Class Four

Class Four

• destructor

struct point  
{ 
    int x, y;  
    point(int x, int y) : x(x), y(y) {}  
    ~point() { cout << "destructor" << endl; }  
}  

• the call of the destructor is automatic, thus the latter object created will be destroyed first.

• living life span of a local object: from the beginning of the block to the end of the block.

• goto: jump to the label, which is a bad practice.

• aggregate initialization with Ctor

• use {} to initialize the object.

point p1 = {1, 2};  

if there is a initialization funtion
we should use the initialization function to initialize the object.

point p1[]={point(1, 2), point(3, 4)};  

inside Object

• A program is a bounch of objects telling each other what to do by sending messages.----Alan Kay

• access control

• public: can be accessed by any function.

• private: can only be accessed by the member functions of the class.

  • b.j is illegal if b is an object of class B and j is a private member of class B.
• if no access control is specified, the default is public (struct)

Tip

Different objects of the same class, their private members can be accessed by each other.

• Friend:

• a friend function can access the private members of the class.
  

  class A  
  {  
      friend void f();  
  };  
  

Class

• the difference between class and struct is the default access control.
• the default access control of class is private.
• the default access control of struct is public.

Where are the objects?

• Fields, parameter, local variables
• global variable

Static Initialization Dependency

• Order between files is unspecified
• the tendency is not to use any global variables.

Static

• two basic meanings:

  static storage
  restricted access

the use of "static" in C++

• static applied to objects

create when called, destroyed when the program ends.

• Can we apply static to members?

static member: shared by all objects of the class, thus not belongs to any object
therefore, a definition of the static member is necessary. int StatMem::m_h;
static funtion: