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 </p>
  27
  28 <!-- ####################################################### -->
  29 <hr />
  30 <h1>Questions</h1>
  31 <ol>
  32    <li><a href="#1_0">General Information</a>
  33    <!-- I suspect these will mostly be links to/into existing documents. -->
  34    <ol>
  35       <li><a href="#1_1">What is libstdc++-v3?</a> </li>
  36       <li><a href="#1_2">Why should I use libstdc++?</a> </li>
  37       <li><a href="#1_3">Who's in charge of it?</a> </li>
  38       <li><a href="#1_4">How do I get libstdc++?</a> </li>
  39       <li><a href="#1_5">When is libstdc++ going to be finished?</a> </li>
  40       <li><a href="#1_6">How do I contribute to the effort?</a> </li>
  41       <li><a href="#1_7">What happened to libg++?  I need that!</a> </li>
  42       <li><a href="#1_8">What if I have more questions?</a> </li>
  43       <li><a href="#1_9">What are the license terms for libstdc++-v3?</a> </li>
  44    </ol>
  45    </li>
  46
  47    <li><a href="#2_0">Installation</a>
  48       <ol>
  49          <li><a href="#2_1">How do I install libstdc++-v3?</a> </li>
  50          <li><a href="#2_2">[removed]</a> </li>
  51          <li><a href="#2_3">What is this CVS thing that you keep
  52                             mentioning?</a> </li>
  53          <li><a href="#2_4">How do I know if it works?</a> </li>
  54          <li><a href="#2_5">This library is HUGE!  And what's libsupc++?</a> </li>
  55       </ol>
  56    </li>
  57
  58    <li><a href="#3_0">Platform-Specific Issues</a>
  59       <ol>
  60          <li><a href="#3_1">Can libstdc++-v3 be used with &lt;my
  61                             favorite compiler&gt;?</a> </li>
  62          <li><a href="#3_2">[removed]</a> </li>
  63          <li><a href="#3_3">[removed]</a> </li>
  64          <li><a href="#3_4">I can't use 'long long' on Solaris</a> </li>
  65          <li><a href="#3_5"><code>_XOPEN_SOURCE</code> /
  66                             <code>_GNU_SOURCE</code> / etc is always defined</a>
  67          </li>
  68          <li><a href="#3_6">OS X ctype.h is broken!  How can I hack it?</a> </li>
  69       </ol>
  70    </li>
  71
  72    <li><a href="#4_0">Known Bugs and Non-Bugs</a>
  73       <ol>
  74          <li><a href="#4_1">What works already?</a> </li>
  75          <li><a href="#4_2">Bugs in gcc/g++ (not libstdc++-v3)</a> </li>
  76          <li><a href="#4_3">Bugs in the C++ language/lib specification</a> </li>
  77          <li><a href="#4_4">Things in libstdc++ that only look like bugs</a><ul>
  78            <li><a href="#4_4_iostreamclear">reopening a stream fails</a> </li>
  79            <li><a href="#4_4_Weff">-Weffc++ complains too much</a> </li>
  80            <li><a href="#4_4_rel_ops">&quot;ambiguous overloads&quot;
  81                                after including an old-style header</a> </li>
  82            <li><a href="#4_4_interface">The g++-3 headers are
  83                                <strong>not ours</strong></a> </li>
  84            <li><a href="#4_4_glibc">compilation errors from streambuf.h</a> </li>
  85            <li><a href="#4_4_checks">errors about <em>*Concept</em> and
  86                                <em>constraints</em> in the STL...</a> </li>
  87            <li><a href="#4_4_dlsym">program crashes when using library code
  88                                in a dynamically-loaded library</a> </li>
  89          </ul>
  90          </li>
  91          <li><a href="#4_5">Aw, that's easy to fix!</a> </li>
  92       </ol>
  93    </li>
  94
  95    <li><a href="#5_0">Miscellaneous</a>
  96       <ol>
  97          <li><a href="#5_1">string::iterator is not char*;
  98                             vector&lt;T&gt;::iterator is not T*</a> </li>
  99          <li><a href="#5_2">What's next after libstdc++-v3?</a> </li>
 100          <li><a href="#5_3">What about the STL from SGI?</a> </li>
 101          <li><a href="#5_4">Extensions and Backward Compatibility</a> </li>
 102          <li><a href="#5_5">[removed]</a> </li>
 103          <li><a href="#5_6">Is libstdc++-v3 thread-safe?</a> </li>
 104          <li><a href="#5_7">How do I get a copy of the ISO C++ Standard?</a> </li>
 105          <li><a href="#5_8">What's an ABI and why is it so messy?</a> </li>
 106       </ol>
 107    </li>
 108
 109 </ol>
 110
 111 <hr />
 112
 113 <!-- ####################################################### -->
 114
 115 <h1><a name="1_0">1.0 General Information</a></h1>
 116 <!-- I suspect these will mostly be links to/into existing documents. -->
 117    <h2><a name="1_1">1.1 What is libstdc++-v3?</a></h2>
 118       <p>The GNU Standard C++ Library v3 is an
 119          ongoing project to implement the ISO 14882 Standard C++ library
 120          as described in chapters 17 through 27 and annex D.  As the
 121          library reaches stable plateaus, it is captured in a snapshot
 122          and released.  The current release is
 123          <a href="http://gcc.gnu.org/libstdc++/index.html#download">the
 124          fourteenth snapshot</a>.  For those who want to see exactly how
 125          far the project has come, or just want the latest
 126          bleeding-edge code, the up-to-date source is available over
 127          anonymous CVS, and can even be browsed over the Web (see below).
 128       </p>
 129       <p>The older libstdc++-v2 project is no longer maintained; the code
 130          has been completely replaced and rewritten.
 131          <a href="#4_4_interface">If you are using V2</a>, then you need to
 132          report bugs to your system vendor, not to the V3 list.
 133       </p>
 134       <p>A more formal description of the V3 goals can be found in the
 135          official <a href="../17_intro/DESIGN">design document</a>.
