2012-03-27 23:13:14 +00:00
<section xmlns= "http://docbook.org/ns/docbook" version= "5.0"
xml:id="manual.appendix.porting.backwards" xreflabel="backwards">
<?dbhtml filename="backwards.html"?>
<info > <title > Backwards Compatibility</title>
<keywordset >
2014-09-21 17:33:12 +00:00
<keyword > ISO C++</keyword>
<keyword > backwards</keyword>
2012-03-27 23:13:14 +00:00
</keywordset>
</info>
<section xml:id= "backwards.first" > <info > <title > First</title> </info>
<para > The first generation GNU C++ library was called libg++. It was a
separate GNU project, although reliably paired with GCC. Rumors imply
that it had a working relationship with at least two kinds of
dinosaur.
</para>
<para > Some background: libg++ was designed and created when there was no
ISO standard to provide guidance. Classes like linked lists are now
provided for by <classname > list< T> </classname> and do not need to be
created by <function > genclass</function> . (For that matter, templates exist
now and are well-supported, whereas genclass (mostly) predates them.)
</para>
<para > There are other classes in libg++ that are not specified in the
ISO Standard (e.g., statistical analysis). While there are a lot of
really useful things that are used by a lot of people, the Standards
Committee couldn't include everything, and so a lot of those
<quote > obvious</quote> classes didn't get included.
</para>
<para > Known Issues include many of the limitations of its immediate ancestor.</para>
<para > Portability notes and known implementation limitations are as follows.</para>
<section xml:id= "backwards.first.ios_base" > <info > <title > No <code > ios_base</code> </title> </info>
<para > At least some older implementations don't have <code > std::ios_base</code> , so you should use <code > std::ios::badbit</code> , <code > std::ios::failbit</code> and <code > std::ios::eofbit</code> and <code > std::ios::goodbit</code> .
</para>
</section>
<section xml:id= "backwards.first.cout_cin" > <info > <title > No <code > cout</code> in <filename class= "headerfile" > < ostream.h> </filename> , no <code > cin</code> in <filename class= "headerfile" > < istream.h> </filename> </title> </info>
<para >
In earlier versions of the standard,
<filename class= "headerfile" > < fstream.h> </filename> ,
<filename class= "headerfile" > < ostream.h> </filename>
and <filename class= "headerfile" > < istream.h> </filename>
used to define
<code > cout</code> , <code > cin</code> and so on. ISO C++ specifies that one needs to include
<filename class= "headerfile" > < iostream> </filename>
explicitly to get the required definitions.
</para>
<para > Some include adjustment may be required.</para>
<para > This project is no longer maintained or supported, and the sources
archived. For the desperate,
the <link xmlns:xlink= "http://www.w3.org/1999/xlink" xlink:href= "http://gcc.gnu.org/extensions.html" > GCC extensions
page</link> describes where to find the last libg++ source. The code is
considered replaced and rewritten.
</para>
</section>
</section>
<section xml:id= "backwards.second" > <info > <title > Second</title> </info>
<para >
The second generation GNU C++ library was called libstdc++, or
libstdc++-v2. It spans the time between libg++ and pre-ISO C++
standardization and is usually associated with the following GCC
releases: egcs 1.x, gcc 2.95, and gcc 2.96.
</para>
<para >
The STL portions of this library are based on SGI/HP STL release 3.11.
</para>
<para >
This project is no longer maintained or supported, and the sources
archived. The code is considered replaced and rewritten.
</para>
<para >
Portability notes and known implementation limitations are as follows.
</para>
<section xml:id= "backwards.second.std" > <info > <title > Namespace <code > std::</code> not supported</title> </info>
<para >
Some care is required to support C++ compiler and or library
implementation that do not have the standard library in
<code > namespace std</code> .
</para>
<para >
The following sections list some possible solutions to support compilers
that cannot ignore <code > std::</code> -qualified names.
</para>
<para >
First, see if the compiler has a flag for this. Namespace
back-portability-issues are generally not a problem for g++
compilers that do not have libstdc++ in <code > std::</code> , as the
compilers use <option > -fno-honor-std</option> (ignore
<code > std::</code> , <code > :: = std::</code> ) by default. That is,
the responsibility for enabling or disabling <code > std::</code> is
on the user; the maintainer does not have to care about it. This
probably applies to some other compilers as well.
