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

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Backwards Compatibility</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, backwards" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="appendix_porting.html" title="Appendix B.  Porting and Maintenance" /><link rel="prev" href="api.html" title="API Evolution and Deprecation History" /><link rel="next" href="appendix_free.html" title="Appendix C.  Free Software Needs Free Documentation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Backwards Compatibility</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><th width="60%" align="center">Appendix B.
   3   Porting and Maintenance
   4
   5 </th><td width="20%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr></table><hr /></div><div class="section"><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="section"><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
   6 separate GNU project, although reliably paired with GCC. Rumors imply
   7 that it had a working relationship with at least two kinds of
   8 dinosaur.
   9 </p><p>Some background: libg++ was designed and created when there was no
  10 ISO standard to provide guidance.  Classes like linked lists are now
  11 provided for by <code class="classname">std::list&lt;T&gt;</code> and do not need to be
  12 created by <code class="function">genclass</code>.  (For that matter, templates exist
  13 now and are well-supported, whereas genclass (mostly) predates them.)
  14 </p><p>There are other classes in libg++ that are not specified in the
  15 ISO Standard (e.g., statistical analysis).  While there are a lot of
  16 really useful things that are used by a lot of people, the Standards
  17 Committee couldn't include everything, and so a lot of those
  18 <span class="quote">“<span class="quote">obvious</span>”</span> classes didn't get included.
  19 </p><p>That project is no longer maintained or supported, and the sources
  20 archived. For the desperate, the
  21 <a class="link" href="https://ftp.gnu.org/old-gnu/libg++/" target="_top">ftp.gnu.org</a>
  22 server still has the libg++ source.
  23 </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p>
  24   The second generation GNU C++ library was called libstdc++, or
  25   libstdc++-v2. It spans the time between libg++ and pre-ISO C++
  26   standardization and is usually associated with the following GCC
  27   releases: egcs 1.x, gcc 2.95, and gcc 2.96.
  28 </p><p>
  29   The STL portions of that library are based on SGI/HP STL release 3.11.
  30 </p><p>
  31   That project is no longer maintained or supported, and the sources
  32   archived.  The code was replaced and rewritten for libstdc++-v3.
  33 </p></div><div class="section"><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
  34 libstdc++-v3.
  35 </p><p>The subset commonly known as the Standard Template Library
  36          (clauses 23 through 25 in C++98, mostly) is adapted from the final release
  37          of the SGI STL (version 3.3), with extensive changes.
  38       </p><p>A more formal description of the V3 goals can be found in the
  39          official <a class="link" href="source_design_notes.html" title="Design Notes">design document</a>.
  40       </p><p>Portability notes and known implementation limitations are as follows.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.headers"></a>Pre-ISO headers removed</h4></div></div></div><p> The pre-ISO C++ headers
  41       (<code class="filename">&lt;iostream.h&gt;</code>,
  42       <code class="filename">&lt;defalloc.h&gt;</code> etc.) are
  43       not supported.
  44 </p><p>For those of you new to ISO C++ (welcome, time travelers!), the
  45       ancient pre-ISO headers have new names.
  46       The C++ FAQ has a good explanation in <a class="link" href="https://isocpp.org/wiki/faq/coding-standards#std-headers" target="_top">What's
  47       the difference between &lt;xxx&gt; and &lt;xxx.h&gt; headers?</a>.
  48    </p><p>Porting between pre-ISO headers and ISO headers is simple: headers
  49 like <code class="filename">&lt;vector.h&gt;</code> can be replaced with <code class="filename">&lt;vector&gt;</code> and a using
  50 directive <code class="code">using namespace std;</code> can be put at the global
  51 scope. This should be enough to get this code compiling, assuming the
  52 other usage is correct.
  53 </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.hash"></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
  54          replaced by standardized libraries.
  55          In particular, the <code class="classname">unordered_map</code> and
  56          <code class="classname">unordered_set</code> containers of TR1 and C++ 2011
  57          are suitable replacements for the non-standard
  58          <code class="classname">hash_map</code> and <code class="classname">hash_set</code>
  59          containers in the SGI STL.
