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| <!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. |
| Porting and Maintenance |
| |
| </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 |
| separate GNU project, although reliably paired with GCC. Rumors imply |
| that it had a working relationship with at least two kinds of |
| dinosaur. |
| </p><p>Some background: libg++ was designed and created when there was no |
| ISO standard to provide guidance. Classes like linked lists are now |
| provided for by <code class="classname">std::list<T></code> and do not need to be |
| created by <code class="function">genclass</code>. (For that matter, templates exist |
| now and are well-supported, whereas genclass (mostly) predates them.) |
| </p><p>There are other classes in libg++ that are not specified in the |
| ISO Standard (e.g., statistical analysis). While there are a lot of |
| really useful things that are used by a lot of people, the Standards |
| Committee couldn't include everything, and so a lot of those |
| <span class="quote">“<span class="quote">obvious</span>”</span> classes didn't get included. |
| </p><p>That project is no longer maintained or supported, and the sources |
| archived. For the desperate, the |
| <a class="link" href="https://ftp.gnu.org/old-gnu/libg++/" target="_top">ftp.gnu.org</a> |
| server still has the libg++ source. |
| </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p> |
| The second generation GNU C++ library was called libstdc++, or |
| libstdc++-v2. It spans the time between libg++ and pre-ISO C++ |
| standardization and is usually associated with the following GCC |
| releases: egcs 1.x, gcc 2.95, and gcc 2.96. |
| </p><p> |
| The STL portions of that library are based on SGI/HP STL release 3.11. |
| </p><p> |
| That project is no longer maintained or supported, and the sources |
| archived. The code was replaced and rewritten for libstdc++-v3. |
| </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 |
| libstdc++-v3. |
| </p><p>The subset commonly known as the Standard Template Library |
| (clauses 23 through 25 in C++98, mostly) is adapted from the final release |
| of the SGI STL (version 3.3), with extensive changes. |
| </p><p>A more formal description of the V3 goals can be found in the |
| official <a class="link" href="source_design_notes.html" title="Design Notes">design document</a>. |
| </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 |
| (<code class="filename"><iostream.h></code>, |
| <code class="filename"><defalloc.h></code> etc.) are |
| not supported. |
| </p><p>For those of you new to ISO C++ (welcome, time travelers!), the |
| ancient pre-ISO headers have new names. |
| 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 |
| the difference between <xxx> and <xxx.h> headers?</a>. |
| </p><p>Porting between pre-ISO headers and ISO headers is simple: headers |
| like <code class="filename"><vector.h></code> can be replaced with <code class="filename"><vector></code> and a using |
| directive <code class="code">using namespace std;</code> can be put at the global |
| scope. This should be enough to get this code compiling, assuming the |
| other usage is correct. |
| </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 |
| replaced by standardized libraries. |
| In particular, the <code class="classname">unordered_map</code> and |
| <code class="classname">unordered_set</code> containers of TR1 and C++ 2011 |
| are suitable replacements for the non-standard |
| <code class="classname">hash_map</code> and <code class="classname">hash_set</code> |
| containers in the SGI STL. |
| </p><p> Header files <code class="filename"><hash_map></code> and <code class="filename"><hash_set></code> moved |
| to <code class="filename"><ext/hash_map></code> and <code class="filename"><ext/hash_set></code>, |
| respectively. At the same time, all types in these files are enclosed |
| in <code class="code">namespace __gnu_cxx</code>. Later versions deprecate |
| these files, and suggest using TR1's <code class="filename"><unordered_map></code> |
| and <code class="filename"><unordered_set></code> instead. |
| </p><p>The extensions are no longer in the global or <code class="code">std</code> |
| namespaces, instead they are declared in the <code class="code">__gnu_cxx</code> |
| namespace. For maximum portability, consider defining a namespace |
