libstdc++-v3/doc/html/manual/backwards.html

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   4   Porting and Maintenance
   5
   6 </th><td width="20%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="Backwards Compatibility"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.appendix.porting.backwards"></a>Backwards Compatibility</h2></div></div></div><div class="sect2" title="First"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.first"></a>First</h3></div></div></div><p>The first generation GNU C++ library was called libg++.  It was a
   7 separate GNU project, although reliably paired with GCC. Rumors imply
   8 that it had a working relationship with at least two kinds of
   9 dinosaur.
  10 </p><p>Some background: libg++ was designed and created when there was no
  11 ISO standard to provide guidance.  Classes like linked lists are now
  12 provided for by <code class="classname">list&lt;T&gt;</code> and do not need to be
  13 created by <code class="function">genclass</code>.  (For that matter, templates exist
  14 now and are well-supported, whereas genclass (mostly) predates them.)
  15 </p><p>There are other classes in libg++ that are not specified in the
  16 ISO Standard (e.g., statistical analysis).  While there are a lot of
  17 really useful things that are used by a lot of people, the Standards
  18 Committee couldn't include everything, and so a lot of those
  19 <span class="quote">“<span class="quote">obvious</span>”</span> classes didn't get included.
  20 </p><p>Known Issues include many of the limitations of its immediate ancestor.</p><p>Portability notes and known implementation limitations are as follows.</p><div class="sect3" title="No ios_base"><div class="titlepage"><div><div><h4 class="title"><a id="id508624"></a>No <code class="code">ios_base</code></h4></div></div></div><p> At least some older implementations don't have <code class="code">std::ios_base</code>, so you should use <code class="code">std::ios::badbit</code>, <code class="code">std::ios::failbit</code> and <code class="code">std::ios::eofbit</code> and <code class="code">std::ios::goodbit</code>.
  21 </p></div><div class="sect3" title="No cout in ostream.h, no cin in istream.h"><div class="titlepage"><div><div><h4 class="title"><a id="id508656"></a>No <code class="code">cout</code> in <code class="code">ostream.h</code>, no <code class="code">cin</code> in <code class="code">istream.h</code></h4></div></div></div><p>
  22         In earlier versions of the standard,
  23         <code class="filename">fstream.h</code>,
  24         <code class="filename">ostream.h</code>
  25         and <code class="filename">istream.h</code>
  26         used to define
  27         <code class="code">cout</code>, <code class="code">cin</code> and so on. ISO C++ specifies that one needs to include
  28         <code class="filename">iostream</code>
  29         explicitly to get the required definitions.
  30  </p><p> Some include adjustment may be required.</p><p>This project is no longer maintained or supported, and the sources
  31 archived. For the desperate,
  32 the <a class="ulink" href="http://gcc.gnu.org/extensions.html" target="_top">GCC extensions
  33 page</a> describes where to find the last libg++ source. The code is
  34 considered replaced and rewritten.
  35 </p></div></div><div class="sect2" title="Second"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p>
  36   The second generation GNU C++ library was called libstdc++, or
  37   libstdc++-v2. It spans the time between libg++ and pre-ISO C++
  38   standardization and is usually associated with the following GCC
  39   releases: egcs 1.x, gcc 2.95, and gcc 2.96.
  40 </p><p>
  41   The STL portions of this library are based on SGI/HP STL release 3.11.
  42 </p><p>
  43   This project is no longer maintained or supported, and the sources
  44   archived.  The code is considered replaced and rewritten.
  45 </p><p>
  46   Portability notes and known implementation limitations are as follows.
  47 </p><div class="sect3" title="Namespace std:: not supported"><div class="titlepage"><div><div><h4 class="title"><a id="id508754"></a>Namespace <code class="code">std::</code> not supported</h4></div></div></div><p>
  48     Some care is required to support C++ compiler and or library
  49     implementation that do not have the standard library in
  50     <code class="code">namespace std</code>.
  51   </p><p>
  52     The following sections list some possible solutions to support compilers
  53     that cannot ignore <code class="code">std::</code>-qualified names.
  54   </p><p>
  55     First, see if the compiler has a flag for this. Namespace
  56     back-portability-issues are generally not a problem for g++
  57     compilers that do not have libstdc++ in <code class="code">std::</code>, as the
  58     compilers use <code class="code">-fno-honor-std</code> (ignore
  59     <code class="code">std::</code>, <code class="code">:: = std::</code>) by default. That is,
  60     the responsibility for enabling or disabling <code class="code">std::</code> is
  61     on the user; the maintainer does not have to care about it. This
  62     probably applies to some other compilers as well.
  63   </p><p>
  64     Second, experiment with a variety of pre-processor tricks.
  65   </p><p>
  66     By defining <code class="code">std</code> as a macro, fully-qualified namespace
  67     calls become global. Volia.
  68   </p><pre class="programlisting">
  69 #ifdef WICKEDLY_OLD_COMPILER
  70 # define std
  71 #endif
  72 </pre><p>
  73     Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help.
  74   </p><p>
  75     Another pre-processor based approach is to define a macro
  76     <code class="code">NAMESPACE_STD</code>, which is defined to either
  77     <span class="quote">“<span class="quote"> </span>”</span> or <span class="quote">“<span class="quote">std</span>”</span> based on a compile-type
  78     test. On GNU systems, this can be done with autotools by means of
  79     an autoconf test (see below) for <code class="code">HAVE_NAMESPACE_STD</code>,
  80     then using that to set a value for the <code class="code">NAMESPACE_STD</code>
  81     macro.  At that point, one is able to use
  82     <code class="code">NAMESPACE_STD::string</code>, which will evaluate to
  83     <code class="code">std::string</code> or <code class="code">::string</code> (i.e., in the
  84     global namespace on systems that do not put <code class="code">string</code> in
  85     <code class="code">std::</code>).
  86   </p><pre class="programlisting">
  87 dnl @synopsis AC_CXX_NAMESPACE_STD
  88 dnl
  89 dnl If the compiler supports namespace std, define
  90 dnl HAVE_NAMESPACE_STD.
