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<p class="MsoNormal">We have a mangling mismatch between the declaration and definitions of the streams otherwise.
<a href="https://reviews.llvm.org/D23378">https://reviews.llvm.org/D23378</a> explains it further.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">libcxx-dev <libcxx-dev-bounces@lists.llvm.org> on behalf of Louis Dionne via libcxx-dev <libcxx-dev@lists.llvm.org><br>
<b>Reply-To: </b>Louis Dionne <ldionne@apple.com><br>
<b>Date: </b>Wednesday, November 28, 2018 at 8:36 AM<br>
<b>To: </b>"libcxx-dev@lists.llvm.org" <libcxx-dev@lists.llvm.org><br>
<b>Subject: </b>[libcxx-dev] Question on how libc++ defines cin and other streams<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In <span style="font-family:Monaco">src/iostream.cpp</span>, I can find the following beautiful declarations:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> _ALIGNAS_TYPE (istream) _LIBCPP_FUNC_VIS char cin[sizeof(istream)]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> #if defined(_LIBCPP_ABI_MICROSOFT) && defined(__clang__)</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> __asm__("?cin@" _LIBCPP_ABI_NAMESPACE_STR "@std@@3V?$basic_istream@DU?$char_traits@D@" _LIBCPP_ABI_NAMESPACE_STR "@std@@@12@A")</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> #endif</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> ;</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> // etc...</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">And then we have this a little lower in <span style="font-family:Monaco">
src/iostream.cpp</span>:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> _LIBCPP_HIDDEN ios_base::Init __start_std_streams;</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> ios_base::Init::Init() {</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> istream* cin_ptr = ::new(cin) istream(::new(__cin) __stdinbuf <char>(stdin, &mb_cin));</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> // ...</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Monaco"> }</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I understand we're basically allocating a char array and then placement newing the stream into it during static initialization. However, why is that dance necessary with Clang-on-Windows?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Louis<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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