Miri Ben-Nissan (Kopel) (2017)

Transcription

1 Miri Ben-Nissan (Kopel) (2017)

2 int attributes set of operations Attributes: 4 bytes. Integer numbers. Operations: numerical operators logical operations bit operations I/O operations Data Types define the way you use storage (memory) in the programs you write. Miri Kopel, Bar-Ilan University 2

3 How should we describe a car? attributes operations window engine door wheel Miri Kopel, Bar-Ilan University 3

4 A data type (int, float etc.) is characterized by: (1) A set of values that can be assumed by objects of the type. (2) A set of operations that can be performed on objects of the type. Abstract Data Type (ADT) = user defined data type. Miri Kopel, Bar-Ilan University 4

5 ADT = packaging data with functions to create a new data type. This is also called encapsulation. Built-in types: int, bool, float. User-defined types: stacks, queue, tree, student, text-editor. ADT interfaces provide a list of operations ( what ) rather than an implementation description ( how ). Miri Kopel, Bar-Ilan University 5

6 Car inum_of_doors; iyear_of_manufacturing; bis_automatic; turnon(); lock(); ADT = Car Miri Kopel, Bar-Ilan University 6

7 In C++ we use classes for defining ADTs. The syntax: class ClassName //attributes and operations ; Objects are instances of classes. That is, objects are to classes what variables are to types. A class definition does not allocate storage for any objects. Miri Kopel, Bar-Ilan University 7

8 Example of Object Oriented Analysis N elevators for M floors. Every elevator has M buttons. Miri Kopel, Bar-Ilan University 8

9 When pushing a button in the elevator: button is lighted. elevator arrives. doors are opened and button is turns off. On every floor, except first and last floors, there are two buttons (up & down). When pushing a button on a floor: button is lighted. when the elevator arrives the doors open and the button s light turns off. After a delay, the doors get closed, and the elevator moves to the requested way (if there are any requests). When there are no requests for the elevator it parks in the current floor with closed doors. Miri Kopel, Bar-Ilan University 9

10 elevator elevator button button floor button door floor 2 uses of class functions: What to do Message Method How to do Miri Kopel, Bar-Ilan University 10

11 #include <iostream> class Point public: int x,y; void Show () std::cout<<"x="<<x<<" y="<<y<<std::endl; ; int main () Point p; p.x=15; p.y=10; p.show (); std::cout<<"please enter x and y values: "; std::cin >> p.x >> p.y; p.show (); Miri Kopel, Bar-Ilan University 11

12 The users of the class can clearly see exactly what they can use and what to ignore. The ability to ensure that no client programmer becomes dependent on any part the underlying implementation of a class. public = all member declarations that follows are available to everyone. private = no one can access that member except the creator of the type inside function members of that type. It s a brick wall between the object and the client programmer. Miri Kopel, Bar-Ilan University 12

13 class MyClass public: //Data and methods accessible to any user of //the class. protected: //Data and methods accessible to class //methods, derived classes, and friends only. private: //Data and methods accessible to class //methods and friends only. ; Miri Kopel, Bar-Ilan University 13

14 #include <iostream> class Point private: int m_x, m_y; public: void Set_x(int val) m_x=val; int Get_x() return m_x; void Set_y(int val) m_y=val; int Get_y()return m_y; void Show()std::cout<<"x="<<m_x<< " y="<<m_y<<std::endl; ; Miri Kopel, Bar-Ilan University 14

15 Example 2 (cont.): int main () Point p; //p.m_x=15; -----ERROR p.set_x (15); //p.m_y=10; -----ERROR p.set_y (10); p.show (); p.set_x (17); p.set_y (5); std::cout<<"x= "<< p.get_x() <<" y= <<p.get_y()<<std::endl; Miri Kopel, Bar-Ilan University 15

16 Composition Data members may be objects of built-in types as well as user-defined types. Example 3: #include <iostream> #include Point.h class Line private: Point m_p1, m_p2; //composition public: void SetLine(int x1,int y1,int x2,int y2); void SetLine(const Point& p1,const Point& p2); void Show(); ; Miri Kopel, Bar-Ilan University 16

17 void Line::SetLine(int x1,int y1,int x2,int y2) m_p1.set_x(x1); m_p1.set_y(y1); m_p2.set_x(x2); m_p2.set_y(y2); void Line::SetLine(const Point& p1,const Point& p2) m_p1 = p1; //operator = between 2 Points m_p2 = p2; void Line::Show() std::cout<<"line from: "; m_p1.show(); std::cout<<" To: "; m_p2.show(); Miri Kopel, Bar-Ilan University 17

18 int main () Point p1,p2; p1.set_x(15); p1.set_y(10); p2.set_x(0); p2.set_y(0); Line line1,line2; line1.setline(15,10,7,6); line1.show(); line2.setline(p1,p2); line2.show(); Line from: x=15 y=10 To: x=7 y=6 Line from: x=15 y=10 To: x=0 y=0 Miri Kopel, Bar-Ilan University 18