 136       </p>
 137
 138 <hr />
 139    <h2><a name="1_2">1.2 Why should I use libstdc++?</a></h2>
 140       <p>The completion of the ISO C++ standardization gave the
 141          C++ community a powerful set of reuseable tools in the form
 142          of the C++ Standard Library.  However, all existing C++
 143          implementations are (as the Draft Standard used to say)
 144          &quot;incomplet and incorrekt,&quot; and many suffer from
 145          limitations of the compilers that use them.
 146       </p>
 147       <p>The GNU C/C++/FORTRAN/&lt;pick-a-language&gt; compiler
 148          (<code>gcc</code>, <code>g++</code>, etc) is widely considered to be
 149          one of the leading compilers in the world.  Its development
 150          has recently been taken over by the
 151          <a href="http://gcc.gnu.org/">GCC team</a>.  All of
 152          the rapid development and near-legendary
 153          <a href="http://gcc.gnu.org/gcc-3.0/buildstat.html">portability</a>
 154          that are the hallmarks of an open-source project are being
 155          applied to libstdc++.
 156       </p>
 157       <p>That means that all of the Standard classes and functions
 158          (such as <code>string</code>, <code>vector&lt;&gt;</code>, iostreams,
 159          and algorithms) will be freely available and fully compliant.
 160          Programmers will no longer need to &quot;roll their own&quot;
 161          nor be worried about platform-specific incompatibilities.
 162       </p>
 163
 164 <hr />
 165    <h2><a name="1_3">1.3 Who's in charge of it?</a></h2>
 166       <p>The libstdc++ project is contributed to by several developers
 167          all over the world, in the same way as GCC or Linux.
 168          Benjamin Kosnik, Gabriel Dos Reis, Phil Edwards, Ulrich Drepper,
 169          Loren James Rittle, and Paolo Carlini are the lead maintainers of
 170          the CVS archive.
 171       </p>
 172       <p>Development and discussion is held on the libstdc++ mailing
 173          list.  Subscribing to the list, or searching the list
 174          archives, is open to everyone.  You can read instructions for
 175          doing so on the <a href="http://gcc.gnu.org/libstdc++/">homepage</a>.
 176          If you have questions, ideas, code, or are just curious, sign up!
 177       </p>
 178
 179 <hr />
 180    <h2><a name="1_4">1.4 How do I get libstdc++?</a></h2>
 181       <p>The fourteenth (and latest) snapshot of libstdc++-v3 is
 182          <a href="http://gcc.gnu.org/libstdc++/index.html#download">available
 183          via ftp</a>.
 184       </p>
 185       <p>The <a href="http://gcc.gnu.org/libstdc++/">homepage</a>
 186          has instructions for retrieving the latest CVS sources, and for
 187          browsing the CVS sources over the web.
 188       </p>
 189       <p>The subset commonly known as the Standard Template Library
 190          (chapters 23 through 25, mostly) is adapted from the final release
 191          of the SGI STL.
 192       </p>
 193
 194 <hr />
 195    <h2><a name="1_5">1.5 When is libstdc++ going to be finished?</a></h2>
 196 <!--      <p>Nathan Myers gave the best of all possible answers in <a
 197          href="http://www.deja.com/getdoc.xp?AN=469581698&fmt=text">a
 198          Usenet article</a>.</p>
 199 which is no longer available, thanks deja...-->
 200       <p>Nathan Myers gave the best of all possible answers, responding to a
 201          Usenet article asking this question:  <em>Sooner, if you help.</em>
 202       </p>
 203
 204 <hr />
 205    <h2><a name="1_6">1.6 How do I contribute to the effort?</a></h2>
 206       <p>Here is <a href="../17_intro/contribute.html">a
 207          page devoted to this topic</a>.  Subscribing to the mailing
 208          list (see above, or the homepage) is a very good idea if you
 209          have something to contribute, or if you have spare time and
 210          want to help.  Contributions don't have to be in the form of
 211          source code; anybody who is willing to help write
 212          documentation, for example, or has found a bug in code that
 213          we all thought was working, is more than welcome!
 214       </p>
 215
 216 <hr />
 217    <h2><a name="1_7">1.7 What happened to libg++?  I need that!</a></h2>
 218       <p>The most recent libg++ README states that libg++ is no longer
 219          being actively maintained.  It should not be used for new
 220          projects, and is only being kicked along to support older code.
 221       </p>
 222       <p>The libg++ was designed and created when there was no Standard
 223          to provide guidance.  Classes like linked lists are now provided
 224          for by <code>list&lt;T&gt;</code> and do not need to be created by
 225          <code>genclass</code>.  (For that matter, templates exist now and
 226          are well-supported, whereas genclass (mostly) predates them.)
 227       </p>
 228       <p>There are other classes in libg++ that are not specified in the
 229          ISO Standard (e.g., statistical analysis).  While there are a
 230          lot of really useful things that are used by a lot of people
 231          (e.g., statistics :-), the Standards Committee couldn't include
 232          everything, and so a lot of those &quot;obvious&quot; classes
 233          didn't get included.
 234       </p>
 235       <p>Since libstdc++ is an implementation of the Standard Library, we
 236          have no plans at this time to include non-Standard utilities
 237          in the implementation, however handy they are.  (The extensions
 238          provided in the SGI STL aren't maintained by us and don't get
 239          a lot of our attention, because they don't require a lot of our
 240          time.)  It is entirely plausable that the &quot;useful stuff&quot;
 241          from libg++ might be extracted into an updated utilities library,
 242          but nobody has stated such a project yet.
 243       </p>
 244       <!-- The advertisement, so to speak, might have to go.  Hmmmmm.  -->
 245       <p>(The <a href="http://www.boost.org/">Boost</a> site houses free
 246          C++ libraries that do varying things, and happened to be started
 247          by members of the Standards Committee.  Certain &quot;useful
 248          stuff&quot; classes will probably migrate there.)
 249       </p>
 250       <p>For the bold and/or desperate, the
 251          <a href="http://gcc.gnu.org/fom_serv/cache/33.html">GCC FAQ</a>
 252          describes where to find the last libg++ source.
