https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102013
Bug ID: 102013 Summary: Incorrect aggregate initialization of union Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: fchelnokov at gmail dot com Target Milestone: --- In this program: ``` #include <iostream> struct A { int x = 1; }; struct B { int x = 0; }; union U { A a; B b; }; int main() { U u{}; std::cout << u.a.x; } ``` GCC prints `0`: https://gcc.godbolt.org/z/8Tj4Y1Pv1 But the correct result is `1`, which is the default initializer of the first union member `a` (see Clang 's result)