| alias to use to talk about extensions, e.g.: |
| </p><pre class="programlisting"> |
| #ifdef __GNUC__ |
| #if __GNUC__ < 3 |
| #include <hash_map.h> |
| namespace extension { using ::hash_map; }; // inherit globals |
| #else |
| #include <backward/hash_map> |
| #if __GNUC__ == 3 && __GNUC_MINOR__ == 0 |
| namespace extension = std; // GCC 3.0 |
| #else |
| namespace extension = ::__gnu_cxx; // GCC 3.1 and later |
| #endif |
| #endif |
| #else // ... there are other compilers, right? |
| namespace extension = std; |
| #endif |
| |
| extension::hash_map<int,int> my_map; |
| </pre><p>This is a bit cleaner than defining typedefs for all the |
| instantiations you might need. |
| </p><p>The following autoconf tests check for working HP/SGI hash containers. |
| </p><pre class="programlisting"> |
| # AC_HEADER_EXT_HASH_MAP |
| AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [ |
| AC_CACHE_CHECK(for ext/hash_map, |
| ac_cv_cxx_ext_hash_map, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -Werror" |
| AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;], |
| ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_ext_hash_map" = yes; then |
| AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_EXT_HASH_SET |
| AC_DEFUN([AC_HEADER_EXT_HASH_SET], [ |
| AC_CACHE_CHECK(for ext/hash_set, |
| ac_cv_cxx_ext_hash_set, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -Werror" |
| AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;], |
| ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_ext_hash_set" = yes; then |
| AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ]) |
| fi |
| ]) |
| </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>. |
| </h4></div></div></div><p>Historically these flags were used with iostreams to control whether |
| new files are created or not when opening a file stream, similar to the |
| <code class="code">O_CREAT</code> and <code class="code">O_EXCL</code> flags for the |
| <code class="function">open(2)</code> system call. Because iostream modes correspond |
| to <code class="function">fopen(3)</code> modes these flags are not supported. |
| For input streams a new file will not be created anyway, so |
| <code class="code">ios::nocreate</code> is not needed. |
| For output streams, a new file will be created if it does not exist, which is |
| consistent with the behaviour of <code class="function">fopen</code>. |
| </p><p>When one of these flags is needed a possible alternative is to attempt |
| to open the file using <span class="type">std::ifstream</span> first to determine whether |
| the file already exists or not. This may not be reliable however, because |
| whether the file exists or not could change between opening the |
| <span class="type">std::istream</span> and re-opening with an output stream. If you need |
| to check for existence and open a file as a single operation then you will |
| need to use OS-specific facilities outside the C++ standard library, such |
| as <code class="function">open(2)</code>. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.streamattach"></a> |
| No <code class="code">stream::attach(int fd)</code> |
| </h4></div></div></div><p> |
| Phil Edwards writes: It was considered and rejected for the ISO |
| standard. Not all environments use file descriptors. Of those |
| that do, not all of them use integers to represent them. |
| </p><p> |
| For a portable solution (among systems which use |
| file descriptors), you need to implement a subclass of |
| <code class="code">std::streambuf</code> (or |
| <code class="code">std::basic_streambuf<..></code>) which opens a file |
| given a descriptor, and then pass an instance of this to the |
| stream-constructor. |
| </p><p> |
| An extension is available that implements this. |
| <code class="filename"><ext/stdio_filebuf.h></code> |
| contains a derived class called |
| <code class="classname">__gnu_cxx::stdio_filebuf</code>. |
| This class can be constructed from a C <code class="code">FILE*</code> or a file |
| descriptor, and provides the <code class="code">fd()</code> function. |
| </p><p> |
| For another example of this, refer to |
| <a class="link" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a> |
| by Nicolai Josuttis. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx98"></a> |
| Support for C++98 dialect. |
| </h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard. |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_98 |
