There's no mandated order between compilation units. It's a problem significant enough to have its own snarky name: the Static Initialization Order Fiasco https

There's no mandated order between compilation units. It's a problem significant enough to have its own snarky name: the Static Initialization Order Fiasco https://en.cppreference.com/w/cpp/language/siof https://en.cppreference.com/w/cpp/language/siof