</para>
<para >
Second, experiment with a variety of pre-processor tricks.
</para>
<para >
By defining <code > std</code> as a macro, fully-qualified namespace
calls become global. Volia.
</para>
<programlisting >
#ifdef WICKEDLY_OLD_COMPILER
# define std
#endif
</programlisting>
<para >
Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help.
</para>
<para >
Another pre-processor based approach is to define a macro
<code > NAMESPACE_STD</code> , which is defined to either
<quote > </quote> or <quote > std</quote> based on a compile-type
test. On GNU systems, this can be done with autotools by means of
an autoconf test (see below) for <code > HAVE_NAMESPACE_STD</code> ,
then using that to set a value for the <code > NAMESPACE_STD</code>
macro. At that point, one is able to use
<code > NAMESPACE_STD::string</code> , which will evaluate to
<code > std::string</code> or <code > ::string</code> (i.e., in the
global namespace on systems that do not put <code > string</code> in
<code > std::</code> ).
</para>
<programlisting >
dnl @synopsis AC_CXX_NAMESPACE_STD
dnl
dnl If the compiler supports namespace std, define
dnl HAVE_NAMESPACE_STD.
dnl
dnl @category Cxx
dnl @author Todd Veldhuizen
dnl @author Luc Maisonobe < luc@spaceroots.org>
dnl @version 2004-02-04
dnl @license AllPermissive
AC_DEFUN([AC_CXX_NAMESPACE_STD], [
AC_CACHE_CHECK(if g++ supports namespace std,
ac_cv_cxx_have_std_namespace,
[AC_LANG_SAVE
AC_LANG_CPLUSPLUS
AC_TRY_COMPILE([#include < iostream>
std::istream& is = std::cin;],,
ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no)
AC_LANG_RESTORE
])
if test "$ac_cv_cxx_have_std_namespace" = yes; then
AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ])
fi
])
</programlisting>
</section>
<section xml:id= "backwards.second.iterators" > <info > <title > Illegal iterator usage</title> </info>
<para >
The following illustrate implementation-allowed illegal iterator
use, and then correct use.
</para>
<itemizedlist >
<listitem >
<para >
you cannot do <code > ostream::operator< < (iterator)</code>
to print the address of the iterator => use
<code > operator< < & *iterator</code> instead
</para>
</listitem>
<listitem >
<para >
you cannot clear an iterator's reference (<code > iterator =
0</code> ) => use <code > iterator = iterator_type();</code>
</para>
</listitem>
<listitem >
<para >
<code > if (iterator)</code> won't work any more => use
<code > if (iterator != iterator_type())</code>
</para>
</listitem>
</itemizedlist>
</section>
<section xml:id= "backwards.second.isspace" > <info > <title > <code > isspace</code> from <filename class= "headerfile" > < cctype> </filename> is a macro
</title> </info>
<para >
Glibc 2.0.x and 2.1.x define <filename class= "headerfile" > < ctype.h> </filename> functionality as macros
(isspace, isalpha etc.).
</para>
<para >
This implementations of libstdc++, however, keep these functions
as macros, and so it is not back-portable to use fully qualified
names. For example:
</para>
<programlisting >
#include < cctype>
int main() { std::isspace('X'); }
</programlisting>
<para >
Results in something like this:
</para>
<programlisting >
std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ;
</programlisting>
<para >
A solution is to modify a header-file so that the compiler tells
<filename class= "headerfile" > < ctype.h> </filename> to define functions
instead of macros:
</para>
<programlisting >
// This keeps isalnum, et al from being propagated as macros.
#if __linux__
# define __NO_CTYPE 1
#endif
</programlisting>
<para >
Then, include <filename class= "headerfile" > < ctype.h> </filename>
</para>
<para >
Another problem arises if you put a <code > using namespace
std;</code> declaration at the top, and include
<filename class= "headerfile" > < ctype.h> </filename> . This will
result in ambiguities between the definitions in the global namespace
(<filename class= "headerfile" > < ctype.h> </filename> ) and the
definitions in namespace <code > std::</code>
(<code > < cctype> </code> ).
