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+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Backwards Compatibility</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , backwards " /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="prev" href="api.html" title="API Evolution and Deprecation History" /><link rel="next" href="appendix_free.html" title="Appendix C. Free Software Needs Free Documentation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Backwards Compatibility</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><th width="60%" align="center">Appendix B.
+ Porting and Maintenance
+
+</th><td width="20%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.appendix.porting.backwards"></a>Backwards Compatibility</h2></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.first"></a>First</h3></div></div></div><p>The first generation GNU C++ library was called libg++. It was a
+separate GNU project, although reliably paired with GCC. Rumors imply
+that it had a working relationship with at least two kinds of
+dinosaur.
+</p><p>Some background: libg++ was designed and created when there was no
+ISO standard to provide guidance. Classes like linked lists are now
+provided for by <code class="classname">list<T></code> and do not need to be
+created by <code class="function">genclass</code>. (For that matter, templates exist
+now and are well-supported, whereas genclass (mostly) predates them.)
+</p><p>There are other classes in libg++ that are not specified in the
+ISO Standard (e.g., statistical analysis). While there are a lot of
+really useful things that are used by a lot of people, the Standards
+Committee couldn't include everything, and so a lot of those
+“<span class="quote">obvious</span>” classes didn't get included.
+</p><p>Known Issues include many of the limitations of its immediate ancestor.</p><p>Portability notes and known implementation limitations are as follows.</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id459608"></a>No <code class="code">ios_base</code></h4></div></div></div><p> At least some older implementations don't have <code class="code">std::ios_base</code>, so you should use <code class="code">std::ios::badbit</code>, <code class="code">std::ios::failbit</code> and <code class="code">std::ios::eofbit</code> and <code class="code">std::ios::goodbit</code>.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id444641"></a>No <code class="code">cout</code> in <code class="code">ostream.h</code>, no <code class="code">cin</code> in <code class="code">istream.h</code></h4></div></div></div><p>
+ In earlier versions of the standard,
+ <code class="filename">fstream.h</code>,
+ <code class="filename">ostream.h</code>
+ and <code class="filename">istream.h</code>
+ used to define
+ <code class="code">cout</code>, <code class="code">cin</code> and so on. ISO C++ specifies that one needs to include
+ <code class="filename">iostream</code>
+ explicitly to get the required definitions.
+ </p><p> Some include adjustment may be required.</p><p>This project is no longer maintained or supported, and the sources
+archived. For the desperate,
+the <a class="ulink" href="http://gcc.gnu.org/extensions.html" target="_top">GCC extensions
+page</a> describes where to find the last libg++ source. The code is
+considered replaced and rewritten.
+</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p>
+ The second generation GNU C++ library was called libstdc++, or
+ libstdc++-v2. It spans the time between libg++ and pre-ISO C++
+ standardization and is usually associated with the following GCC
+ releases: egcs 1.x, gcc 2.95, and gcc 2.96.
+</p><p>
+ The STL portions of this library are based on SGI/HP STL release 3.11.
+</p><p>
+ This project is no longer maintained or supported, and the sources
+ archived. The code is considered replaced and rewritten.
+</p><p>
+ Portability notes and known implementation limitations are as follows.
+</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id444741"></a>Namespace <code class="code">std::</code> not supported</h4></div></div></div><p>
+ Some care is required to support C++ compiler and or library
+ implementation that do not have the standard library in
+ <code class="code">namespace std</code>.
+ </p><p>
+ The following sections list some possible solutions to support compilers
+ that cannot ignore <code class="code">std::</code>-qualified names.
+ </p><p>
+ 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 class="code">std::</code>, as the
+ compilers use <code class="code">-fno-honor-std</code> (ignore
+ <code class="code">std::</code>, <code class="code">:: = std::</code>) by default. That is,
+ the responsibility for enabling or disabling <code class="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.
+ </p><p>
+ Second, experiment with a variety of pre-processor tricks.
+ </p><p>
+ By defining <code class="code">std</code> as a macro, fully-qualified namespace
+ calls become global. Volia.
+ </p><pre class="programlisting">
+#ifdef WICKEDLY_OLD_COMPILER
+# define std
+#endif
+</pre><p>
+ Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help.