 253       </p>
 254
 255 <hr />
 256    <h2><a name="1_8">1.8 What if I have more questions?</a></h2>
 257       <p>If you have read the README and RELEASE-NOTES files, and your
 258          question remains unanswered, then just ask the mailing list.
 259          At present, you do not need to be subscribed to the list to
 260          send a message to it.  More information is available on the
 261          homepage (including how to browse the list archives); to send
 262          to the list, use <a href="mailto:libstdc++@gcc.gnu.org">
 263          <code>libstdc++@gcc.gnu.org</code></a>.
 264       </p>
 265       <p>If you have a question that you think should be included here,
 266          or if you have a question <em>about</em> a question/answer here,
 267          contact <a href="mailto:pme@gcc.gnu.org">Phil Edwards</a>
 268          or <a href="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</a>.
 269       </p>
 270
 271 <hr />
 272    <h2><a name="1_9">1.9 What are the license terms for libstdc++-v3?</a></h2>
 273       <p>See <a href="../17_intro/license.html">our license description</a>
 274          for these and related questions.
 275       </p>
 276
 277 <hr />
 278 <h1><a name="2_0">2.0 Installation</a></h1>
 279    <h2><a name="2_1">2.1 How do I install libstdc++-v3?</a></h2>
 280       <p>Complete instructions are not given here (this is a FAQ, not
 281          an installation document), but the tools required are few:
 282       </p>
 283          <ul>
 284             <li> A 3.x release of GCC.  Note that building GCC is much
 285                  easier and more automated than building the GCC 2.[78]
 286                  series was.  If you are using GCC 2.95, you can still
 287                  build earlier snapshots of libstdc++.
 288             </li>
 289             <li> GNU Make is recommended, but should not be required.
 290             </li>
 291             <li> The GNU Autotools are needed if you are messing with
 292                  the configury or makefiles.
 293             </li>
 294          </ul>
 295       <p>The file <a href="../documentation.html">documentation.html</a>
 296          provides a good overview of the steps necessary to build, install,
 297          and use the library.  Instructions for configuring the library
 298          with new flags such as --enable-threads are there also, as well as
 299          patches and instructions for working with GCC 2.95.
 300       </p>
 301       <p>The top-level install.html and
 302          <a href="../17_intro/RELEASE-NOTES">RELEASE-NOTES</a> files contain
 303          the exact build and installation instructions.  You may wish to
 304          browse those files over CVSweb ahead of time to get a feel for
 305          what's required.  RELEASE-NOTES is located in the
 306          &quot;.../docs/17_intro/&quot; directory of the distribution.
 307       </p>
 308
 309 <hr />
 310    <h2><a name="2_2">2.2 [removed]</a></h2>
 311       <p>This question has become moot and has been removed.  The stub
 312          is here to preserve numbering (and hence links/bookmarks).
 313       </p>
 314
 315 <hr />
 316    <h2><a name="2_3">2.3 What is this CVS thing that you
 317                          keep mentioning?</a></h2>
 318       <p>The <em>Concurrent Versions System</em> is one of several revision
 319          control packages.  It was selected for GNU projects because it's
 320          free (speech), free (beer), and very high quality.  The <a
 321          href="http://www.gnu.org/software/cvs/cvs.html">CVS entry in
 322          the GNU software catalogue</a> has a better description as
 323          well as a
 324          <a href="http://www.cvshome.org/">link to the makers of CVS</a>.
 325       </p>
 326       <p>The &quot;anonymous client checkout&quot; feature of CVS is
 327          similar to anonymous FTP in that it allows anyone to retrieve
 328          the latest libstdc++ sources.
 329       </p>
 330       <p>After the first of April, American users will have a
 331          &quot;/pharmacy&quot; command-line option...
 332          <!-- wonder how long that'll live -->
 333       </p>
 334
 335 <hr />
 336    <h2><a name="2_4">2.4 How do I know if it works?</a></h2>
 337       <p>libstdc++-v3 comes with its own testsuite.  You do not need
 338          to actually install the library (&quot;<code>make
 339          install</code>&quot;) to run the testsuite.
 340       </p>
 341       <p>To run the testsuite on the library after building it, use
 342          &quot;make check&quot; while in your build directory.  To run
 343          the testsuite on the library after building and installing it,
 344          use &quot;make check-install&quot; instead.
 345       </p>
 346       <p>If you find bugs in the testsuite programs themselves, or if you
 347          think of a new test program that should be added to the suite,
 348          <strong>please</strong> write up your idea and send it to the list!
 349       </p>
 350
 351 <hr />
 352    <h2><a name="2_5">2.4 This library is HUGE!  And what's libsupc++?</a></h2>
 353       <p>Usually the size of libraries on disk isn't noticeable.  When a
 354          link editor (or simply &quot;linker&quot;) pulls things from a
 355          static archive library, only the necessary object files are copied
 356          into your executable, not the entire library.  Unfortunately, even
 357          if you only need a single function or variable from an object file,
 358          the entire object file is extracted.  (There's nothing unique to C++
 359          or libstdc++-v3 about this; it's just common behavior, given here
 360          for background reasons.)
 361       </p>
 362       <p>Some of the object files which make up libstdc++.a are rather large.
 363          If you create a statically-linked executable with
 364          <code> -static</code>, those large object files are suddenly part
 365          of your executable.  Historically the best way around this was to
 366          only place a very few functions (often only a single one) in each
 367          source/object file; then extracting a single function is the same
 368          as extracting a single .o file.  For libstdc++-v3 this is only
 369          possible to a certain extent; the object files in question contain
 370          template classes and template functions, pre-instantiated, and
 371          splitting those up causes severe maintenance headaches.
