Backwards Compatibility

Backwards Compatibility
Prev	Appendix B. + Porting and Maintenance + +	Next

+#ifdef WICKEDLY_OLD_COMPILER
+# define std
+#endif
+

+ Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help. +

+ Another pre-processor based approach is to define a macro + NAMESPACE_STD, which is defined to either + “ ” or “std” based on a compile-type + test. On GNU systems, this can be done with autotools by means of + an autoconf test (see below) for HAVE_NAMESPACE_STD, + then using that to set a value for the NAMESPACE_STD + macro. At that point, one is able to use + NAMESPACE_STD::string, which will evaluate to + std::string or ::string (i.e., in the + global namespace on systems that do not put string in + std::). +

+dnl @synopsis AC_CXX_NAMESPACE_STD
+dnl
+dnl If the compiler supports namespace std, define
+dnl HAVE_NAMESPACE_STD.
+dnl
+dnl @category Cxx
+dnl @author Todd Veldhuizen
+dnl @author Luc Maisonobe <luc@spaceroots.org>
+dnl @version 2004-02-04
+dnl @license AllPermissive
+AC_DEFUN([AC_CXX_NAMESPACE_STD], [
+  AC_CACHE_CHECK(if g++ supports namespace std,
+  ac_cv_cxx_have_std_namespace,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  AC_TRY_COMPILE([#include <iostream>
+		  std::istream& is = std::cin;],,
+  ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no)
+  AC_LANG_RESTORE
+  ])
+  if test "$ac_cv_cxx_have_std_namespace" = yes; then
+    AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ])
+  fi
+])
+

Illegal iterator usage

+ The following illustrate implementation-allowed illegal iterator + use, and then correct use. +

+ you cannot do ostream::operator<<(iterator) + to print the address of the iterator => use + operator<< &*iterator instead +
+ you cannot clear an iterator's reference (iterator = + 0) => use iterator = iterator_type(); +
+ if (iterator) won't work any more => use + if (iterator != iterator_type()) +

`isspace` from `cctype` is a macro +

+ Glibc 2.0.x and 2.1.x define ctype.h functionality as macros + (isspace, isalpha etc.). +

+ This implementations of libstdc++, however, keep these functions + as macros, and so it is not back-portable to use fully qualified + names. For example: +

+#include <cctype>
+int main() { std::isspace('X'); }
+

+ Results in something like this: +

+std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ;
+

+ A solution is to modify a header-file so that the compiler tells + ctype.h to define functions + instead of macros: +

+// This keeps isalnum, et al from being propagated as macros.
+#if __linux__
+# define __NO_CTYPE 1
+#endif
+

+ Then, include ctype.h +

+ Another problem arises if you put a using namespace + std; declaration at the top, and include ctype.h. This will result in + ambiguities between the definitions in the global namespace + (ctype.h) and the + definitions in namespace std:: + (<cctype>). +

No `vector::at`, `deque::at`, `string::at`

+ One solution is to add an autoconf-test for this: +

+AC_MSG_CHECKING(for container::at)
+AC_TRY_COMPILE(
+[
+#include <vector>
+#include <deque>
+#include <string>
+
+using namespace std;
+],
+[
+deque<int> test_deque(3);
+test_deque.at(2);
+vector<int> test_vector(2);
+test_vector.at(1);
+string test_string(“test_string”);
+test_string.at(3);
+],
+[AC_MSG_RESULT(yes)
+AC_DEFINE(HAVE_CONTAINER_AT)],
+[AC_MSG_RESULT(no)])
+

+ If you are using other (non-GNU) compilers it might be a good idea + to check for string::at separately. +

No `std::char_traits<char>::eof`

+ Use some kind of autoconf test, plus this: +

+#ifdef HAVE_CHAR_TRAITS
+#define CPP_EOF std::char_traits<char>::eof()
+#else
+#define CPP_EOF EOF
+#endif
+

No `string::clear`

+ There are two functions for deleting the contents of a string: + clear and erase (the latter returns the + string). +

+void
+clear() { _M_mutate(0, this->size(), 0); }
+

+basic_string&
+erase(size_type __pos = 0, size_type __n = npos)
+{
+  return this->replace(_M_check(__pos), _M_fold(__pos, __n),
+			  _M_data(), _M_data());
+}
+

+ Unfortunately, clear is not implemented in this + version, so you should use erase (which is probably + faster than operator=(charT*)). +

+ Removal of `ostream::form` and `istream::scan` + extensions +

+ These are no longer supported. Please use stringstreams instead. +

No `basic_stringbuf`, `basic_stringstream`

+ Although the ISO standard i/ostringstream-classes are + provided, (sstream), for + compatibility with older implementations the pre-ISO + i/ostrstream (strstream) interface is also provided, + with these caveats: +