+ </p><p>
+ Another pre-processor based approach is to define a macro
+ <code class="code">NAMESPACE_STD</code>, which is defined to either
+ “<span class="quote"> </span>” or “<span class="quote">std</span>” 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 class="code">HAVE_NAMESPACE_STD</code>,
+ then using that to set a value for the <code class="code">NAMESPACE_STD</code>
+ macro. At that point, one is able to use
+ <code class="code">NAMESPACE_STD::string</code>, which will evaluate to
+ <code class="code">std::string</code> or <code class="code">::string</code> (i.e., in the
+ global namespace on systems that do not put <code class="code">string</code> in
+ <code class="code">std::</code>).
+ </p><pre class="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
+])
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id444864"></a>Illegal iterator usage</h4></div></div></div><p>
+ The following illustrate implementation-allowed illegal iterator
+ use, and then correct use.
+</p><div class="itemizedlist"><ul type="disc"><li><p>
+ you cannot do <code class="code">ostream::operator<<(iterator)</code>
+ to print the address of the iterator => use
+ <code class="code">operator<< &*iterator</code> instead
+ </p></li><li><p>
+ you cannot clear an iterator's reference (<code class="code">iterator =
+ 0</code>) => use <code class="code">iterator = iterator_type();</code>
+ </p></li><li><p>
+ <code class="code">if (iterator)</code> won't work any more => use
+ <code class="code">if (iterator != iterator_type())</code>
+ </p></li></ul></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id444925"></a><code class="code">isspace</code> from <code class="filename">cctype</code> is a macro
+ </h4></div></div></div><p>
+ Glibc 2.0.x and 2.1.x define <code class="filename">ctype.h</code> functionality as macros
+ (isspace, isalpha etc.).
+ </p><p>
+ This implementations of libstdc++, however, keep these functions
+ as macros, and so it is not back-portable to use fully qualified
+ names. For example:
+ </p><pre class="programlisting">
+#include <cctype>
+int main() { std::isspace('X'); }
+</pre><p>
+ Results in something like this:
+</p><pre class="programlisting">
+std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ;
+</pre><p>
+ A solution is to modify a header-file so that the compiler tells
+ <code class="filename">ctype.h</code> to define functions
+ instead of macros:
+</p><pre class="programlisting">
+// This keeps isalnum, et al from being propagated as macros.
+#if __linux__
+# define __NO_CTYPE 1
+#endif
+</pre><p>
+ Then, include <code class="filename">ctype.h</code>
+</p><p>
+ Another problem arises if you put a <code class="code">using namespace
+ std;</code> declaration at the top, and include <code class="filename">ctype.h</code>. This will result in
+ ambiguities between the definitions in the global namespace
+ (<code class="filename">ctype.h</code>) and the
+ definitions in namespace <code class="code">std::</code>
+ (<code class="code"><cctype></code>).
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id445019"></a>No <code class="code">vector::at</code>, <code class="code">deque::at</code>, <code class="code">string::at</code></h4></div></div></div><p>
+ One solution is to add an autoconf-test for this:
+</p><pre class="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(“<span class="quote">test_string</span>”);
+test_string.at(3);
+],
+[AC_MSG_RESULT(yes)
+AC_DEFINE(HAVE_CONTAINER_AT)],
+[AC_MSG_RESULT(no)])
+</pre><p>
+ If you are using other (non-GNU) compilers it might be a good idea
+ to check for <code class="code">string::at</code> separately.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id445057"></a>No <code class="code">std::char_traits<char>::eof</code></h4></div></div></div><p>
+ Use some kind of autoconf test, plus this:
+</p><pre class="programlisting">
+#ifdef HAVE_CHAR_TRAITS
+#define CPP_EOF std::char_traits<char>::eof()
+#else
+#define CPP_EOF EOF
+#endif
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id445075"></a>No <code class="code">string::clear</code></h4></div></div></div><p>
+ There are two functions for deleting the contents of a string:
+ <code class="code">clear</code> and <code class="code">erase</code> (the latter returns the
+ string).
+</p><pre class="programlisting">
+void
+clear() { _M_mutate(0, this->size(), 0); }
+</pre><pre class="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());
+}
+</pre><p>
+ Unfortunately, <code class="code">clear</code> is not implemented in this
+ version, so you should use <code class="code">erase</code> (which is probably
+ faster than <code class="code">operator=(charT*)</code>).