19 In C we have macro: #define SUM(X,Y) ((X)+(Y)) Implemented by the pre-processor. An inline function is a function whose code gets inserted into the caller's code stream. Like a #define macro, inline functions improve performance by avoiding the overhead of the call itself and (especially!) by the compiler being able to optimize through the call ("procedural integration"). Miri Kopel, Bar-Ilan University 19

20 inline functions (cont.): To define an inline function, you must ordinarily precede the function definition with the inline keyword. It is not necessary inside a class definition. A member function defined within the class definition is taken automatically to be an inline member function. That is, in-class definition of member functions is for small, frequently-used functions. Miri Kopel, Bar-Ilan University 20

21 inline functions (cont.): An inline is just a suggestion to the compiler. When the function is too complicated the compiler may reject the inline request. When the compiler must produce an address of the function, it will always reject our request. Constructors and Destructors may have hidden activities inside them since the class can contain sub-objects whose constructors and destructors must be called. You should consider its efficiency before making them inline. Miri Kopel, Bar-Ilan University 21

22 inline functions (cont.): Since the inline mechanism is done by the compiler (before the linkage), it's usually imperative that the function's definition (the part between the...) be placed in a header file. If you put the inline function's definition into a.cpp file, and if it is called from some other.cpp file, you'll get an "unresolved external" error from the linker. You should consider the information hiding subject in this case. Beware that overuse of inline functions can cause code bloat, which can in turn have a negative performance impact in paging environments. Miri Kopel, Bar-Ilan University 22

23 The class designer can guarantee initialization of every object by providing a special function, called the constructor. If a class has a constructor, the compiler automatically calls that constructor at the point an object is created. The name of the constructor is the same as the name of the class. Like any function, the constructor can have arguments to allow us to specify how an object is created, give it initialization values, and so on. Miri Kopel, Bar-Ilan University 23

24 The destructor is guarantee for cleaning up the object. It is called automatically be the compiler when the object goes out of scope. The syntax for the destructor is similar to that for the constructor: the class name with a leading ~. The destructor never has any arguments because destruction never needs any options. Both the constructor and the destructor have no return values. Miri Kopel, Bar-Ilan University 24

25 A default constructor is one that can be called with no arguments. The default constructor is so important that if (and only if) there are no constructors for a class, the compiler will automatically create one for you. If I declared other Ctor in the class, do I get the Default one too? Miri Kopel, Bar-Ilan University 25

26 #include <iostream> using namespace std; class Point private: int m_x, m_y; public: Point () m_x=0; m_y=0; //default constructor Point (int valx, int valy) m_x=valx; m_y=valy; ~Point () cout<<"goodbye"<<endl; //destructor ; void set_x (int val) m_x=val; int get_x () return m_x; void set_y (int val) m_y=val; int get_y () return m_y; void show ()cout<<"x="<<m_x<<" y="<<m_y<<endl; Miri Kopel, Bar-Ilan University 26

27 Example 3 (cont.): int main () Point p1 (15,10); Point p2; //default point std::cout<<"the first point - "; p1.show(); std::cout<<"the second point - "; p2.show(); The first point - x=15 y=10 The second point - x=0 y=0 GoodBye GoodBye Miri Kopel, Bar-Ilan University 27

28 class Point Example 5: private: int m_x, m_y; public: Point(); Point(int x, int y); ~Point()std::cout<<"Deleting a point...\n"; //the set & get methods as before... ; Point::Point() //default constructor std::cout<< Creating a default point \n"; m_x=0; m_y=0; Point::Point(int x, int y) //constructor with args std::cout<<"creating a point...\n"; m_x=x; m_y=y; 28 Miri Kopel, Bar-Ilan University

29 class Line private: Point m_p1, m_p2; public: Line()std::cout<<"Creating a default line...\n";; Line(int x1,int y1,int x2,int y2); ~Line() std::cout<<"deleting a line...\n"; ; Line::Line(int x1,int y1,int x2,int y2) std::cout<<"creating a line...\n"; //set the x and y values of p1 and p2 //with the arguments x1,y1,x2,y2. //... Miri Kopel, Bar-Ilan University 29

30 int main() Line l1; Line l2(2,5,7,8); Line l1 Point m_p1 int m_x int m_y =0 =0 Line l2 Point m_p1 int m_x int m_y =2 =0 =0 =5 Creating a default point... Creating a default point... Creating a default line... Creating a default point... Creating a default point... Creating a line... Deleting a line... Deleting a point... Deleting a point... Deleting a line... Deleting a point... Deleting a point... Point m_p2 Point m_p2 int m_x =0 int m_x =7 =0 int m_y =0 =0 int m_y =8 Miri Kopel, Bar-Ilan University 30

31 In composition, the constructors are called in the following order: Internal object s constructor. External class s constructor. The destructors are called in the reversed order. Miri Kopel, Bar-Ilan University 31