+ strstream is considered to be deprecated +
+ strstream is limited to char +
+ with ostringstream you don't have to take care of + terminating the string or freeing its memory +
+ istringstream can be re-filled (clear(); + str(input);) +

+ You can then use output-stringstreams like this: +

+#ifdef HAVE_SSTREAM
+# include <sstream>
+#else
+# include <strstream>
+#endif
+
+#ifdef HAVE_SSTREAM
+  std::ostringstream oss;
+#else
+  std::ostrstream oss;
+#endif
+
+oss << “Name=” << m_name << “, number=” << m_number << std::endl;
+...
+#ifndef HAVE_SSTREAM
+  oss << std::ends; // terminate the char*-string
+#endif
+
+// str() returns char* for ostrstream and a string for ostringstream
+// this also causes ostrstream to think that the buffer's memory
+// is yours
+m_label.set_text(oss.str());
+#ifndef HAVE_SSTREAM
+  // let the ostrstream take care of freeing the memory
+  oss.freeze(false);
+#endif
+

+ Input-stringstreams can be used similarly: +

+std::string input;
+...
+#ifdef HAVE_SSTREAM
+std::istringstream iss(input);
+#else
+std::istrstream iss(input.c_str());
+#endif
+
+int i;
+iss >> i;
+

One (the only?) restriction is that an istrstream cannot be re-filled: +

+std::istringstream iss(numerator);
+iss >> m_num;
+// this is not possible with istrstream
+iss.clear();
+iss.str(denominator);
+iss >> m_den;
+

+If you don't care about speed, you can put these conversions in + a template-function: +

+template <class X>
+void fromString(const string& input, X& any)
+{
+#ifdef HAVE_SSTREAM
+std::istringstream iss(input);
+#else
+std::istrstream iss(input.c_str());
+#endif
+X temp;
+iss >> temp;
+if (iss.fail())
+throw runtime_error(..)
+any = temp;
+}
+

+ Another example of using stringstreams is in this howto. +

There is additional information in the libstdc++-v2 info files, in +particular “info iostream”. +

Little or no wide character support

+ Classes wstring and + char_traits<wchar_t> are + not supported. +

No templatized iostreams

+ Classes wfilebuf and + wstringstream are not supported. +

Thread safety issues

+ Earlier GCC releases had a somewhat different approach to + threading configuration and proper compilation. Before GCC 3.0, + configuration of the threading model was dictated by compiler + command-line options and macros (both of which were somewhat + thread-implementation and port-specific). There were no + guarantees related to being able to link code compiled with one + set of options and macro setting with another set. +

+ For GCC 3.0, configuration of the threading model used with + libraries and user-code is performed when GCC is configured and + built using the --enable-threads and --disable-threads options. + The ABI is stable for symbol name-mangling and limited functional + compatibility exists between code compiled under different + threading models. +

+ The libstdc++ library has been designed so that it can be used in + multithreaded applications (with libstdc++-v2 this was only true + of the STL parts.) The first problem is finding a + fast method of implementation portable to + all platforms. Due to historical reasons, some of the library is + written against per-CPU-architecture spinlocks and other parts + against the gthr.h abstraction layer which is provided by gcc. A + minor problem that pops up every so often is different + interpretations of what "thread-safe" means for a + library (not a general program). We currently use the same + definition that SGI uses for their STL subset. However, + the exception for read-only containers only applies to the STL + components. This definition is widely-used and something similar + will be used in the next version of the C++ standard library. +

+ Here is a small link farm to threads (no pun) in the mail + archives that discuss the threading problem. Each link is to the + first relevant message in the thread; from there you can use + "Thread Next" to move down the thread. This farm is in + latest-to-oldest order. +

+ Our threading expert Loren gives a breakdown of the + six situations involving threads for the 3.0 + release series. +
+ + This message inspired a recent updating of issues with + threading and the SGI STL library. It also contains some + example POSIX-multithreaded STL code. +

+ (A large selection of links to older messages has been removed; + many of the messages from 1999 were lost in a disk crash, and the + few people with access to the backup tapes have been too swamped + with work to restore them. Many of the points have been + superseded anyhow.) +

Third

The third generation GNU C++ library is called libstdc++, or +libstdc++-v3. +

The subset commonly known as the Standard Template Library + (chapters 23 through 25, mostly) is adapted from the final release + of the SGI STL (version 3.3), with extensive changes. +

A more formal description of the V3 goals can be found in the + official design document. +

Portability notes and known implementation limitations are as follows.

