Classes and Objects - BU Computer Science

Classes and Objects - BU Computer Science

Classes and Objects const (Constant) Objects and const Member Functions Principle of least privilege Only give objects permissions they need, no more Keyword const Specify that an object is not modifiable Any attempt to modify the object is a syntax error Example const Time noon( 12, 0, 0 ); Declares a const object noon of class Time and initializes it to 12 const (Constant) Objects and const Member Functions const objects require const functions Member functions declared const cannot modify their object const must be specified in function prototype and definition Prototype: ReturnType FunctionName(param1,param2) const; Definition: ReturnType FunctionName(param1,param2) const { } Example: int A::getValue() const { return privateDataMember }; Returns the value of a data member but doesnt modify anything so is declared const Constructors / Destructors cannot be const They need to initialize variables, therefore modifying them 1 // Fig. 7.1: time5.h 2 3

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 // Declaration of the class Time. // Member functions defined in time5.cpp #ifndef TIME5_H #define TIME5_H class Time { public: Time( int = 0, int = 0, int = 0 ); // default constructor

// set functions void setTime( int, int, int ); // set time void setHour( int ); // set hour void setMinute( int ); // set minute void setSecond( int ); // set second // get functions (normally declared const) int getHour() const; // return hour int getMinute() const; // return minute int getSecond() const; // return second // print functions (normally declared const) void printMilitary() const; // print military time void printStandard(); // print standard time private: int hour; // 0 - 23 int minute; // 0 - 59 int second; // 0 - 59 }; #endif 32 33 34 35 36 37 38 39 40 41

42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 // Fig. 7.1: time5.cpp // Member function definitions for Time class. #include using std::cout; The constructor is non-const but it can be called for const objects. #include "time5.h" // Constructor function to initialize private data. // Default values are 0 (see class definition). Time::Time( int hr, int min, int sec ) { setTime( hr, min, sec ); } // Set the values of hour, minute, and second. void Time::setTime( int h, int m, int s ) {

setHour( h ); setMinute( m ); setSecond( s ); } // Set the hour value void Time::setHour( int h ) { hour = ( h >= 0 && h < 24 ) ? h : 0; } // Set the minute value void Time::setMinute( int m ) { minute = ( m >= 0 && m < 60 ) ? m : 0; } // Set the second value void Time::setSecond( int s ) { second = ( s >= 0 && s < 60 ) ? s : 0; } 64 65 // Get the hour value 66 int Time::getHour() const { return hour; } 67 68 // Get the minute value 69 int Time::getMinute() const { return minute; } 70 71 // Get the second value 72 int Time::getSecond() const { return second; } 73 74 // Display military format time: HH:MM 75 void Time::printMilitary() const 76 { 77 cout << ( hour < 10 ? "0" : "" ) 78 << ( minute < 10 ? "0" : "" Non-const functions cannot use const objects, even if they dont << hour << ":" modify them (such as

) << minute;printStandard). 79 } 80 81 // Display standard format time: HH:MM:SS AM (or PM) 82 void Time::printStandard() // should be const 83 { 84 cout << ( ( hour == 12 ) ? 12 : hour % 12 ) << ":" 85 << ( minute < 10 ? "0" : "" ) << minute << ":" 86 << ( second < 10 ? "0" : "" ) << second 87 << ( hour < 12 ? " AM" : " PM" ); 88 } 89 // Fig. 7.1: fig07_01.cpp 90 // Attempting to access a const object with 91 // non-const member functions. 92 #include "time5.h" 93 94 int main() 95 { 96 Time wakeUp( 6, 45, 0 ); // non-constant object 97

const Time noon( 12, 0, 0 ); // constant object 98 99 // MEMBER FUNCTION OBJECT 100 wakeUp.setHour( 18 ); // non-const non-const 101 102 noon.setHour( 12 ); // non-const const 103 104 wakeUp.getHour(); // const non-const 105 106 noon.getMinute(); // const const 107 noon.printMilitary(); // const const 108 noon.printStandard(); // non-const const 109 return 0; 110 } Compiling... Fig07_01.cpp d:fig07_01.cpp(14) : error C2662: 'setHour' : cannot convert 'this' pointer from 'const class Time' to 'class Time &' Conversion loses qualifiers d:\fig07_01.cpp(20) : error C2662: 'printStandard' : cannot convert