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id445120"></a>
+ Removal of <code class="code">ostream::form</code> and <code class="code">istream::scan</code>
+ extensions
+</h4></div></div></div><p>
+ These are no longer supported. Please use stringstreams instead.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id445139"></a>No <code class="code">basic_stringbuf</code>, <code class="code">basic_stringstream</code></h4></div></div></div><p>
+ Although the ISO standard <code class="code">i/ostringstream</code>-classes are
+ provided, (<code class="filename">sstream</code>), for
+ compatibility with older implementations the pre-ISO
+ <code class="code">i/ostrstream</code> (<code class="filename">strstream</code>) interface is also provided,
+ with these caveats:
+</p><div class="itemizedlist"><ul type="disc"><li><p>
+ <code class="code">strstream</code> is considered to be deprecated
+ </p></li><li><p>
+ <code class="code">strstream</code> is limited to <code class="code">char</code>
+ </p></li><li><p>
+ with <code class="code">ostringstream</code> you don't have to take care of
+ terminating the string or freeing its memory
+ </p></li><li><p>
+ <code class="code">istringstream</code> can be re-filled (clear();
+ str(input);)
+ </p></li></ul></div><p>
+ You can then use output-stringstreams like this:
+</p><pre class="programlisting">
+#ifdef HAVE_SSTREAM
+# include <sstream>
+#else
+# include <strstream>
+#endif
+
+#ifdef HAVE_SSTREAM
+ std::ostringstream oss;
+#else
+ std::ostrstream oss;
+#endif
+
+oss << “<span class="quote">Name=</span>” << m_name << “<span class="quote">, number=</span>” << 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
+</pre><p>
+ Input-stringstreams can be used similarly:
+</p><pre class="programlisting">
+std::string input;
+...
+#ifdef HAVE_SSTREAM
+std::istringstream iss(input);
+#else
+std::istrstream iss(input.c_str());
+#endif
+
+int i;
+iss >> i;
+</pre><p> One (the only?) restriction is that an istrstream cannot be re-filled:
+</p><pre class="programlisting">
+std::istringstream iss(numerator);
+iss >> m_num;
+// this is not possible with istrstream
+iss.clear();
+iss.str(denominator);
+iss >> m_den;
+</pre><p>
+If you don't care about speed, you can put these conversions in
+ a template-function:
+</p><pre class="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;
+}
+</pre><p>
+ Another example of using stringstreams is in <a class="link" href="bk01pt05ch13s05.html" title="Shrink to Fit">this howto</a>.
+</p><p> There is additional information in the libstdc++-v2 info files, in
+particular “<span class="quote">info iostream</span>”.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id448793"></a>Little or no wide character support</h4></div></div></div><p>
+ Classes <code class="classname">wstring</code> and
+ <code class="classname">char_traits<wchar_t></code> are
+ not supported.
+ </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id448812"></a>No templatized iostreams</h4></div></div></div><p>
+ Classes <code class="classname">wfilebuf</code> and
+ <code class="classname">wstringstream</code> are not supported.
+ </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id448831"></a>Thread safety issues</h4></div></div></div><p>
+ 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.
+ </p><p>
+ 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.
+ </p><p>
+ 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
+ <span class="emphasis"><em>fast</em></span> 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 <a class="ulink" href="http://www.sgi.com/tech/stl/thread_safety.html" target="_top">same
+ definition that SGI</a> 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.
+ </p><p>
+ 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.
+ </p><div class="itemizedlist"><ul type="disc"><li><p>
+ Our threading expert Loren gives a breakdown of <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-10/msg00024.html" target="_top">the
+ six situations involving threads</a> for the 3.0
+ release series.
+ </p></li><li><p>
+ <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html" target="_top">
+ This message</a> inspired a recent updating of issues with
+ threading and the SGI STL library. It also contains some
+ example POSIX-multithreaded STL code.
+ </p></li></ul></div><p>
+ (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.)
+ </p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.third"></a>Third</h3></div></div></div><p> The third generation GNU C++ library is called libstdc++, or
+libstdc++-v3.
+</p><p>The subset commonly known as the Standard Template Library
+ (chapters 23 through 25, mostly) is adapted from the final release
+ of the SGI STL (version 3.3), with extensive changes.
+ </p><p>A more formal description of the V3 goals can be found in the
+ official <a class="ulink" href="../17_intro/DESIGN" target="_top">design document</a>.
