mirror of git://gcc.gnu.org/git/gcc.git
1327 lines
40 KiB
XML
1327 lines
40 KiB
XML
<section xmlns="http://docbook.org/ns/docbook" version="5.0"
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xml:id="manual.appendix.porting.backwards" xreflabel="backwards">
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<?dbhtml filename="backwards.html"?>
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<info><title>Backwards Compatibility</title>
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<keywordset>
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<keyword>ISO C++</keyword>
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<keyword>backwards</keyword>
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</keywordset>
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</info>
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<section xml:id="backwards.first"><info><title>First</title></info>
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<para>The first generation GNU C++ library was called libg++. It was a
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separate GNU project, although reliably paired with GCC. Rumors imply
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that it had a working relationship with at least two kinds of
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dinosaur.
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</para>
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<para>Some background: libg++ was designed and created when there was no
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ISO standard to provide guidance. Classes like linked lists are now
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provided for by <classname>list<T></classname> and do not need to be
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created by <function>genclass</function>. (For that matter, templates exist
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now and are well-supported, whereas genclass (mostly) predates them.)
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</para>
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<para>There are other classes in libg++ that are not specified in the
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ISO Standard (e.g., statistical analysis). While there are a lot of
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really useful things that are used by a lot of people, the Standards
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Committee couldn't include everything, and so a lot of those
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<quote>obvious</quote> classes didn't get included.
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</para>
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<para>Known Issues include many of the limitations of its immediate ancestor.</para>
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<para>Portability notes and known implementation limitations are as follows.</para>
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<section xml:id="backwards.first.ios_base"><info><title>No <code>ios_base</code></title></info>
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<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>.
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</para>
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</section>
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<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>
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<para>
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In earlier versions of the standard,
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<filename class="headerfile"><fstream.h></filename>,
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<filename class="headerfile"><ostream.h></filename>
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and <filename class="headerfile"><istream.h></filename>
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used to define
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<code>cout</code>, <code>cin</code> and so on. ISO C++ specifies that one needs to include
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<filename class="headerfile"><iostream></filename>
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explicitly to get the required definitions.
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</para>
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<para> Some include adjustment may be required.</para>
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<para>This project is no longer maintained or supported, and the sources
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archived. For the desperate,
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the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/extensions.html">GCC extensions
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page</link> describes where to find the last libg++ source. The code is
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considered replaced and rewritten.
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</para>
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</section>
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</section>
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<section xml:id="backwards.second"><info><title>Second</title></info>
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<para>
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The second generation GNU C++ library was called libstdc++, or
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libstdc++-v2. It spans the time between libg++ and pre-ISO C++
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standardization and is usually associated with the following GCC
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releases: egcs 1.x, gcc 2.95, and gcc 2.96.
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</para>
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<para>
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The STL portions of this library are based on SGI/HP STL release 3.11.
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</para>
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<para>
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This project is no longer maintained or supported, and the sources
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archived. The code is considered replaced and rewritten.
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</para>
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<para>
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Portability notes and known implementation limitations are as follows.
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</para>
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<section xml:id="backwards.second.std"><info><title>Namespace <code>std::</code> not supported</title></info>
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<para>
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Some care is required to support C++ compiler and or library
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implementation that do not have the standard library in
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<code>namespace std</code>.
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</para>
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<para>
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The following sections list some possible solutions to support compilers
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that cannot ignore <code>std::</code>-qualified names.
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</para>
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<para>
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First, see if the compiler has a flag for this. Namespace
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back-portability-issues are generally not a problem for g++
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compilers that do not have libstdc++ in <code>std::</code>, as the
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compilers use <option>-fno-honor-std</option> (ignore
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<code>std::</code>, <code>:: = std::</code>) by default. That is,
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the responsibility for enabling or disabling <code>std::</code> is
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on the user; the maintainer does not have to care about it. This
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probably applies to some other compilers as well.
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</para>
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<para>
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Second, experiment with a variety of pre-processor tricks.
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</para>
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<para>
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By defining <code>std</code> as a macro, fully-qualified namespace
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calls become global. Volia.
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</para>
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<programlisting>
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#ifdef WICKEDLY_OLD_COMPILER
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# define std
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#endif
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</programlisting>
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<para>
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Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help.
