VC + + Programming the second lesson notes

Lesson two C + + inheritance encapsulation polymorphism Simple Type conversions

• type int to char, truncation, loss of precision (3Bytes), warning.

• Char-type conversion bit int, no truncation, no warning.

Type conversions for parent subclass subclasses

#include  <iostream>using namespace std;class Animal{public:     Animal () {}  //constructor overload     animal (Int height, int weight) {}     //constructor Parameters     void eat ()     {         cout<< "Animal eat" <<endl;    }     void sleep ()     {        cout< < "Animal sleep" <<endl;    }    void breathe ()      {        cout<< "Animal breathe" << endl;    }};class fish : public animal{public:     Fish (): Animal (150,200), a (1) {}   //can assign an initial value to a constant in a class and pass the parameters of the base class constructor     void  Breathe ()   //overwrite of function (subclass parent Class)     {//      animal::breathe ();   // You can continue calling the parent class function in this way         cout<< "fish bubble" <<endl;     }private:    const int a;}; Void fun (Animal* pan) {    pan->breathe ();} Void main () {    fish fh;    animal* pan;     pan = &fh;  //Parent class Subclass type conversion     fun (PAN);}

Run the result (call the function of the parent class breathe() ):

Animal breathepress any key to continue

Fish Object Memory Layout:

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It can be concluded that when the pointer of a fish object is converted to a pointer to a animal object, truncation occurs and the subsequent "Fish Inheritance part" memory is lost.

Virtual functions (polymorphism)

At this point, if you want to display the results for the breath of fish, you can precede the previous code with the breathe() Virtual identifier in front of the animal function:

virtual void Breathe () {cout<< "Animal breathe" <<ENDL;}

Results:

Fish bubblepress any key to continue

virtual , breathe () This function is a virtual function.

polymorphism

breathe () function is virtual function, this time C + + will use late binding (late binding) The technique of , at run time, is called C + + polymorphism, depending on the type of object (the address of the fish class object we pass in the program) to confirm which function is called.

Pure virtual function and abstract class

If you modify the above code again:

virtual void breathe () = 0;

Then this function is pure virtual function, and the corresponding animal class is abstract class.

• An abstract class cannot instantiate an object, only as a base class for a derived class service.

VC + + Program compiling link principle and process

Icon:

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VC + + Programming the second lesson notes