C++ Things to remember

1. Size of empty class is 1, compiler needs to distinguish better the classes.
2.Static variable part of class do not take part in size of the class.
3.Static Integer variables can be initialized in the class declaration
Class XYZ
{
private:
static const int n=10;
};
4.A static function can not be virtual : Static works on class without object where as virtual needs and instance to be created and works at runtime.
5.Avoid calling virtual functions from constructor, as they behave like non-virtual as the instance of the class/object creation is not yet completed.
6.Class with private destructor should be created only on heap : If you create an instance on stack, compiler will have no clue on how to call destructor as it is private.
7.Reference and Const variables should be initialized using member initialization list: This helps the initialization of these member at the tile of object creation.
8.Compiler generated functions are public and inline AND they will be created only if they are used some where in the code else compiler will not generate them.
9.Reference and Const can not be copied, so compiler will not generate assignment operator and forces the user to create an assignment operator if the class has const or reference members.
10. What happens if there is a default constructor in Base class and user tries to initialize using the default constructor.

class Base
{
public:
Base(int a)
{
}
};

class Derived: public Base
{
public:
void display()
{
}
};

Derived obj; //Compiler Error

Reason : Default Constructor calls base class default constructor and also default constructor of the members. If any of the default constructor is missing then compiler throws error.
 11.Assignment Operator is member by member copy, where as Copy constructor is member by member initialization.
12.Size of a class with virtual function is SizeOf(Class) + SizeOf(vPtr) = Class + 4
13.Following are NOT inherited from Base Class

• Constructor
• Destructor
• Assignment Operator
• Friends

 14.No Virtual constructors in C++ : C++ is a staitc typed language and needs to know the type of the object at the time of creation.
   Virtual constructor can be achieved using Factory Method Design Pattern.
15.You should not delete the variables that are created using placement new.You should delete the complete buffer once its no longer required.
16.Volatile variables are modified by some external system other than the current code. Like,

•  CPU clocks
•  Interrupt signals

 17.Static global variables have only local linkage and are accessible  only in the current file.
      Where as global(non-static) variables have external linkage and are accessible using extern keyword.
18.When dynamic_cast is applied on reference variable of a base(Not referring to derived object) then "bast_cast" exception will be thrown.If it is a pointer type then NULL will be returned.
19.VTable is created per class , VPtr is created per object.
20. Vptr Address : (int*) (&obj+0)
       VTable Address : (int*)*(int*)(&obj+0)
  Vptr is vtable starting address.