  60       </p><p> Header files <code class="filename">&lt;hash_map&gt;</code> and <code class="filename">&lt;hash_set&gt;</code> moved
  61 to <code class="filename">&lt;ext/hash_map&gt;</code> and  <code class="filename">&lt;ext/hash_set&gt;</code>,
  62 respectively. At the same time, all types in these files are enclosed
  63 in <code class="code">namespace __gnu_cxx</code>. Later versions deprecate
  64 these files, and suggest using TR1's  <code class="filename">&lt;unordered_map&gt;</code>
  65 and  <code class="filename">&lt;unordered_set&gt;</code> instead.
  66 </p><p>The extensions are no longer in the global or <code class="code">std</code>
  67          namespaces, instead they are declared in the <code class="code">__gnu_cxx</code>
  68          namespace. For maximum portability, consider defining a namespace
  69          alias to use to talk about extensions, e.g.:
  70       </p><pre class="programlisting">
  71       #ifdef __GNUC__
  72       #if __GNUC__ &lt; 3
  73         #include &lt;hash_map.h&gt;
  74         namespace extension { using ::hash_map; }; // inherit globals
  75       #else
  76         #include &lt;backward/hash_map&gt;
  77         #if __GNUC__ == 3 &amp;&amp; __GNUC_MINOR__ == 0
  78           namespace extension = std;               // GCC 3.0
  79         #else
  80           namespace extension = ::__gnu_cxx;       // GCC 3.1 and later
  81         #endif
  82       #endif
  83       #else      // ...  there are other compilers, right?
  84         namespace extension = std;
  85       #endif
  86
  87       extension::hash_map&lt;int,int&gt; my_map;
  88       </pre><p>This is a bit cleaner than defining typedefs for all the
  89          instantiations you might need.
  90       </p><p>The following autoconf tests check for working HP/SGI hash containers.
  91 </p><pre class="programlisting">
  92 # AC_HEADER_EXT_HASH_MAP
  93 AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [
  94   AC_CACHE_CHECK(for ext/hash_map,
  95   ac_cv_cxx_ext_hash_map,
  96   [AC_LANG_SAVE
  97   AC_LANG_CPLUSPLUS
  98   ac_save_CXXFLAGS="$CXXFLAGS"
  99   CXXFLAGS="$CXXFLAGS -Werror"
 100   AC_TRY_COMPILE([#include &lt;ext/hash_map&gt;], [using __gnu_cxx::hash_map;],
 101   ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no)
 102   CXXFLAGS="$ac_save_CXXFLAGS"
 103   AC_LANG_RESTORE
 104   ])
 105   if test "$ac_cv_cxx_ext_hash_map" = yes; then
 106     AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ])
 107   fi
 108 ])
 109 </pre><pre class="programlisting">
 110 # AC_HEADER_EXT_HASH_SET
 111 AC_DEFUN([AC_HEADER_EXT_HASH_SET], [
 112   AC_CACHE_CHECK(for ext/hash_set,
 113   ac_cv_cxx_ext_hash_set,
 114   [AC_LANG_SAVE
 115   AC_LANG_CPLUSPLUS
 116   ac_save_CXXFLAGS="$CXXFLAGS"
 117   CXXFLAGS="$CXXFLAGS -Werror"
 118   AC_TRY_COMPILE([#include &lt;ext/hash_set&gt;], [using __gnu_cxx::hash_set;],
 119   ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no)
 120   CXXFLAGS="$ac_save_CXXFLAGS"
 121   AC_LANG_RESTORE
 122   ])
 123   if test "$ac_cv_cxx_ext_hash_set" = yes; then
 124     AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ])
 125   fi
 126 ])
 127 </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.nocreate_noreplace"></a>No <code class="code">ios::nocreate/ios::noreplace</code>.
