C++ calling base class constructors

Question

#include 
#include  
using namespace std;

// Base class
class Shape 
{
   public:
      void setWidth(int w)
      {
         width =         


        

Answer 1

When objects are constructed, it is always first construct base class subobject, therefore, base class constructor is called first, then call derived class constructors. The reason is that derived class objects contain subobjects inherited from base class. You always need to call the base class constructor to initialze base class subobjects. We usually call the base class constructor on derived class's member initialization list. If you do not call base class constructor explicitly, the compile will call the default constructor of base class to initialize base class subobject. However, implicit call on default constructor does not necessary work at all times (for example, if base class defines a constructor that could not be called without arguments).

When objects are out of scope, it will first call destructor of derived class,then call destructor of base class.