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libstdc++: Remove outdated docs on libg++ and libstdc++-v2

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The libstdc++-v3 manual doesn't need to document how to use its
predecessors.

libstdc++-v3/ChangeLog:

	* doc/xml/manual/backwards_compatibility.xml: Remove porting
	notes for libg++ and libstdc++-v2, and bibliography.
	* doc/html/*: Regenerated.
This commit is contained in:
Jonathan Wakely 2021-04-13 16:30:16 +01:00
parent 39fa0de599
commit 989e512f71
6 changed files with 25 additions and 934 deletions
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@ -8,7 +8,7 @@ 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&lt;T&gt;</code> and do not need to be
provided for by <code class="classname">std::list&lt;T&gt;</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
@ -16,351 +16,24 @@ 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">“<span class="quote">obvious</span>”</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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.first.ios_base"></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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.first.cout_cin"></a>No <code class="code">cout</code> in <code class="filename">&lt;ostream.h&gt;</code>, no <code class="code">cin</code> in <code class="filename">&lt;istream.h&gt;</code></h4></div></div></div><p>
In earlier versions of the standard,
<code class="filename">&lt;fstream.h&gt;</code>,
<code class="filename">&lt;ostream.h&gt;</code>
and <code class="filename">&lt;istream.h&gt;</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">&lt;iostream&gt;</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="link" 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="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p>
</p><p>That project is no longer maintained or supported, and the sources
archived. For the desperate, the
<a class="link" href="https://ftp.gnu.org/old-gnu/libg++/" target="_top">ftp.gnu.org</a>
server still has the libg++ source.
</p></div><div class="section"><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.
The STL portions of that 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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.std"></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="option">-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 class="quote"> </span>”</span> or <span class="quote">“<span class="quote">std</span>”</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 &lt;luc@spaceroots.org&gt;
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 &lt;iostream&gt;
std::istream&amp; 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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.iterators"></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 class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
you cannot do <code class="code">ostream::operator&lt;&lt;(iterator)</code>
to print the address of the iterator =&gt; use
<code class="code">operator&lt;&lt; &amp;*iterator</code> instead
</p></li><li class="listitem"><p>
you cannot clear an iterator's reference (<code class="code">iterator =
0</code>) =&gt; use <code class="code">iterator = iterator_type();</code>
</p></li><li class="listitem"><p>
<code class="code">if (iterator)</code> won't work any more =&gt; use
<code class="code">if (iterator != iterator_type())</code>
</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.isspace"></a><code class="code">isspace</code> from <code class="filename">&lt;cctype&gt;</code> is a macro
</h4></div></div></div><p>
Glibc 2.0.x and 2.1.x define <code class="filename">&lt;ctype.h&gt;</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 &lt;cctype&gt;
int main() { std::isspace('X'); }
</pre><p>
Results in something like this:
</p><pre class="programlisting">
std:: (__ctype_b[(int) ( ( 'X' ) )] &amp; (unsigned short int) _ISspace ) ;
</pre><p>
A solution is to modify a header-file so that the compiler tells
<code class="filename">&lt;ctype.h&gt;</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">&lt;ctype.h&gt;</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">&lt;ctype.h&gt;</code>. This will
result in ambiguities between the definitions in the global namespace
(<code class="filename">&lt;ctype.h&gt;</code>) and the
definitions in namespace <code class="code">std::</code>
(<code class="code">&lt;cctype&gt;</code>).
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.at"></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 &lt;vector&gt;
#include &lt;deque&gt;
#include &lt;string&gt;
using namespace std;
],
[
deque&lt;int&gt; test_deque(3);
test_deque.at(2);
vector&lt;int&gt; test_vector(2);
test_vector.at(1);
string test_string(<span class="quote">“<span class="quote">test_string</span>”</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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.eof"></a>No <code class="code">std::char_traits&lt;char&gt;::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&lt;char&gt;::eof()
#else
#define CPP_EOF EOF
#endif
</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.stringclear"></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-&gt;size(), 0); }
</pre><pre class="programlisting">
basic_string&amp;
erase(size_type __pos = 0, size_type __n = npos)
{
return this-&gt;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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.ostreamform_istreamscan"></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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.stringstreams"></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">&lt;sstream&gt;</code>), for
compatibility with older implementations the pre-ISO
<code class="code">i/ostrstream</code> (<code class="filename">&lt;strstream&gt;</code>) interface is also provided,
with these caveats:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<code class="code">strstream</code> is considered to be deprecated
</p></li><li class="listitem"><p>
<code class="code">strstream</code> is limited to <code class="code">char</code>
</p></li><li class="listitem"><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 class="listitem"><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 &lt;sstream&gt;
#else
# include &lt;strstream&gt;
#endif
#ifdef HAVE_SSTREAM
std::ostringstream oss;
#else
std::ostrstream oss;
#endif
oss &lt;&lt; "Name=" &lt;&lt; m_name &lt;&lt; ", number=" &lt;&lt; m_number &lt;&lt; std::endl;
...