| AC_DEFUN([AC_HEADER_STDCXX_98], [ |
| AC_CACHE_CHECK(for ISO C++ 98 include files, |
| ac_cv_cxx_stdcxx_98, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| #include <cassert> |
| #include <cctype> |
| #include <cerrno> |
| #include <cfloat> |
| #include <ciso646> |
| #include <climits> |
| #include <clocale> |
| #include <cmath> |
| #include <csetjmp> |
| #include <csignal> |
| #include <cstdarg> |
| #include <cstddef> |
| #include <cstdio> |
| #include <cstdlib> |
| #include <cstring> |
| #include <ctime> |
| |
| #include <algorithm> |
| #include <bitset> |
| #include <complex> |
| #include <deque> |
| #include <exception> |
| #include <fstream> |
| #include <functional> |
| #include <iomanip> |
| #include <ios> |
| #include <iosfwd> |
| #include <iostream> |
| #include <istream> |
| #include <iterator> |
| #include <limits> |
| #include <list> |
| #include <locale> |
| #include <map> |
| #include <memory> |
| #include <new> |
| #include <numeric> |
| #include <ostream> |
| #include <queue> |
| #include <set> |
| #include <sstream> |
| #include <stack> |
| #include <stdexcept> |
| #include <streambuf> |
| #include <string> |
| #include <typeinfo> |
| #include <utility> |
| #include <valarray> |
| #include <vector> |
| ],, |
| ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_stdcxx_98" = yes; then |
| AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_tr1"></a> |
| Support for C++TR1 dialect. |
| </h4></div></div></div><p>Check for library coverage of the TR1 standard. |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_TR1 |
| AC_DEFUN([AC_HEADER_STDCXX_TR1], [ |
| AC_CACHE_CHECK(for ISO C++ TR1 include files, |
| ac_cv_cxx_stdcxx_tr1, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| #include <tr1/array> |
| #include <tr1/ccomplex> |
| #include <tr1/cctype> |
| #include <tr1/cfenv> |
| #include <tr1/cfloat> |
| #include <tr1/cinttypes> |
| #include <tr1/climits> |
| #include <tr1/cmath> |
| #include <tr1/complex> |
| #include <tr1/cstdarg> |
| #include <tr1/cstdbool> |
| #include <tr1/cstdint> |
| #include <tr1/cstdio> |
| #include <tr1/cstdlib> |
| #include <tr1/ctgmath> |
| #include <tr1/ctime> |
| #include <tr1/cwchar> |
| #include <tr1/cwctype> |
| #include <tr1/functional> |
| #include <tr1/memory> |
| #include <tr1/random> |
| #include <tr1/regex> |
| #include <tr1/tuple> |
| #include <tr1/type_traits> |
| #include <tr1/unordered_set> |
| #include <tr1/unordered_map> |
| #include <tr1/utility> |
| ],, |
| ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_stdcxx_tr1" = yes; then |
| AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ]) |
| fi |
| ]) |
| </pre><p>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. |
| </p><pre class="programlisting"> |
| # AC_HEADER_TR1_UNORDERED_MAP |
| AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [ |
| AC_CACHE_CHECK(for tr1/unordered_map, |
| ac_cv_cxx_tr1_unordered_map, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;], |
| ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_tr1_unordered_map" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_TR1_UNORDERED_SET |
| AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [ |
| AC_CACHE_CHECK(for tr1/unordered_set, |
| ac_cv_cxx_tr1_unordered_set, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;], |
| ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_tr1_unordered_set" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx11"></a> |
| Support for C++11 dialect. |
| </h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++11 standard. |
| </p><pre class="programlisting"> |
| # AC_COMPILE_STDCXX_11 |
| AC_DEFUN([AC_COMPILE_STDCXX_11], [ |
| AC_CACHE_CHECK(if g++ supports C++11 features without additional flags, |
| ac_cv_cxx_compile_cxx11_native, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no) |
| AC_LANG_RESTORE |
| ]) |
| |
| AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11, |
| ac_cv_cxx_compile_cxx11_cxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=c++11" |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| |
| AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11, |
| ac_cv_cxx_compile_cxx11_gxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| |
| if test "$ac_cv_cxx_compile_cxx11_native" = yes || |
| test "$ac_cv_cxx_compile_cxx11_cxx" = yes || |
| test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then |
| AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ]) |
| fi |
| ]) |
| </pre><p>Check for library coverage of the C++2011 standard. |
| (Some library headers are commented out in this check, they are |
| not currently provided by libstdc++). |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_11 |
| AC_DEFUN([AC_HEADER_STDCXX_11], [ |
| AC_CACHE_CHECK(for ISO C++11 include files, |
| ac_cv_cxx_stdcxx_11, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| |
| AC_TRY_COMPILE([ |
| #include <cassert> |
| #include <ccomplex> |
| #include <cctype> |
| #include <cerrno> |
| #include <cfenv> |
| #include <cfloat> |
| #include <cinttypes> |
| #include <ciso646> |
| #include <climits> |
| #include <clocale> |
| #include <cmath> |
| #include <csetjmp> |
| #include <csignal> |
| #include <cstdalign> |
| #include <cstdarg> |
| #include <cstdbool> |
| #include <cstddef> |
| #include <cstdint> |
| #include <cstdio> |
| #include <cstdlib> |
| #include <cstring> |
| #include <ctgmath> |
| #include <ctime> |
| // #include <cuchar> |
| #include <cwchar> |
| #include <cwctype> |
| |
| #include <algorithm> |
| #include <array> |
| #include <atomic> |
| #include <bitset> |
| #include <chrono> |
| // #include <codecvt> |
| #include <complex> |
| #include <condition_variable> |
| #include <deque> |
| #include <exception> |
| #include <forward_list> |
| #include <fstream> |
| #include <functional> |
| #include <future> |
| #include <initializer_list> |
| #include <iomanip> |
| #include <ios> |
| #include <iosfwd> |
| #include <iostream> |
| #include <istream> |
| #include <iterator> |
| #include <limits> |
| #include <list> |
| #include <locale> |
| #include <map> |
| #include <memory> |
| #include <mutex> |
| #include <new> |
| #include <numeric> |
| #include <ostream> |
| #include <queue> |
| #include <random> |
| #include <ratio> |
| #include <regex> |
| #include <scoped_allocator> |
| #include <set> |
| #include <sstream> |
| #include <stack> |
| #include <stdexcept> |
| #include <streambuf> |
| #include <string> |
| #include <system_error> |
| #include <thread> |
| #include <tuple> |
| #include <typeindex> |
| #include <typeinfo> |
| #include <type_traits> |
| #include <unordered_map> |
| #include <unordered_set> |
| #include <utility> |
| #include <valarray> |
| #include <vector> |
| ],, |
| ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no) |
| AC_LANG_RESTORE |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| ]) |
| if test "$ac_cv_cxx_stdcxx_11" = yes; then |
| AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ]) |
| fi |
| ]) |
| </pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For |
| <code class="filename"><unordered_map></code> |
| </p><pre class="programlisting"> |
| # AC_HEADER_UNORDERED_MAP |
| AC_DEFUN([AC_HEADER_UNORDERED_MAP], [ |
| AC_CACHE_CHECK(for unordered_map, |
| ac_cv_cxx_unordered_map, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;], |
| ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_unordered_map" = yes; then |
| AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_UNORDERED_SET |
| AC_DEFUN([AC_HEADER_UNORDERED_SET], [ |
| AC_CACHE_CHECK(for unordered_set, |
| ac_cv_cxx_unordered_set, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([#include <unordered_set>], [using std::unordered_set;], |
| ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_unordered_set" = yes; then |
| AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ]) |
| fi |
| ]) |
| </pre><p> |
| Some C++11 features first appeared in GCC 4.3 and could be enabled by |
| <code class="option">-std=c++0x</code> and <code class="option">-std=gnu++0x</code> for GCC |
| releases which pre-date the 2011 standard. Those C++11 features and GCC's |
| support for them were still changing until the 2011 standard was finished, |
| but the autoconf checks above could be extended to test for incomplete |
| C++11 support with <code class="option">-std=c++0x</code> and |
| <code class="option">-std=gnu++0x</code>. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.iterator_type"></a> |
| <code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code> |
| </h4></div></div></div><p> |
| This is a change in behavior from older versions. Now, most |
| <span class="type">iterator_type</span> typedefs in container classes are POD |
| objects, not <span class="type">value_type</span> pointers. |
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