart.  We'd like to find a cleaner
 470          solution, but nobody yet has contributed the time.
 471       </p>
 472
 473 <hr>
 474    <h2><a name="3_6">3.6 OS X ctype.h is broken!  How can I hack it?</a></h2>
 475       <p>This is a long-standing bug in the OS X support.  Fortunately,
 476          the patch is quite simple, and well-known.
 477          <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
 478          link to the solution.</a>
 479       </p>
 480
 481 <hr>
 482 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
 483    <em>Note that this section can get rapdily outdated -- such is the
 484    nature of an open-source project.  For the latest information, join
 485    the mailing list or look through recent archives.   The RELEASE-
 486    NOTES and BUGS files are generally kept up-to-date.</em>
 487
 488    <p>For 3.0.1, the most common &quot;bug&quot; is an apparently missing
 489       &quot;<code>../</code>&quot; in include/Makefile, resulting in files
 490       like gthr.h and gthr-single.h not being found.  Please read
 491       <a href="http://gcc.gnu.org/install/configure.html">the configuration
 492       instructions for GCC</a>,
 493       specifically the part about configuring in a separate build directory,
 494       and how strongly recommended it is.  Building in the source directory
 495       is fragile, is rarely tested, and tends to break, as in this case.
 496       This was fixed for 3.0.2.
 497    </p>
 498
 499    <p>For 3.1, the most common &quot;bug&quot; is a parse error when using
 500       <code>&lt;fstream&gt;</code>, ending with a message,
 501       &quot;<code>bits/basic_file.h:52: parse error before `{'
 502       token</code>.&quot;  Please read
 503       <a href="http://gcc.gnu.org/install/">the installation instructions for
 504       GCC</a>, specifically the part about not installing newer versions on
 505       top of older versions.  If you install 3.1 over a 3.0.x release, then
 506       the wrong basic_file.h header will be found (its location changed
 507       between releases).
 508    </p>
 509
 510    <p><strong>Please do not report these as bugs.  We know about them.</strong>
 511       Reporting this -- or any other problem that's already been fixed --
 512       hinders the development of GCC, because we have to take time to
 513       respond to your report.  Thank you.
 514    </p>
 515
 516    <h2><a name="4_1">4.1 What works already?</a></h2>
 517       <p>This is a verbatim clip from the &quot;Status&quot; section
 518          of the RELEASE-NOTES for the latest snapshot.  For a list of
 519          fixed bugs, see that file.
 520       </p>
 521
 522 <!-- Yeah, I meant that "verbatim clip" thing literally... :-)  -->
 523
 524 <pre>
 525 New:
 526 ---
 527 (post 3.0.97)
 528 - more doxygen documentation
 529 - more named locale fixups
 530 - stdio_filebuf that takes fd, FILE
 531 - io performance tuning
 532 - allocation tuning, valgrind fixups
 533 - __cxa_demangle now supported
 534 (3.0.97)
 535 - more doxygen documentation.
 536 - more named locale bug fixes
 537 - support for symbol versioning when using GNU ld &gt;= 2.12
 538 - wide-io
 539 - tuning for executable size
 540 (3.0.96)
 541 - more doxygen documentation.
 542 - extensions moved out of namespace std
 543 - HPUX long long support
 544 - more string optimizations
 545 - support for NetBSD cross compiles
 546 - concept_check merge from boost
 547 - header simplification
 548 - named locale bug shakeout
 549 - thread testsuite
 550 (3.0.95)
 551 - add S390, m68k, x86-64 support.
 552 - doxygen documentation has been extended, including man pages.
 553 - verbose terminate handling has been added.
 554 - some libsupc++ tweaks
 555 - warnings for deprecated headers now active.
 556 - dejagnu testsuite preliminary documentation.
 557 - dejagnu testsuite default.
 558 - dejagnu testsuite cross compiler, multilib safe.
 559 - long long iostreams on by default, rework of ISO C99 support.
 560 - iterator re-write and testsuites.
 561 - container testsuites.
 562 - allocator revamp and testsuites.
 563 - more concept-checking work.
 564 - basic_string optimization and MT fixes.
 565 - new limits implementation.
 566 - update -fno-exceptions code, verify it works.
 567 - full named locale support fpr all facets, choice of gnu,
 568   ieee_1003.1-200x (POSIX 2), or generic models. Full support depends
 569   on target OS and underlying &quot;C&quot; library support.