#ifndef HAVE_SSTREAM
oss &lt;&lt; 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 &gt;&gt; i;
</pre><p> One (the only?) restriction is that an istrstream cannot be re-filled:
</p><pre class="programlisting">
std::istringstream iss(numerator);
iss &gt;&gt; m_num;
// this is not possible with istrstream
iss.clear();
iss.str(denominator);
iss &gt;&gt; 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 &lt;class X&gt;
void fromString(const string&amp; input, X&amp; any)
{
#ifdef HAVE_SSTREAM
std::istringstream iss(input);
#else
std::istrstream iss(input.c_str());
#endif
X temp;
iss &gt;&gt; temp;
if (iss.fail())
throw runtime_error(..)
any = temp;
}
</pre><p>
Another example of using stringstreams is in <a class="link" href="strings.html#strings.string.shrink" title="Shrink to Fit">this howto</a>.
</p><p> There is additional information in the libstdc++-v2 info files, in
particular <span class="quote">“<span class="quote">info iostream</span>”</span>.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.wchar"></a>Little or no wide character support</h4></div></div></div><p>
Classes <code class="classname">wstring</code> and
<code class="classname">char_traits&lt;wchar_t&gt;</code> are
not supported.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.iostream_templates"></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="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.thread_safety"></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="link" href="https://web.archive.org/web/20171225062613/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 class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
Our threading expert Loren gives a breakdown of <a class="link" 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 class="listitem"><p>
<a class="link" 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="section"><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
That project is no longer maintained or supported, and the sources
archived. The code was replaced and rewritten for libstdc++-v3.
</p></div><div class="section"><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
(clauses 23 through 25, mostly) is adapted from the final release
(clauses 23 through 25 in C++98, 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="link" href="source_design_notes.html" title="Design Notes">design document</a>.
@ -888,19 +561,7 @@ AC_DEFUN([AC_HEADER_UNORDERED_SET], [
This is a change in behavior from older versions. 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="id-1.3.6.3.8.5.2"></a><p><span class="title"><em>
<a class="link" href="http://www.kegel.com/gcc/gcc4.html" target="_top">
Migrating to GCC 4.1
</a>
</em>. </span><span class="author"><span class="firstname">Dan</span> <span class="surname">Kegel</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.8.5.3"></a><p><span class="title"><em>
<a class="link" href="https://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top">
Building the Whole Debian Archive with GCC 4.1: A Summary
</a>
</em>. </span><span class="author"><span class="firstname">Martin</span> <span class="surname">Michlmayr</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.8.5.4"></a><p><span class="title"><em>
<a class="link" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top">
Migration guide for GCC-3.2
</a>
</em>. </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="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix C. 
</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="../index.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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@ -22,7 +22,7 @@ dinosaur.
<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&lt;T&gt;</classname> and do not need to be
provided for by <classname>std::list&lt;T&gt;</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>
@ -34,41 +34,13 @@ 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>That 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="https://ftp.gnu.org/old-gnu/libg++/">ftp.gnu.org</link>
server still has the libg++ source.
</para>
</section>
<section xml:id="backwards.first.cout_cin"><info><title>No <code>cout</code> in <filename class="headerfile">&lt;ostream.h&gt;</filename>, no <code>cin</code> in <filename class="headerfile">&lt;istream.h&gt;</filename></title></info>
<para>
In earlier versions of the standard,
<filename class="headerfile">&lt;fstream.h&gt;</filename>,
<filename class="headerfile">&lt;ostream.h&gt;</filename>
and <filename class="headerfile">&lt;istream.h&gt;</filename>
used to define
<code>cout</code>, <code>cin</code> and so on. ISO C++ specifies that one needs to include
<filename class="headerfile">&lt;iostream&gt;</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>
@ -80,504 +52,14 @@ considered replaced and rewritten.
</para>
<para>
The STL portions of this library are based on SGI/HP STL release 3.11.
The STL portions of that 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.
That project is no longer maintained or supported, and the sources
archived. The code was replaced and rewritten for libstdc++-v3.