+ </p><p>Portability notes and known implementation limitations are as follows.</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id448950"></a>Pre-ISO headers moved to backwards or removed</h4></div></div></div><p> The pre-ISO C++ headers
+ (<code class="code">iostream.h</code>, <code class="code">defalloc.h</code> etc.) are
+ available, unlike previous libstdc++ versions, but inclusion
+ generates a warning that you are using deprecated headers.
+</p><p>This compatibility layer is constructed by including the
+ standard C++ headers, and injecting any items in
+ <code class="code">std::</code> into the global namespace.
+ </p><p>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 <a class="ulink" href="http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.4" target="_top">item
+ [27.4]</a>.
+ </p><p> Some include adjustment may be required. What follows is an
+autoconf test that defines <code class="code">PRE_STDCXX_HEADERS</code> when they
+exist.</p><pre class="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
+])
+</pre><p>Porting between pre-ISO headers and ISO headers is simple: headers
+like <code class="filename">vector.h</code> can be replaced with <code class="filename">vector</code> and a using
+directive <code class="code">using namespace std;</code> can be put at the global
+scope. This should be enough to get this code compiling, assuming the
+other usage is correct.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id449032"></a>Extension headers hash_map, hash_set moved to ext or backwards</h4></div></div></div><p>At this time most of the features of the SGI STL extension have been
+ replaced by standardized libraries.
+ In particular, the 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.
+ </p><p> Header files <code class="filename">hash_map</code> and <code class="filename">hash_set</code> moved
+to <code class="filename">ext/hash_map</code> and <code class="filename">ext/hash_set</code>,
+respectively. At the same time, all types in these files are enclosed
+in <code class="code">namespace __gnu_cxx</code>. Later versions move deprecate
+these files, and suggest using TR1's <code class="filename">unordered_map</code>
+and <code class="filename">unordered_set</code> instead.
+</p><p>The extensions are no longer in the global or <code class="code">std</code>
+ namespaces, instead they are declared in the <code class="code">__gnu_cxx</code>
+ namespace. For maximum portability, consider defining a namespace
+ alias to use to talk about extensions, e.g.:
+ </p><pre class="programlisting">
+ #ifdef __GNUC__
+ #if __GNUC__ < 3
+ #include <hash_map.h>
+ namespace extension { using ::hash_map; }; // inherit globals
+ #else
+ #include <backward/hash_map>
+ #if __GNUC__ == 3 && __GNUC_MINOR__ == 0
+ namespace extension = std; // GCC 3.0
+ #else
+ namespace extension = ::__gnu_cxx; // GCC 3.1 and later
+ #endif
+ #endif
+ #else // ... there are other compilers, right?
+ namespace extension = std;
+ #endif
+
+ extension::hash_map<int,int> my_map;
+ </pre><p>This is a bit cleaner than defining typedefs for all the
+ instantiations you might need.
+ </p><p>The following autoconf tests check for working HP/SGI hash containers.
+</p><pre class="programlisting">
+# AC_HEADER_EXT_HASH_MAP
+AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [
+ AC_CACHE_CHECK(for ext/hash_map,
+ ac_cv_cxx_ext_hash_map,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ ac_save_CXXFLAGS="$CXXFLAGS"
+ CXXFLAGS="$CXXFLAGS -Werror"
+ AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;],
+ ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no)
+ CXXFLAGS="$ac_save_CXXFLAGS"
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_ext_hash_map" = yes; then
+ AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ])
+ fi
+])
+</pre><pre class="programlisting">
+# AC_HEADER_EXT_HASH_SET
+AC_DEFUN([AC_HEADER_EXT_HASH_SET], [
+ AC_CACHE_CHECK(for ext/hash_set,
+ ac_cv_cxx_ext_hash_set,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ ac_save_CXXFLAGS="$CXXFLAGS"
+ CXXFLAGS="$CXXFLAGS -Werror"
+ AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;],
+ ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no)
+ CXXFLAGS="$ac_save_CXXFLAGS"
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_ext_hash_set" = yes; then
+ AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ])
+ fi
+])
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id449135"></a>No <code class="code">ios::nocreate/ios::noreplace</code>.
+</h4></div></div></div><p> The existence of <code class="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.
+</p><p>For output streams, “<span class="quote">nocreate</span>” is probably the default,
+unless you specify <code class="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 class="code">app</code>, <code class="code">ate</code>
+and <code class="code">trunc</code> (except for <code class="code">app</code> ?).
