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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_config.guidelines_for_boost_authors"></a><a class="link" href="guidelines_for_boost_authors.html" title="Guidelines for Boost Authors">Guidelines for
Boost Authors</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.warnings">
Disabling Compiler Warnings</a></span></dt>
<dt><span class="section"><a href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.adding_new_defect_macros">Adding
New Defect Macros</a></span></dt>
<dt><span class="section"><a href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.adding_new_feature_test_macros">Adding
New Feature Test Macros</a></span></dt>
<dt><span class="section"><a href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.modifying_the_boost_configuration_headers">Modifying
the Boost Configuration Headers</a></span></dt>
</dl></div>
<p>
The <a href="../../../../../boost/config.hpp" target="_top"><boost/config.hpp></a>
header is used to pass configuration information to other boost files, allowing
them to cope with platform dependencies such as arithmetic byte ordering, compiler
pragmas, or compiler shortcomings. Without such configuration information,
many current compilers would not work with the Boost libraries.
</p>
<p>
Centralizing configuration information in this header reduces the number of
files that must be modified when porting libraries to new platforms, or when
compilers are updated. Ideally, no other files would have to be modified when
porting to a new platform.
</p>
<p>
Configuration headers are controversial because some view them as condoning
broken compilers and encouraging non-standard subsets. Adding settings for
additional platforms and maintaining existing settings can also be a problem.
In other words, configuration headers are a necessary evil rather than a desirable
feature. The boost config.hpp policy is designed to minimize the problems and
maximize the benefits of a configuration header.
</p>
<p>
Note that:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
Boost library implementers are not required to "<code class="computeroutput"><span class="preprocessor">#include</span>
<span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>", and are not required in any
way to support compilers that do not comply with the C++ Standard (ISO/IEC
14882).
</li>
<li class="listitem">
If a library implementer wishes to support some non-conforming compiler,
or to support some platform specific feature, "<code class="computeroutput"><span class="preprocessor">#include</span>
<span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>" is the preferred way to obtain
configuration information not available from the standard headers such
as <code class="computeroutput"><span class="special"><</span><span class="identifier">climits</span><span class="special">></span></code>, etc.
</li>
<li class="listitem">
If configuration information can be deduced from standard headers such
as <code class="computeroutput"><span class="special"><</span><span class="identifier">climits</span><span class="special">></span></code>, use those standard headers rather
than <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>.
</li>
<li class="listitem">
Boost files that use macros defined in <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
should have sensible, standard conforming, default behavior if the macro
is not defined. This means that the starting point for porting <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> to a new platform is simply to define
nothing at all specific to that platform. In the rare case where there
is no sensible default behavior, an #error message should describe the
problem.
</li>
<li class="listitem">
If a Boost library implementer wants something added to <code class="computeroutput"><span class="identifier">config</span><span class="special">.</span><span class="identifier">hpp</span></code>,
post a request on the Boost mailing list. There is no guarantee such a
request will be honored; the intent is to limit the complexity of config.hpp.
</li>
<li class="listitem">
The intent is to support only compilers which appear on their way to becoming
C++ Standard compliant, and only recent releases of those compilers at
that.
</li>
<li class="listitem">
The intent is not to disable mainstream features now well-supported by
the majority of compilers, such as namespaces, exceptions, RTTI, or templates.
</li>
</ul></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_config.guidelines_for_boost_authors.warnings"></a><a class="link" href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.warnings" title="Disabling Compiler Warnings">
Disabling Compiler Warnings</a>
</h3></div></div></div>
<p>
The header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">config</span><span class="special">/</span><span class="identifier">warning_disable</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
can be used to disable certain compiler warings that are hard or impossible
to otherwise remove.
</p>
<p>
Note that:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
This header <span class="bold"><strong><span class="emphasis"><em>should never be included
by another Boost header</em></span></strong></span>, it should only ever be
used by a library source file or a test case.
</li>
<li class="listitem">
The header should be included <span class="bold"><strong><span class="emphasis"><em>before
you include any other header</em></span></strong></span>.
</li>
<li class="listitem">
This header only disables warnings that are hard or impossible to otherwise
deal with, and which are typically emitted by one compiler only, or in
one compilers own standard library headers.
</li>
</ul></div>
<p>
Currently it disables the following warnings:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Compiler
</p>
</th>
<th>
<p>
Warning
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Visual C++ 8 and later
</p>
</td>
<td>
<p>
<a href="http://msdn2.microsoft.com/en-us/library/ttcz0bys(VS.80).aspx" target="_top">C4996</a>:
Error 'function': was declared deprecated
</p>
</td>
</tr>
<tr>
<td>
<p>
Intel C++
</p>
</td>
<td>
<p>
Warning 1786: relates to the use of "deprecated" standard
library functions rather like C4996 in Visual C++.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_config.guidelines_for_boost_authors.adding_new_defect_macros"></a><a class="link" href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.adding_new_defect_macros" title="Adding New Defect Macros">Adding
New Defect Macros</a>
</h3></div></div></div>
<p>
When you need to add a new defect macro - either to fix a problem with an
existing library, or when adding a new library - distil the issue down to
a simple test case; often, at this point other (possibly better) workarounds
may become apparent. Secondly always post the test case code to the boost
mailing list and invite comments; remember that C++ is complex and that sometimes
what may appear a defect, may in fact turn out to be a problem with the authors
understanding of the standard.
