Avoid calling constructor of member variable

Question

I have the following C++-class:

// Header-File
class A
{
    public:
    A();

    private:
    B m_B;
    C m_C;
};

// cpp-File
A::A()
: m_B(1)
{
    m_B.doSom         


        

Answer 1

Here we have the building blocks:

#include 

class C
{
public:
  C(int i){std::cout << "C::C(" << i << ")" << std::endl;}
};

class B
{
public:
  B(int i){std::cout << "B::B(" << i << ")" << std::endl;}
  void doSomething(){std::cout << "B::doSomething()" << std::endl;}
  void doMore(){std::cout << "B::doMore()" << std::endl;}
  int getSomeValue(){return 42;}
};

If you want to make a new kind of construction for B consider making a derived class:

class B1 : public B
{
public:
  B1() : B(1)
  {
    doSomething();
    doMore();
  }
};

Now use the class B1 that is derived from B:

class A
{
private:
  B1 _b;
  C _c;
public:
  A() : _c(_b.getSomeValue()){std::cout << "A::A()" << std::endl;}
};

And then:

int main()
{
  A a;
}

Output:

B::B(1)
B::doSomething()
B::doMore()
C::C(42)
A::A()