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</para>
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<para>
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Another pre-processor based approach is to define a macro
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<code>NAMESPACE_STD</code>, which is defined to either
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<quote> </quote> or <quote>std</quote> based on a compile-type
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test. On GNU systems, this can be done with autotools by means of
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an autoconf test (see below) for <code>HAVE_NAMESPACE_STD</code>,
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then using that to set a value for the <code>NAMESPACE_STD</code>
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macro. At that point, one is able to use
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<code>NAMESPACE_STD::string</code>, which will evaluate to
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<code>std::string</code> or <code>::string</code> (i.e., in the
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global namespace on systems that do not put <code>string</code> in
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<code>std::</code>).
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</para>
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<programlisting>
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dnl @synopsis AC_CXX_NAMESPACE_STD
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dnl
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dnl If the compiler supports namespace std, define
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dnl HAVE_NAMESPACE_STD.
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dnl
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dnl @category Cxx
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dnl @author Todd Veldhuizen
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dnl @author Luc Maisonobe <luc@spaceroots.org>
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dnl @version 2004-02-04
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dnl @license AllPermissive
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AC_DEFUN([AC_CXX_NAMESPACE_STD], [
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AC_CACHE_CHECK(if g++ supports namespace std,
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ac_cv_cxx_have_std_namespace,
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[AC_LANG_SAVE
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AC_LANG_CPLUSPLUS
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AC_TRY_COMPILE([#include <iostream>
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std::istream& is = std::cin;],,
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ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no)
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AC_LANG_RESTORE
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])
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if test "$ac_cv_cxx_have_std_namespace" = yes; then
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AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ])
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fi
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])
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</programlisting>
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</section>
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<section xml:id="backwards.second.iterators"><info><title>Illegal iterator usage</title></info>
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<para>
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The following illustrate implementation-allowed illegal iterator
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use, and then correct use.
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</para>
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<itemizedlist>
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<listitem>
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<para>
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you cannot do <code>ostream::operator<<(iterator)</code>
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to print the address of the iterator => use
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<code>operator<< &*iterator</code> instead
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</para>
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</listitem>
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<listitem>
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<para>
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you cannot clear an iterator's reference (<code>iterator =
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0</code>) => use <code>iterator = iterator_type();</code>
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</para>
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</listitem>
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<listitem>
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<para>
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<code>if (iterator)</code> won't work any more => use
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<code>if (iterator != iterator_type())</code>
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</para>
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</listitem>
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</itemizedlist>
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</section>
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<section xml:id="backwards.second.isspace"><info><title><code>isspace</code> from <filename class="headerfile"><cctype></filename> is a macro
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</title></info>
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<para>
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Glibc 2.0.x and 2.1.x define <filename class="headerfile"><ctype.h></filename> functionality as macros
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(isspace, isalpha etc.).
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</para>
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<para>
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This implementations of libstdc++, however, keep these functions
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as macros, and so it is not back-portable to use fully qualified
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names. For example:
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</para>
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<programlisting>
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#include <cctype>
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int main() { std::isspace('X'); }
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</programlisting>
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<para>
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Results in something like this:
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</para>
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<programlisting>
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std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ;
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</programlisting>
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<para>
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A solution is to modify a header-file so that the compiler tells
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<filename class="headerfile"><ctype.h></filename> to define functions
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instead of macros:
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</para>
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<programlisting>
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// This keeps isalnum, et al from being propagated as macros.
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#if __linux__
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# define __NO_CTYPE 1
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#endif
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</programlisting>
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<para>
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Then, include <filename class="headerfile"><ctype.h></filename>
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</para>
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<para>
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Another problem arises if you put a <code>using namespace
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std;</code> declaration at the top, and include
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<filename class="headerfile"><ctype.h></filename>. This will
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result in ambiguities between the definitions in the global namespace
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(<filename class="headerfile"><ctype.h></filename>) and the
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definitions in namespace <code>std::</code>
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(<code><cctype></code>).
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</para>
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</section>
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<section xml:id="backwards.second.at"><info><title>No <code>vector::at</code>, <code>deque::at</code>, <code>string::at</code></title></info>
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<para>
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One solution is to add an autoconf-test for this:
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</para>
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<programlisting>
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AC_MSG_CHECKING(for container::at)
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AC_TRY_COMPILE(
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[
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#include <vector>
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#include <deque>
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#include <string>
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using namespace std;
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],
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[
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deque<int> test_deque(3);
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test_deque.at(2);
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vector<int> test_vector(2);
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test_vector.at(1);
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string test_string(<quote>test_string</quote>);
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test_string.at(3);
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],
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[AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_CONTAINER_AT)],
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[AC_MSG_RESULT(no)])
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</programlisting>
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<para>
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If you are using other (non-GNU) compilers it might be a good idea
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to check for <code>string::at</code> separately.
