https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111771
--- Comment #2 from Egor <iamsupermouse at mail dot ru> --- Before calling A's constructor, it will zero `x` anyway. I was also surprised when I learned this yesterday, but it's what the standard says. 1. `()` performs value-initialization on B: http://eel.is/c++draft/dcl.dcl#dcl.init.general-16.4 2. Since B's ctor is not user-provided, that resolves to zero-initialization followed by default-initialization: http://eel.is/c++draft/dcl.dcl#dcl.init.general-9.1.2 3. Zero-initialization of B propagates to A, then propagates to `x` and zeroes it, regardless of A having a user-provided constructor or not: http://eel.is/c++draft/dcl.dcl#dcl.init.general-6.2 4. Lastly default-initialization of B calls B's constructor and in turn calls A's constructor.