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id449183"></a>
+No <code class="code">stream::attach(int fd)</code>
+</h4></div></div></div><p>
+ Phil Edwards writes: It was considered and rejected for the ISO
+ standard. Not all environments use file descriptors. Of those
+ that do, not all of them use integers to represent them.
+ </p><p>
+ For a portable solution (among systems which use
+ file descriptors), you need to implement a subclass of
+ <code class="code">std::streambuf</code> (or
+ <code class="code">std::basic_streambuf<..></code>) which opens a file
+ given a descriptor, and then pass an instance of this to the
+ stream-constructor.
+ </p><p>
+ An extension is available that implements this.
+ <code class="filename">ext/stdio_filebuf.h</code> contains a derived class called
+ <a class="ulink" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/class____gnu__cxx_1_1stdio__filebuf.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>.
+ This class can be constructed from a C <code class="code">FILE*</code> or a file
+ descriptor, and provides the <code class="code">fd()</code> function.
+ </p><p>
+ For another example of this, refer to
+ <a class="ulink" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a>
+ by Nicolai Josuttis.
+</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id511531"></a>
+Support for C++98 dialect.
+</h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard.
+</p><pre class="programlisting">
+# AC_HEADER_STDCXX_98
+AC_DEFUN([AC_HEADER_STDCXX_98], [
+ AC_CACHE_CHECK(for ISO C++ 98 include files,
+ ac_cv_cxx_stdcxx_98,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([
+ #include <cassert>
+ #include <cctype>
+ #include <cerrno>
+ #include <cfloat>
+ #include <ciso646>
+ #include <climits>
+ #include <clocale>
+ #include <cmath>
+ #include <csetjmp>
+ #include <csignal>
+ #include <cstdarg>
+ #include <cstddef>
+ #include <cstdio>
+ #include <cstdlib>
+ #include <cstring>
+ #include <ctime>
+
+ #include <algorithm>
+ #include <bitset>
+ #include <complex>
+ #include <deque>
+ #include <exception>
+ #include <fstream>
+ #include <functional>
+ #include <iomanip>
+ #include <ios>
+ #include <iosfwd>
+ #include <iostream>
+ #include <istream>
+ #include <iterator>
+ #include <limits>
+ #include <list>
+ #include <locale>
+ #include <map>
+ #include <memory>
+ #include <new>
+ #include <numeric>
+ #include <ostream>
+ #include <queue>
+ #include <set>
+ #include <sstream>
+ #include <stack>
+ #include <stdexcept>
+ #include <streambuf>
+ #include <string>
+ #include <typeinfo>
+ #include <utility>
+ #include <valarray>
+ #include <vector>
+ ],,
+ ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no)
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_stdcxx_98" = yes; then
+ AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ])
+ fi
+])
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id511558"></a>
+Support for C++TR1 dialect.
+</h4></div></div></div><p>Check for library coverage of the TR1 standard.
+</p><pre class="programlisting">
+# AC_HEADER_STDCXX_TR1
+AC_DEFUN([AC_HEADER_STDCXX_TR1], [
+ AC_CACHE_CHECK(for ISO C++ TR1 include files,
+ ac_cv_cxx_stdcxx_tr1,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([
+ #include <tr1/array>
+ #include <tr1/ccomplex>
+ #include <tr1/cctype>
+ #include <tr1/cfenv>
+ #include <tr1/cfloat>
+ #include <tr1/cinttypes>
+ #include <tr1/climits>
+ #include <tr1/cmath>
+ #include <tr1/complex>
+ #include <tr1/cstdarg>
+ #include <tr1/cstdbool>
+ #include <tr1/cstdint>
+ #include <tr1/cstdio>
+ #include <tr1/cstdlib>
+ #include <tr1/ctgmath>
+ #include <tr1/ctime>
+ #include <tr1/cwchar>
+ #include <tr1/cwctype>
+ #include <tr1/functional>
+ #include <tr1/memory>
+ #include <tr1/random>
+ #include <tr1/regex>
+ #include <tr1/tuple>
+ #include <tr1/type_traits>
+ #include <tr1/unordered_set>
+ #include <tr1/unordered_map>
+ #include <tr1/utility>
+ ],,
+ ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no)
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_stdcxx_tr1" = yes; then
+ AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ])
+ fi
+])
+</pre><p>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>.