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</para>
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</section>
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<section xml:id="backwards.second.eof"><info><title>No <code>std::char_traits<char>::eof</code></title></info>
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<para>
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Use some kind of autoconf test, plus this:
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</para>
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<programlisting>
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#ifdef HAVE_CHAR_TRAITS
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#define CPP_EOF std::char_traits<char>::eof()
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#else
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#define CPP_EOF EOF
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#endif
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</programlisting>
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</section>
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<section xml:id="backwards.second.stringclear"><info><title>No <code>string::clear</code></title></info>
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<para>
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There are two functions for deleting the contents of a string:
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<code>clear</code> and <code>erase</code> (the latter returns the
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string).
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</para>
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<programlisting>
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void
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clear() { _M_mutate(0, this->size(), 0); }
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</programlisting>
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<programlisting>
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basic_string&
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erase(size_type __pos = 0, size_type __n = npos)
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{
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return this->replace(_M_check(__pos), _M_fold(__pos, __n),
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_M_data(), _M_data());
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}
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</programlisting>
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<para>
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Unfortunately, <code>clear</code> is not implemented in this
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version, so you should use <code>erase</code> (which is probably
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faster than <code>operator=(charT*)</code>).
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</para>
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</section>
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<section xml:id="backwards.second.ostreamform_istreamscan"><info><title>
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Removal of <code>ostream::form</code> and <code>istream::scan</code>
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extensions
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</title></info>
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<para>
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These are no longer supported. Please use stringstreams instead.
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</para>
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</section>
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<section xml:id="backwards.second.stringstreams"><info><title>No <code>basic_stringbuf</code>, <code>basic_stringstream</code></title></info>
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<para>
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Although the ISO standard <code>i/ostringstream</code>-classes are
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provided, (<filename class="headerfile"><sstream></filename>), for
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compatibility with older implementations the pre-ISO
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<code>i/ostrstream</code> (<filename class="headerfile"><strstream></filename>) interface is also provided,
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with these caveats:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<code>strstream</code> is considered to be deprecated
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</para>
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</listitem>
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<listitem>
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<para>
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<code>strstream</code> is limited to <code>char</code>
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</para>
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</listitem>
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<listitem>
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<para>
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with <code>ostringstream</code> you don't have to take care of
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terminating the string or freeing its memory
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</para>
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</listitem>
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<listitem>
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<para>
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<code>istringstream</code> can be re-filled (clear();
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str(input);)
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</para>
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</listitem>
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</itemizedlist>
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<para>
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You can then use output-stringstreams like this:
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</para>
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<programlisting>
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#ifdef HAVE_SSTREAM
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# include <sstream>
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#else
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# include <strstream>
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#endif
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#ifdef HAVE_SSTREAM
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std::ostringstream oss;
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#else
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std::ostrstream oss;
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#endif
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oss << "Name=" << m_name << ", number=" << m_number << std::endl;
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...
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#ifndef HAVE_SSTREAM
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oss << std::ends; // terminate the char*-string
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#endif
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// str() returns char* for ostrstream and a string for ostringstream
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// this also causes ostrstream to think that the buffer's memory
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// is yours
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m_label.set_text(oss.str());
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#ifndef HAVE_SSTREAM
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// let the ostrstream take care of freeing the memory
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oss.freeze(false);
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#endif
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</programlisting>
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<para>
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Input-stringstreams can be used similarly:
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</para>
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<programlisting>
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std::string input;
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...
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#ifdef HAVE_SSTREAM
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std::istringstream iss(input);
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#else
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std::istrstream iss(input.c_str());
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#endif
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int i;
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iss >> i;
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</programlisting>
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<para> One (the only?) restriction is that an istrstream cannot be re-filled:
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</para>
|
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<programlisting>
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std::istringstream iss(numerator);
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iss >> m_num;
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// this is not possible with istrstream
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iss.clear();
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iss.str(denominator);
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iss >> m_den;
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</programlisting>
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|
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<para>
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If you don't care about speed, you can put these conversions in
|
|
a template-function:
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|
</para>
|
|
<programlisting>
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|
template <class X>
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void fromString(const string& input, X& any)
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{
|
|
#ifdef HAVE_SSTREAM
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std::istringstream iss(input);
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|
#else
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std::istrstream iss(input.c_str());
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|
#endif
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X temp;
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iss >> temp;
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if (iss.fail())
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throw runtime_error(..)
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any = temp;
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}
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</programlisting>
|
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|
|
<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>
|
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|
|
<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.
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|
</para>
|
|
</section>
|
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|
|
<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="https://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>
|