 372       </p>
 373       <p>It's not a bug, and it's not really a problem.  Nevertheless, some
 374          people don't like it, so here are two pseudo-solutions:
 375       </p>
 376       <p>If the only functions from libstdc++.a which you need are language
 377          support functions (those listed in
 378          <a href="../18_support/howto.html">clause 18</a> of the standard,
 379          e.g., <code>new</code> and <code>delete</code>), then try linking
 380          against <code>libsupc++.a</code> (usually specifying
 381          <code>-lsupc++</code> when calling g++ for the final link step will
 382          do it).  This library contains only those support routines, one per
 383          object file.  But if you are using anything from the rest of the
 384          library, such as IOStreams or vectors, then you'll still need
 385          pieces from <code>libstdc++.a</code>.
 386       </p>
 387       <p>The second method is one we hope to incorporate into the library
 388          build process.  Some platforms can place each function and variable
 389          into its own section in a .o file.  The GNU linker can then perform
 390          garbage collection on unused sections; this reduces the situation
 391          to only copying needed functions into the executable, as before,
 392          but all happens automatically.
 393       </p>
 394       <p>Unfortunately the garbage collection in GNU ld is buggy; sections
 395          (corresponding to functions and variables) which <em>are</em> used
 396          are mistakenly removed, leading to horrible crashes when your
 397          executable starts up.  For the time being, this feature is not used
 398          when building the library.
 399       </p>
 400
 401 <hr />
 402 <h1><a name="3_0">3.0 Platform-Specific Issues</a></h1>
 403    <h2><a name="3_1">3.1 Can libstdc++-v3 be used with &lt;my
 404                          favorite compiler&gt;?</a></h2>
 405       <p>Probably not.  Yet.</p>
 406       <p>Because GCC advances so rapidly, development and testing of
 407          libstdc++ is being done almost entirely under that compiler.
 408          If you are curious about whether other, lesser compilers
 409          (*grin*) support libstdc++, you are more than welcome to try.
 410          Configuring and building the library (see above) will still
 411          require certain tools, however.  Also keep in mind that
 412          <em>building</em> libstdc++ does not imply that your compiler
 413          will be able to <em>use</em> all of the features found in the
 414          C++ Standard Library.
 415       </p>
 416       <p>Since the goal of ISO Standardization is for all C++
 417          implementations to be able to share code, the final libstdc++
 418          should, in theory, be usable under any ISO-compliant
 419          compiler.  It will still be targeted and optimized for
 420          GCC/g++, however.
 421       </p>
 422
 423 <hr />
 424    <h2><a name="3_2">3.2 [removed]</a></h2>
 425       <p>This question has become moot and has been removed.  The stub
 426          is here to preserve numbering (and hence links/bookmarks).
 427       </p>
 428
 429 <hr />
 430    <h2><a name="3_3">3.3 [removed]</a></h2>
 431       <p>This question has become moot and has been removed.  The stub
 432          is here to preserve numbering (and hence links/bookmarks).
 433       </p>
 434
 435 <hr />
 436    <h2><a name="3_4">3.4 I can't use 'long long' on Solaris</a></h2>
 437       <p>By default we try to support the C99 <code>long long</code> type.
 438          This requires that certain functions from your C library be present.
 439       </p>
 440       <p>Up through release 3.0.2 the tests performed were too general, and
 441          this feature was disabled when it did not need to be.  The most
 442          commonly reported platform affected was Solaris.
 443       </p>
 444       <p>This has been fixed for 3.0.3 and onwards.
 445       </p>
 446
 447 <hr />
 448    <h2><a name="3_5">3.5 <code>_XOPEN_SOURCE</code> / <code>_GNU_SOURCE</code>
 449                          / etc is always defined</a></h2>
 450       <p>On Solaris, g++ (but not gcc) always defines the preprocessor
 451          macro <code>_XOPEN_SOURCE</code>.  On GNU/Linux, the same happens
 452          with <code>_GNU_SOURCE</code>.  (This is not an exhaustive list;
 453          other macros and other platforms are also affected.)
 454       </p>
 455       <p>These macros are typically used in C library headers, guarding new
 456          versions of functions from their older versions.  The C++ standard
 457          library includes the C standard library, but it requires the C90
 458          version, which for backwards-compatability reasons is often not the
 459          default for many vendors.
 460       </p>
 461       <p>More to the point, the C++ standard requires behavior which is only
 462          available on certain platforms after certain symbols are defined.
 463          Usually the issue involves I/O-related typedefs.  In order to
 464          ensure correctness, the compiler simply predefines those symbols.
 465       </p>
 466       <p>Note that it's not enough to #define them only when the library is
 467          being built (during installation).  Since we don't have an 'export'
 468          keyword, much of the library exists as headers, which means that
 469          the symbols must also be defined as your programs are parsed and
 470          compiled.
 471       </p>
 472       <p>To see which symbols are defined, look for CPLUSPLUS_CPP_SPEC in
 473          the gcc config headers for your target (and try changing them to
 474          see what happens when building complicated code).  You can also run
 475          <code>&quot;g++ -E -dM - &lt; /dev/null&quot;</code> to display
 476          a list of predefined macros for any particular installation.
 477       </p>
 478       <p>This has been discussed on the mailing lists
 479          <a href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&amp;format=builtin-long&amp;sort=score&amp;words=_XOPEN_SOURCE+Solaris">quite a bit</a>.
 480       </p>
 481       <p>This method is something of a wart.  We'd like to find a cleaner
 482          solution, but nobody yet has contributed the time.
 483       </p>
 484
 485 <hr />
 486    <h2><a name="3_6">3.6 OS X ctype.h is broken!  How can I hack it?</a></h2>
 487       <p>This is a long-standing bug in the OS X support.  Fortunately,
 488          the patch is quite simple, and well-known.