+</p><pre class="programlisting">
+# AC_HEADER_TR1_UNORDERED_MAP
+AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [
+ AC_CACHE_CHECK(for tr1/unordered_map,
+ ac_cv_cxx_tr1_unordered_map,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;],
+ ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no)
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_tr1_unordered_map" = yes; then
+ AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ])
+ fi
+])
+</pre><pre class="programlisting">
+# AC_HEADER_TR1_UNORDERED_SET
+AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [
+ AC_CACHE_CHECK(for tr1/unordered_set,
+ ac_cv_cxx_tr1_unordered_set,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;],
+ ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no)
+ AC_LANG_RESTORE
+ ])
+ if test "$ac_cv_cxx_tr1_unordered_set" = yes; then
+ AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ])
+ fi
+])
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id511602"></a>
+Support for C++0x dialect.
+</h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++0xstandard.
+</p><pre class="programlisting">
+# AC_COMPILE_STDCXX_OX
+AC_DEFUN([AC_COMPILE_STDCXX_0X], [
+ AC_CACHE_CHECK(if g++ supports C++0x features without additional flags,
+ ac_cv_cxx_compile_cxx0x_native,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([
+ template <typename T>
+ struct check
+ {
+ static_assert(sizeof(int) <= sizeof(T), "not big enough");
+ };
+
+ typedef check<check<bool>> right_angle_brackets;
+
+ int a;
+ decltype(a) b;
+
+ typedef check<int> check_type;
+ check_type c;
+ check_type&& cr = c;],,
+ ac_cv_cxx_compile_cxx0x_native=yes, ac_cv_cxx_compile_cxx0x_native=no)
+ AC_LANG_RESTORE
+ ])
+
+ AC_CACHE_CHECK(if g++ supports C++0x features with -std=c++0x,
+ ac_cv_cxx_compile_cxx0x_cxx,
+ [AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ ac_save_CXXFLAGS="$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
+])
+</pre><p>Check for library coverage of the C++0xstandard.
+</p><pre class="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
+])
+</pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For <unordered_map>
+</p><pre class="programlisting">
+# AC_HEADER_UNORDERED_MAP
+AC_DEFUN([AC_HEADER_UNORDERED_MAP], [
+ AC_CACHE_CHECK(for unordered_map,
+ ac_cv_cxx_unordered_map,
+ [AC_REQUIRE([AC_COMPILE_STDCXX_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
+])
+</pre><pre class="programlisting">
+# AC_HEADER_UNORDERED_SET
+AC_DEFUN([AC_HEADER_UNORDERED_SET], [
+ AC_CACHE_CHECK(for unordered_set,
+ ac_cv_cxx_unordered_set,
+ [AC_REQUIRE([AC_COMPILE_STDCXX_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
+])
+</pre></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id511679"></a>
+ Container::iterator_type is not necessarily Container::value_type*
+</h4></div></div></div><p>
+ This is a change in behavior from the previous version. Now, most
+ <span class="type">iterator_type</span> typedefs in container classes are POD
+ objects, not <span class="type">value_type</span> pointers.
+</p></div></div><div class="bibliography"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.biblio"></a>Bibliography</h3></div></div></div><div class="biblioentry"><a id="id511711"></a><p>[<abbr class="abbrev">
+ kegel41
+ </abbr>] <span class="title"><i>
+ Migrating to GCC 4.1
+ </i>. </span><span class="author"><span class="firstname">Dan</span> <span class="surname">Kegel</span>. </span><span class="biblioid">
+ <a class="ulink" href="http://www.kegel.com/gcc/gcc4.html" target="_top">
+ </a>
+ . </span></p></div><div class="biblioentry"><a id="id511743"></a><p>[<abbr class="abbrev">
+ kegel41
+ </abbr>] <span class="title"><i>
+ Building the Whole Debian Archive with GCC 4.1: A Summary
+ </i>. </span><span class="author"><span class="firstname">Martin</span> <span class="surname">Michlmayr</span>. </span><span class="biblioid">
+ <a class="ulink" href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top">
+ </a>
+ . </span></p></div><div class="biblioentry"><a id="id511776"></a><p>[<abbr class="abbrev">
+ lbl32
+ </abbr>] <span class="title"><i>
+ Migration guide for GCC-3.2
+ </i>. </span><span class="biblioid">
+ <a class="ulink" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top">
+ </a>
+ . </span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">API Evolution and Deprecation History </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix C.
+ Free Software Needs Free Documentation
+
+</td></tr></table></div></body></html>
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