Multiple Inheritance and Object Layout in C++

Transcription

1 Multiple Inheritance and Object Layout in C++ Tutorial 08 Leonid Barenboim 8/6/2009

2 Outline 1 The Academia 2 Makefile

3 Outline 1 The Academia 2 Makefile

4 The Academia Person Has an name and an id. Academician Studies or teaches courses. Student An academician person that studies courses in a given year. Course Has enrolled students. Staff An academician person that teaches courses. Has a rank. Assistant A student that is also a staff member.

5 The Academia class diagram

6 Person Class Person.hpp #ifndef _PERSON_H_ #define _PERSON_H_ #include <string> using namespace std; class Person { string _name; string _id; public: Person(string s, string id); string getname() { return _name; } string getid() { return _id; } }; #endif

7 Person Class Person.hpp #ifndef _PERSON_H_ #define _PERSON_H_ #include <string> using namespace std; class Person { string _name; string _id; public: Person(string s, string id); string getname() { return _name; } string getid() { return _id; } }; #endif

8 C++.h File Gotchas #ifndef... #endif protection Include the definitions you need For STL, use using namesace std; Semicolon at the end of a class Default visibility is private Methods in.h files are in-lines

9 Person Class (cont d) Person.cpp #include <Person.hpp> Person::Person(string s, string id) : _name(s), _id(id)

10 C++.cpp File Gotchas Include the class.h file and other dependencies Methods and constructors must have a Class:: prefix Notice special constructor syntax

11 Academician Class Academician.hpp class Academician { list<course*> _courses; public: void addcourse(course* c) { _courses.push_back(c); } void listcourses(); };

12 Academician Class (cont d) Academician.cpp #include <Academician.hpp> #include <iostream> void Academician::listCourses() { list<course*>::iterator iter; for ( iter=_courses.begin(); iter!= _courses.end(); iter++ ) { cout << (*iter)->getid() << endl; } }

13 Course Class Course.hpp 1 class Student; // avoid circular includes class Course{ string _id; list<student*> _students; // No need to initialize public: Course(string id); string getid() { return _id; } void addstudent(student* s) {_students.push_front(s);} list<student*> getstudents() { return _students; } }; 1 Implementation is trivial

14 Student Class Student.hpp class Student : public virtual Person, public Academician { int _year; public: Student(string name, string id, int year); Student(int year); int getyear() { return _year; } }; Virtual inheritance from Person, because there should not be two instance of this base.

15 Student Constructors Student.cpp Student::Student(string name, string id, int year) : Person(name, id), Academician(), year(year) {}; Student::Student(int year) : Academician(), year(year) {}; The second constructor is required in order to allow to create the student part without the shared ancestor part.

16 Staff Class Staff.hpp enum Rank { GRAD = 1, DR, PROF }; class Staff : public virtual Person, public Academician { Rank _rank; public: Staff(string name, string id, Rank r); Staff(Rank r); Rank getrank() { return _rank; } }; Again, there should be only one shared instance of a person.

17 Staff Constructors Staff.cpp Staff::Staff(string name, string id, Rank r) : Person(name, id), Academician(), _rank(r) {}; Staff::Staff(Rank r) : Academician(), _rank(r) {}; The second constructor is required in order to allow to create the staff part without the shared ancestor part.

18 Assistant Class Assistant.hpp class Assistant : public Staff, public Student { public: Assistant(string name, string id, int year); }; Assistant.cpp Assistant::Assistant(string name, string id, int year): Person(name, id), Staff(GRAD), Student(year) {}; The Ctr. creates the shared ancestor separately.

19 Running the Example Main.cpp int main() { Course c1("tise081"), c2("oosd082"), c3("dmweb082"); Student s1("david","468", 3); s1.addcourse(&c1) c1.addstudent(&s1); Assistant a("guy", "456", 2); Staff& staff = a; Student& student = a; staff.addcourse(&c1); staff.addcourse(&c2); student.addcourse(&c3); c3.addstudent(&student);...

20 Running the Example (cont d) Main.cpp (cont d) }... cout << a.getname() << " rank: " << a.getrank() << endl; cout << a.getname() << " year: " << a.getyear() << endl; cout << staff.getname() << " teaches:" << endl; staff.listcourses(); cout << student.getname() << " studies:" << endl; student.listcourses();

21 Running the Example Output Output Guy rank: 1 Guy year: 2 Guy teaches: tise081 oosd082 Guy studies: DMWeb082 Since the Academician ancestor instance is not shared, there are two separate courses lists.

22 Running the Example Output Output Guy rank: 1 Staff field Guy year: 2 Student field Guy teaches: Staff courses list tise081 oosd082 Guy studies: Student courses list DMWeb082 Since the Academician ancestor instance is not shared, there are two separate courses lists.

23 The Objects Memory Layout

24 Outline 1 The Academia 2 Makefile

25 Reminder: Building a C++ Application Makefile CPP = $(wildcard *.cpp) HPP = $(wildcard *.hpp) OBJ = $(CPP:.cpp=.o) EXE = acad.phoney: all clean all: $(EXE) $(EXE): $(OBJ) g++ -g -o $(EXE) $(OBJ) %.o: %.cpp $(HPP) g++ -g -I. -c $< clean: rm -f $(OBJ) Auto. Variables % Pattern matcher $@ Target $< First dependency $^ All dependencies $? Dependencies that are newer then the target Compiler flags g++ Use C++ as default -g Debug information