  91 dnl
  92 dnl @category Cxx
  93 dnl @author Todd Veldhuizen
  94 dnl @author Luc Maisonobe &lt;luc@spaceroots.org&gt;
  95 dnl @version 2004-02-04
  96 dnl @license AllPermissive
  97 AC_DEFUN([AC_CXX_NAMESPACE_STD], [
  98   AC_CACHE_CHECK(if g++ supports namespace std,
  99   ac_cv_cxx_have_std_namespace,
 100   [AC_LANG_SAVE
 101   AC_LANG_CPLUSPLUS
 102   AC_TRY_COMPILE([#include &lt;iostream&gt;
 103                   std::istream&amp; is = std::cin;],,
 104   ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no)
 105   AC_LANG_RESTORE
 106   ])
 107   if test "$ac_cv_cxx_have_std_namespace" = yes; then
 108     AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ])
 109   fi
 110 ])
 111 </pre></div><div class="sect3" title="Illegal iterator usage"><div class="titlepage"><div><div><h4 class="title"><a id="id508877"></a>Illegal iterator usage</h4></div></div></div><p>
 112   The following illustrate implementation-allowed illegal iterator
 113   use, and then correct use.
 114 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
 115       you cannot do <code class="code">ostream::operator&lt;&lt;(iterator)</code>
 116       to print the address of the iterator =&gt; use
 117       <code class="code">operator&lt;&lt; &amp;*iterator</code> instead
 118     </p></li><li class="listitem"><p>
 119       you cannot clear an iterator's reference (<code class="code">iterator =
 120       0</code>) =&gt; use <code class="code">iterator = iterator_type();</code>
 121     </p></li><li class="listitem"><p>
 122       <code class="code">if (iterator)</code> won't work any more =&gt; use
 123       <code class="code">if (iterator != iterator_type())</code>
 124     </p></li></ul></div></div><div class="sect3" title="isspace from cctype is a macro"><div class="titlepage"><div><div><h4 class="title"><a id="id508938"></a><code class="code">isspace</code> from <code class="filename">cctype</code> is a macro
 125   </h4></div></div></div><p>
 126     Glibc 2.0.x and 2.1.x define <code class="filename">ctype.h</code> functionality as macros
 127     (isspace, isalpha etc.).
 128   </p><p>
 129     This implementations of libstdc++, however, keep these functions
 130     as macros, and so it is not back-portable to use fully qualified
 131     names. For example:
 132   </p><pre class="programlisting">
 133 #include &lt;cctype&gt;
 134 int main() { std::isspace('X'); }
 135 </pre><p>
 136   Results in something like this:
 137 </p><pre class="programlisting">
 138 std:: (__ctype_b[(int) ( ( 'X' ) )] &amp; (unsigned short int) _ISspace ) ;
 139 </pre><p>
 140   A solution is to modify a header-file so that the compiler tells
 141   <code class="filename">ctype.h</code> to define functions
 142   instead of macros:
 143 </p><pre class="programlisting">
 144 // This keeps isalnum, et al from being propagated as macros.
 145 #if __linux__
 146 # define __NO_CTYPE 1
 147 #endif
 148 </pre><p>
 149   Then, include <code class="filename">ctype.h</code>
 150 </p><p>
 151   Another problem arises if you put a <code class="code">using namespace
 152   std;</code> declaration at the top, and include <code class="filename">ctype.h</code>. This will result in
 153   ambiguities between the definitions in the global namespace
 154   (<code class="filename">ctype.h</code>) and the
 155   definitions in namespace <code class="code">std::</code>
 156   (<code class="code">&lt;cctype&gt;</code>).
 157 </p></div><div class="sect3" title="No vector::at, deque::at, string::at"><div class="titlepage"><div><div><h4 class="title"><a id="id502656"></a>No <code class="code">vector::at</code>, <code class="code">deque::at</code>, <code class="code">string::at</code></h4></div></div></div><p>
 158   One solution is to add an autoconf-test for this:
 159 </p><pre class="programlisting">
 160 AC_MSG_CHECKING(for container::at)
 161 AC_TRY_COMPILE(
 162 [
 163 #include &lt;vector&gt;
 164 #include &lt;deque&gt;
 165 #include &lt;string&gt;
 166
 167 using namespace std;
 168 ],
 169 [
 170 deque&lt;int&gt; test_deque(3);
 171 test_deque.at(2);
 172 vector&lt;int&gt; test_vector(2);
 173 test_vector.at(1);
 174 string test_string(<span class="quote">“<span class="quote">test_string</span>”</span>);
 175 test_string.at(3);
 176 ],
 177 [AC_MSG_RESULT(yes)
 178 AC_DEFINE(HAVE_CONTAINER_AT)],
 179 [AC_MSG_RESULT(no)])
 180 </pre><p>
 181   If you are using other (non-GNU) compilers it might be a good idea
 182   to check for <code class="code">string::at</code> separately.
 183 </p></div><div class="sect3" title="No std::char_traits&lt;char&gt;::eof"><div class="titlepage"><div><div><h4 class="title"><a id="id502694"></a>No <code class="code">std::char_traits&lt;char&gt;::eof</code></h4></div></div></div><p>
 184   Use some kind of autoconf test, plus this:
 185 </p><pre class="programlisting">
 186 #ifdef HAVE_CHAR_TRAITS
 187 #define CPP_EOF std::char_traits&lt;char&gt;::eof()
 188 #else
 189 #define CPP_EOF EOF
 190 #endif
 191 </pre></div><div class="sect3" title="No string::clear"><div class="titlepage"><div><div><h4 class="title"><a id="id502712"></a>No <code class="code">string::clear</code></h4></div></div></div><p>
 192   There are two functions for deleting the contents of a string:
 193   <code class="code">clear</code> and <code class="code">erase</code> (the latter returns the
 194   string).
 195 </p><pre class="programlisting">
 196 void
 197 clear() { _M_mutate(0, this-&gt;size(), 0); }
 198 </pre><pre class="programlisting">
 199 basic_string&amp;
 200 erase(size_type __pos = 0, size_type __n = npos)
 201 {
 202   return this-&gt;replace(_M_check(__pos), _M_fold(__pos, __n),
 203                           _M_data(), _M_data());
 204 }
 205 </pre><p>
 206   Unfortunately, <code class="code">clear</code> is not implemented in this
 207   version, so you should use <code class="code">erase</code> (which is probably
 208   faster than <code class="code">operator=(charT*)</code>).
