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| author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
|---|---|---|
| committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
| commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
| tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libstdc++-v3/doc/xml/manual/backwards_compatibility.xml | |
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diff --git a/libstdc++-v3/doc/xml/manual/backwards_compatibility.xml b/libstdc++-v3/doc/xml/manual/backwards_compatibility.xml new file mode 100644 index 000000000..1f7348a0e --- /dev/null +++ b/libstdc++-v3/doc/xml/manual/backwards_compatibility.xml @@ -0,0 +1,1282 @@ +<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><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><info><title>No <code>cout</code> in <code>ostream.h</code>, no <code>cin</code> in <code>istream.h</code></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><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 <code>-fno-honor-std</code> (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><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><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><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><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><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><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><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><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><info><title>No templatized iostreams</title></info> + + <para> + Classes <classname>wfilebuf</classname> and + <classname>wstringstream</classname> are not supported. + </para> +</section> + +<section><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 + (chapters 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><info><title>Pre-ISO headers moved to backwards or removed</title></info> + + +<para> The pre-ISO C++ headers + (<code>iostream.h</code>, <code>defalloc.h</code> 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/coding-standards.html#faq-27.4">item + [27.4]</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><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 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. + </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 move 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><info><title>No <code>ios::nocreate/ios::noreplace</code>. +</title></info> + + +<para> The existence of <code>ios::nocreate</code> 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. +</para> + +<para>For output streams, <quote>nocreate</quote> is probably the default, +unless you specify <code>std::ios::trunc</code> ? 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 <code>app</code>, <code>ate</code> +and <code>trunc</code> (except for <code>app</code> ?). +</para> +</section> + +<section><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><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><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 "$ac_cv_cxx_tr1_unordered_set" = yes; then + AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) + fi +]) +</programlisting> +</section> + + +<section><info><title> +Support for C++0x dialect. +</title></info> + + +<para>Check for baseline language coverage in the compiler for the C++0xstandard. +</para> + +<programlisting> +# AC_COMPILE_STDCXX_OX +AC_DEFUN([AC_COMPILE_STDCXX_0X], [ + AC_CACHE_CHECK(if g++ supports C++0x features without additional flags, + ac_cv_cxx_compile_cxx0x_native, + [AC_LANG_SAVE + AC_LANG_CPLUSPLUS + AC_TRY_COMPILE([ + template <typename T> + struct check + { + static_assert(sizeof(int) <= sizeof(T), "not big enough"); + }; + + typedef check<check<bool>> right_angle_brackets; + + int a; + decltype(a) b; + + typedef check<int> check_type; + check_type c; + check_type&& cr = c;],, + ac_cv_cxx_compile_cxx0x_native=yes, ac_cv_cxx_compile_cxx0x_native=no) + AC_LANG_RESTORE + ]) + + AC_CACHE_CHECK(if g++ supports C++0x features with -std=c++0x, + ac_cv_cxx_compile_cxx0x_cxx, + [AC_LANG_SAVE + AC_LANG_CPLUSPLUS + ac_save_CXXFLAGS="$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 +]) +</programlisting> + + +<para>Check for library coverage of the C++0xstandard. +</para> + +<programlisting> +# 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 +]) +</programlisting> + +<para>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For <unordered_map> +</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_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 +]) +</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_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 +]) +</programlisting> +</section> + +<section><info><title> + Container::iterator_type is not necessarily Container::value_type* +</title></info> + + +<para> + This is a change in behavior from the previous version. 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> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.kegel.com/gcc/gcc4.html" class="uri"> + </biblioid> + <citetitle> + Migrating to GCC 4.1 + </citetitle> + + <author><personname><firstname>Dan</firstname><surname>Kegel</surname></personname></author> + </biblioentry> + + <biblioentry> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html" class="uri"> + </biblioid> + <citetitle> + Building the Whole Debian Archive with GCC 4.1: A Summary + </citetitle> + + <author><personname><firstname>Martin</firstname><surname>Michlmayr</surname></personname></author> + </biblioentry> + + <biblioentry> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" class="uri"> + </biblioid> + <citetitle> + Migration guide for GCC-3.2 + </citetitle> + + </biblioentry> + +</bibliography> + +</section> |