 128 </h4></div></div></div><p>Historically these flags were used with iostreams to control whether
 129 new files are created or not when opening a file stream, similar to the
 130 <code class="code">O_CREAT</code> and <code class="code">O_EXCL</code> flags for the
 131 <code class="function">open(2)</code> system call. Because iostream modes correspond
 132 to <code class="function">fopen(3)</code> modes these flags are not supported.
 133 For input streams a new file will not be created anyway, so
 134 <code class="code">ios::nocreate</code> is not needed.
 135 For output streams, a new file will be created if it does not exist, which is
 136 consistent with the behaviour of <code class="function">fopen</code>.
 137 </p><p>When one of these flags is needed a possible alternative is to attempt
 138 to open the file using <span class="type">std::ifstream</span> first to determine whether
 139 the file already exists or not. This may not be reliable however, because
 140 whether the file exists or not could change between opening the
 141 <span class="type">std::istream</span> and re-opening with an output stream. If you need
 142 to check for existence and open a file as a single operation then you will
 143 need to use OS-specific facilities outside the C++ standard library, such
 144 as <code class="function">open(2)</code>.
 145 </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.streamattach"></a>
 146 No <code class="code">stream::attach(int fd)</code>
 147 </h4></div></div></div><p>
 148       Phil Edwards writes: It was considered and rejected for the ISO
 149       standard.  Not all environments use file descriptors.  Of those
 150       that do, not all of them use integers to represent them.
 151     </p><p>
 152       For a portable solution (among systems which use
 153       file descriptors), you need to implement a subclass of
 154       <code class="code">std::streambuf</code> (or
 155       <code class="code">std::basic_streambuf&lt;..&gt;</code>) which opens a file
 156       given a descriptor, and then pass an instance of this to the
 157       stream-constructor.
 158     </p><p>
 159       An extension is available that implements this.
 160       <code class="filename">&lt;ext/stdio_filebuf.h&gt;</code>
 161       contains a derived class called
 162       <code class="classname">__gnu_cxx::stdio_filebuf</code>.
 163       This class can be constructed from a C <code class="code">FILE*</code> or a file
 164       descriptor, and provides the <code class="code">fd()</code> function.
 165     </p><p>
 166  For another example of this, refer to
 167       <a class="link" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a>
 168       by Nicolai Josuttis.
 169 </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx98"></a>
 170 Support for C++98 dialect.
 171 </h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard.
 172 </p><pre class="programlisting">
 173 # AC_HEADER_STDCXX_98
 174 AC_DEFUN([AC_HEADER_STDCXX_98], [
 175   AC_CACHE_CHECK(for ISO C++ 98 include files,
 176   ac_cv_cxx_stdcxx_98,
 177   [AC_LANG_SAVE
 178   AC_LANG_CPLUSPLUS
 179   AC_TRY_COMPILE([
 180     #include &lt;cassert&gt;
 181     #include &lt;cctype&gt;
 182     #include &lt;cerrno&gt;
 183     #include &lt;cfloat&gt;
 184     #include &lt;ciso646&gt;
 185     #include &lt;climits&gt;
 186     #include &lt;clocale&gt;
 187     #include &lt;cmath&gt;
 188     #include &lt;csetjmp&gt;
 189     #include &lt;csignal&gt;
 190     #include &lt;cstdarg&gt;
 191     #include &lt;cstddef&gt;
 192     #include &lt;cstdio&gt;
 193     #include &lt;cstdlib&gt;
 194     #include &lt;cstring&gt;
 195     #include &lt;ctime&gt;
 196
 197     #include &lt;algorithm&gt;
 198     #include &lt;bitset&gt;
 199     #include &lt;complex&gt;
 200     #include &lt;deque&gt;
 201     #include &lt;exception&gt;
 202     #include &lt;fstream&gt;
 203     #include &lt;functional&gt;
 204     #include &lt;iomanip&gt;
 205     #include &lt;ios&gt;
 206     #include &lt;iosfwd&gt;
 207     #include &lt;iostream&gt;
 208     #include &lt;istream&gt;
 209     #include &lt;iterator&gt;
 210     #include &lt;limits&gt;
 211     #include &lt;list&gt;
 212     #include &lt;locale&gt;
 213     #include &lt;map&gt;
 214     #include &lt;memory&gt;
 215     #include &lt;new&gt;
 216     #include &lt;numeric&gt;
 217     #include &lt;ostream&gt;
 218     #include &lt;queue&gt;
 219     #include &lt;set&gt;
 220     #include &lt;sstream&gt;
 221     #include &lt;stack&gt;
 222     #include &lt;stdexcept&gt;
 223     #include &lt;streambuf&gt;
 224     #include &lt;string&gt;
 225     #include &lt;typeinfo&gt;
 226     #include &lt;utility&gt;
 227     #include &lt;valarray&gt;
 228     #include &lt;vector&gt;
 229   ],,
 230   ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no)
 231   AC_LANG_RESTORE
 232   ])
 233   if test "$ac_cv_cxx_stdcxx_98" = yes; then
 234     AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ])
 235   fi
 236 ])
