Question

My concern is a default constructor and its initialisation list. In a simple case it’s clear, like:

class A
{
  protected:
       double d1;
       //classB obj1; //how to initialize this one in a default constructor?
  public:
       A (double x = 0.0): d1(x){} //constructor
       virtual ~A(void) {};
  //something
}

But how to initialize the object of classB, which has a big amount of members? Or how in general initialize in default constructor some type that has a big or unknown amount of parameters to be initialized?

Answer 1

You could initialize obj1 in member initializer list by calling its default constructor or other constructors

class A
{
  protected:
       double d1;
       classB obj1; 
       pthread_mutex_t m_mutex;
  public:
       A (double x = 0.0): d1(x), obj1(), m_mutex(PTHREAD_MUTEX_INITIALIZER) {} 
       virtual ~A(void) {}
       //something
}

if classB has big of members like you described, you may break the rule of class design – one class does one thing. You might want to break classB into small independent classes.