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PODifferent results between gcc and clang when compiling a rather simple c++11 program
 

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  1. PODifferent results between gcc and clang when compiling a rather simple c++11 program
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    <p>I'm trying to understand whether the different behavior exposed by gcc vs. clang in the output of this simple C++11 program is due to a bug in clang (Xcode 5.0.2, OS X 10.8.5). The code is as follows:</p> <pre><code>#include &lt;iostream&gt; int main() { int matrix[][3]{{1,2,3}, {4,5,6}, {7,8,9}}; auto dyn_matrix = new int[3][3]{{1,2,3}, {4,5,6}, {7,8,9}}; std::cout &lt;&lt; matrix[0][1] &lt;&lt; std::endl; std::cout &lt;&lt; dyn_matrix[0][1] &lt;&lt; std::endl; return 0; } </code></pre> <p>As shown, I'm trying to use uniform initialization to initialize an anonymous (resp. named) multidimensional array of size <code>3x3</code>. When compiling with gcc 4.7 from MacPorts the expected output is obtained:</p> <pre><code>$g++-mp-4.7 -std=c++11 dyn_matrix.cpp -o dyn_matrix $ ./dyn_matrix 2 2 $ </code></pre> <p>Conversely, in case clang is used the output reads:</p> <pre><code>$ clang++ -std=c++11 -stdlib=libc++ dyn_matrix.cpp -o dyn_matrix_clang $ ./dyn_matrix_clang 2 4 $ </code></pre> <p>In this case the result is (apparently) wrong. <code>clang --version</code> reports:</p> <pre><code>Apple LLVM version 5.0 (clang-500.2.75) (based on LLVM 3.3svn) Target: x86_64-apple-darwin12.5.0 Thread model: posix </code></pre> <p>Who's to blame? me, gcc or clang?</p> <p><strong>UPDATE Dec 11th, 2013:</strong> The bug should have been fixed in r196995. Unfortunately, we still do not know how long it will take before Apple updates the version of clang that ships with Xcode. </p> <p><strong>UPDATE Dec 9th, 2013:</strong> I submitted a bug report on the LLVM bugzilla platform. It has indeed been recognized as a bug, a patch is currently under review, see <a href="http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20131209/095099.html" rel="noreferrer">http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20131209/095099.html</a>. </p> <p>Thanks.</p>
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    1. USIlio Catallo
    1. USIlio Catallo
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      1. PODifferent results between gcc and clang when compiling a rather simple c++11 program
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    1. COVisual Studio 2013 says `2 2` for another statistic.
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    2. COWhich version of clang++ are you using?
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      1. USjuanchopanza
    3. CO+1 for asking a good and interesting question. Confirmed that `clang++` v4.2 on OS X 10.7.5 also produces code outputting "2 4". My intuition says it's wrong.
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