 570 </pre>
 571
 572
 573 <hr>
 574    <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
 575       <p>This is by no means meant to be complete nor exhaustive, but
 576          mentions some problems that users may encounter when building
 577          or using libstdc++.  If you are experiencing one of these
 578          problems, you can find more information on the libstdc++ and
 579          the GCC mailing lists.
 580       </p>
 581       <p>Before reporting a bug, examine the
 582          <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
 583          category set to &quot;libstdc++&quot;.  The BUGS file in the source
 584          tree also tracks known serious problems.
 585       </p>
 586       <ul>
 587          <li>Debugging is problematic, due to bugs in line-number generation
 588              (mostly fixed in the compiler) and gdb lagging behind the
 589              compiler (lack of personnel).  We recommend configuring the
 590              compiler using <code>--with-dwarf2</code> if the DWARF2
 591              debugging format is not already the default on your platform.
 592              Also,
 593 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
 594              GDB settings</a> can have a profound effect on your C++ debugging
 595              experiences.  :-)</li>
 596       </ul>
 597
 598 <hr>
 599    <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
 600       <p>Yes, unfortunately, there are some.  In a
 601          <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
 602          to the list</a>, Nathan Myers announced that he has started a list of
 603          problems in the ISO C++ Standard itself, especially with
 604          regard to the chapters that concern the library.  The list
 605          itself is
 606          <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
 607          website</a>.  Developers who are having problems interpreting
 608          the Standard may wish to consult his notes.
 609       </p>
 610       <p>For those people who are not part of the ISO Library Group
 611          (i.e., nearly all of us needing to read this page in the first
 612          place :-), a public list of the library defects is occasionally
 613          published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
 614          Some of these have resulted in <a href="#5_2">code changes</a>.
 615       </p>
 616
 617 <hr>
 618    <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
 619       <p>There are things which are not bugs in the compiler (4.2) nor
 620          the language specification (4.3), but aren't really bugs in
 621          libstdc++, either.  Really!  Please do not report these as bugs.
 622       </p>
 623       <a name="4_4_Weff">
 624         <p><strong>-Weffc++</strong>
 625            The biggest of these is the quadzillions of warnings about the
 626            library headers emitted when <code>-Weffc++</code> is used.  Making
 627            libstdc++ &quot;-Weffc++-clean&quot; is not a goal of the project,
 628            for a few reasons.  Mainly, that option tries to enforce
 629            object-oriented programming, while the Standard Library isn't
 630            necessarily trying to be OO.
 631         </p>
 632       </a>
 633       <a name="4_4_iostreamclear">
 634         <p><strong>reopening a stream fails</strong>
 635            Did I just say that -Weffc++ was our biggest false-bug report?  I
 636            lied.  (It used to be.)  Today it seems to be reports that after
 637            executing a sequence like
 638            <pre>
 639     #include &lt;fstream&gt;
 640     ...
 641     std::fstream  fs(&quot;a_file&quot;);
 642     // .
 643     // . do things with fs...
 644     // .
 645     fs.close();
 646     fs.open(&quot;a_new_file&quot;);</pre>
 647            all operations on the re-opened <code>fs</code> will fail, or at
 648            least act very strangely.  Yes, they often will, especially if
 649            <code>fs</code> reached the EOF state on the previous file.  The
 650            reason is that the state flags are <strong>not</strong> cleared
 651            on a successful call to open().  The standard unfortunately did
 652            not specify behavior in this case, and to everybody's great sorrow,
 653            the <a href="../ext/howto.html#5">proposed LWG resolution</a> (see
 654            DR #22) is to leave the flags unchanged.  You must insert a call
 655            to <code>fs.clear()</code> between the calls to close() and open(),
 656            and then everything will work like we all expect it to work.
 657         </p>
 658       </a>
 659       <a name="4_4_rel_ops">
 660         <p><strong>rel_ops</strong>
 661            Another is the <code>rel_ops</code> namespace and the template
 662            comparison operator functions contained therein.  If they become
 663            visible in the same namespace as other comparison functions
 664            (e.g., '<code>using</code>' them and the &lt;iterator&gt; header),
 665            then you will suddenly be faced with huge numbers of ambiguity
 666            errors.  This was discussed on the -v3 list; Nathan Myers
 667            <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
 668            things up here</a>.  The collisions with vector/string iterator
 669            types have been fixed for 3.1.  <!-- more links to email here -->
 670         </p>
 671       </a>
 672       <a name="4_4_interface"><h3>The g++-3 headers are
 673                                       <em>not ours</em></h3>
 674         <p>If you have found an extremely broken header file which is
 675            causing problems for you, look carefully before submitting a
 676            &quot;high&quot; priority bug report (which you probably shouldn't
 677            do anyhow; see the last paragraph of the page describing
 678          <a href="http://gcc.gnu.org/gnatswrite.html">the GCC bug database</a>).
