2000-07-27 14:04:40 +00:00
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<td bgcolor="#FFFFFF"><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" width="277" height="86"></td>
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<td><a href="../../index.htm"><font face="Arial" color="#FFFFFF"><big>Home</big></font></a></td>
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2000-11-10 15:39:05 +00:00
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<td><a href="../libraries.htm"><font face="Arial" color="#FFFFFF"><big>Libraries</big></font></a></td>
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<td><a href="../../people/people.htm"><font face="Arial" color="#FFFFFF"><big>People</big></font></a></td>
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2000-07-27 14:04:40 +00:00
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<td><a href="../../more/faq.htm"><font face="Arial" color="#FFFFFF"><big>FAQ</big></font></a></td>
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<h1>Configuration Header <a href="../../boost/config.hpp">boost/config.hpp</a></h1>
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<p>The <a href="../../boost/config.hpp">boost/config.hpp</a> header is used to
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pass configuration information to other boost files, allowing them to cope with
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platform dependencies such as arithmetic byte ordering, compiler pragmas, or
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compiler shortcomings. Without such configuration information, many current
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compilers would not work with the Boost libraries.</p>
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<p>Centralizing configuration information is this header reduces the number of
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files which must be modified when porting libraries to new platforms, or when
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compilers are updated. Ideally, no other files would have to be modified when
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porting to a new platform.</p>
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<p>Configuration headers are controversial because some view them as condoning
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broken compilers and encouraging non-standard subsets. Adding settings for
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additional platforms and maintaining existing settings can also be a problem. In
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other words, configuration headers are a necessary evil rather than a desirable
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feature. The boost config.hpp policy is designed to minimize the problems and
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maximize the benefits of a configuration header.</p>
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<h2>Boost config.hpp policy</h2>
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<p>For Library Users:</p>
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<ul>
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<li>Boost library users are never required to #include boost/config.hpp, and
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are discouraged from including it on their own.</li>
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<li>Boost library users can request support for additional platforms be added
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to config.hpp by emailing <a href="mailto:config@boost.org">config@boost.org</a>
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describing their request.</li>
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</ul>
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<p>For Library Implementors:</p>
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<ul>
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<li>Boost library implementors are not required to #include boost/config.hpp,
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and are not required in any way to support compilers which do not comply
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with the C++ Standard (ISO/IEC 14882).</li>
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<li>If a library implementor wishes to support some nonconforming compiler, or
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to support some platform specific feature, #include boost/config.hpp is the
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preferred way to obtain configuration information not available from the
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standard headers such as <climits>, etc.</li>
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<li>If configuration information can be deduced from standard headers such as
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<climits>, use those standard headers rather than boost/config.hpp.</li>
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<li>Boost files that use macros defined in boost/config.hpp should have
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sensible, standard conforming, default behavior if the macro is not defined.
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This means that the starting point for porting boost/config.hpp to a new
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platform is simply to define nothing at all specific to that platform. In
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the rare case where there is no sensible default behavior, an #error message
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should describe the problem.</li>
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<li>If a Boost library implementor wants something added to config.hpp, post a
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request on the Boost mailing list. There is no guarantee such a request will
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be honored; the intent is to limit the complexity of config.hpp.</li>
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</ul>
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<p>General:</p>
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<ul>
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<li>The intent is to support only compilers which appear on their way to
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becoming C++ Standard compliant, and only recent releases of those compilers
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at that.</li>
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<li>The intent is not to disable mainstream features now well-supported by the
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majority of compilers, such as namespaces, exceptions, RTTI, or templates.</li>
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</ul>
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<h2>Documentation</h2>
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<p>See <a href="../../boost/config.hpp">boost/config.hpp</a>; it is designed to
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be self documenting.</p>
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<h2>Test program</h2>
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<p>The <a href="config_test.cpp">config_test.cpp</a> program can be used to
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verify which #defines are in effect for your compiler.</p>
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<hr>
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2000-11-10 15:39:05 +00:00
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<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan -->10 Nov 2000<!--webbot bot="Timestamp" endspan i-checksum="15233" --></p>
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2000-07-27 14:04:40 +00:00
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