C++: Virtual Functions - Static Binding 

  1 #include <iostream>
  2 #include <string>
  3 using namespace std;
  4 
  5 #define DEBUGBUILD 0
  6 #define DEBUG if (DEBUGBUILD) cout 
  7 
  8 class Date {
  9 private:
 10     int day;
 11     int month;
 12     int year;
 13 public:
 14     Date() { DEBUG << "Date: default ctor" << endl; }
 15     Date(int m, int d, int y)  
 16     {
 17         DEBUG << "Date: 3 int ctor" << endl;
 18         day=d;
 19         month=m;
 20         year=y;
 21     }
 22     void Display(void) {
 23         cout << month << "/" << day << "/" << year << endl;
 24     }
 25 };
 26 
 27 class Time {
 28 private:
 29     int hour;
 30     int minute;
 31     int second;
 32 public:
 33     Time() { DEBUG << "Time: default ctor" << endl; }
 34     Time(int h, int m, int s) {
 35         DEBUG << "Time: 3 int ctor" << endl;
 36         hour=h;
 37         minute=m;
 38         second=s;
 39     }
 40     void Display() { cout << hour << ":" << minute << ":" << second << endl; }
 41 };
 42 
 43 class Report {
 44 private:
 45     Date repDate;
 46     Time repTime;
 47     string repDesc;
 48 public:
 49     Report() : repDate(1,1,1970), repTime(0,0,0), repDesc("") {
 50         DEBUG << "Report: default ctor" << endl;
 51         repDesc = "";
 52     }
 53     Report(Date d, Time t, string desc) : repDate(d), repTime(t) {
 54         DEBUG << "Report: date time string ctor" << endl;
 55         repDesc = desc;
 56     }
 57 
 58     void Display() {
 59         cout << "Date: ";
 60         repDate.Display();
 61         cout << "Time: ";
 62         repTime.Display();
 63         cout << "Description: ";
 64         DisplayDesc();
 65     }
 66     void DisplayDesc() { cout << repDesc << endl;  }
 67 }; 
 68 
 69 class GradeReport : public Report {
 70 private:
 71     int StudentID;
 72     int CourseID;
 73 public:
 74     GradeReport() : StudentID(0), CourseID(0)
 75     { DEBUG << "GradeReport: default ctor" << endl; }
 76 
 77     GradeReport(Date d, Time t, string desc, int sid, int cid) : 
 78     Report(d, t, desc), StudentID(sid), CourseID(cid)
 79     { DEBUG << "GradeReport: 5 parameters ctor" << endl; }
 80 
 81     GradeReport(const GradeReport& gr) : 
 82     Report(gr), StudentID(gr.StudentID), CourseID(gr.CourseID)
 83     { DEBUG << "GradeReport: Copy ctor" << endl; }
 84 
 85     ~GradeReport() { DEBUG << "GradeReport: dtor" << endl; }
 86 
 87     void Display() {
 88         DisplayID();
 89         cout << "Course ID: " << CourseID << endl;
 90         Report::Display();
 91     }
 92 
 93     void DisplayID() { cout << "Student ID: " << StudentID << endl; }
 94 };
 95 
 96 class OnlineGradeReport : public GradeReport {
 97 public:
 98     enum ReportStatus { LOGGED, INFORMED, CONFIRMED };  
 99 private:
100     string program;
101     string deptDesc;
102     ReportStatus repStatus;
103 public:
104     OnlineGradeReport() : program(""), deptDesc(""), repStatus(LOGGED)
105     { DEBUG << "OnlineGradeReport: default ctor" << endl; }
106 
107     OnlineGradeReport(Date d, Time t, string desc, int sid, int cid, string pro, string dept, 
108         ReportStatus s) : 
109     GradeReport(d, t, desc, sid, cid), program(pro), deptDesc(dept), repStatus(s)
110     { DEBUG << "OnlineGradeReport: 8 parameters ctor" << endl; }
111 
112     OnlineGradeReport(const OnlineGradeReport& or) : 
113     GradeReport(or), program(or.program), deptDesc(or.deptDesc), repStatus(or.repStatus)
114     { DEBUG << "OnlineGradeReport: Copy ctor" << endl; }
115 
116     ~OnlineGradeReport()
117     { DEBUG << "OnlineGradeReport: dtor" << endl; }
118 
119     void Display() {
120         DisplayStatus();
121         cout << "Program: " << program << endl;
122         cout << "Department: " << deptDesc << endl;
123         GradeReport::Display();
124     } // end fun Display()
125 
126     void DisplayStatus() {
127         switch(repStatus)
128         {
129         case LOGGED:
130             cout << "The grade is logged by the professor." << endl;
131             break;
132         case INFORMED:
133             cout << "The Records Office has informed the student of the grade." << 
134                 endl;
135             break;
136         case CONFIRMED:
137             cout << "The student has confirmed receiving the grade report." << endl;
138             break;
139         } // end switch
140     } // end fun DisplayStatus()
141 };
142 
143 void main() {
144     Date today(6, 4, 2011);
145     Time t(8, 0, 0);
146     GradeReport gradeA(today, t, "CS360", 1234, 100);
147 
148     Date today2(7, 4, 2011);
149     Time t2(18, 0, 0);
150     Report status(today2, t2, "July Report");
151 
152     Date today3(8, 4, 2011);
153     Time t3(26, 5, 0);
154     OnlineGradeReport or = OnlineGradeReport(today3, t3, "CS350", 1234, 100, "MSCS", 
155         "Computer Science", OnlineGradeReport::ReportStatus::CONFIRMED);
156 
157     Report *rpt[3];
158     rpt[0] = &gradeA;
159     rpt[1] = &status;
160     rpt[2] = &or;
161 
162     for(int i = 0; i < 3; i++)
163         rpt[i]->Display();
164 }
● The method that is called is determined at compile time.

● The method that is called is decided by the type of the pointer.

　　○ In main(), rpt is an array of Report pointer so Report’s Display() method will be called.

● This behavior is known as static binding.

posted @ 2011-06-28 12:08  Mayus  阅读(198)  评论(0)    收藏  举报