 679         </p>
 680         <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
 681            the installed library's name looks like <code>libstdc++-2.10.a</code>
 682            or <code>libstdc++-libc6-2.10.so</code>,
 683            then you are using the old libstdc++-v2 library, which is nonstandard
 684            and unmaintained.  Do not report problems with -v2 to the -v3
 685            mailing list.
 686         </p>
 687         <p>Currently our header files are installed in
 688            <code>${prefix}/include/g++-v3</code> (see the 'v'?).  This may
 689            change with the next release of GCC, as it may be too confusing,
 690            but <a href="http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html">the
 691            question has not yet been decided</a>.
 692         </p>
 693       </a>
 694       <a name="4_4_glibc">
 695         <p><strong>glibc</strong>
 696            If you're on a GNU/Linux system and have just upgraded to
 697            glibc 2.2, but are still using gcc 2.95.2, then you should have
 698            read the glibc FAQ, specifically 2.34:
 699    <pre>
 700 2.34.   When compiling C++ programs, I get a compilation error in streambuf.h.
 701
 702 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
 703 apply a patch to the include files in /usr/include/g++, because the fpos_t
 704 type has changed in glibc 2.2.  The patch is at
 705 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
 706    </pre>
 707            Note that 2.95.x shipped with the
 708            <a href="#4_4_interface">old v2 library</a> which is no longer
 709            maintained.  Also note that gcc 2.95.3 fixes this problem, but
 710            requires a separate patch for libstdc++-v3.
 711         </p>
 712       </a>
 713       <a name="4_4_checks">
 714         <p><strong>concept checks</strong>
 715            If you see compilation errors containing messages about
 716            <code> <em>foo</em>Concept </code>and a<code> constraints </code>
 717            member function, then most likely you have violated one of the
 718            requirements for types used during instantiation of template
 719            containers and functions.  For example, EqualityComparableConcept
 720            appears if your types must be comparable with == and you have not
 721            provided this capability (a typo, or wrong visibility, or you
 722            just plain forgot, etc).
 723         </p>
 724         <p>More information, including how to optionally enable/disable the
 725            checks, is available
 726            <a href="../19_diagnostics/howto.html#3">here</a>.
 727         </p>
 728       </a>
 729       <a name="4_4_dlsym">
 730         <p><strong>dlopen/dlsym</strong>
 731            If you are using the C++ library across dynamically-loaded
 732            objects, make certain that you are passing the correct options
 733            when compiling and linking:
 734            <pre>
 735     // compile the library components
 736     g++ -fPIC -c a.cc
 737     g++ -fPIC -c b.cc
 738     ...
 739     g++ -fPIC -c z.cc
 740
 741     // create the library
 742     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
 743
 744     // link the executable
 745     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre></p>
 746       </a>
 747
 748 <hr>
 749    <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
 750       <p>If you have found a bug in the library and you think you have
 751          a working fix, then send it in!  The main GCC site has a page
 752          on <a href="http://gcc.gnu.org/contribute.html">submitting
 753          patches</a> that covers the procedure, but for libstdc++ you
 754          should also send the patch to our mailing list in addition to
 755          the GCC patches mailing list.  The libstdc++
 756          <a href="../17_intro/contribute.html">contributors' page</a>
 757          also talks about how to submit patches.
 758       </p>
 759       <p>In addition to the description, the patch, and the ChangeLog
 760          entry, it is a Good Thing if you can additionally create a small
 761          test program to test for the presence of the bug that your
 762          patch fixes.  Bugs have a way of being reintroduced; if an old
 763          bug creeps back in, it will be caught immediately by the
 764          <a href="#2_4">testsuite</a> -- but only if such a test exists.
 765       </p>
 766
 767 <hr>
 768 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
 769    <h2><a name="5_1">5.1 string::iterator is not char*;
 770                      vector&lt;T&gt;::iterator is not T*</a></h2>
 771       <p>If you have code that depends on container&lt;T&gt; iterators
 772          being implemented as pointer-to-T, your code is broken.
 773       </p>
 774       <p>While there are arguments for iterators to be implemented in
 775          that manner, A) they aren't very good ones in the long term,
 776          and B) they were never guaranteed by the Standard anyway.  The
 777          type-safety achieved by making iterators a real class rather
 778          than a typedef for <code>T*</code> outweighs nearly all opposing
 779          arguments.