 237 </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_tr1"></a>
 238 Support for C++TR1 dialect.
 239 </h4></div></div></div><p>Check for library coverage of the TR1 standard.
 240 </p><pre class="programlisting">
 241 # AC_HEADER_STDCXX_TR1
 242 AC_DEFUN([AC_HEADER_STDCXX_TR1], [
 243   AC_CACHE_CHECK(for ISO C++ TR1 include files,
 244   ac_cv_cxx_stdcxx_tr1,
 245   [AC_LANG_SAVE
 246   AC_LANG_CPLUSPLUS
 247   AC_TRY_COMPILE([
 248   #include &lt;tr1/array&gt;
 249   #include &lt;tr1/ccomplex&gt;
 250   #include &lt;tr1/cctype&gt;
 251   #include &lt;tr1/cfenv&gt;
 252   #include &lt;tr1/cfloat&gt;
 253   #include &lt;tr1/cinttypes&gt;
 254   #include &lt;tr1/climits&gt;
 255   #include &lt;tr1/cmath&gt;
 256   #include &lt;tr1/complex&gt;
 257   #include &lt;tr1/cstdarg&gt;
 258   #include &lt;tr1/cstdbool&gt;
 259   #include &lt;tr1/cstdint&gt;
 260   #include &lt;tr1/cstdio&gt;
 261   #include &lt;tr1/cstdlib&gt;
 262   #include &lt;tr1/ctgmath&gt;
 263   #include &lt;tr1/ctime&gt;
 264   #include &lt;tr1/cwchar&gt;
 265   #include &lt;tr1/cwctype&gt;
 266   #include &lt;tr1/functional&gt;
 267   #include &lt;tr1/memory&gt;
 268   #include &lt;tr1/random&gt;
 269   #include &lt;tr1/regex&gt;
 270   #include &lt;tr1/tuple&gt;
 271   #include &lt;tr1/type_traits&gt;
 272   #include &lt;tr1/unordered_set&gt;
 273   #include &lt;tr1/unordered_map&gt;
 274   #include &lt;tr1/utility&gt;
 275   ],,
 276   ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no)
 277   AC_LANG_RESTORE
 278   ])
 279   if test "$ac_cv_cxx_stdcxx_tr1" = yes; then
 280     AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ])
 281   fi
 282 ])
 283 </pre><p>An alternative is to check just for specific TR1 includes, such as &lt;unordered_map&gt; and &lt;unordered_set&gt;.