 209 </p></div><div class="sect3" title="Removal of ostream::form and istream::scan extensions"><div class="titlepage"><div><div><h4 class="title"><a id="id502758"></a>
 210   Removal of <code class="code">ostream::form</code> and <code class="code">istream::scan</code>
 211   extensions
 212 </h4></div></div></div><p>
 213   These are no longer supported. Please use stringstreams instead.
 214 </p></div><div class="sect3" title="No basic_stringbuf, basic_stringstream"><div class="titlepage"><div><div><h4 class="title"><a id="id502777"></a>No <code class="code">basic_stringbuf</code>, <code class="code">basic_stringstream</code></h4></div></div></div><p>
 215   Although the ISO standard <code class="code">i/ostringstream</code>-classes are
 216   provided, (<code class="filename">sstream</code>), for
 217   compatibility with older implementations the pre-ISO
 218   <code class="code">i/ostrstream</code> (<code class="filename">strstream</code>) interface is also provided,
 219   with these caveats:
 220 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
 221       <code class="code">strstream</code> is considered to be deprecated
 222     </p></li><li class="listitem"><p>
 223       <code class="code">strstream</code> is limited to <code class="code">char</code>
 224     </p></li><li class="listitem"><p>
 225       with <code class="code">ostringstream</code> you don't have to take care of
 226       terminating the string or freeing its memory
 227     </p></li><li class="listitem"><p>
 228       <code class="code">istringstream</code> can be re-filled (clear();
 229       str(input);)
 230     </p></li></ul></div><p>
 231   You can then use output-stringstreams like this:
 232 </p><pre class="programlisting">
 233 #ifdef HAVE_SSTREAM
 234 # include &lt;sstream&gt;
 235 #else
 236 # include &lt;strstream&gt;
 237 #endif
 238
 239 #ifdef HAVE_SSTREAM
 240   std::ostringstream oss;
 241 #else
 242   std::ostrstream oss;
 243 #endif
 244
 245 oss &lt;&lt; <span class="quote">“<span class="quote">Name=</span>”</span> &lt;&lt; m_name &lt;&lt; <span class="quote">“<span class="quote">, number=</span>”</span> &lt;&lt; m_number &lt;&lt; std::endl;
 246 ...
 247 #ifndef HAVE_SSTREAM
 248   oss &lt;&lt; std::ends; // terminate the char*-string
 249 #endif
 250
 251 // str() returns char* for ostrstream and a string for ostringstream
 252 // this also causes ostrstream to think that the buffer's memory
 253 // is yours
 254 m_label.set_text(oss.str());
 255 #ifndef HAVE_SSTREAM
 256   // let the ostrstream take care of freeing the memory
 257   oss.freeze(false);
 258 #endif
 259 </pre><p>
 260       Input-stringstreams can be used similarly:
 261 </p><pre class="programlisting">
 262 std::string input;
 263 ...
 264 #ifdef HAVE_SSTREAM
 265 std::istringstream iss(input);
 266 #else
 267 std::istrstream iss(input.c_str());
 268 #endif
 269
 270 int i;
 271 iss &gt;&gt; i;
 272 </pre><p> One (the only?) restriction is that an istrstream cannot be re-filled:
 273 </p><pre class="programlisting">
 274 std::istringstream iss(numerator);
 275 iss &gt;&gt; m_num;
 276 // this is not possible with istrstream
 277 iss.clear();
 278 iss.str(denominator);
 279 iss &gt;&gt; m_den;
 280 </pre><p>
 281 If you don't care about speed, you can put these conversions in
 282       a template-function:
 283 </p><pre class="programlisting">
 284 template &lt;class X&gt;
 285 void fromString(const string&amp; input, X&amp; any)
 286 {
 287 #ifdef HAVE_SSTREAM
 288 std::istringstream iss(input);
 289 #else
 290 std::istrstream iss(input.c_str());
 291 #endif
 292 X temp;
 293 iss &gt;&gt; temp;
 294 if (iss.fail())
 295 throw runtime_error(..)
 296 any = temp;
 297 }
 298 </pre><p>
 299   Another example of using stringstreams is in <a class="link" href="strings.html#strings.string.shrink" title="Shrink to Fit">this howto</a>.
 300 </p><p> There is additional information in the libstdc++-v2 info files, in
 301 particular <span class="quote">“<span class="quote">info iostream</span>”</span>.
 302 </p></div><div class="sect3" title="Little or no wide character support"><div class="titlepage"><div><div><h4 class="title"><a id="id502928"></a>Little or no wide character support</h4></div></div></div><p>
 303     Classes <code class="classname">wstring</code> and
 304     <code class="classname">char_traits&lt;wchar_t&gt;</code> are
 305     not supported.
 306   </p></div><div class="sect3" title="No templatized iostreams"><div class="titlepage"><div><div><h4 class="title"><a id="id502947"></a>No templatized iostreams</h4></div></div></div><p>
 307     Classes <code class="classname">wfilebuf</code> and
 308     <code class="classname">wstringstream</code> are not supported.
 309   </p></div><div class="sect3" title="Thread safety issues"><div class="titlepage"><div><div><h4 class="title"><a id="id502966"></a>Thread safety issues</h4></div></div></div><p>
 310     Earlier GCC releases had a somewhat different approach to
 311     threading configuration and proper compilation.  Before GCC 3.0,
 312     configuration of the threading model was dictated by compiler
 313     command-line options and macros (both of which were somewhat
 314     thread-implementation and port-specific).  There were no
 315     guarantees related to being able to link code compiled with one
 316     set of options and macro setting with another set.
 317   </p><p>
 318     For GCC 3.0, configuration of the threading model used with
 319     libraries and user-code is performed when GCC is configured and
 320     built using the --enable-threads and --disable-threads options.
 321     The ABI is stable for symbol name-mangling and limited functional
 322     compatibility exists between code compiled under different
 323     threading models.