</p>
<p>
When you name the macro, follow the <code class="computeroutput"><span class="identifier">BOOST_NO_</span></code><span class="emphasis"><em>SOMETHING</em></span>
naming convention, so that it's obvious that this is a macro reporting a
defect.
</p>
<p>
Finally, add the test program to the regression tests. You will need to place
the test case in a <code class="computeroutput"><span class="special">.</span><span class="identifier">ipp</span></code>
file with the following comments near the top:
</p>
<pre class="programlisting"><span class="comment">// MACRO: BOOST_NO_FOO
</span><span class="comment">// TITLE: foo
</span><span class="comment">// DESCRIPTION: If the compiler fails to support foo
</span></pre>
<p>
These comments are processed by the autoconf script, so make sure the format
follows the one given. The file should be named "<code class="computeroutput"><span class="identifier">boost_no_foo</span><span class="special">.</span><span class="identifier">ipp</span></code>",
where foo is the defect description - try and keep the file name under the
Mac 30 character filename limit though. You will also need to provide a function
prototype "<code class="computeroutput"><span class="keyword">int</span> <span class="identifier">test</span><span class="special">()</span></code>" that is declared in a namespace with
the same name as the macro, but in all lower case, and which returns zero
on success:
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost_no_foo</span> <span class="special">{</span>
<span class="keyword">int</span> <span class="identifier">test</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// test code goes here:
</span> <span class="comment">//
</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<p>
Once the test code is in place in libs/config/test, updating the configuration
test system proceeds as:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
cd into <code class="computeroutput"><span class="identifier">libs</span><span class="special">/</span><span class="identifier">config</span><span class="special">/</span><span class="identifier">tools</span></code> and run <code class="computeroutput"><span class="identifier">bjam</span></code>.
This generates the <code class="computeroutput"><span class="special">.</span><span class="identifier">cpp</span></code>
file test cases from the <code class="computeroutput"><span class="special">.</span><span class="identifier">ipp</span></code> file, updates the libs/config/test/all/Jamfile.v2,
<code class="computeroutput"><span class="identifier">config_test</span><span class="special">.</span><span class="identifier">cpp</span></code> and <code class="computeroutput"><span class="identifier">config_info</span><span class="special">.</span><span class="identifier">cpp</span></code>.<br>
<br>
</li>
<li class="listitem">
cd into <code class="computeroutput"><span class="identifier">libs</span><span class="special">/</span><span class="identifier">config</span><span class="special">/</span><span class="identifier">test</span><span class="special">/</span><span class="identifier">all</span></code> and run <code class="computeroutput"><span class="identifier">bjam</span>
</code><span class="emphasis"><em>MACRONAME<code class="computeroutput"> <span class="identifier">compiler</span><span class="special">-</span><span class="identifier">list</span></code></em></span>,
where <span class="emphasis"><em>MACRONAME</em></span> is the name of the new macro, and
<span class="emphasis"><em><code class="computeroutput"><span class="identifier">compiler</span><span class="special">-</span><span class="identifier">list</span></code></em></span> is a space separated
list of compilers to test with.<br> <br> The xxx_pass_test and the
xxx_fail_test <span class="bold"><strong>should both report <code class="computeroutput"><span class="special">**</span><span class="identifier">passed</span><span class="special">**</span></code></strong></span>.<br> <br> If <span class="emphasis"><em>MACRONAME</em></span>
is not defined when it should be defined, xxx_pass_test will not report
<code class="computeroutput"><span class="special">**</span><span class="identifier">passed</span><span class="special">**</span></code>. If <span class="emphasis"><em>MACRONAME</em></span>
is defined when it should not be defined, xxx_fail_test will not report
<code class="computeroutput"><span class="special">**</span><span class="identifier">passed</span><span class="special">**</span></code>.<br> <br>
</li>
<li class="listitem">
cd into <code class="computeroutput"><span class="identifier">libs</span><span class="special">/</span><span class="identifier">config</span><span class="special">/</span><span class="identifier">test</span></code> and run <code class="computeroutput"><span class="identifier">bjam</span>
<span class="identifier">config_info</span> <span class="identifier">config_test</span>
</code><span class="emphasis"><em><code class="computeroutput"><span class="identifier">compiler</span><span class="special">-</span><span class="identifier">list</span></code></em></span>.