 489          <a href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html"> Here's a
 490          link to the solution.</a>
 491       </p>
 492
 493 <hr />
 494 <h1><a name="4_0">4.0 Known Bugs and Non-Bugs</a></h1>
 495    <em>Note that this section can get rapdily outdated -- such is the
 496    nature of an open-source project.  For the latest information, join
 497    the mailing list or look through recent archives.   The RELEASE-
 498    NOTES and BUGS files are generally kept up-to-date.</em>
 499
 500    <p>For 3.0.1, the most common &quot;bug&quot; is an apparently missing
 501       &quot;<code>../</code>&quot; in include/Makefile, resulting in files
 502       like gthr.h and gthr-single.h not being found.  Please read
 503       <a href="http://gcc.gnu.org/install/configure.html">the configuration
 504       instructions for GCC</a>,
 505       specifically the part about configuring in a separate build directory,
 506       and how strongly recommended it is.  Building in the source directory
 507       is fragile, is rarely tested, and tends to break, as in this case.
 508       This was fixed for 3.0.2.
 509    </p>
 510
 511    <p>For 3.1, the most common &quot;bug&quot; is a parse error when using
 512       <code>&lt;fstream&gt;</code>, ending with a message,
 513       &quot;<code>bits/basic_file.h:52: parse error before `{'
 514       token</code>.&quot;  Please read
 515       <a href="http://gcc.gnu.org/install/">the installation instructions for
 516       GCC</a>, specifically the part about not installing newer versions on
 517       top of older versions.  If you install 3.1 over a 3.0.x release, then
 518       the wrong basic_file.h header will be found (its location changed
 519       between releases).
 520    </p>
 521
 522    <p><strong>Please do not report these as bugs.  We know about them.</strong>
 523       Reporting this -- or any other problem that's already been fixed --
 524       hinders the development of GCC, because we have to take time to
 525       respond to your report.  Thank you.
 526    </p>
 527
 528    <h2><a name="4_1">4.1 What works already?</a></h2>
 529       <p>This is a verbatim clip from the &quot;Status&quot; section
 530          of the RELEASE-NOTES for the latest snapshot.  For a list of
 531          fixed bugs, see that file.
 532       </p>
 533
 534 <!-- Yeah, I meant that "verbatim clip" thing literally... :-)  -->
 535
 536 <pre>
 537 New:
 538 ---
 539 (post 3.0.97)
 540 - more doxygen documentation
 541 - more named locale fixups
 542 - stdio_filebuf that takes fd, FILE
 543 - io performance tuning
 544 - allocation tuning, valgrind fixups
 545 - __cxa_demangle now supported
 546 (3.0.97)
 547 - more doxygen documentation.
 548 - more named locale bug fixes
 549 - support for symbol versioning when using GNU ld &gt;= 2.12
 550 - wide-io
 551 - tuning for executable size
 552 (3.0.96)
 553 - more doxygen documentation.
 554 - extensions moved out of namespace std
 555 - HPUX long long support
 556 - more string optimizations
 557 - support for NetBSD cross compiles
 558 - concept_check merge from boost
 559 - header simplification
 560 - named locale bug shakeout
 561 - thread testsuite
 562 (3.0.95)
 563 - add S390, m68k, x86-64 support.
 564 - doxygen documentation has been extended, including man pages.
 565 - verbose terminate handling has been added.
 566 - some libsupc++ tweaks
 567 - warnings for deprecated headers now active.
 568 - dejagnu testsuite preliminary documentation.
 569 - dejagnu testsuite default.
 570 - dejagnu testsuite cross compiler, multilib safe.
 571 - long long iostreams on by default, rework of ISO C99 support.
 572 - iterator re-write and testsuites.
 573 - container testsuites.
 574 - allocator revamp and testsuites.
 575 - more concept-checking work.
 576 - basic_string optimization and MT fixes.
 577 - new limits implementation.
 578 - update -fno-exceptions code, verify it works.
 579 - full named locale support fpr all facets, choice of gnu,
 580   ieee_1003.1-200x (POSIX 2), or generic models. Full support depends
 581   on target OS and underlying &quot;C&quot; library support.
 582 </pre>
 583
 584
 585 <hr />
 586    <h2><a name="4_2">4.2 Bugs in gcc/g++ (not libstdc++-v3)</a></h2>
 587       <p>This is by no means meant to be complete nor exhaustive, but
 588          mentions some problems that users may encounter when building
 589          or using libstdc++.  If you are experiencing one of these
 590          problems, you can find more information on the libstdc++ and
 591          the GCC mailing lists.
 592       </p>
 593       <p>Before reporting a bug, examine the
 594          <a href="http://gcc.gnu.org/bugs.html">bugs database</a> with the
 595          category set to &quot;libstdc++&quot;.  The BUGS file in the source
 596          tree also tracks known serious problems.
 597       </p>
 598       <ul>
 599          <li>Debugging is problematic, due to bugs in line-number generation
 600              (mostly fixed in the compiler) and gdb lagging behind the
 601              compiler (lack of personnel).  We recommend configuring the
 602              compiler using <code>--with-dwarf2</code> if the DWARF2
 603              debugging format is not already the default on your platform.
 604              Also,
 605 <a href="http://gcc.gnu.org/ml/libstdc++/2002-02/msg00034.html">changing your
 606              GDB settings</a> can have a profound effect on your C++ debugging
 607              experiences.  :-)</li>
 608       </ul>
 609
 610 <hr />
 611    <h2><a name="4_3">4.3 Bugs in the C++ language/lib specification</a></h2>
 612       <p>Yes, unfortunately, there are some.  In a
 613          <a href="http://gcc.gnu.org/ml/libstdc++/1998/msg00006.html">message
 614          to the list</a>, Nathan Myers announced that he has started a list of
 615          problems in the ISO C++ Standard itself, especially with
 616          regard to the chapters that concern the library.  The list
 617          itself is
 618          <a href="http://www.cantrip.org/draft-bugs.txt">posted on his
 619          website</a>.  Developers who are having problems interpreting
 620          the Standard may wish to consult his notes.
 621       </p>
 622       <p>For those people who are not part of the ISO Library Group
 623          (i.e., nearly all of us needing to read this page in the first
 624          place :-), a public list of the library defects is occasionally
 625          published <a href="http://anubis.dkuug.dk/jtc1/sc22/wg21/">here</a>.
