Are parent class constructors called before initializing variables, or will the compiler initialize the variables of the class first?
For example:
class parent {
int a;
public:
parent() : a(123) {};
};
class child : public parent {
int b;
public:
// question: is parent constructor done before init b?
child() : b(456), parent() {};
}
Yes, the base class is initialized before the members of the derived class and before the constructor body executes.
In a non-delegating constructor, initialization proceeds in the following order:
— First, and only for the constructor of the most derived class (1.8), virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base classes in the derived class base-specifier-list.
— Then, direct base classes are initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).
— Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).
— Finally, the compound-statement of the constructor body is executed.
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