| <section xmlns="http://docbook.org/ns/docbook" version="5.0" |
| xml:id="manual.appendix.porting.backwards" xreflabel="backwards"> |
| <?dbhtml filename="backwards.html"?> |
| |
| <info><title>Backwards Compatibility</title> |
| <keywordset> |
| <keyword>ISO C++</keyword> |
| <keyword>backwards</keyword> |
| </keywordset> |
| </info> |
| |
| |
| |
| <section xml:id="backwards.first"><info><title>First</title></info> |
| |
| |
| <para>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. |
| </para> |
| |
| <para>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 <classname>list<T></classname> and do not need to be |
| created by <function>genclass</function>. (For that matter, templates exist |
| now and are well-supported, whereas genclass (mostly) predates them.) |
| </para> |
| |
| <para>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 |
| <quote>obvious</quote> classes didn't get included. |
| </para> |
| |
| <para>Known Issues include many of the limitations of its immediate ancestor.</para> |
| |
| <para>Portability notes and known implementation limitations are as follows.</para> |
| |
| <section xml:id="backwards.first.ios_base"><info><title>No <code>ios_base</code></title></info> |
| |
| |
| <para> At least some older implementations don't have <code>std::ios_base</code>, so you should use <code>std::ios::badbit</code>, <code>std::ios::failbit</code> and <code>std::ios::eofbit</code> and <code>std::ios::goodbit</code>. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.first.cout_cin"><info><title>No <code>cout</code> in <filename class="headerfile"><ostream.h></filename>, no <code>cin</code> in <filename class="headerfile"><istream.h></filename></title></info> |
| |
| |
| <para> |
| In earlier versions of the standard, |
| <filename class="headerfile"><fstream.h></filename>, |
| <filename class="headerfile"><ostream.h></filename> |
| and <filename class="headerfile"><istream.h></filename> |
| used to define |
| <code>cout</code>, <code>cin</code> and so on. ISO C++ specifies that one needs to include |
| <filename class="headerfile"><iostream></filename> |
| explicitly to get the required definitions. |
| </para> |
| <para> Some include adjustment may be required.</para> |
| |
| <para>This project is no longer maintained or supported, and the sources |
| archived. For the desperate, |
| the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/extensions.html">GCC extensions |
| page</link> describes where to find the last libg++ source. The code is |
| considered replaced and rewritten. |
| </para> |
| </section> |
| </section> |
| |
| <section xml:id="backwards.second"><info><title>Second</title></info> |
| |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| The STL portions of this library are based on SGI/HP STL release 3.11. |
| </para> |
| |
| <para> |
| This project is no longer maintained or supported, and the sources |
| archived. The code is considered replaced and rewritten. |
| </para> |
| |
| <para> |
| Portability notes and known implementation limitations are as follows. |
| </para> |
| |
| <section xml:id="backwards.second.std"><info><title>Namespace <code>std::</code> not supported</title></info> |
| |
| |
| <para> |
| Some care is required to support C++ compiler and or library |
| implementation that do not have the standard library in |
| <code>namespace std</code>. |
| </para> |
| |
| <para> |
| The following sections list some possible solutions to support compilers |
| that cannot ignore <code>std::</code>-qualified names. |
| </para> |
| |
| <para> |
| First, see if the compiler has a flag for this. Namespace |
| back-portability-issues are generally not a problem for g++ |
| compilers that do not have libstdc++ in <code>std::</code>, as the |
| compilers use <option>-fno-honor-std</option> (ignore |
| <code>std::</code>, <code>:: = std::</code>) by default. That is, |
| the responsibility for enabling or disabling <code>std::</code> is |
| on the user; the maintainer does not have to care about it. This |
| probably applies to some other compilers as well. |
| </para> |
| |
| <para> |
| Second, experiment with a variety of pre-processor tricks. |
| </para> |
| |
| <para> |
| By defining <code>std</code> as a macro, fully-qualified namespace |
| calls become global. Volia. |
| </para> |
| |
| <programlisting> |
| #ifdef WICKEDLY_OLD_COMPILER |
| # define std |
| #endif |
| </programlisting> |
| |
| <para> |
| Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help. |
| </para> |
| |
| <para> |
| Another pre-processor based approach is to define a macro |
| <code>NAMESPACE_STD</code>, which is defined to either |
| <quote> </quote> or <quote>std</quote> based on a compile-type |
| test. On GNU systems, this can be done with autotools by means of |
| an autoconf test (see below) for <code>HAVE_NAMESPACE_STD</code>, |
| then using that to set a value for the <code>NAMESPACE_STD</code> |
| macro. At that point, one is able to use |
| <code>NAMESPACE_STD::string</code>, which will evaluate to |
| <code>std::string</code> or <code>::string</code> (i.e., in the |
| global namespace on systems that do not put <code>string</code> in |
| <code>std::</code>). |
| </para> |
| |
| <programlisting> |
| 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 |
| ]) |
| </programlisting> |
| </section> |
| |
| <section xml:id="backwards.second.iterators"><info><title>Illegal iterator usage</title></info> |
| |
| <para> |
| The following illustrate implementation-allowed illegal iterator |
| use, and then correct use. |
| </para> |
| |
| <itemizedlist> |
| <listitem> |
| <para> |
| you cannot do <code>ostream::operator<<(iterator)</code> |
| to print the address of the iterator => use |
| <code>operator<< &*iterator</code> instead |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| you cannot clear an iterator's reference (<code>iterator = |
| 0</code>) => use <code>iterator = iterator_type();</code> |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <code>if (iterator)</code> won't work any more => use |
| <code>if (iterator != iterator_type())</code> |
| </para> |
| </listitem> |
| </itemizedlist> |
| </section> |
| |
| <section xml:id="backwards.second.isspace"><info><title><code>isspace</code> from <filename class="headerfile"><cctype></filename> is a macro |
| </title></info> |
| |
| |
| <para> |
| Glibc 2.0.x and 2.1.x define <filename class="headerfile"><ctype.h></filename> functionality as macros |
| (isspace, isalpha etc.). |
| </para> |
| |
| <para> |
| This implementations of libstdc++, however, keep these functions |
| as macros, and so it is not back-portable to use fully qualified |
| names. For example: |
| </para> |
| |
| <programlisting> |
| #include <cctype> |
| int main() { std::isspace('X'); } |
| </programlisting> |
| |
| <para> |
| Results in something like this: |
| </para> |
| |
| <programlisting> |
| std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ; |
| </programlisting> |
| |
| <para> |
| A solution is to modify a header-file so that the compiler tells |
| <filename class="headerfile"><ctype.h></filename> to define functions |
| instead of macros: |
| </para> |
| |
| <programlisting> |
| // This keeps isalnum, et al from being propagated as macros. |
| #if __linux__ |
| # define __NO_CTYPE 1 |
| #endif |
| </programlisting> |
| |
| <para> |
| Then, include <filename class="headerfile"><ctype.h></filename> |
| </para> |
| |
| <para> |
| Another problem arises if you put a <code>using namespace |
| std;</code> declaration at the top, and include |
| <filename class="headerfile"><ctype.h></filename>. This will |
| result in ambiguities between the definitions in the global namespace |
| (<filename class="headerfile"><ctype.h></filename>) and the |
| definitions in namespace <code>std::</code> |
| (<code><cctype></code>). |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.at"><info><title>No <code>vector::at</code>, <code>deque::at</code>, <code>string::at</code></title></info> |
| |
| |
| <para> |
| One solution is to add an autoconf-test for this: |
| </para> |
| |
| <programlisting> |
| 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(<quote>test_string</quote>); |
| test_string.at(3); |
| ], |
| [AC_MSG_RESULT(yes) |
| AC_DEFINE(HAVE_CONTAINER_AT)], |
| [AC_MSG_RESULT(no)]) |
| </programlisting> |
| |
| <para> |
| If you are using other (non-GNU) compilers it might be a good idea |
| to check for <code>string::at</code> separately. |
| </para> |
| |
| </section> |
| |
| <section xml:id="backwards.second.eof"><info><title>No <code>std::char_traits<char>::eof</code></title></info> |
| |
| |
| <para> |
| Use some kind of autoconf test, plus this: |
| </para> |
| |
| <programlisting> |
| #ifdef HAVE_CHAR_TRAITS |
| #define CPP_EOF std::char_traits<char>::eof() |
| #else |
| #define CPP_EOF EOF |
| #endif |
| </programlisting> |
| |
| </section> |
| |
| <section xml:id="backwards.second.stringclear"><info><title>No <code>string::clear</code></title></info> |
| |
| |
| <para> |
| There are two functions for deleting the contents of a string: |
| <code>clear</code> and <code>erase</code> (the latter returns the |
| string). |
| </para> |
| |
| <programlisting> |
| void |
| clear() { _M_mutate(0, this->size(), 0); } |
| </programlisting> |
| |
| <programlisting> |
| 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()); |
| } |
| </programlisting> |
| |
| <para> |
| Unfortunately, <code>clear</code> is not implemented in this |
| version, so you should use <code>erase</code> (which is probably |
| faster than <code>operator=(charT*)</code>). |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.ostreamform_istreamscan"><info><title> |
| Removal of <code>ostream::form</code> and <code>istream::scan</code> |
| extensions |
| </title></info> |
| |
| |
| <para> |
| These are no longer supported. Please use stringstreams instead. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.stringstreams"><info><title>No <code>basic_stringbuf</code>, <code>basic_stringstream</code></title></info> |