32 Data members may be object of built-in types as well as user-defined types. When an object is created, the compiler guarantees that constructors for all of its subobjects are called. In case all the sub-objects have default constructors, this is what the compiler automatically calls. QUESTION: How do we initialize class data members that are objects of userdefined types whose constructors require arguments? Miri Kopel, Bar-Ilan University 32

33 ANSWER: Use the member initialization section. That is the part of the constructor after the : following the constructor s parameter list (up to the first ). It s a good habit to always use the member initialization section. Member initialization section only applies to constructors. Miri Kopel, Bar-Ilan University 33

34 class Line private: Point m_p1,m_p2; public: Line(int x1, int y1, int x2, int y2); ~Line(); //destructor ; double Length (); void SetLine (int x1,int x2,int y1,int y2); void Show (); Miri Kopel, Bar-Ilan University 34

35 //~~~~~~~~~~~~~~~~~~~~~~~~ // Constructor with initialization list //~~~~~~~~~~~~~~~~~~~~~~~~ Line::Line(int x1,int y1,int x2,int y2) : m_p1(x1,y1), m_p2(x2,y2) //~~~~~~~~~~~~~~~~~~~~~~~~ // Destructor //~~~~~~~~~~~~~~~~~~~~~~~~ Line::~Line( ) cout<<"see you again soon!\n"; //~~~~~~~~~~~~~~~~~~~~~~~~ // Length //~~~~~~~~~~~~~~~~~~~~~~~~ double Line::Length () return sqrt(pow(m_p1.get_x()-m_p2.get_x(),2) + pow(m_p1.get_y()-m_p2.get_y(),2)); Miri Kopel, Bar-Ilan University 35

36 void Line::SetLine (int x1,int x2,int y1,int y2) m_p1.set_x(x1); m_p1.set_y(y1); m_p2.set_x(x2); m_p2.set_y(y2); void Line::Show() std::cout<<"the first point - "; m_p1.show(); cout<<std::endl; std::cout<<"the second point - "; m_p2.show(); cout<<std::endl; Miri Kopel, Bar-Ilan University 36

37 int main () Point p(15,10); p.show(); Line l(2,90,16,1); l.show(); std::cout<<"l's length is - <<l.length()<<std::endl; x=15 y=10 The first point - x=2 y=90 The second point - x=16 y=1 l's length is See you again soon! GoodBye GoodBye GoodBye 37 Miri Kopel, Bar-Ilan University

38 Stack Heap Global Data Segment Code Segment Miri Kopel, Bar-Ilan University 38

39 Handling passing and returning variables by value during function calls: int f(int x, char c); int g = f(a,b); push b push a call f() add sp, 4 mov g, register a Function arguments Return address Local variables Miri Kopel, Bar-Ilan University 39

40 When you pass an object by value, you create a new object (the passed object inside the function frame) from an existing object (the original object outside the function frame). This is also true when returning an object by value. The compiler s assumption is that you want to perform this creation using a bitcopy. object_1 m_parray object_2 m_parray 1024 Miri Kopel, Bar-Ilan University 40

41 In order to prevent the compiler from doing a bitcopy, you define your own function to be used whenever the compiler needs to make a new object from an existing object. This function is called copy constructor. The single argument to this constructor has to do with the object you re constructing from. The object can t be passed into the constructor by value, because you re trying to define the function that handles passing by value Miri Kopel, Bar-Ilan University 41

42 class String Example 7: private: char* m_str; //... public: String(const char* str=null); String(const String& str); //copy constructor ~String(); //... ; If I declare a C.Ctor only, do I get also the Default Ctor? String::String(const String& str) //str cannot be NULL since it s passed by reference m_str = new char[strlen(str.m_str)+1]; strcpy(m_str,str.m_str); Miri Kopel, Bar-Ilan University 42

43 In some cases, it is necessary for the compiler to create temporary objects. These temporary objects can be created for the following reasons: Result of expression evaluation. Result of expressions using the built-in (not overloaded) logical operators ( and &&). Initializing const references. To store the result of a cast to a user-defined type. To store the return value of a function that returns a user-defined type. Miri Kopel, Bar-Ilan University 43

44 Temporary objects have a lifetime that is defined by their point of creation and the point at which they are destroyed. class MyString public: MyString(const char* str=null); ~MyString(); private: char* m_str; ; Example 8: Miri Kopel, Bar-Ilan University 44

45 MyString::MyString(const char* str1/*=null*/) std::cout<<"creating a string\n"; if(str1) m_str = new char[strlen(str1)+1]; strcpy(m_str,str1); else m_str = NULL; MyString::~MyString() if(m_str) delete[] m_str; m_str = NULL; std::cout<<"deleting a string\n"; Miri Kopel, Bar-Ilan University 45

46 MyString GetString() MyString str2("testing"); return str2; int main() MyString str3( GetString() ); main() GetString() str3 temp str2 m_str Miri Kopel, Bar-Ilan University 46