</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 &lt;luc@spaceroots.org&gt;
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 &lt;iostream&gt;
std::istream&amp; 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&lt;&lt;(iterator)</code>
to print the address of the iterator =&gt; use
<code>operator&lt;&lt; &amp;*iterator</code> instead
</para>
</listitem>
<listitem>
<para>
you cannot clear an iterator's reference (<code>iterator =
0</code>) =&gt; use <code>iterator = iterator_type();</code>
</para>
</listitem>
<listitem>
<para>
<code>if (iterator)</code> won't work any more =&gt; 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">&lt;cctype&gt;</filename> is a macro
</title></info>
<para>
Glibc 2.0.x and 2.1.x define <filename class="headerfile">&lt;ctype.h&gt;</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 &lt;cctype&gt;
int main() { std::isspace('X'); }
</programlisting>
<para>
Results in something like this:
</para>
<programlisting>
std:: (__ctype_b[(int) ( ( 'X' ) )] &amp; (unsigned short int) _ISspace ) ;
</programlisting>
<para>
A solution is to modify a header-file so that the compiler tells
<filename class="headerfile">&lt;ctype.h&gt;</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">&lt;ctype.h&gt;</filename>
</para>
<para>
Another problem arises if you put a <code>using namespace
std;</code> declaration at the top, and include
<filename class="headerfile">&lt;ctype.h&gt;</filename>. This will
result in ambiguities between the definitions in the global namespace
(<filename class="headerfile">&lt;ctype.h&gt;</filename>) and the
definitions in namespace <code>std::</code>
(<code>&lt;cctype&gt;</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 &lt;vector&gt;
#include &lt;deque&gt;
#include &lt;string&gt;
using namespace std;
],
[
deque&lt;int&gt; test_deque(3);
test_deque.at(2);
vector&lt;int&gt; 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&lt;char&gt;::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&lt;char&gt;::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-&gt;size(), 0); }
</programlisting>
<programlisting>
basic_string&amp;
erase(size_type __pos = 0, size_type __n = npos)
{
return this-&gt;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">&lt;sstream&gt;</filename>), for
compatibility with older implementations the pre-ISO
<code>i/ostrstream</code> (<filename class="headerfile">&lt;strstream&gt;</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 &lt;sstream&gt;
#else
# include &lt;strstream&gt;
#endif
#ifdef HAVE_SSTREAM
std::ostringstream oss;
#else
std::ostrstream oss;
#endif
oss &lt;&lt; "Name=" &lt;&lt; m_name &lt;&lt; ", number=" &lt;&lt; m_number &lt;&lt; std::endl;
...
#ifndef HAVE_SSTREAM
oss &lt;&lt; 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 &gt;&gt; i;
</programlisting>
<para> One (the only?) restriction is that an istrstream cannot be re-filled:
</para>
<programlisting>
std::istringstream iss(numerator);
iss &gt;&gt; m_num;
// this is not possible with istrstream
iss.clear();
iss.str(denominator);
iss &gt;&gt; m_den;
</programlisting>
<para>
If you don't care about speed, you can put these conversions in
a template-function:
</para>
<programlisting>
template &lt;class X&gt;
void fromString(const string&amp; input, X&amp; any)
{
#ifdef HAVE_SSTREAM
std::istringstream iss(input);
#else
std::istrstream iss(input.c_str());
#endif
X temp;
iss &gt;&gt; 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&lt;wchar_t&gt;</classname> are
not supported.
</para>
</section>
<section xml:id="backwards.second.iostream_templates"><info><title>No templatized iostreams</title></info>
<para>
Classes <classname>wfilebuf</classname> and
<classname>wstringstream</classname> are not supported.
</para>
</section>
<section xml:id="backwards.second.thread_safety"><info><title>Thread safety issues</title></info>
<para>
Earlier GCC releases had a somewhat different approach to
threading configuration and proper compilation. Before GCC 3.0,
configuration of the threading model was dictated by compiler
command-line options and macros (both of which were somewhat
thread-implementation and port-specific). There were no
guarantees related to being able to link code compiled with one
set of options and macro setting with another set.
</para>
<para>
For GCC 3.0, configuration of the threading model used with
libraries and user-code is performed when GCC is configured and
built using the --enable-threads and --disable-threads options.
The ABI is stable for symbol name-mangling and limited functional
compatibility exists between code compiled under different
threading models.
</para>
<para>
The libstdc++ library has been designed so that it can be used in
multithreaded applications (with libstdc++-v2 this was only true
of the STL parts.) The first problem is finding a
<emphasis>fast</emphasis> method of implementation portable to
all platforms. Due to historical reasons, some of the library is
written against per-CPU-architecture spinlocks and other parts
against the gthr.h abstraction layer which is provided by gcc. A
minor problem that pops up every so often is different
interpretations of what "thread-safe" means for a
library (not a general program). We currently use the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://web.archive.org/web/20171225062613/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>
@ -588,7 +70,7 @@ libstdc++-v3.
</para>
<para>The subset commonly known as the Standard Template Library
(clauses 23 through 25, mostly) is adapted from the final release
(clauses 23 through 25 in C++98, mostly) is adapted from the final release
of the SGI STL (version 3.3), with extensive changes.
</para>
@ -1223,40 +705,4 @@ AC_DEFUN([AC_HEADER_UNORDERED_SET], [
</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>