 324   </p><p>
 325      The libstdc++ library has been designed so that it can be used in
 326      multithreaded applications (with libstdc++-v2 this was only true
 327      of the STL parts.)  The first problem is finding a
 328      <span class="emphasis"><em>fast</em></span> method of implementation portable to
 329      all platforms.  Due to historical reasons, some of the library is
 330      written against per-CPU-architecture spinlocks and other parts
 331      against the gthr.h abstraction layer which is provided by gcc.  A
 332      minor problem that pops up every so often is different
 333      interpretations of what "thread-safe" means for a
 334      library (not a general program).  We currently use the <a class="ulink" href="http://www.sgi.com/tech/stl/thread_safety.html" target="_top">same
 335      definition that SGI</a> uses for their STL subset.  However,
 336      the exception for read-only containers only applies to the STL
 337      components. This definition is widely-used and something similar
 338      will be used in the next version of the C++ standard library.
 339    </p><p>
 340      Here is a small link farm to threads (no pun) in the mail
 341      archives that discuss the threading problem.  Each link is to the
 342      first relevant message in the thread; from there you can use
 343      "Thread Next" to move down the thread.  This farm is in
 344      latest-to-oldest order.
 345    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
 346             Our threading expert Loren gives a breakdown of <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-10/msg00024.html" target="_top">the
 347             six situations involving threads</a> for the 3.0
 348             release series.
 349           </p></li><li class="listitem"><p>
 350             <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html" target="_top">
 351         This message</a> inspired a recent updating of issues with
 352         threading and the SGI STL library.  It also contains some
 353         example POSIX-multithreaded STL code.
 354           </p></li></ul></div><p>
 355      (A large selection of links to older messages has been removed;
 356      many of the messages from 1999 were lost in a disk crash, and the
 357      few people with access to the backup tapes have been too swamped
 358      with work to restore them.  Many of the points have been
 359      superseded anyhow.)
 360    </p></div></div><div class="sect2" title="Third"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.third"></a>Third</h3></div></div></div><p> The third generation GNU C++ library is called libstdc++, or
 361 libstdc++-v3.
 362 </p><p>The subset commonly known as the Standard Template Library
 363          (chapters 23 through 25, mostly) is adapted from the final release
 364          of the SGI STL (version 3.3), with extensive changes.
 365       </p><p>A more formal description of the V3 goals can be found in the
 366          official <a class="link" href="source_design_notes.html" title="Design Notes">design document</a>.
 367       </p><p>Portability notes and known implementation limitations are as follows.</p><div class="sect3" title="Pre-ISO headers moved to backwards or removed"><div class="titlepage"><div><div><h4 class="title"><a id="id426691"></a>Pre-ISO headers moved to backwards or removed</h4></div></div></div><p> The pre-ISO C++ headers
 368       (<code class="code">iostream.h</code>, <code class="code">defalloc.h</code> etc.) are
 369       available, unlike previous libstdc++ versions, but inclusion
 370       generates a warning that you are using deprecated headers.
 371 </p><p>This compatibility layer is constructed by including the
 372     standard C++ headers, and injecting any items in
 373     <code class="code">std::</code> into the global namespace.
 374    </p><p>For those of you new to ISO C++ (welcome, time travelers!), no,
 375       that isn't a typo. Yes, the headers really have new names.
 376       Marshall Cline's C++ FAQ Lite has a good explanation in <a class="ulink" href="http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.4" target="_top">item
 377       [27.4]</a>.
 378    </p><p> Some include adjustment may be required. What follows is an
 379 autoconf test that defines <code class="code">PRE_STDCXX_HEADERS</code> when they
 380 exist.</p><pre class="programlisting">
 381 # AC_HEADER_PRE_STDCXX
 382 AC_DEFUN([AC_HEADER_PRE_STDCXX], [
 383   AC_CACHE_CHECK(for pre-ISO C++ include files,
 384   ac_cv_cxx_pre_stdcxx,
 385   [AC_LANG_SAVE
 386   AC_LANG_CPLUSPLUS
 387   ac_save_CXXFLAGS="$CXXFLAGS"
 388   CXXFLAGS="$CXXFLAGS -Wno-deprecated"
 389
 390   # Omit defalloc.h, as compilation with newer compilers is problematic.
 391   AC_TRY_COMPILE([
 392   #include &lt;new.h&gt;
 393   #include &lt;iterator.h&gt;
 394   #include &lt;alloc.h&gt;
 395   #include &lt;set.h&gt;
 396   #include &lt;hashtable.h&gt;
 397   #include &lt;hash_set.h&gt;
 398   #include &lt;fstream.h&gt;
 399   #include &lt;tempbuf.h&gt;
 400   #include &lt;istream.h&gt;
 401   #include &lt;bvector.h&gt;
 402   #include &lt;stack.h&gt;
 403   #include &lt;rope.h&gt;
 404   #include &lt;complex.h&gt;
 405   #include &lt;ostream.h&gt;
 406   #include &lt;heap.h&gt;
 407   #include &lt;iostream.h&gt;
 408   #include &lt;function.h&gt;
 409   #include &lt;multimap.h&gt;
 410   #include &lt;pair.h&gt;
 411   #include &lt;stream.h&gt;
 412   #include &lt;iomanip.h&gt;
 413   #include &lt;slist.h&gt;
 414   #include &lt;tree.h&gt;
 415   #include &lt;vector.h&gt;
 416   #include &lt;deque.h&gt;
 417   #include &lt;multiset.h&gt;
 418   #include &lt;list.h&gt;
 419   #include &lt;map.h&gt;
 420   #include &lt;algobase.h&gt;
 421   #include &lt;hash_map.h&gt;
 422   #include &lt;algo.h&gt;
 423   #include &lt;queue.h&gt;
 424   #include &lt;streambuf.h&gt;
 425   ],,
 426   ac_cv_cxx_pre_stdcxx=yes, ac_cv_cxx_pre_stdcxx=no)
 427   CXXFLAGS="$ac_save_CXXFLAGS"
 428   AC_LANG_RESTORE
 429   ])
 430   if test "$ac_cv_cxx_pre_stdcxx" = yes; then
 431     AC_DEFINE(PRE_STDCXX_HEADERS,,[Define if pre-ISO C++ header files are present. ])
 432   fi
 433 ])
 434 </pre><p>Porting between pre-ISO headers and ISO headers is simple: headers
 435 like <code class="filename">vector.h</code> can be replaced with <code class="filename">vector</code> and a using
 436 directive <code class="code">using namespace std;</code> can be put at the global
 437 scope. This should be enough to get this code compiling, assuming the
 438 other usage is correct.
