Pointers, virtual functions, abstract classes

• Use pointers
• Use virtual functions
• Use pure virtual functions
• Explain what makes a class abstract

• Declaring a pointer: int *p;
• Initializing a pointer: p = &n; // assumes n is an int variable
• Using a pointer: *p = 55;
• Using a pointer to a struct: struct obj { int i; }; obj* pobj = new obj; (*pobj).i = 32; pobj->i = 16;

• Allocating memory dynamically: int *p = new int;
• Deallocating memory: delete p;
• Allocating an array dynamically: int *p2 = new int[10];
• Deallocating an array: delete[] p2;
• Allocating an object's memory dynamically: obj *p3 = new obj;
• Deallocating an object's memory: delete p3;
• If a class dynamically allocates memory, you should write a destructor for it to deallocate the memory (to replace the default one written for it)
• If a class dynamically allocates memory, you should probably write an assignment operator overload for it (to replace the default one written for it)
• If a class dynamically allocates memory, you should write a copy constructor for it (to replace the default one written for it)
• If a class dynamically allocates memory, you should write a default constructor if one is wanted (to replace the default constructor provided)
• A base class with a destructor to deallocate memory should make the destructor virtual

• Compile-time binding is also called static binding and early binding
• Early binding sets what functions will be called at compilation
• Run-time binding is also called dynamic binding and late binding
• Late binding decides which functions to call (base or derived class) at run time
• The keyword virtual makes a function late binding
• The keyword virtual is only used in the base class
• A pure virtual function has no body; it is specified with this in place of the body: =0;
• It is up to derived classes to implement the pure virtual functions of the base class
• Classes with one or more virtual functions are called abstract classes
• Abstract classes can not be instantiated