Question

i wrote this code:

class A {
  public:
    A(){d=2.2;cout<<d;}
    A(double d):d(d){cout<<d;}
    double getD(){return d;}

  private:
    double d;
};

class Bing  {
  public:
    Bing(){a=A(5.3);}
    void f(){cout<<a.getD();}
  private:
    A a;
};

int main() {
  Bing b;
  b.f();
}

i get the output: 2.2 5.3 5.3 instead of 5.3 5.3. it’s something in the constructor…. why am i getting this? how can i fix it?

Answer 1

Your class A has two constructors: a default constructor, which sets d to 2.2, and a constructor taking a double, which sets d to whatever you pass into the constructor.

You have a member variable of type A in your class Bing. This member variable is initialized before the body of the Bing constructor is entered. Since you don’t list the Bing member in the constructor’s initializer list, its default constructor is called. You can explicitly initialize it with the desired value by initializing it in the initializer list:

Bing() : a(5.3) { }