| |
| |
| <para> |
| Although the ISO standard <code>i/ostringstream</code>-classes are |
| provided, (<filename class="headerfile"><sstream></filename>), for |
| compatibility with older implementations the pre-ISO |
| <code>i/ostrstream</code> (<filename class="headerfile"><strstream></filename>) interface is also provided, |
| with these caveats: |
| </para> |
| |
| <itemizedlist> |
| <listitem> |
| <para> |
| <code>strstream</code> is considered to be deprecated |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <code>strstream</code> is limited to <code>char</code> |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| with <code>ostringstream</code> you don't have to take care of |
| terminating the string or freeing its memory |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <code>istringstream</code> can be re-filled (clear(); |
| str(input);) |
| </para> |
| </listitem> |
| </itemizedlist> |
| |
| <para> |
| You can then use output-stringstreams like this: |
| </para> |
| |
| <programlisting> |
| #ifdef HAVE_SSTREAM |
| # include <sstream> |
| #else |
| # include <strstream> |
| #endif |
| |
| #ifdef HAVE_SSTREAM |
| std::ostringstream oss; |
| #else |
| std::ostrstream oss; |
| #endif |
| |
| oss << <quote>Name=</quote> << m_name << <quote>, number=</quote> << 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 |
| </programlisting> |
| |
| <para> |
| Input-stringstreams can be used similarly: |
| </para> |
| |
| <programlisting> |
| std::string input; |
| ... |
| #ifdef HAVE_SSTREAM |
| std::istringstream iss(input); |
| #else |
| std::istrstream iss(input.c_str()); |
| #endif |
| |
| int i; |
| iss >> i; |
| </programlisting> |
| |
| <para> One (the only?) restriction is that an istrstream cannot be re-filled: |
| </para> |
| |
| <programlisting> |
| std::istringstream iss(numerator); |
| iss >> m_num; |
| // this is not possible with istrstream |
| iss.clear(); |
| iss.str(denominator); |
| iss >> m_den; |
| </programlisting> |
| |
| <para> |
| If you don't care about speed, you can put these conversions in |
| a template-function: |
| </para> |
| <programlisting> |
| 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; |
| } |
| </programlisting> |
| |
| <para> |
| Another example of using stringstreams is in <link linkend="strings.string.shrink">this howto</link>. |
| </para> |
| |
| <para> There is additional information in the libstdc++-v2 info files, in |
| particular <quote>info iostream</quote>. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.wchar"><info><title>Little or no wide character support</title></info> |
| |
| <para> |
| Classes <classname>wstring</classname> and |
| <classname>char_traits<wchar_t></classname> are |
| not supported. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.iostream_templates"><info><title>No templatized iostreams</title></info> |
| |
| <para> |
| Classes <classname>wfilebuf</classname> and |
| <classname>wstringstream</classname> are not supported. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.second.thread_safety"><info><title>Thread safety issues</title></info> |
| |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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 |
| <emphasis>fast</emphasis> 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 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.sgi.com/tech/stl/thread_safety.html">same |
| definition that SGI</link> 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. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <itemizedlist> |
| <listitem> |
| <para> |
| Our threading expert Loren gives a breakdown of <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/ml/libstdc++/2001-10/msg00024.html">the |
| six situations involving threads</link> for the 3.0 |
| release series. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html"> |
| This message</link> inspired a recent updating of issues with |
| threading and the SGI STL library. It also contains some |
| example POSIX-multithreaded STL code. |
| </para> |
| </listitem> |
| </itemizedlist> |
| |
| <para> |
| (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.) |
| </para> |
| </section> |
| |
| </section> |
| |
| <section xml:id="backwards.third"><info><title>Third</title></info> |
| |
| |
| <para> The third generation GNU C++ library is called libstdc++, or |
| libstdc++-v3. |
| </para> |
| |
| <para>The subset commonly known as the Standard Template Library |
| (clauses 23 through 25, mostly) is adapted from the final release |
| of the SGI STL (version 3.3), with extensive changes. |
| </para> |
| |
| <para>A more formal description of the V3 goals can be found in the |
| official <link linkend="contrib.design_notes">design document</link>. |
| </para> |
| |
| <para>Portability notes and known implementation limitations are as follows.</para> |
| |
| <section xml:id="backwards.third.headers"><info><title>Pre-ISO headers moved to backwards or removed</title></info> |
| |
| |
