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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Preprocessor macro expansion bug on Windows"
href="https://bugs.llvm.org/show_bug.cgi?id=42112">42112</a>
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<th>Summary</th>
<td>Preprocessor macro expansion bug on Windows
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows 2000
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>woodstock@gmx.us
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>The following code
#define BOOST_PP_CAT_II(p, res) res
#define BOOST_PP_CAT_I(a, b) BOOST_PP_CAT_II(~, a ## b)
#define BOOST_PP_CAT(a, b) BOOST_PP_CAT_I(a, b)
#define BOOST_PP_VARIADIC_ELEM_0(e0, ...) e0
#define BOOST_PP_VARIADIC_ELEM_I(n, ...)
BOOST_PP_CAT(BOOST_PP_CAT(BOOST_PP_VARIADIC_ELEM_, n)(__VA_ARGS__,),)
#define BOOST_PP_VARIADIC_ELEM(n, ...) BOOST_PP_VARIADIC_ELEM_I(n,__VA_ARGS__)
BOOST_PP_VARIADIC_ELEM(0,,)
should expand to nothing, which works fine on Linux with clang and gcc and on
Windows with VC++, but on Windows with clang it expands to
,
This can be reproduced simply with "clang.exe -E code.cpp", so it is
independent of Visual Studio, etc.
Obviously the code comes from the Boost Preprocessor library, but it affects
more the Boost VMD library, e.g. the macro BOOST_VMD_IS_TUPLE() works
incorrectly.</pre>
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