 284 </p><pre class="programlisting">
 285 # AC_HEADER_TR1_UNORDERED_MAP
 286 AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [
 287   AC_CACHE_CHECK(for tr1/unordered_map,
 288   ac_cv_cxx_tr1_unordered_map,
 289   [AC_LANG_SAVE
 290   AC_LANG_CPLUSPLUS
 291   AC_TRY_COMPILE([#include &lt;tr1/unordered_map&gt;], [using std::tr1::unordered_map;],
 292   ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no)
 293   AC_LANG_RESTORE
 294   ])
 295   if test "$ac_cv_cxx_tr1_unordered_map" = yes; then
 296     AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ])
 297   fi
 298 ])
 299 </pre><pre class="programlisting">
 300 # AC_HEADER_TR1_UNORDERED_SET
 301 AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [
 302   AC_CACHE_CHECK(for tr1/unordered_set,
 303   ac_cv_cxx_tr1_unordered_set,
 304   [AC_LANG_SAVE
 305   AC_LANG_CPLUSPLUS
 306   AC_TRY_COMPILE([#include &lt;tr1/unordered_set&gt;], [using std::tr1::unordered_set;],
 307   ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no)
 308   AC_LANG_RESTORE
 309   ])
 310   if test "$ac_cv_cxx_tr1_unordered_set" = yes; then
 311     AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ])
 312   fi
 313 ])
 314 </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx11"></a>
 315 Support for C++11 dialect.
 316 </h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++11 standard.
 317 </p><pre class="programlisting">
 318 # AC_COMPILE_STDCXX_11
 319 AC_DEFUN([AC_COMPILE_STDCXX_11], [
 320   AC_CACHE_CHECK(if g++ supports C++11 features without additional flags,
 321   ac_cv_cxx_compile_cxx11_native,
 322   [AC_LANG_SAVE
 323   AC_LANG_CPLUSPLUS
 324   AC_TRY_COMPILE([
 325   template &lt;typename T&gt;
 326     struct check final
 327     {
 328       static constexpr T value{ __cplusplus };
 329     };
 330
 331     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 332
 333     int a;
 334     decltype(a) b;
 335
 336     typedef check&lt;int&gt; check_type;
 337     check_type c{};
 338     check_type&amp;&amp; cr = static_cast&lt;check_type&amp;&amp;&gt;(c);
 339
 340     static_assert(check_type::value == 201103L, "C++11 compiler");],,
 341   ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no)
 342   AC_LANG_RESTORE
 343   ])
 344
 345   AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11,
 346   ac_cv_cxx_compile_cxx11_cxx,
 347   [AC_LANG_SAVE
 348   AC_LANG_CPLUSPLUS
 349   ac_save_CXXFLAGS="$CXXFLAGS"
 350   CXXFLAGS="$CXXFLAGS -std=c++11"
 351   AC_TRY_COMPILE([
 352   template &lt;typename T&gt;
 353     struct check final
 354     {
 355       static constexpr T value{ __cplusplus };
 356     };
 357
 358     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 359
 360     int a;
 361     decltype(a) b;
 362
 363     typedef check&lt;int&gt; check_type;
 364     check_type c{};
 365     check_type&amp;&amp; cr = static_cast&lt;check_type&amp;&amp;&gt;(c);
 366
 367     static_assert(check_type::value == 201103L, "C++11 compiler");],,
 368   ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no)
 369   CXXFLAGS="$ac_save_CXXFLAGS"
 370   AC_LANG_RESTORE
 371   ])
 372
 373   AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11,
 374   ac_cv_cxx_compile_cxx11_gxx,
 375   [AC_LANG_SAVE
 376   AC_LANG_CPLUSPLUS
 377   ac_save_CXXFLAGS="$CXXFLAGS"
 378   CXXFLAGS="$CXXFLAGS -std=gnu++11"
 379   AC_TRY_COMPILE([
 380   template &lt;typename T&gt;
 381     struct check final
 382     {
 383       static constexpr T value{ __cplusplus };
 384     };
 385
 386     typedef check&lt;check&lt;bool&gt;&gt; right_angle_brackets;
 387
 388     int a;
 389     decltype(a) b;
 390
 391     typedef check&lt;int&gt; check_type;
 392     check_type c{};
 393     check_type&amp;&amp; cr = static_cast&lt;check_type&amp;&amp;&gt;(c);
 394
 395     static_assert(check_type::value == 201103L, "C++11 compiler");],,
 396   ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no)
 397   CXXFLAGS="$ac_save_CXXFLAGS"
 398   AC_LANG_RESTORE
 399   ])
 400
 401   if test "$ac_cv_cxx_compile_cxx11_native" = yes ||
 402      test "$ac_cv_cxx_compile_cxx11_cxx" = yes ||
 403      test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then
 404     AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ])
 405   fi
 406 ])
 407 </pre><p>Check for library coverage of the C++2011 standard.
