[LLVMbugs] [Bug 18177] New: Different results between gcc and clang when compiling a rather simple c++11 program

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Sun Dec 8 05:11:12 PST 2013


            Bug ID: 18177
           Summary: Different results between gcc and clang when compiling
                    a rather simple c++11 program
           Product: clang
           Version: 3.3
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: cilio.c at email.it
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 11688
  --> http://llvm.org/bugs/attachment.cgi?id=11688&action=edit
Short, Self Contained, Correct (Compilable), Example

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:

#include <iostream>

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 << matrix[0][1] << std::endl;
    std::cout << dyn_matrix[0][1] << std::endl;

    return 0;   

As shown, I'm trying to use uniform initialization to initialize an anonymous
(resp. named) multidimensional array of size 3x3. When compiling with gcc 4.7
from MacPorts the expected output is obtained:

$g++-mp-4.7 -std=c++11 dyn_matrix.cpp -o dyn_matrix 
$ ./dyn_matrix

Conversely, in case clang is used the output reads:

$ clang++ -std=c++11 -stdlib=libc++ dyn_matrix.cpp -o dyn_matrix_clang
$ ./dyn_matrix_clang 

In this case the result is (apparently) wrong. clang --version reports:

Apple LLVM version 5.0 (clang-500.2.75) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix

I've also tried with clang 3.4 (trunk 187030). In that case clang crashes when
trying to compile that code.


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