| <para> The pre-ISO C++ headers |
| (<filename class="headerfile"><iostream.h></filename>, |
| <filename class="headerfile"><defalloc.h></filename> etc.) are |
| available, unlike previous libstdc++ versions, but inclusion |
| generates a warning that you are using deprecated headers. |
| </para> |
| |
| <para>This compatibility layer is constructed by including the |
| standard C++ headers, and injecting any items in |
| <code>std::</code> into the global namespace. |
| </para> |
| <para>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 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.parashift.com/c++-faq-lite/std-headers.html">What's |
| the difference between <xxx> and <xxx.h> headers?</link>. |
| </para> |
| |
| <para> Some include adjustment may be required. What follows is an |
| autoconf test that defines <code>PRE_STDCXX_HEADERS</code> when they |
| exist.</para> |
| |
| <programlisting> |
| # 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 |
| ]) |
| </programlisting> |
| |
| <para>Porting between pre-ISO headers and ISO headers is simple: headers |
| like <filename class="headerfile"><vector.h></filename> can be replaced with <filename class="headerfile"><vector></filename> and a using |
| directive <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. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.third.hash"><info><title>Extension headers hash_map, hash_set moved to ext or backwards</title></info> |
| |
| |
| <para>At this time most of the features of the SGI STL extension have been |
| replaced by standardized libraries. |
| In particular, the <classname>unordered_map</classname> and |
| <classname>unordered_set</classname> containers of TR1 and C++ 2011 |
| are suitable replacements for the non-standard |
| <classname>hash_map</classname> and <classname>hash_set</classname> |
| containers in the SGI STL. |
| </para> |
| <para> Header files <filename class="headerfile"><hash_map></filename> and <filename class="headerfile"><hash_set></filename> moved |
| to <filename class="headerfile"><ext/hash_map></filename> and <filename class="headerfile"><ext/hash_set></filename>, |
| respectively. At the same time, all types in these files are enclosed |
| in <code>namespace __gnu_cxx</code>. Later versions deprecate |
| these files, and suggest using TR1's <filename class="headerfile"><unordered_map></filename> |
| and <filename class="headerfile"><unordered_set></filename> instead. |
| </para> |
| |
| <para>The extensions are no longer in the global or <code>std</code> |
| namespaces, instead they are declared in the <code>__gnu_cxx</code> |
| namespace. For maximum portability, consider defining a namespace |
| alias to use to talk about extensions, e.g.: |
| </para> |
| <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; |
| </programlisting> |
| <para>This is a bit cleaner than defining typedefs for all the |
| instantiations you might need. |
| </para> |
| |
| |
| <para>The following autoconf tests check for working HP/SGI hash containers. |
| </para> |
| |
| <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 "$ac_cv_cxx_ext_hash_map" = yes; then |
| AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ]) |
| fi |
| ]) |
| </programlisting> |
| |
| <programlisting> |
| # AC_HEADER_EXT_HASH_SET |
| AC_DEFUN([AC_HEADER_EXT_HASH_SET], [ |
| AC_CACHE_CHECK(for ext/hash_set, |
| ac_cv_cxx_ext_hash_set, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$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 |
| ]) |
| </programlisting> |
| </section> |
| |
| <section xml:id="backwards.third.nocreate_noreplace"><info><title>No <code>ios::nocreate/ios::noreplace</code>. |
| </title></info> |
| |
| |
| <para>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>O_CREAT</code> and <code>O_EXCL</code> flags for the |
| <function>open(2)</function> system call. Because iostream modes correspond |
| to <function>fopen(3)</function> modes these flags are not supported. |
| For input streams a new file will not be created anyway, so |
| <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 <function>fopen</function>. |
| </para> |
| |
| <para>When one of these flags is needed a possible alternative is to attempt |
| to open the file using <type>std::ifstream</type> 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 |
| <type>std::istream</type> 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 <function>open(2)</function>. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.third.streamattach"><info><title> |
| No <code>stream::attach(int fd)</code> |
| </title></info> |
| |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| For a portable solution (among systems which use |
| file descriptors), you need to implement a subclass of |
| <code>std::streambuf</code> (or |
| <code>std::basic_streambuf<..></code>) which opens a file |
| given a descriptor, and then pass an instance of this to the |
| stream-constructor. |
| </para> |
| |
| <para> |
| An extension is available that implements this. |