 439 </p></div><div class="sect3" title="Extension headers hash_map, hash_set moved to ext or backwards"><div class="titlepage"><div><div><h4 class="title"><a id="id426772"></a>Extension headers hash_map, hash_set moved to ext or backwards</h4></div></div></div><p>At this time most of the features of the SGI STL extension have been
 440          replaced by standardized libraries.
 441          In particular, the unordered_map and unordered_set containers of TR1
 442          are suitable replacement for the non-standard hash_map and hash_set
 443          containers in the SGI STL.
 444       </p><p> Header files <code class="filename">hash_map</code> and <code class="filename">hash_set</code> moved
 445 to <code class="filename">ext/hash_map</code> and  <code class="filename">ext/hash_set</code>,
 446 respectively. At the same time, all types in these files are enclosed
 447 in <code class="code">namespace __gnu_cxx</code>. Later versions move deprecate
 448 these files, and suggest using TR1's  <code class="filename">unordered_map</code>
 449 and  <code class="filename">unordered_set</code> instead.
 450 </p><p>The extensions are no longer in the global or <code class="code">std</code>
 451          namespaces, instead they are declared in the <code class="code">__gnu_cxx</code>
 452          namespace. For maximum portability, consider defining a namespace
 453          alias to use to talk about extensions, e.g.:
 454       </p><pre class="programlisting">
 455       #ifdef __GNUC__
 456       #if __GNUC__ &lt; 3
 457         #include &lt;hash_map.h&gt;
 458         namespace extension { using ::hash_map; }; // inherit globals
 459       #else
 460         #include &lt;backward/hash_map&gt;
 461         #if __GNUC__ == 3 &amp;&amp; __GNUC_MINOR__ == 0
 462           namespace extension = std;               // GCC 3.0
 463         #else
 464           namespace extension = ::__gnu_cxx;       // GCC 3.1 and later
 465         #endif
 466       #endif
 467       #else      // ...  there are other compilers, right?
 468         namespace extension = std;
 469       #endif
 470
 471       extension::hash_map&lt;int,int&gt; my_map;
 472       </pre><p>This is a bit cleaner than defining typedefs for all the
 473          instantiations you might need.
 474       </p><p>The following autoconf tests check for working HP/SGI hash containers.
 475 </p><pre class="programlisting">
 476 # AC_HEADER_EXT_HASH_MAP
 477 AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [
 478   AC_CACHE_CHECK(for ext/hash_map,
 479   ac_cv_cxx_ext_hash_map,
 480   [AC_LANG_SAVE
 481   AC_LANG_CPLUSPLUS
 482   ac_save_CXXFLAGS="$CXXFLAGS"
 483   CXXFLAGS="$CXXFLAGS -Werror"
 484   AC_TRY_COMPILE([#include &lt;ext/hash_map&gt;], [using __gnu_cxx::hash_map;],
 485   ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no)
 486   CXXFLAGS="$ac_save_CXXFLAGS"
 487   AC_LANG_RESTORE
 488   ])
 489   if test "$ac_cv_cxx_ext_hash_map" = yes; then
 490     AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ])
 491   fi
 492 ])
 493 </pre><pre class="programlisting">
 494 # AC_HEADER_EXT_HASH_SET
 495 AC_DEFUN([AC_HEADER_EXT_HASH_SET], [
 496   AC_CACHE_CHECK(for ext/hash_set,
 497   ac_cv_cxx_ext_hash_set,
 498   [AC_LANG_SAVE
 499   AC_LANG_CPLUSPLUS
 500   ac_save_CXXFLAGS="$CXXFLAGS"
 501   CXXFLAGS="$CXXFLAGS -Werror"
 502   AC_TRY_COMPILE([#include &lt;ext/hash_set&gt;], [using __gnu_cxx::hash_set;],
 503   ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no)
 504   CXXFLAGS="$ac_save_CXXFLAGS"
 505   AC_LANG_RESTORE
 506   ])
 507   if test "$ac_cv_cxx_ext_hash_set" = yes; then
 508     AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ])
 509   fi
 510 ])
 511 </pre></div><div class="sect3" title="No ios::nocreate/ios::noreplace."><div class="titlepage"><div><div><h4 class="title"><a id="id426874"></a>No <code class="code">ios::nocreate/ios::noreplace</code>.
 512 </h4></div></div></div><p> The existence of <code class="code">ios::nocreate</code> being used for
 513 input-streams has been confirmed, most probably because the author
 514 thought it would be more correct to specify nocreate explicitly.  So
 515 it can be left out for input-streams.
 516 </p><p>For output streams, <span class="quote">“<span class="quote">nocreate</span>”</span> is probably the default,
 517 unless you specify <code class="code">std::ios::trunc</code> ? To be safe, you can
 518 open the file for reading, check if it has been opened, and then
 519 decide whether you want to create/replace or not. To my knowledge,
 520 even older implementations support <code class="code">app</code>, <code class="code">ate</code>
 521 and <code class="code">trunc</code> (except for <code class="code">app</code> ?).
 522 </p></div><div class="sect3" title="No stream::attach(int fd)"><div class="titlepage"><div><div><h4 class="title"><a id="id426921"></a>
 523 No <code class="code">stream::attach(int fd)</code>
 524 </h4></div></div></div><p>
 525       Phil Edwards writes: It was considered and rejected for the ISO
 526       standard.  Not all environments use file descriptors.  Of those
 527       that do, not all of them use integers to represent them.
 528     </p><p>
 529       For a portable solution (among systems which use
 530       file descriptors), you need to implement a subclass of
 531       <code class="code">std::streambuf</code> (or
 532       <code class="code">std::basic_streambuf&lt;..&gt;</code>) which opens a file
 533       given a descriptor, and then pass an instance of this to the
 534       stream-constructor.
 535     </p><p>
 536       An extension is available that implements this.
 537       <code class="filename">ext/stdio_filebuf.h</code> contains a derived class called
 538       <a class="ulink" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00074.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>.