 626          Some of these have resulted in <a href="#5_2">code changes</a>.
 627       </p>
 628
 629 <hr />
 630    <h2><a name="4_4">4.4 Things in libstdc++ that only look like bugs</a></h2>
 631       <p>There are things which are not bugs in the compiler (4.2) nor
 632          the language specification (4.3), but aren't really bugs in
 633          libstdc++, either.  Really!  Please do not report these as bugs.
 634       </p>
 635       <p><a name="4_4_Weff"><strong>-Weffc++</strong></a>
 636          The biggest of these is the quadzillions of warnings about the
 637          library headers emitted when <code>-Weffc++</code> is used.  Making
 638          libstdc++ &quot;-Weffc++-clean&quot; is not a goal of the project,
 639          for a few reasons.  Mainly, that option tries to enforce
 640          object-oriented programming, while the Standard Library isn't
 641          necessarily trying to be OO.
 642       </p>
 643       <p><a name="4_4_iostreamclear"><strong>reopening a stream fails</strong>
 644          </a> Did I just say that -Weffc++ was our biggest false-bug report?
 645          I lied.  (It used to be.)  Today it seems to be reports that after
 646          executing a sequence like
 647       </p>
 648       <pre>
 649     #include &lt;fstream&gt;
 650     ...
 651     std::fstream  fs(&quot;a_file&quot;);
 652     // .
 653     // . do things with fs...
 654     // .
 655     fs.close();
 656     fs.open(&quot;a_new_file&quot;);</pre>
 657       <p>all operations on the re-opened <code>fs</code> will fail, or at
 658          least act very strangely.  Yes, they often will, especially if
 659          <code>fs</code> reached the EOF state on the previous file.  The
 660          reason is that the state flags are <strong>not</strong> cleared
 661          on a successful call to open().  The standard unfortunately did
 662          not specify behavior in this case, and to everybody's great sorrow,
 663          the <a href="../ext/howto.html#5">proposed LWG resolution</a> (see
 664          DR #22) is to leave the flags unchanged.  You must insert a call
 665          to <code>fs.clear()</code> between the calls to close() and open(),
 666          and then everything will work like we all expect it to work.
 667       </p>
 668       <p><a name="4_4_rel_ops"><strong>rel_ops</strong></a>
 669          Another is the <code>rel_ops</code> namespace and the template
 670          comparison operator functions contained therein.  If they become
 671          visible in the same namespace as other comparison functions
 672          (e.g., '<code>using</code>' them and the &lt;iterator&gt; header),
 673          then you will suddenly be faced with huge numbers of ambiguity
 674          errors.  This was discussed on the -v3 list; Nathan Myers
 675          <a href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html">sums
 676          things up here</a>.  The collisions with vector/string iterator
 677          types have been fixed for 3.1.  <!-- more links to email here -->
 678       </p>
 679       <h3><a name="4_4_interface">The g++-3 headers are <em>not ours</em></a></h3>
 680       <p>If you have found an extremely broken header file which is
 681          causing problems for you, look carefully before submitting a
 682          &quot;high&quot; priority bug report (which you probably shouldn't
 683          do anyhow; see the last paragraph of the page describing
 684          <a href="http://gcc.gnu.org/gnatswrite.html">the GCC bug database</a>).
 685       </p>
 686       <p>If the headers are in <code>${prefix}/include/g++-3</code>, or if
 687          the installed library's name looks like <code>libstdc++-2.10.a</code>
 688          or <code>libstdc++-libc6-2.10.so</code>,
 689          then you are using the old libstdc++-v2 library, which is nonstandard
 690          and unmaintained.  Do not report problems with -v2 to the -v3
 691          mailing list.
 692       </p>
 693       <p>Currently our header files are installed in
 694          <code>${prefix}/include/g++-v3</code> (see the 'v'?).  This may
 695          change with the next release of GCC, as it may be too confusing,
 696          but <a href="http://gcc.gnu.org/ml/gcc/2000-10/msg00732.html">the
 697          question has not yet been decided</a>.
 698       </p>
 699       <p><a name="4_4_glibc"><strong>glibc</strong></a>
 700          If you're on a GNU/Linux system and have just upgraded to
 701          glibc 2.2, but are still using gcc 2.95.2, then you should have
 702          read the glibc FAQ, specifically 2.34:
 703       </p>
 704       <pre>
 705 2.34.   When compiling C++ programs, I get a compilation error in streambuf.h.
 706
 707 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
 708 apply a patch to the include files in /usr/include/g++, because the fpos_t
 709 type has changed in glibc 2.2.  The patch is at
 710 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
 711    </pre>
 712       <p>Note that 2.95.x shipped with the
 713          <a href="#4_4_interface">old v2 library</a> which is no longer
 714          maintained.  Also note that gcc 2.95.3 fixes this problem, but
 715          requires a separate patch for libstdc++-v3.
 716       </p>
 717       <p><a name="4_4_checks"><strong>concept checks</strong></a>
 718          If you see compilation errors containing messages about
 719          <code> <em>foo</em>Concept </code>and a<code> constraints </code>
 720          member function, then most likely you have violated one of the
 721          requirements for types used during instantiation of template
 722          containers and functions.  For example, EqualityComparableConcept
 723          appears if your types must be comparable with == and you have not
 724          provided this capability (a typo, or wrong visibility, or you
 725          just plain forgot, etc).
 726       </p>
 727       <p>More information, including how to optionally enable/disable the
 728          checks, is available
 729          <a href="../19_diagnostics/howto.html#3">here</a>.
 730       </p>
 731       <p><a name="4_4_dlsym"><strong>dlopen/dlsym</strong></a>
 732          If you are using the C++ library across dynamically-loaded
 733          objects, make certain that you are passing the correct options
 734          when compiling and linking:
 735       </p>
 736       <pre>
 737     // compile the library components
 738     g++ -fPIC -c a.cc
 739     g++ -fPIC -c b.cc
 740     ...