</para>
</section>
<section xml:id= "backwards.second.at" > <info > <title > No <code > vector::at</code> , <code > deque::at</code> , <code > string::at</code> </title> </info>
<para >
One solution is to add an autoconf-test for this:
</para>
<programlisting >
AC_MSG_CHECKING(for container::at)
AC_TRY_COMPILE(
[
#include < vector>
#include < deque>
#include < string>
using namespace std;
],
[
deque< int> test_deque(3);
test_deque.at(2);
vector< int> test_vector(2);
test_vector.at(1);
string test_string(<quote > test_string</quote> );
test_string.at(3);
],
[AC_MSG_RESULT(yes)
AC_DEFINE(HAVE_CONTAINER_AT)],
[AC_MSG_RESULT(no)])
</programlisting>
<para >
If you are using other (non-GNU) compilers it might be a good idea
to check for <code > string::at</code> separately.
</para>
</section>
<section xml:id= "backwards.second.eof" > <info > <title > No <code > std::char_traits< char> ::eof</code> </title> </info>
<para >
Use some kind of autoconf test, plus this:
</para>
<programlisting >
#ifdef HAVE_CHAR_TRAITS
#define CPP_EOF std::char_traits< char> ::eof()
#else
#define CPP_EOF EOF
#endif
</programlisting>
</section>
<section xml:id= "backwards.second.stringclear" > <info > <title > No <code > string::clear</code> </title> </info>
<para >
There are two functions for deleting the contents of a string:
<code > clear</code> and <code > erase</code> (the latter returns the
string).
</para>
<programlisting >
void
clear() { _M_mutate(0, this-> size(), 0); }
</programlisting>
<programlisting >
basic_string&
erase(size_type __pos = 0, size_type __n = npos)
{
return this-> replace(_M_check(__pos), _M_fold(__pos, __n),
_M_data(), _M_data());
}
</programlisting>
<para >
Unfortunately, <code > clear</code> is not implemented in this
version, so you should use <code > erase</code> (which is probably
faster than <code > operator=(charT*)</code> ).
</para>
</section>
<section xml:id= "backwards.second.ostreamform_istreamscan" > <info > <title >
Removal of <code > ostream::form</code> and <code > istream::scan</code>
extensions
</title> </info>
<para >
These are no longer supported. Please use stringstreams instead.
</para>
</section>
<section xml:id= "backwards.second.stringstreams" > <info > <title > No <code > basic_stringbuf</code> , <code > basic_stringstream</code> </title> </info>
<para >
Although the ISO standard <code > i/ostringstream</code> -classes are
provided, (<filename class= "headerfile" > < sstream> </filename> ), for
compatibility with older implementations the pre-ISO
<code > i/ostrstream</code> (<filename class= "headerfile" > < strstream> </filename> ) interface is also provided,
with these caveats:
</para>
<itemizedlist >
<listitem >
<para >
<code > strstream</code> is considered to be deprecated
</para>
</listitem>
<listitem >
<para >
<code > strstream</code> is limited to <code > char</code>
</para>
</listitem>
<listitem >
<para >
with <code > ostringstream</code> you don't have to take care of
terminating the string or freeing its memory
</para>
</listitem>
<listitem >
<para >
<code > istringstream</code> can be re-filled (clear();
str(input);)
</para>
</listitem>
</itemizedlist>
<para >
You can then use output-stringstreams like this:
</para>
<programlisting >
#ifdef HAVE_SSTREAM
# include < sstream>
#else
# include < strstream>
#endif
#ifdef HAVE_SSTREAM
std::ostringstream oss;
#else
std::ostrstream oss;
#endif
2015-08-28 15:33:40 +00:00
oss < < "Name=" < < m_name < < ", number=" < < m_number < < std::endl;
2012-03-27 23:13:14 +00:00
...
#ifndef HAVE_SSTREAM
oss < < std::ends; // terminate the char*-string
#endif
// str() returns char* for ostrstream and a string for ostringstream
// this also causes ostrstream to think that the buffer's memory
// is yours
m_label.set_text(oss.str());
#ifndef HAVE_SSTREAM
// let the ostrstream take care of freeing the memory
oss.freeze(false);
#endif
</programlisting>
<para >
Input-stringstreams can be used similarly:
</para>
<programlisting >
std::string input;
...