| <filename class="headerfile"><ext/stdio_filebuf.h></filename> contains a derived class called |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00074.html"><code>__gnu_cxx::stdio_filebuf</code></link>. |
| This class can be constructed from a C <code>FILE*</code> or a file |
| descriptor, and provides the <code>fd()</code> function. |
| </para> |
| |
| <para> |
| For another example of this, refer to |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.josuttis.com/cppcode/fdstream.html">fdstream example</link> |
| by Nicolai Josuttis. |
| </para> |
| </section> |
| |
| <section xml:id="backwards.third.support_cxx98"><info><title> |
| Support for C++98 dialect. |
| </title></info> |
| |
| |
| <para>Check for complete library coverage of the C++1998/2003 standard. |
| </para> |
| |
| <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 |
| ]) |
| </programlisting> |
| </section> |
| |
| <section xml:id="backwards.third.support_tr1"><info><title> |
| Support for C++TR1 dialect. |
| </title></info> |
| |
| |
| <para>Check for library coverage of the TR1 standard. |
| </para> |
| |
| <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 "$ac_cv_cxx_stdcxx_tr1" = yes; then |
| AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ]) |
| fi |
| ]) |
| </programlisting> |
| |
| <para>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. |
| </para> |
| |
| <programlisting> |
| # AC_HEADER_TR1_UNORDERED_MAP |
| AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [ |
| AC_CACHE_CHECK(for tr1/unordered_map, |
| ac_cv_cxx_tr1_unordered_map, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;], |
| ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_tr1_unordered_map" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ]) |
| fi |
| ]) |
| </programlisting> |
| |
| <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 "$ac_cv_cxx_tr1_unordered_set" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) |
| fi |
| ]) |
| </programlisting> |
| </section> |
| |
| |
| <section xml:id="backwards.third.support_cxx11"><info><title> |
| Support for C++11 dialect. |
| </title></info> |
| |
| |
| <para>Check for baseline language coverage in the compiler for the C++11 standard. |
| </para> |
| |
| <programlisting> |
| # AC_COMPILE_STDCXX_11 |
| AC_DEFUN([AC_COMPILE_STDCXX_11], [ |
| AC_CACHE_CHECK(if g++ supports C++11 features without additional flags, |
| ac_cv_cxx_compile_cxx11_native, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no) |
| AC_LANG_RESTORE |
| ]) |
| |
| AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11, |
| ac_cv_cxx_compile_cxx11_cxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$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 |
| ]) |
| </programlisting> |
| |
| |
| <para>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++). |
| </para> |
| |
| <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 |
| ]) |
| </programlisting> |
| |
| <para>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For |
| <filename class="headerfile"><unordered_map></filename> |
| </para> |
| |
| <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 |
| ]) |
| </programlisting> |
| |
| <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 |
| ]) |
| </programlisting> |
| |
| <para> |
| Some C++11 features first appeared in GCC 4.3 and could be enabled by |
| <option>-std=c++0x</option> and <option>-std=gnu++0x</option> 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 <option>-std=c++0x</option> and |
| <option>-std=gnu++0x</option>. |
| </para> |
| |
| </section> |
| |
| <section xml:id="backwards.third.iterator_type"><info><title> |
| <code>Container::iterator_type</code> is not necessarily <code>Container::value_type*</code> |
| </title></info> |
| |
| |
| <para> |
| This is a change in behavior from older versions. Now, most |
| <type>iterator_type</type> typedefs in container classes are POD |
| objects, not <type>value_type</type> pointers. |
| </para> |
| </section> |
| |
| </section> |
| |
| <bibliography xml:id="backwards.biblio"><info><title>Bibliography</title></info> |
| |
| |
| <biblioentry> |
| <title> |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" |
| xlink:href="http://www.kegel.com/gcc/gcc4.html"> |
| Migrating to GCC 4.1 |
| </link> |
| </title> |
| |
| <author><personname><firstname>Dan</firstname><surname>Kegel</surname></personname></author> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" |
| xlink:href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html"> |
| Building the Whole Debian Archive with GCC 4.1: A Summary |
| </link> |
| </title> |
| <author><personname><firstname>Martin</firstname><surname>Michlmayr</surname></personname></author> |
| </biblioentry> |
| |
| <biblioentry> |
| <title> |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" |
| xlink:href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html"> |
| Migration guide for GCC-3.2 |
| </link> |
| </title> |
| |
| </biblioentry> |
| |
| </bibliography> |
| |
| </section> |