 408   (Some library headers are commented out in this check, they are
 409   not currently provided by libstdc++).
 410 </p><pre class="programlisting">
 411 # AC_HEADER_STDCXX_11
 412 AC_DEFUN([AC_HEADER_STDCXX_11], [
 413   AC_CACHE_CHECK(for ISO C++11 include files,
 414   ac_cv_cxx_stdcxx_11,
 415   [AC_REQUIRE([AC_COMPILE_STDCXX_11])
 416   AC_LANG_SAVE
 417   AC_LANG_CPLUSPLUS
 418   ac_save_CXXFLAGS="$CXXFLAGS"
 419   CXXFLAGS="$CXXFLAGS -std=gnu++11"
 420
 421   AC_TRY_COMPILE([
 422     #include &lt;cassert&gt;
 423     #include &lt;ccomplex&gt;
 424     #include &lt;cctype&gt;
 425     #include &lt;cerrno&gt;
 426     #include &lt;cfenv&gt;
 427     #include &lt;cfloat&gt;
 428     #include &lt;cinttypes&gt;
 429     #include &lt;ciso646&gt;
 430     #include &lt;climits&gt;
 431     #include &lt;clocale&gt;
 432     #include &lt;cmath&gt;
 433     #include &lt;csetjmp&gt;
 434     #include &lt;csignal&gt;
 435     #include &lt;cstdalign&gt;
 436     #include &lt;cstdarg&gt;
 437     #include &lt;cstdbool&gt;
 438     #include &lt;cstddef&gt;
 439     #include &lt;cstdint&gt;
 440     #include &lt;cstdio&gt;
 441     #include &lt;cstdlib&gt;
 442     #include &lt;cstring&gt;
 443     #include &lt;ctgmath&gt;
 444     #include &lt;ctime&gt;
 445     // #include &lt;cuchar&gt;
 446     #include &lt;cwchar&gt;
 447     #include &lt;cwctype&gt;
 448
 449     #include &lt;algorithm&gt;
 450     #include &lt;array&gt;
 451     #include &lt;atomic&gt;
 452     #include &lt;bitset&gt;
 453     #include &lt;chrono&gt;
 454     // #include &lt;codecvt&gt;
 455     #include &lt;complex&gt;
 456     #include &lt;condition_variable&gt;
 457     #include &lt;deque&gt;
 458     #include &lt;exception&gt;
 459     #include &lt;forward_list&gt;
 460     #include &lt;fstream&gt;
 461     #include &lt;functional&gt;
 462     #include &lt;future&gt;
 463     #include &lt;initializer_list&gt;
 464     #include &lt;iomanip&gt;
 465     #include &lt;ios&gt;
 466     #include &lt;iosfwd&gt;
 467     #include &lt;iostream&gt;
 468     #include &lt;istream&gt;
 469     #include &lt;iterator&gt;
 470     #include &lt;limits&gt;
 471     #include &lt;list&gt;
 472     #include &lt;locale&gt;
 473     #include &lt;map&gt;
 474     #include &lt;memory&gt;
 475     #include &lt;mutex&gt;
 476     #include &lt;new&gt;
 477     #include &lt;numeric&gt;
 478     #include &lt;ostream&gt;
 479     #include &lt;queue&gt;
 480     #include &lt;random&gt;
 481     #include &lt;ratio&gt;
 482     #include &lt;regex&gt;
 483     #include &lt;scoped_allocator&gt;
 484     #include &lt;set&gt;
 485     #include &lt;sstream&gt;
 486     #include &lt;stack&gt;
 487     #include &lt;stdexcept&gt;
 488     #include &lt;streambuf&gt;
 489     #include &lt;string&gt;
 490     #include &lt;system_error&gt;
 491     #include &lt;thread&gt;
 492     #include &lt;tuple&gt;
 493     #include &lt;typeindex&gt;
 494     #include &lt;typeinfo&gt;
 495     #include &lt;type_traits&gt;
 496     #include &lt;unordered_map&gt;
 497     #include &lt;unordered_set&gt;