 780       </p>
 781       <p>Code which does assume that a vector iterator <code> i </code>
 782          is a pointer can often be fixed by changing <code> i </code> in
 783          certain expressions to <code> &amp;*i </code>.  Future revisions
 784          of the Standard are expected to bless this usage for
 785          vector&lt;&gt; (but not for basic_string&lt;&gt;).
 786       </p>
 787
 788 <hr>
 789    <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
 790       <p>Hopefully, not much.  The goal of libstdc++-v3 is to produce
 791          a fully-compliant, fully-portable Standard Library.  After that,
 792          we're mostly done:  there won't <em>be</em> any more compliance
 793          work to do.  However:
 794       </p>
 795       <ol>
 796       <li><p>The ISO Committee will meet periodically to review Defect Reports
 797          in the C++ Standard.  Undoubtedly some of these will result in
 798          changes to the Standard, which will be reflected in patches to
 799          libstdc++.  Some of that is already happening, see 4.2.  Some of
 800          those changes are being predicted by the library maintainers, and
 801          we add code to the library based on what the current proposed
 802          resolution specifies.  Those additions are listed in
 803          <a href="../ext/howto.html#5">the extensions page</a>.
 804       </p>
 805       <li><p>Performance tuning.  Lots of performance tuning.  This too is
 806          already underway for post-3.0 releases, starting with memory
 807          expansion in container classes and buffer usage in synchronized
 808          stream objects.
 809       </p>
 810       <li><p>An ABI for libstdc++ is being developed, so that
 811          multiple binary-incompatible copies of the library can be replaced
 812          with a single backwards-compatible library, like libgcc_s.so is.
 813       </p>
 814       <li><p>The current libstdc++ contains extensions to the Library which
 815          must be explicitly requested by client code (for example, the
 816          hash tables from SGI).  Other extensions may be added to
 817          libstdc++-v3 if they seem to be &quot;standard&quot; enough.
 818          (For example, the &quot;long long&quot; type from C99.)
 819          Bugfixes and rewrites (to improve or fix thread safety, for
 820          instance) will of course be a continuing task.
 821       </p>
 822       </ol>
 823       <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
 824          question</a> about the next libstdc++ prompted some brief but
 825          interesting
 826          <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
 827       </p>
 828
 829 <hr>
 830    <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
 831       <p>The <a href="http://www.sgi.com/Technology/STL/">STL from SGI</a>,
 832          version 3.3, was the most recent merge of the STL codebase.  The
 833          code in libstdc++ contains many fixes and changes, and it is
 834          very likely that the SGI code is no longer under active
 835          development.  We expect that no future merges will take place.
 836       </p>
 837       <p>In particular, <code>string</code> is not from SGI and makes no
 838          use of their &quot;rope&quot; class (which is included as an
 839          optional extension), nor is <code>valarray</code> and some others.
 840          Classes like <code>vector&lt;&gt;</code> are, however.
 841       </p>
 842       <p>The FAQ for SGI's STL (one jump off of their main page) is
 843          recommended reading.
 844       </p>
 845
 846 <hr>
 847    <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
 848       <p>Although you can specify <code>-I</code> options to make the
 849          preprocessor search the g++-v3/ext and /backward directories,
 850          it is better to refer to files there by their path, as in:
 851          <!-- Careful, the leading spaces in PRE show up directly. -->
 852       </p>
 853          <pre>
 854        #include &lt;ext/hash_map&gt;
 855          </pre>
 856       <p>Extensions to the library have
 857          <a href="../ext/howto.html">their own page</a>.
 858       </p>
 859
 860 <hr>
 861    <h2><a name="5_5">5.5 [removed]</a></h2>
 862       <p>This question has become moot and has been removed.  The stub
 863          is here to preserve numbering (and hence links/bookmarks).