'this' pointer from 'const class Time' to 'class Time &' Conversion loses qualifiers Time5.cpp Error executing cl.exe. test.exe - 2 error(s), 0 warning(s) const (Constant) Objects and const Member Functions Member initializer syntax Data member increment in class Increment constructor for Increment is modified as follows: Increment::Increment( int c, int i ) : increment( i ) { count = c; } : increment( i ) initializes increment to i All data members can be initialized using member initializer syntax consts and references must be initialized using member initializer syntax Multiple member initializers Use comma-separated list after the colon 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 // Fig. 7.2: fig07_02.cpp // Using a member initializer to initialize a // constant of a built-in data type. #include using std::cout; using std::endl; class Increment { public: Increment( int c = 0, int i = 1 ); void addIncrement() { count += increment; } void print() const; private: int count; const int increment; }; // const data member // Constructor for class Increment Increment::Increment( int c, int i ) : increment( i )

// initializer for const member { count = c; } // Print the data void Increment::print() const { cout << "count = " << count << ", increment = " << increment << endl; } int main() { If we try to initialize increment with an assignment statement (such as increment = i ) instead of a member initializer we get an error. 34 Increment value( 10, 5 ); 35 36 cout << "Before incrementing: "; 37 value.print(); 38 39 for ( int j = 0; j < 3; j++ ) { 40 value.addIncrement();

41 cout << "After increment " << j + 1 << ": "; 42 value.print(); 43 } 44 45 return 0; 46 } Before incrementing: count After increment 1: count = After increment 2: count = After increment 3: count = = 10, increment 15, increment = 20, increment = 25, increment = = 5 5 5 5 Objects as Members of Classes Composition Class has objects of other classes as members Construction of objects

Member objects constructed in order declared Not in order of constructors member initializer list Constructed before their enclosing class objects (host objects) 1 // Fig. 7.4: date1.h 2 // Declaration of the Date class. 3 // Member functions defined in date1.cpp 4 #ifndef DATE1_H 5 #define DATE1_H 6 7 class Date { 8 public: 9 Date( int = 1, int = 1, int = 1900 ); // default constructor

10 void print() const; 11 ~Date(); // print date in month/day/year format // provided to confirm destruction order 12 private: 13 int month; // 1-12 14 int day; // 1-31 based on month 15 int year; // any year 16 17 // utility function to test proper day for month and year 18 int checkDay( int );

19 }; 20 21 #endif 22 // Fig. 7.4: date1.cpp 23 // Member function definitions for Date class. 24 #include 25 26 using std::cout; 27 using std::endl; 28 29 #include "date1.h" 30 31 // Constructor: Confirm proper value for month; 32 // call utility function checkDay to confirm proper 33 // value for day. 34 Date::Date( int mn, int dy, int yr ) 35 { 36 if ( mn > 0 && mn <= 12 ) 37 38 // validate the month month = mn; else { 39 month = 1; 40 cout << "Month " << mn << " invalid. Set to month 1.\n";

41 } 42 43 year = yr; // should validate yr 44 day = checkDay( dy ); // validate the day 45 46 cout << "Date object constructor for date "; 47 print(); 48 cout << endl; 49 } 50 // interesting: a print with no arguments Constructor will print a line when called. 51

52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 // Print Date object in form month/day/year void Date::print() const { cout << month << '/' << day << '/' << year; } // Destructor: provided to confirm destruction order Date::~Date() {

cout << "Date object destructor for date "; print(); cout << endl; } // Utility function to confirm proper day value // based on month and year. // Is the year 2000 a leap year? int Date::checkDay( int testDay ) { static const int daysPerMonth[ 13 ] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; if ( testDay > 0 && testDay <= daysPerMonth[ month ] ) return testDay; if ( month == 2 && // February: Check for leap year testDay == 29 && ( year % 400 == 0 || ( year % 4 == 0 && year % 100 != 0 ) ) ) return testDay; cout << "Day " << testDay << " invalid. Set to day 1.\n"; return 1; } // leave object in consistent state if bad value 84 // Fig. 7.4: emply1.h 85 // Declaration of the Employee class. 86 // Member functions defined in emply1.cpp 87 #ifndef EMPLY1_H 88 #define EMPLY1_H 89 90 #include "date1.h" 91 92 class Employee { 93 public: 94 Employee( char *, char *, int, int, int, int, int, int );

