My gcc is 10.0.0, and the code is: template <int N> void test() { constexpr int N2 = N; typedef int T alignas(N2); // error: requested alignment is not an integer constant } int main() { test<4>(); return 0; } gcc accepts the code. clang rejects it: source>:4:16: error: 'alignas' attribute only applies to variables, data members and tag types typedef int T alignas(N2); ^ 1 error generated. Compiler returned: 1 icc gives a warning: <source>(4): warning #3463: alignas does not apply here typedef int T alignas(N2); ^ Compiler returned: 0
(In reply to zhonghao from comment #0) > My gcc is 10.0.0, and the code is: > > template <int N> > void test() { > constexpr int N2 = N; > typedef int T alignas(N2); > // error: requested alignment is not an integer constant What is this comment here for? G++ does not give this error, and it should not give this error. Neither Clang nor icc gives this error either. It's not helpful to provide code with misleading comments about bogus errors. It makes it look like the comment is somehow relevant to your bug report, and it's not. Anyway, confirmed, G++ should issue a diagnostic here: An alignment-specifier may be applied to a variable or to a class data member, but it shall not be applied to a bit-field, a function parameter, or an exception-declaration (14.3). An alignment-specifier may also be applied to the declaration of a class (in an elaborated-type-specifier (9.1.7.3) or class-head (Clause 11), respectively).
Extended testcase. I would expect 6 errors but we only issue 2: struct S { alignas(4) int a : 4; // error int b : 4 alignas(4); // error typedef int T alignas(4); // error }; void fn (alignas(4) int, // error alignas(4) int n) // error { try { } catch (alignas(4) int &e) // error { } }
Fixing the title.
*** Bug 96039 has been marked as a duplicate of this bug. ***