Pre-ISO headers moved to backwards or removed

The pre-ISO C++ headers + (iostream.h, defalloc.h etc.) are + available, unlike previous libstdc++ versions, but inclusion + generates a warning that you are using deprecated headers. +

This compatibility layer is constructed by including the + standard C++ headers, and injecting any items in + std:: into the global namespace. +

For those of you new to ISO C++ (welcome, time travelers!), no, + that isn't a typo. Yes, the headers really have new names. + Marshall Cline's C++ FAQ Lite has a good explanation in item + [27.4]. +

Some include adjustment may be required. What follows is an +autoconf test that defines PRE_STDCXX_HEADERS when they +exist.

+# AC_HEADER_PRE_STDCXX
+AC_DEFUN([AC_HEADER_PRE_STDCXX], [
+  AC_CACHE_CHECK(for pre-ISO C++ include files,
+  ac_cv_cxx_pre_stdcxx,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -Wno-deprecated"
+
+  # Omit defalloc.h, as compilation with newer compilers is problematic.
+  AC_TRY_COMPILE([
+  #include <new.h>
+  #include <iterator.h>
+  #include <alloc.h>
+  #include <set.h>
+  #include <hashtable.h>
+  #include <hash_set.h>
+  #include <fstream.h>
+  #include <tempbuf.h>
+  #include <istream.h>
+  #include <bvector.h>
+  #include <stack.h>
+  #include <rope.h>
+  #include <complex.h>
+  #include <ostream.h>
+  #include <heap.h>
+  #include <iostream.h>
+  #include <function.h>
+  #include <multimap.h>
+  #include <pair.h>
+  #include <stream.h>
+  #include <iomanip.h>
+  #include <slist.h>
+  #include <tree.h>
+  #include <vector.h>
+  #include <deque.h>
+  #include <multiset.h>
+  #include <list.h>
+  #include <map.h>
+  #include <algobase.h>
+  #include <hash_map.h>
+  #include <algo.h>
+  #include <queue.h>
+  #include <streambuf.h>
+  ],,
+  ac_cv_cxx_pre_stdcxx=yes, ac_cv_cxx_pre_stdcxx=no)
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+  if test "$ac_cv_cxx_pre_stdcxx" = yes; then
+    AC_DEFINE(PRE_STDCXX_HEADERS,,[Define if pre-ISO C++ header files are present. ])
+  fi
+])
+

Porting between pre-ISO headers and ISO headers is simple: headers +like vector.h can be replaced with vector and a using +directive using namespace std; can be put at the global +scope. This should be enough to get this code compiling, assuming the +other usage is correct. +

Extension headers hash_map, hash_set moved to ext or backwards

At this time most of the features of the SGI STL extension have been + replaced by standardized libraries. + In particular, the unordered_map and unordered_set containers of TR1 + are suitable replacement for the non-standard hash_map and hash_set + containers in the SGI STL. +

Header files hash_map and hash_set moved +to ext/hash_map and ext/hash_set, +respectively. At the same time, all types in these files are enclosed +in namespace __gnu_cxx. Later versions move deprecate +these files, and suggest using TR1's unordered_map +and unordered_set instead. +

The extensions are no longer in the global or std + namespaces, instead they are declared in the __gnu_cxx + namespace. For maximum portability, consider defining a namespace + alias to use to talk about extensions, e.g.: +

+      #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;
+

This is a bit cleaner than defining typedefs for all the + instantiations you might need. +

The following autoconf tests check for working HP/SGI hash containers. +

+# 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
+])
+

+# 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
+])
+

No `ios::nocreate/ios::noreplace`. +

The existence of ios::nocreate being used for +input-streams has been confirmed, most probably because the author +thought it would be more correct to specify nocreate explicitly. So +it can be left out for input-streams. +

For output streams, “nocreate” is probably the default, +unless you specify std::ios::trunc ? To be safe, you can +open the file for reading, check if it has been opened, and then +decide whether you want to create/replace or not. To my knowledge, +even older implementations support app, ate +and trunc (except for app ?). +

+No `stream::attach(int fd)` +

+ 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. +

+ For a portable solution (among systems which use + file descriptors), you need to implement a subclass of + std::streambuf (or + std::basic_streambuf<..>) which opens a file + given a descriptor, and then pass an instance of this to the + stream-constructor. +

+ An extension is available that implements this. + ext/stdio_filebuf.h contains a derived class called + __gnu_cxx::stdio_filebuf. + This class can be constructed from a C FILE* or a file + descriptor, and provides the fd() function. +

+ For another example of this, refer to + fdstream example + by Nicolai Josuttis. +