#ifdef HAVE_SSTREAM
std::istringstream iss(input);
#else
std::istrstream iss(input.c_str());
#endif
int i;
iss > > i;
</programlisting>
<para > One (the only?) restriction is that an istrstream cannot be re-filled:
</para>
<programlisting >
std::istringstream iss(numerator);
iss > > m_num;
// this is not possible with istrstream
iss.clear();
iss.str(denominator);
iss > > m_den;
</programlisting>
<para >
If you don't care about speed, you can put these conversions in
a template-function:
</para>
<programlisting >
template < class X>
void fromString(const string& input, X& any)
{
#ifdef HAVE_SSTREAM
std::istringstream iss(input);
#else
std::istrstream iss(input.c_str());
#endif
X temp;
iss > > temp;
if (iss.fail())
throw runtime_error(..)
any = temp;
}
</programlisting>
<para >
Another example of using stringstreams is in <link linkend= "strings.string.shrink" > this howto</link> .
</para>
<para > There is additional information in the libstdc++-v2 info files, in
particular <quote > info iostream</quote> .
</para>
</section>
<section xml:id= "backwards.second.wchar" > <info > <title > Little or no wide character support</title> </info>
<para >
Classes <classname > wstring</classname> and
<classname > char_traits< wchar_t> </classname> are
not supported.
</para>
</section>
<section xml:id= "backwards.second.iostream_templates" > <info > <title > No templatized iostreams</title> </info>
<para >
Classes <classname > wfilebuf</classname> and
<classname > wstringstream</classname> are not supported.
</para>
</section>
<section xml:id= "backwards.second.thread_safety" > <info > <title > Thread safety issues</title> </info>
<para >
Earlier GCC releases had a somewhat different approach to
threading configuration and proper compilation. Before GCC 3.0,
configuration of the threading model was dictated by compiler
command-line options and macros (both of which were somewhat
thread-implementation and port-specific). There were no
guarantees related to being able to link code compiled with one
set of options and macro setting with another set.
</para>
<para >
For GCC 3.0, configuration of the threading model used with
libraries and user-code is performed when GCC is configured and
built using the --enable-threads and --disable-threads options.
The ABI is stable for symbol name-mangling and limited functional
compatibility exists between code compiled under different
threading models.
</para>
<para >
The libstdc++ library has been designed so that it can be used in
multithreaded applications (with libstdc++-v2 this was only true
of the STL parts.) The first problem is finding a
<emphasis > fast</emphasis> method of implementation portable to
all platforms. Due to historical reasons, some of the library is
written against per-CPU-architecture spinlocks and other parts
against the gthr.h abstraction layer which is provided by gcc. A
minor problem that pops up every so often is different
interpretations of what "thread-safe" means for a
2018-12-28 15:30:48 +00:00
library (not a general program). We currently use the <link xmlns:xlink= "http://www.w3.org/1999/xlink" xlink:href= "https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/thread_safety.html" > same
2012-03-27 23:13:14 +00:00
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
2014-09-21 17:33:12 +00:00
(clauses 23 through 25, mostly) is adapted from the final release
2012-03-27 23:13:14 +00:00
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>
2017-10-07 00:16:47 +00:00
<section xml:id= "backwards.third.headers" > <info > <title > Pre-ISO headers removed</title> </info>
2012-03-27 23:13:14 +00:00
<para > The pre-ISO C++ headers
(<filename class= "headerfile" > < iostream.h> </filename> ,
<filename class= "headerfile" > < defalloc.h> </filename> etc.) are
2017-10-07 00:16:47 +00:00
not supported.
2012-03-27 23:13:14 +00:00
</para>
2017-10-07 00:16:47 +00:00
<para > For those of you new to ISO C++ (welcome, time travelers!), the
ancient pre-ISO headers have new names.
The C++ FAQ has a good explanation in <link xmlns:xlink= "http://www.w3.org/1999/xlink" xlink:href= "https://isocpp.org/wiki/faq/coding-standards#std-headers" > What's
2014-09-21 17:33:12 +00:00
the difference between < xxx> and < xxx.h> headers?</link> .
2012-03-27 23:13:14 +00:00
</para>
<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>
2014-09-21 17:33:12 +00:00
<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> .
2012-03-27 23:13:14 +00:00
</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.
2019-06-02 15:48:37 +00:00
<filename class= "headerfile" > < ext/stdio_filebuf.h> </filename>
contains a derived class called
<classname > __gnu_cxx::stdio_filebuf</classname> .
2012-03-27 23:13:14 +00:00
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"
2017-10-07 00:16:47 +00:00
xlink:href="https://lists.debian.org/debian-gcc/2006/03/msg00405.html">
2012-03-27 23:13:14 +00:00
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>