 539       This class can be constructed from a C <code class="code">FILE*</code> or a file
 540       descriptor, and provides the <code class="code">fd()</code> function.
 541     </p><p>
 542  For another example of this, refer to
 543       <a class="ulink" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a>
 544       by Nicolai Josuttis.
 545 </p></div><div class="sect3" title="Support for C++98 dialect."><div class="titlepage"><div><div><h4 class="title"><a id="id426985"></a>
 546 Support for C++98 dialect.
 547 </h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard.
 548 </p><pre class="programlisting">
 549 # AC_HEADER_STDCXX_98
 550 AC_DEFUN([AC_HEADER_STDCXX_98], [
 551   AC_CACHE_CHECK(for ISO C++ 98 include files,
 552   ac_cv_cxx_stdcxx_98,
 553   [AC_LANG_SAVE
 554   AC_LANG_CPLUSPLUS
 555   AC_TRY_COMPILE([
 556     #include &lt;cassert&gt;
 557     #include &lt;cctype&gt;
 558     #include &lt;cerrno&gt;
 559     #include &lt;cfloat&gt;
 560     #include &lt;ciso646&gt;
 561     #include &lt;climits&gt;
 562     #include &lt;clocale&gt;
 563     #include &lt;cmath&gt;
 564     #include &lt;csetjmp&gt;
 565     #include &lt;csignal&gt;
 566     #include &lt;cstdarg&gt;
 567     #include &lt;cstddef&gt;
 568     #include &lt;cstdio&gt;
 569     #include &lt;cstdlib&gt;
 570     #include &lt;cstring&gt;
 571     #include &lt;ctime&gt;
 572
 573     #include &lt;algorithm&gt;
 574     #include &lt;bitset&gt;
 575     #include &lt;complex&gt;
 576     #include &lt;deque&gt;
 577     #include &lt;exception&gt;
 578     #include &lt;fstream&gt;
 579     #include &lt;functional&gt;
 580     #include &lt;iomanip&gt;
 581     #include &lt;ios&gt;
 582     #include &lt;iosfwd&gt;
 583     #include &lt;iostream&gt;
 584     #include &lt;istream&gt;
 585     #include &lt;iterator&gt;
 586     #include &lt;limits&gt;
 587     #include &lt;list&gt;
 588     #include &lt;locale&gt;
 589     #include &lt;map&gt;
 590     #include &lt;memory&gt;
 591     #include &lt;new&gt;
 592     #include &lt;numeric&gt;
 593     #include &lt;ostream&gt;
 594     #include &lt;queue&gt;
 595     #include &lt;set&gt;
 596     #include &lt;sstream&gt;
 597     #include &lt;stack&gt;
 598     #include &lt;stdexcept&gt;
 599     #include &lt;streambuf&gt;
 600     #include &lt;string&gt;
 601     #include &lt;typeinfo&gt;
 602     #include &lt;utility&gt;
 603     #include &lt;valarray&gt;
 604     #include &lt;vector&gt;
 605   ],,
 606   ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no)
 607   AC_LANG_RESTORE
 608   ])
 609   if test "$ac_cv_cxx_stdcxx_98" = yes; then
 610     AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ])
 611   fi
 612 ])
 613 </pre></div><div class="sect3" title="Support for C++TR1 dialect."><div class="titlepage"><div><div><h4 class="title"><a id="id489807"></a>
 614 Support for C++TR1 dialect.
 615 </h4></div></div></div><p>Check for library coverage of the TR1 standard.
 616 </p><pre class="programlisting">
 617 # AC_HEADER_STDCXX_TR1
 618 AC_DEFUN([AC_HEADER_STDCXX_TR1], [
 619   AC_CACHE_CHECK(for ISO C++ TR1 include files,
 620   ac_cv_cxx_stdcxx_tr1,
 621   [AC_LANG_SAVE
 622   AC_LANG_CPLUSPLUS
 623   AC_TRY_COMPILE([
 624   #include &lt;tr1/array&gt;
 625   #include &lt;tr1/ccomplex&gt;
 626   #include &lt;tr1/cctype&gt;
 627   #include &lt;tr1/cfenv&gt;
 628   #include &lt;tr1/cfloat&gt;
 629   #include &lt;tr1/cinttypes&gt;
 630   #include &lt;tr1/climits&gt;
 631   #include &lt;tr1/cmath&gt;
 632   #include &lt;tr1/complex&gt;
 633   #include &lt;tr1/cstdarg&gt;
 634   #include &lt;tr1/cstdbool&gt;
 635   #include &lt;tr1/cstdint&gt;
 636   #include &lt;tr1/cstdio&gt;
 637   #include &lt;tr1/cstdlib&gt;
 638   #include &lt;tr1/ctgmath&gt;
 639   #include &lt;tr1/ctime&gt;
 640   #include &lt;tr1/cwchar&gt;
 641   #include &lt;tr1/cwctype&gt;
 642   #include &lt;tr1/functional&gt;
 643   #include &lt;tr1/memory&gt;
 644   #include &lt;tr1/random&gt;
 645   #include &lt;tr1/regex&gt;
 646   #include &lt;tr1/tuple&gt;
 647   #include &lt;tr1/type_traits&gt;
 648   #include &lt;tr1/unordered_set&gt;
 649   #include &lt;tr1/unordered_map&gt;
 650   #include &lt;tr1/utility&gt;
 651   ],,
 652   ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no)
 653   AC_LANG_RESTORE
 654   ])
 655   if test "$ac_cv_cxx_stdcxx_tr1" = yes; then
 656     AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ])
 657   fi
 658 ])
 659 </pre><p>An alternative is to check just for specific TR1 includes, such as &lt;unordered_map&gt; and &lt;unordered_set&gt;.