 741     g++ -fPIC -c z.cc
 742
 743     // create the library
 744     g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o
 745
 746     // link the executable
 747     g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</pre>
 748
 749 <hr />
 750    <h2><a name="4_5">4.5 Aw, that's easy to fix!</a></h2>
 751       <p>If you have found a bug in the library and you think you have
 752          a working fix, then send it in!  The main GCC site has a page
 753          on <a href="http://gcc.gnu.org/contribute.html">submitting
 754          patches</a> that covers the procedure, but for libstdc++ you
 755          should also send the patch to our mailing list in addition to
 756          the GCC patches mailing list.  The libstdc++
 757          <a href="../17_intro/contribute.html">contributors' page</a>
 758          also talks about how to submit patches.
 759       </p>
 760       <p>In addition to the description, the patch, and the ChangeLog
 761          entry, it is a Good Thing if you can additionally create a small
 762          test program to test for the presence of the bug that your
 763          patch fixes.  Bugs have a way of being reintroduced; if an old
 764          bug creeps back in, it will be caught immediately by the
 765          <a href="#2_4">testsuite</a> -- but only if such a test exists.
 766       </p>
 767
 768 <hr />
 769 <h1><a name="5_0">5.0 Miscellaneous</a></h1>
 770    <h2><a name="5_1">5.1 string::iterator is not char*;
 771                      vector&lt;T&gt;::iterator is not T*</a></h2>
 772       <p>If you have code that depends on container&lt;T&gt; iterators
 773          being implemented as pointer-to-T, your code is broken.
 774       </p>
 775       <p>While there are arguments for iterators to be implemented in
 776          that manner, A) they aren't very good ones in the long term,
 777          and B) they were never guaranteed by the Standard anyway.  The
 778          type-safety achieved by making iterators a real class rather
 779          than a typedef for <code>T*</code> outweighs nearly all opposing
 780          arguments.
 781       </p>
 782       <p>Code which does assume that a vector iterator <code> i </code>
 783          is a pointer can often be fixed by changing <code> i </code> in
 784          certain expressions to <code> &amp;*i </code>.  Future revisions
 785          of the Standard are expected to bless this usage for
 786          vector&lt;&gt; (but not for basic_string&lt;&gt;).
 787       </p>
 788
 789 <hr />
 790    <h2><a name="5_2">5.2 What's next after libstdc++-v3?</a></h2>
 791       <p>Hopefully, not much.  The goal of libstdc++-v3 is to produce
 792          a fully-compliant, fully-portable Standard Library.  After that,
 793          we're mostly done:  there won't <em>be</em> any more compliance
 794          work to do.  However:
 795       </p>
 796       <ol>
 797       <li><p>The ISO Committee will meet periodically to review Defect Reports
 798          in the C++ Standard.  Undoubtedly some of these will result in
 799          changes to the Standard, which will be reflected in patches to
 800          libstdc++.  Some of that is already happening, see 4.2.  Some of
 801          those changes are being predicted by the library maintainers, and
 802          we add code to the library based on what the current proposed
 803          resolution specifies.  Those additions are listed in
 804          <a href="../ext/howto.html#5">the extensions page</a>.
 805       </p></li>
 806       <li><p>Performance tuning.  Lots of performance tuning.  This too is
 807          already underway for post-3.0 releases, starting with memory
 808          expansion in container classes and buffer usage in synchronized
 809          stream objects.
 810       </p></li>
 811       <li><p>An ABI for libstdc++ is being developed, so that
 812          multiple binary-incompatible copies of the library can be replaced
 813          with a single backwards-compatible library, like libgcc_s.so is.
 814       </p></li>
 815       <li><p>The current libstdc++ contains extensions to the Library which
 816          must be explicitly requested by client code (for example, the
 817          hash tables from SGI).  Other extensions may be added to
 818          libstdc++-v3 if they seem to be &quot;standard&quot; enough.
 819          (For example, the &quot;long long&quot; type from C99.)
 820          Bugfixes and rewrites (to improve or fix thread safety, for
 821          instance) will of course be a continuing task.
 822       </p></li>
 823       </ol>
 824       <p><a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00080.html">This
 825          question</a> about the next libstdc++ prompted some brief but
 826          interesting
 827          <a href="http://gcc.gnu.org/ml/libstdc++/1999/msg00084.html">speculation</a>.
 828       </p>
 829
 830 <hr />
 831    <h2><a name="5_3">5.3 What about the STL from SGI?</a></h2>
 832       <p>The <a href="http://www.sgi.com/Technology/STL/">STL from SGI</a>,
 833          version 3.3, was the most recent merge of the STL codebase.  The
 834          code in libstdc++ contains many fixes and changes, and it is
 835          very likely that the SGI code is no longer under active
 836          development.  We expect that no future merges will take place.
 837       </p>
 838       <p>In particular, <code>string</code> is not from SGI and makes no
 839          use of their &quot;rope&quot; class (which is included as an
 840          optional extension), nor is <code>valarray</code> and some others.
 841          Classes like <code>vector&lt;&gt;</code> are, however.
 842       </p>
 843       <p>The FAQ for SGI's STL (one jump off of their main page) is
 844          recommended reading.
 845       </p>
 846
 847 <hr />
 848    <h2><a name="5_4">5.4 Extensions and Backward Compatibility</a></h2>
 849       <p>Headers in the <code>ext</code> and <code>backward</code>
 850          subdirectories should be referred to by their relative paths:
 851          <!-- Careful, the leading spaces in PRE show up directly. -->
 852       </p>
 853       <pre>
 854       #include &lt;ext/hash_map&gt; </pre>
 855       <p>rather than using <code>-I</code> or other options.  This is more
 856          portable and forward-compatible.  (The situation is the same as
 857          that of other headers whose directories are not searched directly,
 858          e.g., <code>&lt;sys/stat.h&gt;</code>, <code>&lt;X11/Xlib.h&gt;</code>.
 859       </p>
 860       <p>Extensions to the library have
 861          <a href="../ext/howto.html">their own page</a>.
 862       </p>
 863
 864 <hr />
 865    <h2><a name="5_5">5.5 [removed]</a></h2>
 866       <p>This question has become moot and has been removed.  The stub
 867          is here to preserve numbering (and hence links/bookmarks).
