C++ explicitly call parent constructor outside initialization list

user_931154 0
Viewed 958

So, the ordinary way to call a parent class' constructor is in the initialization list:

e.g.

#include <cstdio>

struct Parent {
  explicit Parent(int a) {
    printf("Parent -- int\n");
  }
};

struct Child : public Parent {
  explicit Child(int a) : Parent(1) {
    printf("Child -- int\n");
  }
};

int main(int argc, char **argv) {
  Child c = Child(10);
};

prints Parent -- int then Child -- int.

(Somewhat) disregarding whether it's a good idea or not, I'm wondering whether it's possible to call the parent constructor explicitly in the body of the constructor (on the object being constructed), outside the initialization list.

c++
2 Answers

No, not in the way you want, so it constructs the parent part of the object.

The common way to deal with a situation like this is to have an "init" or "construct" method that you then can invoke from the child constructor:

struct Parent {
    explicit Parent(int a) {
        Construct(a);
    }
protected:
    void Construct(int a) { printf("Parent -- int\n"); }
    Parent() {}
};

struct Child : public Parent {
    explicit Child(int a) {
        Parent::Construct(a);
        printf("Child -- int\n");
    }
};

int main(int argc, char **argv) {
    Child c = Child(10);
};
user_44541240

Well you can but it will not do the same thing.

Doing e.g.

explicit Child(int) {
    Parent(1);
}

will not initialize the Parent part of the object. Instead it will create a new temporary object of type Parent, and then that temporary object will immediately be destructed.

user_4405580
Related