 498     #include &lt;utility&gt;
 499     #include &lt;valarray&gt;
 500     #include &lt;vector&gt;
 501   ],,
 502   ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no)
 503   AC_LANG_RESTORE
 504   CXXFLAGS="$ac_save_CXXFLAGS"
 505   ])
 506   if test "$ac_cv_cxx_stdcxx_11" = yes; then
 507     AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ])
 508   fi
 509 ])
 510 </pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For
 511 <code class="filename">&lt;unordered_map&gt;</code>
 512 </p><pre class="programlisting">
 513 # AC_HEADER_UNORDERED_MAP
 514 AC_DEFUN([AC_HEADER_UNORDERED_MAP], [
 515   AC_CACHE_CHECK(for unordered_map,
 516   ac_cv_cxx_unordered_map,
 517   [AC_REQUIRE([AC_COMPILE_STDCXX_11])
 518   AC_LANG_SAVE
 519   AC_LANG_CPLUSPLUS
 520   ac_save_CXXFLAGS="$CXXFLAGS"
 521   CXXFLAGS="$CXXFLAGS -std=gnu++11"
 522   AC_TRY_COMPILE([#include &lt;unordered_map&gt;], [using std::unordered_map;],
 523   ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no)
 524   CXXFLAGS="$ac_save_CXXFLAGS"
 525   AC_LANG_RESTORE
 526   ])
 527   if test "$ac_cv_cxx_unordered_map" = yes; then
 528     AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ])
 529   fi
 530 ])
 531 </pre><pre class="programlisting">
 532 # AC_HEADER_UNORDERED_SET
 533 AC_DEFUN([AC_HEADER_UNORDERED_SET], [
 534   AC_CACHE_CHECK(for unordered_set,
 535   ac_cv_cxx_unordered_set,
 536   [AC_REQUIRE([AC_COMPILE_STDCXX_11])
 537   AC_LANG_SAVE
 538   AC_LANG_CPLUSPLUS
 539   ac_save_CXXFLAGS="$CXXFLAGS"
 540   CXXFLAGS="$CXXFLAGS -std=gnu++11"
 541   AC_TRY_COMPILE([#include &lt;unordered_set&gt;], [using std::unordered_set;],
 542   ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no)
 543   CXXFLAGS="$ac_save_CXXFLAGS"
 544   AC_LANG_RESTORE
 545   ])
 546   if test "$ac_cv_cxx_unordered_set" = yes; then
 547     AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ])
 548   fi
 549 ])
 550 </pre><p>
 551   Some C++11 features first appeared in GCC 4.3 and could be enabled by
 552   <code class="option">-std=c++0x</code> and <code class="option">-std=gnu++0x</code> for GCC
 553   releases which pre-date the 2011 standard. Those C++11 features and GCC's
 554   support for them were still changing until the 2011 standard was finished,
 555   but the autoconf checks above could be extended to test for incomplete
 556   C++11 support with <code class="option">-std=c++0x</code> and
 557   <code class="option">-std=gnu++0x</code>.
 558 </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.iterator_type"></a>
 559   <code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code>
 560 </h4></div></div></div><p>
 561   This is a change in behavior from older versions. Now, most
 562   <span class="type">iterator_type</span> typedefs in container classes are POD
 563   objects, not <span class="type">value_type</span> pointers.
 564 </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="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix C.
 565   Free Software Needs Free Documentation
 566
 567 </td></tr></table></div></body></html>