https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70076
--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> --- (In reply to Martin Sebor from comment #0) > The G++ 4.9 Changes document (https://gcc.gnu.org/gcc-4.9/changes.html) > claims support for C++ VLAs including initializers (as specified in N3639). I thought that proposal was withdrawn, meaning that VLA support in G++ is now only as a GNU extension again, like it was previously? Or am I getting it confused with something else? > The N3639 proposal specifies that the /expression/ denoting the number of > elements in a VLA declaration is erroneous when "the initializer of the > object is a braced-init-list whose number of (top-level) initializer-clauses > exceeds the number of elements to initialize." The proposal then goes on to > say that if an /expression/ that is not a core-constant expression is > erroneous, an exception of a type that would match a handler (15.3 > except.handle) of type std::bad_array_length (18.6.2.2 xxx) is thrown." > > The following test case shows an example where G++ fails to follow this > requirement. > > AFAICS, the problem is that this checking in G++ 4.9 is implemented in the > wrong function (build_vec_init() in cp/init.c). The checking needs to be > done in its caller, store_init_value(), because it only calls > build_vec_init() when array_of_runtime_bound_p(type) is true, and that > function only consider the major rank of the array, not any of its minor > ranks). > > $ cat z.cpp && /home/msebor/build/gcc-4.9.3/gcc/xgcc > -B/home/msebor/build/gcc-4.9.3/gcc -Wall -Wextra -Wpedantic -xc++ z.cpp && > ./a.out > void __attribute__ ((noclone, noinline)) foo (void*) { } > void __attribute__ ((noclone, noinline)) bar (int n) > { > char a [1][n] = { { 0, 1, 2 } }; > foo (a); > } > > int main () > { > try { > bar (1); > __builtin_abort (); > } > catch (...) { > } > } > z.cpp: In function ‘void bar(int)’: > z.cpp:4:15: warning: ISO C++ forbids variable length array ‘a’ [-Wvla] > char a [1][n] = { { 0, 1, 2 } }; > ^ > Aborted (core dumped)
