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Tuy nhiên, có thể sử dụng ép kiểu để chuyển đổi một con trỏ lớp cơ sở thành một con trỏ lớp dẫn xuất.

Ví dụ 5.1: Chương trình sau sẽ được chia thành nhiều file (gồm các file .H và .CPP) và tạo một project có tên là CT5_1.PRJ gồm các file .cpp

File POINT.H:

1: //POINT.H

2: //Định nghĩa lớp Point

3: #ifndef POINT_H

4: #define POINT_H

5:

6: class Point

7: {

8: protected:

9: float X,Y;

10: public:

11: Point(float A= 0, float B= 0);

12: void SetPoint(float A, float B);

13: float GetX() const

14: {

15: return X;

16: }

17: float GetY() const

18: {

19: return Y;

20: }

21: friend ostream&operator<<(ostream&Output, const Point&P);

22: };

23:

24: #endif

File POINT.CPP

1: //POINT.CPP

2: //Định nghĩa các hàm thành viên của lớp Point

3: #include<iostream.h>

4: #include "point.h"

5:

6: Point::Point(float A, float B)

7: {

8: SetPoint(A, B);

9: }

10:

11: void Point::SetPoint(float A, float B)

12: {

13: X = A;

14: Y = B;

15: }

16:

17: ostream&operator<<(ostream&Output, const Point&P)

18: {

19: Output<<'['<<P.X<<", "<<P.Y<<']';

20: return Output;

21: }

File CIRCLE.H

1: //CIRCLE.H

2: //Định nghĩa lớp Circle

3: #ifndef CIRCLE_H

4: #define CIRCLE_H

5:

6: #include "point.h"

7: class Circle : public Point

8: {

9: protected:

10: float Radius;

11: public:

12: Circle(float R = 0.0, float A = 0, float B = 0);

13: void SetRadius(float R);

14: float GetRadius() const;

15: float Area() const;

16: friend ostream&operator<<(ostream&Output, const Circle&C);

17: };

18:

19: #endif

File CIRCLE.CPP

1: //CIRCLE.CPP

2: //Định nghĩa các hàm thành viên của lớp Circle

3: #include<iostream.h>

4: #include<iomanip.h>

5: #include "circle.h"

6:

7: Circle::Circle(float R, float A, float B): Point(A, B)

8: {

9: Radius = R;

10: }

11:

12: void Circle::SetRadius(float R)

13: {

14: Radius = R;

15: }

16:

17: float Circle::GetRadius() const

18: {

19: return Radius;

20: }

21:

22: float Circle::Area() const

23: {

24: return 3.14159 * Radius * Radius;

25: }

26:

27: //Xuất một Circle theo dạng: Center = [x, y]; Radius = #.##

28: ostream&operator<<(ostream&Output, const Circle&C)

29: {

30: Output<<"Center = ["<<C.X<<", "<<C.Y

31:<<"]; Radius = "<<setiosflags(ios::showpoint)

32:<<setprecision(2)<<C.Radius;

33: return Output;

34: }

File CT5_1.CPP:

1: //CT5_1.CPP

2: //Chương trình 5.1: Ép các con trỏ lớp cơ sở tới các con trỏ lớp dẫn xuất

3: #include<iostream.h>

4: #include<iomanip.h>

5: #include "point.h"

6: #include "circle.h"

7:

8: int main()

9: {

10: Point *PointPtr, P(3.5, 5.3);

11: Circle *CirclePtr, C(2.7, 1.2, 8.9);

12: cout<<"Point P: "<<P<<endl<<"Circle C: "<<C<<endl;

13 //Xử lý một Circle như một Point (chỉ xem một phần lớp cơ sở)

14: PointPtr =&C;

15: cout<<endl<<"Circle C (via *PointPtr): "<<*PointPtr<<endl;

16 //Xử lý một Circle như một Circle

17: PointPtr =&C;

18: CirclePtr = (Circle *) PointPtr;

19: cout<<endl<<"Circle C (via *CirclePtr): "<<endl

20:           <<*CirclePtr<<endl<<"Area of C (via CirclePtr): "

21:           <<CirclePtr->Area()<<endl;

22: //Nguy hiểm: Xem một Point như một Circle

23: PointPtr =&P;

24: CirclePtr = (Circle *) PointPtr;

25: cout<<endl<<"Point P (via *CirclePtr): "<<endl

26:           <<*CirclePtr<<endl<<"Area of object CirclePtr points to: "

Questions & Answers

how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Lập trình hướng đối tượng. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10794/1.1
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