The difference between member function, friend function and general function

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#include <iostream>using namespace Std;class time{public:time (int h,int m,int s): Hour (h), Minute (m), SEC (s) {}    void Display1 ();  Display1 is a member function friend void Display2 (time &);    Display2 is a friend function int gethour () {return hour;    } int Getminute () {return minute;    } int getsec () {return sec;    }private:int hour;    int minute; int sec;}; void time::d isplay1 ()//member function Display1 implementation, DISPALY1 time::{//Direct access to private data members in hour form, essentially this->hour form cout<

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Enter the code:
/* Copyright (c) 2014, Yantai University School of Computer * All rights reserved.        * File name: Sum123.cpp * Author: Lin Haiyun * Completion Date: April 15, 2015 * Version number: v2.0 * * Problem Description: The difference between this project and an example is that "distance is the distance between a point and another point", and different versions are reflected in the parameters. The three versions suggest separate testing, or, as an example, in a program. * Input Description: No * program output: According to the distance between the required points */#include <iostream> #include <cmath>using namespace Std;class cpoint{private:d  Ouble x;  horizontal double y; Ordinate Public:cpoint (double xx=0,double yy=0): X (xx), Y (yy) {} double Distance1 (CPoint &);    Parameters with const CPoint & better friend Double Distance2 (CPoint & CPoint &);    Double GetX () {return x;    } double GetY () {return y;    }};d ouble Distance3 (CPoint &,cpoint &);d ouble CPoint::d istance1 (CPoint &p) {double dx,dy,d;    dx=x-p.x;    DY=Y-P.Y;    D=SQRT (Dx*dx+dy*dy); return D;}    Double Distance2 (CPoint &p1, CPoint &p2)//Note This item does not have CPoint, the function of the friend class does not add the predecessor {double dx,dy,d;    dx=p1.x-p2.x;    DY=P1.Y-P2.Y;    D=SQRT (Dx*dx+dy*dy); return D;} Double DistanCe3 (CPoint &p1,cpoint &p2) {double dx,dy,d;    Dx=p1.getx ()-p2.getx ();    Dy=p1.getx ()-p2.getx ();    D=SQRT (Dx*dx+dy*dy); return D;}    int main () {CPoint P1 (5,8), p2 ( -5,10);  cout<< "1.    "<<p1.distance1 (p2) <<endl;  cout<< "2.    "<<distance2 (P1,P2) <<endl;  cout<< "3.    "<<distance3 (P1,P2) <<endl; return 0;}

Operation Result:
The difference between member function, friend function and general function