+Support for C++98 dialect. +

Check for complete library coverage of the C++1998/2003 standard. +

+# 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
+])
+

+Support for C++TR1 dialect. +

Check for library coverage of the TR1 standard. +

+# 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
+])
+

An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. +

+# 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
+])
+

+# 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
+])
+

+Support for C++0x dialect. +

Check for baseline language coverage in the compiler for the C++0xstandard. +

+# AC_COMPILE_STDCXX_OX
+AC_DEFUN([AC_COMPILE_STDCXX_0X], [
+  AC_CACHE_CHECK(if g++ supports C++0x features without additional flags,
+  ac_cv_cxx_compile_cxx0x_native,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  AC_TRY_COMPILE([
+  template <typename T>
+    struct check
+    {
+      static_assert(sizeof(int) <= sizeof(T), "not big enough");
+    };
+
+    typedef check<check<bool>> right_angle_brackets;
+
+    int a;
+    decltype(a) b;
+
+    typedef check<int> check_type;
+    check_type c;
+    check_type&& cr = c;],,
+  ac_cv_cxx_compile_cxx0x_native=yes, ac_cv_cxx_compile_cxx0x_native=no)
+  AC_LANG_RESTORE
+  ])
+
+  AC_CACHE_CHECK(if g++ supports C++0x features with -std=c++0x,
+  ac_cv_cxx_compile_cxx0x_cxx,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=c++0x"
+  AC_TRY_COMPILE([
+  template <typename T>
+    struct check
+    {
+      static_assert(sizeof(int) <= sizeof(T), "not big enough");
+    };
+
+    typedef check<check<bool>> right_angle_brackets;
+
+    int a;
+    decltype(a) b;
+
+    typedef check<int> check_type;
+    check_type c;
+    check_type&& cr = c;],,
+  ac_cv_cxx_compile_cxx0x_cxx=yes, ac_cv_cxx_compile_cxx0x_cxx=no)
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+
+  AC_CACHE_CHECK(if g++ supports C++0x features with -std=gnu++0x,
+  ac_cv_cxx_compile_cxx0x_gxx,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++0x"
+  AC_TRY_COMPILE([
+  template <typename T>
+    struct check
+    {
+      static_assert(sizeof(int) <= sizeof(T), "not big enough");
+    };
+
+    typedef check<check<bool>> right_angle_brackets;
+
+    int a;
+    decltype(a) b;
+
+    typedef check<int> check_type;
+    check_type c;
+    check_type&& cr = c;],,
+  ac_cv_cxx_compile_cxx0x_gxx=yes, ac_cv_cxx_compile_cxx0x_gxx=no)
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+
+  if test "$ac_cv_cxx_compile_cxx0x_native" = yes ||
+     test "$ac_cv_cxx_compile_cxx0x_cxx" = yes ||
+     test "$ac_cv_cxx_compile_cxx0x_gxx" = yes; then
+    AC_DEFINE(HAVE_STDCXX_0X,,[Define if g++ supports C++0x features. ])
+  fi
+])
+

Check for library coverage of the C++0xstandard. +

+# AC_HEADER_STDCXX_0X
+AC_DEFUN([AC_HEADER_STDCXX_0X], [
+  AC_CACHE_CHECK(for ISO C++ 0x include files,
+  ac_cv_cxx_stdcxx_0x,
+  [AC_REQUIRE([AC_COMPILE_STDCXX_0X])
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++0x"
+
+  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 <cstdarg>
+    #include <cstdbool>
+    #include <cstddef>
+    #include <cstdint>
+    #include <cstdio>
+    #include <cstdlib>
+    #include <cstring>
+    #include <ctgmath>
+    #include <ctime>
+    #include <cwchar>
+    #include <cwctype>
+
+    #include <algorithm>
+    #include <array>
+    #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 <random>
+    #include <regex>
+    #include <set>
+    #include <sstream>
+    #include <stack>
+    #include <stdexcept>
+    #include <streambuf>
+    #include <string>
+    #include <tuple>
+    #include <typeinfo>
+    #include <type_traits>
+    #include <unordered_map>
+    #include <unordered_set>
+    #include <utility>
+    #include <valarray>
+    #include <vector>
+  ],,
+  ac_cv_cxx_stdcxx_0x=yes, ac_cv_cxx_stdcxx_0x=no)
+  AC_LANG_RESTORE
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  ])
+  if test "$ac_cv_cxx_stdcxx_0x" = yes; then
+    AC_DEFINE(STDCXX_0X_HEADERS,,[Define if ISO C++ 0x header files are present. ])
+  fi
+])
+

As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For <unordered_map> +

+# 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_0X])
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++0x"
+  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
+])
+

+# 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_0X])
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++0x"
+  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
+])
+

+ Container::iterator_type is not necessarily Container::value_type* +

+ This is a change in behavior from the previous version. Now, most + iterator_type typedefs in container classes are POD + objects, not value_type pointers. +

Bibliography

+ . + Migrating to GCC 4.1 + . Dan Kegel.

+ . + Building the Whole Debian Archive with GCC 4.1: A Summary + . Martin Michlmayr.

+ . + Migration guide for GCC-3.2 + .

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API Evolution and Deprecation History	Home	Appendix C. + Free Software Needs Free Documentation + +