 868       </p>
 869
 870 <hr />
 871    <h2><a name="5_6">5.6 Is libstdc++-v3 thread-safe?</a></h2>
 872       <p>When the system's libc is itself thread-safe, a non-generic
 873          implementation of atomicity.h exists for the architecture, and gcc
 874          itself reports a thread model other than single; libstdc++-v3
 875          strives to be thread-safe.  The user-code must guard against
 876          concurrent method calls which may access any particular library
 877          object's state.  Typically, the application programmer may infer
 878          what object locks must be held based on the objects referenced in
 879          a method call.  Without getting into great detail, here is an
 880          example which requires user-level locks:
 881       </p>
 882       <pre>
 883      library_class_a shared_object_a;
 884
 885      thread_main () {
 886        library_class_b *object_b = new library_class_b;
 887        shared_object_a.add_b (object_b);   // must hold lock for shared_object_a
 888        shared_object_a.mutate ();          // must hold lock for shared_object_a
 889      }
 890
 891      // Multiple copies of thread_main() are started in independent threads.</pre>
 892       <p>Under the assumption that object_a and object_b are never exposed to
 893          another thread, here is an example that should not require any
 894          user-level locks:
 895       </p>
 896       <pre>
 897      thread_main () {
 898        library_class_a object_a;
 899        library_class_b *object_b = new library_class_b;
 900        object_a.add_b (object_b);
 901        object_a.mutate ();
 902      } </pre>
 903       <p>All library objects are safe to use in a multithreaded program as
 904          long as each thread carefully locks out access by any other thread
 905          while it uses any object visible to another thread.  In general,
 906          this requirement includes both read and write access to objects;
 907          unless otherwise documented as safe, do not assume that two
 908          threads may access a shared standard library object at the
 909          same time.
 910       </p>
 911       <p>See chapters <a href="../17_intro/howto.html#3">17</a> (library
 912          introduction), <a href="../23_containers/howto.html#3">23</a>
 913          (containers), and <a href="../27_io/howto.html#9">27</a> (I/O) for
 914          more information.
 915       </p>
 916
 917 <hr />
 918    <h2><a name="5_7">5.7 How do I get a copy of the ISO C++ Standard?</a></h2>
 919       <p>Copies of the full ISO 14882 standard are available on line via the
 920          ISO mirror site for committee members.  Non-members, or those who
 921          have not paid for the privilege of sitting on the committee and
 922          sustained their two-meeting commitment for voting rights, may get a
 923          copy of the standard from their respective national standards
 924          organization.  In the USA, this national standards organization is
 925          ANSI and their website is right <a href="http://www.ansi.org">here</a>.
 926          (And if you've already registered with them, clicking this link will
 927          take you to directly to the place where you can
 928 <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=ISO%2FIEC+14882%2D1998">buy
 929          the standard on-line</a>.
 930       </p>
 931       <p>Who is your country's member body?  Visit the
 932          <a href="http://www.iso.ch/">ISO homepage</a> and find out!
 933       </p>
 934
 935 <hr />
 936    <h2><a name="5_8">5.8 What's an ABI and why is it so messy?</a></h2>
 937       <p>&quot;ABI&quot; stands for &quot;Application Binary Interface.&quot;
 938          Conventionally, it refers to a great mass of details about how
 939          arguments are arranged on the call stack and/or in registers, and
 940          how various types are arranged and padded in structs.  A single CPU
 941          design may suffer multiple ABIs designed by different development
 942          tool vendors who made different choices, or even by the same vendor
 943          for different target applications or compiler versions.  In ideal
 944          circumstances the CPU designer presents one ABI and all the OSes and
 945          compilers use it.  In practice every ABI omits details that compiler
 946          implementers (consciously or accidentally) must choose for themselves.
 947       </p>
 948       <p>That ABI definition suffices for compilers to generate code so a
 949          program can interact safely with an OS and its lowest-level libraries.
 950          Users usually want an ABI to encompass more detail, allowing libraries
 951          built with different compilers (or different releases of the same
 952          compiler!) to be linked together.  For C++, this includes many more
 953          details than for C, and CPU designers (for good reasons elaborated
 954          below) have not stepped up to publish C++ ABIs.  The details include
 955          virtual function implementation, struct inheritance layout, name
 956          mangling, and exception handling.  Such an ABI has been defined for
 957          GNU C++, and is immediately useful for embedded work relying only on
 958          a &quot;free-standing implementation&quot; that doesn't include (much
 959          of) the standard library.  It is a good basis for the work to come.
 960       </p>
 961       <p>A useful C++ ABI must also incorporate many details of the standard
 962          library implementation.  For a C ABI, the layouts of a few structs
 963          (such as FILE, stat, jmpbuf, and the like) and a few macros suffice.
 964          For C++, the details include the complete set of names of functions
 965          and types used, the offsets of class members and virtual functions,
 966          and the actual definitions of all inlines.  C++ exposes many more
 967          library details to the caller than C does.  It makes defining
 968          a complete ABI a much bigger undertaking, and requires not just
 969          documenting library implementation details, but carefully designing
 970          those details so that future bug fixes and optimizations don't
 971          force breaking the ABI.
 972       </p>
 973       <p>There are ways to help isolate library implementation details from the
 974          ABI, but they trade off against speed.  Library details used in
 975          inner loops (e.g., getchar) must be exposed and frozen for all
 976          time, but many others may reasonably be kept hidden from user code,
 977          so they may later be changed.  Deciding which, and implementing
 978          the decisions, must happen before you can reasonably document a
 979          candidate C++ ABI that encompasses the standard library.
 980       </p>
 981
 982 <!-- ####################################################### -->
 983
 984 <hr />
 985 <p class="fineprint"><em>
 986 See <a href="../17_intro/license.html">license.html</a> for copying conditions.
 987 Comments and suggestions are welcome, and may be sent to
 988 <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
 989 </em></p>
 990
 991
 992 </body>
 993 </html>
 994