https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70075
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |egallager at gcc dot gnu.org
--- Comment #2 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #0)
> Unlike GCC in C mode, G++ accepts explicitly initialized variable length
> arrays (as specified in WG21 N3639,
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3639.html).
> However, when initializing VLAs with more elements than explicitly specified
> in the initializer, G++ fails to zero-initialize the remaining elements as
> would be the case for ordinary arrays.
>
> The following test case demonstrates the problem:
>
> cat z.cpp && /build/gcc-trunk/gcc/xgcc -B /build/gcc-trunk/gcc -Wall
> -Wextra -Wpedantic z.cpp && ./a.out
> void __attribute__ ((noclone, noinline)) bar (int n)
> {
> const int m = 2;
> char a [m][n] = { { 0, 1, 2 } };
>
> for (int i = 0; i < m; ++i)
> for (int j = 0; j < n; ++j)
> __builtin_printf ("%hhi ", a [i][j]);
> __builtin_printf ("\n");
>
> if (a [0][n - 1] != 0)
> __builtin_abort ();
> }
>
> int main ()
> {
> bar (4);
> }
> z.cpp: In function ‘void bar(int)’:
> z.cpp:4:15: warning: ISO C++ forbids variable length array ‘a’ [-Wvla]
> char a [m][n] = { { 0, 1, 2 } };
> ^
> 0 1 2 12 -1 127 0 0
> Aborted (core dumped)
I get this output on i386-apple-darwin9.8.0 with gcc8:
$ /usr/local/bin/g++ -Wall -Wextra -Wpedantic -o 70075.exe 70075.cc
70075.cc: In function ‘void bar(int)’:
70075.cc:4:13: warning: ISO C++ forbids variable length array ‘a’ [-Wvla]
char a[m][n] = { { 0, 1, 2 } };
^
$ ./70075.exe
0 1 2 0 0 0 -32 -113
$
(i.e. no errors)