 864       </p>
 865
 866 <hr>
 867    <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
 868       <p>When the system's libc is itself thread-safe, a non-generic
 869          implementation of atomicity.h exists for the architecture, and gcc
 870          itself reports a thread model other than single; libstdc++-v3
 871          strives to be thread-safe.  The user-code must guard against
 872          concurrent method calls which may access any particular library
 873          object's state.  Typically, the application programmer may infer
 874          what object locks must be held based on the objects referenced in
 875          a method call.  Without getting into great detail, here is an
 876          example which requires user-level locks:
 877          <pre>
 878      library_class_a shared_object_a;
 879
 880      thread_main () {
 881        library_class_b *object_b = new library_class_b;
 882        shared_object_a.add_b (object_b);   // must hold lock for shared_object_a
 883        shared_object_a.mutate ();          // must hold lock for shared_object_a
 884      }
 885
 886      // Multiple copies of thread_main() are started in independent threads.</pre>
 887       </p>
 888       <p>Under the assumption that object_a and object_b are never exposed to
 889          another thread, here is an example that should not require any
 890          user-level locks:
 891          <pre>
 892      thread_main () {
 893        library_class_a object_a;
 894        library_class_b *object_b = new library_class_b;
 895        object_a.add_b (object_b);
 896        object_a.mutate ();
 897      } </pre>
 898       </p>
 899       <p>All library objects are safe to use in a multithreaded program as
 900          long as each thread carefully locks out access by any other thread
 901          while it uses any object visible to another thread.  In general,
 902          this requirement includes both read and write access to objects;
 903          unless otherwise documented as safe, do not assume that two
 904          threads may access a shared standard library object at the
 905          same time.
 906       </p>
 907       <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
 908          introduction), <a href="../23_containers/howto.html#3">23</a>
 909          (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
 910          more information.
 911       </p>
 912
 913 <hr>
 914    <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
 915       <p>Copies of the full ISO 14882 standard are available on line via the
 916          ISO mirror site for committee members.  Non-members, or those who
 917          have not paid for the privilege of sitting on the committee and
 918          sustained their two-meeting commitment for voting rights, may get a
 919          copy of the standard from their respective national standards
 920          organization.  In the USA, this national standards organization is
 921          ANSI and their website is right <a href="http://www.ansi.org">here</a>.
 922          (And if you've already registered with them, clicking this link will
 923          take you to directly to the place where you can
 924 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998">buy
 925          the standard on-line</a>.
 926       </p>
 927       <p>Who is your country's member body?  Visit the
 928          <a href="http://www.iso.ch/">ISO homepage</a> and find out!
 929       </p>
 930
 931 <hr>
 932    <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
 933       <p>&quot;ABI&quot; stands for &quot;Application Binary Interface.&quot;
 934          Conventionally, it refers to a great mass of details about how
 935          arguments are arranged on the call stack and/or in registers, and
 936          how various types are arranged and padded in structs.  A single CPU
 937          design may suffer multiple ABIs designed by different development
 938          tool vendors who made different choices, or even by the same vendor
 939          for different target applications or compiler versions.  In ideal
 940          circumstances the CPU designer presents one ABI and all the OSes and
 941          compilers use it.  In practice every ABI omits details that compiler
 942          implementers (consciously or accidentally) must choose for themselves.
 943       </p>
 944       <p>That ABI definition suffices for compilers to generate code so a
 945          program can interact safely with an OS and its lowest-level libraries.
 946          Users usually want an ABI to encompass more detail, allowing libraries
 947          built with different compilers (or different releases of the same
 948          compiler!) to be linked together.  For C++, this includes many more
 949          details than for C, and CPU designers (for good reasons elaborated
 950          below) have not stepped up to publish C++ ABIs.  The details include
 951          virtual function implementation, struct inheritance layout, name
 952          mangling, and exception handling.  Such an ABI has been defined for
 953          GNU C++, and is immediately useful for embedded work relying only on
 954          a &quot;free-standing implementation&quot; that doesn't include (much
 955          of) the standard library.  It is a good basis for the work to come.
 956       </p>
 957       <p>A useful C++ ABI must also incorporate many details of the standard
 958          library implementation.  For a C ABI, the layouts of a few structs
 959          (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 960          For C++, the details include the complete set of names of functions
 961          and types used, the offsets of class members and virtual functions,
 962          and the actual definitions of all inlines.  C++ exposes many more
 963          library details to the caller than C does.  It makes defining
 964          a complete ABI a much bigger undertaking, and requires not just
 965          documenting library implementation details, but carefully designing
 966          those details so that future bug fixes and optimizations don't
 967          force breaking the ABI.
 968       </p>
 969       <p>There are ways to help isolate library implementation details from the
 970          ABI, but they trade off against speed.  Library details used in
 971          inner loops (e.g., getchar) must be exposed and frozen for all
 972          time, but many others may reasonably be kept hidden from user code,
 973          so they may later be changed.  Deciding which, and implementing
 974          the decisions, must happen before you can reasonably document a
 975          candidate C++ ABI that encompasses the standard library.
 976       </p>
 977
 978 <!-- ####################################################### -->
 979
 980 <hr>
 981 <p class="fineprint"><em>
 982 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
 983 Comments and suggestions are welcome, and may be sent to
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 985 </em></p>
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 990