<code class="computeroutput"><span class="identifier">config_info</span></code> should build
and run cleanly for all the compilers in <span class="emphasis"><em><code class="computeroutput"><span class="identifier">compiler</span><span class="special">-</span><span class="identifier">list</span></code></em></span>
while <code class="computeroutput"><span class="identifier">config_test</span></code> should
fail for those that have the defect, and pass for those that do not.
</li>
</ul></div>
<p>
Then you should:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
Define the defect macro in those config headers that require it.
</li>
<li class="listitem">
Document the macro in this documentation (please do not forget this step!!)
</li>
<li class="listitem">
Commit everything.
</li>
<li class="listitem">
Keep an eye on the regression tests for new failures in Boost.Config
caused by the addition.
</li>
<li class="listitem">
Start using the macro.
</li>
</ul></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_config.guidelines_for_boost_authors.adding_new_feature_test_macros"></a><a class="link" href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.adding_new_feature_test_macros" title="Adding New Feature Test Macros">Adding
New Feature Test Macros</a>
</h3></div></div></div>
<p>
When you need to add a macro that describes a feature that the standard does
not require, follow the convention for adding a new defect macro (above),
but call the macro <code class="computeroutput"><span class="identifier">BOOST_HAS_FOO</span></code>,
and name the test file "<code class="computeroutput"><span class="identifier">boost_has_foo</span><span class="special">.</span><span class="identifier">ipp</span></code>".
Try not to add feature test macros unnecessarily, if there is a platform
specific macro that can already be used (for example <code class="computeroutput"><span class="identifier">_WIN32</span></code>,
<code class="computeroutput"><span class="identifier">__BEOS__</span></code>, or <code class="computeroutput"><span class="identifier">__linux</span></code>) to identify the feature then use
that. Try to keep the macro to a feature group, or header name, rather than
one specific API (for example <code class="computeroutput"><span class="identifier">BOOST_HAS_NL_TYPES_H</span></code>
rather than <code class="computeroutput"><span class="identifier">BOOST_HAS_CATOPEN</span></code>).
If the macro describes a POSIX feature group, then add boilerplate code to
<a href="../../../../../boost/config/user.hpp" target="_top"><boost/config/suffix.hpp></a>
to auto-detect the feature where possible (if you are wondering why we can't
use POSIX feature test macro directly, remember that many of these features
can be added by third party libraries, and are not therefore identified inside
<code class="computeroutput"><span class="special"><</span><span class="identifier">unistd</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span></code>).
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_config.guidelines_for_boost_authors.modifying_the_boost_configuration_headers"></a><a class="link" href="guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.modifying_the_boost_configuration_headers" title="Modifying the Boost Configuration Headers">Modifying
the Boost Configuration Headers</a>
</h3></div></div></div>
<p>
The aim of boost's configuration setup is that the configuration headers
should be relatively stable - a boost user should not have to recompile their
code just because the configuration for some compiler that they're not interested
in has changed. Separating the configuration into separate compiler/standard
library/platform sections provides for part of this stability, but boost
authors require some amount of restraint as well, in particular:
</p>
<p>
<a href="../../../../../boost/config.hpp" target="_top"><boost/config.hpp></a>
should never change, don't alter this file.
</p>
<p>
<a href="../../../../../boost/config/user.hpp" target="_top"><boost/config/user.hpp></a>
is included by default, don't add extra code to this file unless you have
to. If you do, please remember to update <a href="../../../tools/configure.in" target="_top">libs/config/tools/configure.in</a>
as well.
</p>
<p>
<a href="../../../../../boost/config/user.hpp" target="_top"><boost/config/suffix.hpp></a>
is always included so be careful about modifying this file as it breaks dependencies
for everyone. This file should include only "boilerplate" configuration
code, and generally should change only when new macros are added.
</p>
<p>
<a href="../../../../../boost/config/select_compiler_config.hpp" target="_top"><boost/config/select_compiler_config.hpp></a>,
<a href="../../../../../boost/config/select_platform_config.hpp" target="_top"><boost/config/select_platform_config.hpp></a>
and <a href="../../../../../boost/config/select_stdlib_config.hpp" target="_top"><boost/config/select_stdlib_config.hpp></a>
are included by default and should change only if support for a new compiler/standard
library/platform is added.
</p>
<p>
The compiler/platform/standard library selection code is set up so that unknown
platforms are ignored and assumed to be fully standards compliant - this
gives unknown platforms a "sporting chance" of working "as
is" even without running the configure script.
</p>
<p>
When adding or modifying the individual mini-configs, assume that future,
as yet unreleased versions of compilers, have all the defects of the current
version. Although this is perhaps unnecessarily pessimistic, it cuts down
on the maintenance of these files, and experience suggests that pessimism
is better placed than optimism here!
</p>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001 -2007 Beman Dawes, Vesa Karvonen, John Maddock<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
</tr></table>
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