 660 </p><pre class="programlisting">
 661 # AC_HEADER_TR1_UNORDERED_MAP
 662 AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [
 663   AC_CACHE_CHECK(for tr1/unordered_map,
 664   ac_cv_cxx_tr1_unordered_map,
 665   [AC_LANG_SAVE
 666   AC_LANG_CPLUSPLUS
 667   AC_TRY_COMPILE([#include &lt;tr1/unordered_map&gt;], [using std::tr1::unordered_map;],
 668   ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no)
 669   AC_LANG_RESTORE
 670   ])
 671   if test "$ac_cv_cxx_tr1_unordered_map" = yes; then
 672     AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ])
 673   fi
 674 ])
 675 </pre><pre class="programlisting">
 676 # AC_HEADER_TR1_UNORDERED_SET
 677 AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [
 678   AC_CACHE_CHECK(for tr1/unordered_set,
 679   ac_cv_cxx_tr1_unordered_set,
 680   [AC_LANG_SAVE
 681   AC_LANG_CPLUSPLUS
 682   AC_TRY_COMPILE([#include &lt;tr1/unordered_set&gt;], [using std::tr1::unordered_set;],
 683   ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no)
 684   AC_LANG_RESTORE
 685   ])
 686   if test "$ac_cv_cxx_tr1_unordered_set" = yes; then
 687     AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ])
 688   fi
 689 ])
 690 </pre></div><div class="sect3" title="Support for C++0x dialect."><div class="titlepage"><div><div><h4 class="title"><a id="id489851"></a>
 691 Support for C++0x dialect.
 692 </h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++0xstandard.
 693 </p><pre class="programlisting">
 694 # AC_COMPILE_STDCXX_OX
 695 AC_DEFUN([AC_COMPILE_STDCXX_0X], [
 696   AC_CACHE_CHECK(if g++ supports C++0x features without additional flags,
 697   ac_cv_cxx_compile_cxx0x_native,
 698   [AC_LANG_SAVE
 699   AC_LANG_CPLUSPLUS
 700   AC_TRY_COMPILE([
 701   template &lt;typename T&gt;
 702     struct check
 703     {
 704       static_assert(sizeof(int) &lt;= sizeof(T), "not big enough");
 705     };
 706
 707     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 708
 709     int a;
 710     decltype(a) b;
 711
 712     typedef check&lt;int&gt; check_type;
 713     check_type c;
 714     check_type&amp;&amp; cr = c;],,
 715   ac_cv_cxx_compile_cxx0x_native=yes, ac_cv_cxx_compile_cxx0x_native=no)
 716   AC_LANG_RESTORE
 717   ])
 718
 719   AC_CACHE_CHECK(if g++ supports C++0x features with -std=c++0x,
 720   ac_cv_cxx_compile_cxx0x_cxx,
 721   [AC_LANG_SAVE
 722   AC_LANG_CPLUSPLUS
 723   ac_save_CXXFLAGS="$CXXFLAGS"
 724   CXXFLAGS="$CXXFLAGS -std=c++0x"
 725   AC_TRY_COMPILE([
 726   template &lt;typename T&gt;
 727     struct check
 728     {
 729       static_assert(sizeof(int) &lt;= sizeof(T), "not big enough");
 730     };
 731
 732     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 733
 734     int a;
 735     decltype(a) b;
 736
 737     typedef check&lt;int&gt; check_type;
 738     check_type c;
 739     check_type&amp;&amp; cr = c;],,
 740   ac_cv_cxx_compile_cxx0x_cxx=yes, ac_cv_cxx_compile_cxx0x_cxx=no)
 741   CXXFLAGS="$ac_save_CXXFLAGS"
 742   AC_LANG_RESTORE
 743   ])
 744
 745   AC_CACHE_CHECK(if g++ supports C++0x features with -std=gnu++0x,
 746   ac_cv_cxx_compile_cxx0x_gxx,
 747   [AC_LANG_SAVE
 748   AC_LANG_CPLUSPLUS
 749   ac_save_CXXFLAGS="$CXXFLAGS"
 750   CXXFLAGS="$CXXFLAGS -std=gnu++0x"
 751   AC_TRY_COMPILE([
 752   template &lt;typename T&gt;
 753     struct check
 754     {
 755       static_assert(sizeof(int) &lt;= sizeof(T), "not big enough");
 756     };
 757
 758     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 759
 760     int a;
 761     decltype(a) b;
 762
 763     typedef check&lt;int&gt; check_type;
 764     check_type c;
 765     check_type&amp;&amp; cr = c;],,
 766   ac_cv_cxx_compile_cxx0x_gxx=yes, ac_cv_cxx_compile_cxx0x_gxx=no)
 767   CXXFLAGS="$ac_save_CXXFLAGS"
 768   AC_LANG_RESTORE
 769   ])
 770
 771   if test "$ac_cv_cxx_compile_cxx0x_native" = yes ||
 772      test "$ac_cv_cxx_compile_cxx0x_cxx" = yes ||
 773      test "$ac_cv_cxx_compile_cxx0x_gxx" = yes; then
 774     AC_DEFINE(HAVE_STDCXX_0X,,[Define if g++ supports C++0x features. ])
 775   fi
 776 ])
 777 </pre><p>Check for library coverage of the C++0xstandard.
 778 </p><pre class="programlisting">
 779 # AC_HEADER_STDCXX_0X
 780 AC_DEFUN([AC_HEADER_STDCXX_0X], [
 781   AC_CACHE_CHECK(for ISO C++ 0x include files,
 782   ac_cv_cxx_stdcxx_0x,
 783   [AC_REQUIRE([AC_COMPILE_STDCXX_0X])
 784   AC_LANG_SAVE
 785   AC_LANG_CPLUSPLUS
 786   ac_save_CXXFLAGS="$CXXFLAGS"
 787   CXXFLAGS="$CXXFLAGS -std=gnu++0x"
 788
 789   AC_TRY_COMPILE([
 790     #include &lt;cassert&gt;
 791     #include &lt;ccomplex&gt;
 792     #include &lt;cctype&gt;
 793     #include &lt;cerrno&gt;
 794     #include &lt;cfenv&gt;
 795     #include &lt;cfloat&gt;
 796     #include &lt;cinttypes&gt;
 797     #include &lt;ciso646&gt;
 798     #include &lt;climits&gt;
 799     #include &lt;clocale&gt;
 800     #include &lt;cmath&gt;
 801     #include &lt;csetjmp&gt;
 802     #include &lt;csignal&gt;
 803     #include &lt;cstdarg&gt;
 804     #include &lt;cstdbool&gt;
 805     #include &lt;cstddef&gt;
 806     #include &lt;cstdint&gt;
 807     #include &lt;cstdio&gt;
 808     #include &lt;cstdlib&gt;
 809     #include &lt;cstring&gt;
 810     #include &lt;ctgmath&gt;
 811     #include &lt;ctime&gt;
 812     #include &lt;cwchar&gt;
 813     #include &lt;cwctype&gt;
 814
 815     #include &lt;algorithm&gt;
 816     #include &lt;array&gt;
 817     #include &lt;bitset&gt;
 818     #include &lt;complex&gt;
 819     #include &lt;deque&gt;
 820     #include &lt;exception&gt;
 821     #include &lt;fstream&gt;
 822     #include &lt;functional&gt;
 823     #include &lt;iomanip&gt;
 824     #include &lt;ios&gt;
 825     #include &lt;iosfwd&gt;
 826     #include &lt;iostream&gt;
 827     #include &lt;istream&gt;
 828     #include &lt;iterator&gt;
 829     #include &lt;limits&gt;
 830     #include &lt;list&gt;
 831     #include &lt;locale&gt;
 832     #include &lt;map&gt;
 833     #include &lt;memory&gt;
 834     #include &lt;new&gt;
 835     #include &lt;numeric&gt;
 836     #include &lt;ostream&gt;
 837     #include &lt;queue&gt;
 838     #include &lt;random&gt;
 839     #include &lt;regex&gt;
 840     #include &lt;set&gt;
 841     #include &lt;sstream&gt;
 842     #include &lt;stack&gt;
 843     #include &lt;stdexcept&gt;
 844     #include &lt;streambuf&gt;
 845     #include &lt;string&gt;
 846     #include &lt;tuple&gt;
 847     #include &lt;typeinfo&gt;
 848     #include &lt;type_traits&gt;
 849     #include &lt;unordered_map&gt;
 850     #include &lt;unordered_set&gt;
 851     #include &lt;utility&gt;
 852     #include &lt;valarray&gt;
 853     #include &lt;vector&gt;
 854   ],,
 855   ac_cv_cxx_stdcxx_0x=yes, ac_cv_cxx_stdcxx_0x=no)
 856   AC_LANG_RESTORE
 857   CXXFLAGS="$ac_save_CXXFLAGS"
 858   ])
 859   if test "$ac_cv_cxx_stdcxx_0x" = yes; then
 860     AC_DEFINE(STDCXX_0X_HEADERS,,[Define if ISO C++ 0x header files are present. ])
 861   fi
 862 ])
 863 </pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For &lt;unordered_map&gt;
 864 </p><pre class="programlisting">
 865 # AC_HEADER_UNORDERED_MAP
 866 AC_DEFUN([AC_HEADER_UNORDERED_MAP], [
 867   AC_CACHE_CHECK(for unordered_map,
 868   ac_cv_cxx_unordered_map,
 869   [AC_REQUIRE([AC_COMPILE_STDCXX_0X])
 870   AC_LANG_SAVE
 871   AC_LANG_CPLUSPLUS
 872   ac_save_CXXFLAGS="$CXXFLAGS"
 873   CXXFLAGS="$CXXFLAGS -std=gnu++0x"
 874   AC_TRY_COMPILE([#include &lt;unordered_map&gt;], [using std::unordered_map;],
 875   ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no)
 876   CXXFLAGS="$ac_save_CXXFLAGS"
 877   AC_LANG_RESTORE
 878   ])
 879   if test "$ac_cv_cxx_unordered_map" = yes; then
 880     AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ])
 881   fi
 882 ])
 883 </pre><pre class="programlisting">
 884 # AC_HEADER_UNORDERED_SET
 885 AC_DEFUN([AC_HEADER_UNORDERED_SET], [
 886   AC_CACHE_CHECK(for unordered_set,
 887   ac_cv_cxx_unordered_set,
 888   [AC_REQUIRE([AC_COMPILE_STDCXX_0X])
 889   AC_LANG_SAVE
 890   AC_LANG_CPLUSPLUS
 891   ac_save_CXXFLAGS="$CXXFLAGS"
 892   CXXFLAGS="$CXXFLAGS -std=gnu++0x"
 893   AC_TRY_COMPILE([#include &lt;unordered_set&gt;], [using std::unordered_set;],
 894   ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no)
 895   CXXFLAGS="$ac_save_CXXFLAGS"
 896   AC_LANG_RESTORE
 897   ])
 898   if test "$ac_cv_cxx_unordered_set" = yes; then
 899     AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ])
 900   fi
 901 ])
 902 </pre></div><div class="sect3" title="Container::iterator_type is not necessarily Container::value_type*"><div class="titlepage"><div><div><h4 class="title"><a id="id489928"></a>
 903   Container::iterator_type is not necessarily Container::value_type*
 904 </h4></div></div></div><p>
 905   This is a change in behavior from the previous version. Now, most
 906   <span class="type">iterator_type</span> typedefs in container classes are POD
 907   objects, not <span class="type">value_type</span> pointers.
 908 </p></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.biblio"></a>Bibliography</h3></div></div></div><div class="biblioentry"><a id="id489958"></a><p><span class="biblioid">
 909       <a class="ulink" href="http://www.kegel.com/gcc/gcc4.html" target="_top">
 910         <em class="citetitle">
 911           Migrating to GCC 4.1
 912         </em>
 913         </a>
 914     . </span><span class="author"><span class="firstname">Dan</span> <span class="surname">Kegel</span>. </span></p></div><div class="biblioentry"><a id="id489988"></a><p><span class="biblioid">
 915       <a class="ulink" href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top">
 916         <em class="citetitle">
 917           Building the Whole Debian Archive with GCC 4.1: A Summary
 918         </em>
 919       </a>
 920     . </span><span class="author"><span class="firstname">Martin</span> <span class="surname">Michlmayr</span>. </span></p></div><div class="biblioentry"><a id="id490020"></a><p><span class="biblioid">
 921       <a class="ulink" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top">
 922         <em class="citetitle">
 923           Migration guide for GCC-3.2
 924         </em>
 925       </a>
 926     . </span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">API Evolution and Deprecation History </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix C.
 927   Free Software Needs Free Documentation
 928
 929 </td></tr></table></div></body></html>