95 void print() const; 96 ~Employee(); // provided to confirm destruction order 97 private: 98 char firstName[ 25 ]; 99 char lastName[ 25 ]; 100 const Date birthDate; 101 const Date hireDate; 102 }; 103 104 #endif Composition - including objects of other classes. 105 // Fig. 7.4: emply1.cpp 106 // Member function definitions for Employee class. 107 #include 108 109 using std::cout;

110 using std::endl; 111 112 #include 113 #include "emply1.h" 114 #include "date1.h" 115 116 Employee::Employee( char *fname, char *lname, 117 int bmonth, int bday, int byear, 118 int hmonth, int hday, int hyear ) 119 : birthDate( bmonth, bday, byear ), 120 hireDate( hmonth, hday, hyear ) 121 { 122 // copy fname into firstName and be sure that it fits 123 int length = strlen( fname ); 124 length = ( length < 25 ? length : 24 ); 125 strncpy( firstName, fname, length ); 126 firstName[ length ] = '\0'; 127 128 // copy lname into lastName and be sure that it fits 129 length = strlen( lname ); 130 length = ( length < 25 ? length : 24 ); Constructor will 131 strncpy( lastName, lname, length ); print a line when 132 lastName[ length ] = '\0';

called. 133 134 cout << "Employee object constructor: " 135 << firstName << ' ' << lastName << endl; 136 } 137 138 void Employee::print() const 139 { 140 cout << lastName << ", " << firstName << "\nHired: "; 141 hireDate.print(); 142 cout << " 143 birthDate.print(); 144 cout << endl; Birth date: "; 145 } 146 The print function is const and will print whenever a Date object is created or destroyed. It can print const

objects because it is a const function. Print requires no arguments, it is linked implicitly to the object that calls it. 147 // Destructor: provided to confirm destruction order 148 Employee::~Employee() 149 { 150 151 152 } cout << "Employee object destructor: " << lastName << ", " << firstName << endl; Destructor will print a line when called. 153 // Fig. 7.4: fig07_04.cpp 154 // Demonstrating composition: an object with member objects. 155 #include 156 157 using std::cout; 158 using std::endl; 159 160 #include "emply1.h" 161 162 int main() Only emply.h has to be loaded; that file has the command to load date.h. 163 { 164 Employee e( "Bob", "Jones", 7, 24, 1949, 3, 12, 1988 );

165 166 cout << '\n'; 167 e.print(); 168 169 cout << "\nTest Date constructor with invalid values:\n"; 170 Date d( 14, 35, 1994 ); 171 cout << endl; 172 return 0; 173 } // invalid Date values Date object constructor for date 7/24/1949 Date object constructor for date 3/12/1988 Employee object constructor: Bob Jones Jones, Bob Hired: 3/12/1988 Birth date: 7/24/1949 Test Date constructor with invalid values:

Month 14 invalid. Set to month 1. Day 35 invalid. Set to day 1. Date object constructor for date 1/1/1994 Date object destructor for date 1/1/1994 Employee object destructor: Jones, Bob Date object destructor for date 3/12/1988 Date object destructor for date 7/24/1949 Notice how inner objects are created first and destroyed last. Program Output friend Functions and friend Classes friend function and friend classes Can access private and protected members of another class friend functions are not member functions of class Defined outside of class scope Properties of friendship Friendship is granted, not taken Not symmetric (if B a friend of A, A not necessarily a friend of B) Not transitive (if A a friend of B, B a friend of C, A not necessarily a friend of C) friend Functions and friend Classes friend declarations To declare a friend function Type friend before the function prototype in the class that is giving friendship friend int myFunction( int x ); should appear in the class giving friendship To declare a friend class Type friend class Classname in the class that is giving friendship

if ClassOne is granting friendship to ClassTwo, friend class ClassTwo; should appear in ClassOne's definition 1 2 3 // Fig. 7.5: fig07_05.cpp // Friends can access private members of a class. #include 4 5 6 7 using std::cout; using std::endl; 8 // Modified Count class 9 class Count { 10 friend void setX( Count &, int ); // friend declaration 11 public: 12 Count() { x = 0; } // constructor 13 void print() const { cout << x << endl; } // output 14 private: 15 int x; // data member 16 17 18 19 20

}; // Can modify private data of Count because // setX is declared as a friend function of Count void setX( Count &c, int val ) 21 { 22 23 } 24 Changing private variables allowed. c.x = val; // legal: setX is a friend of Count 25 int main() 26 { 27 Count counter; 28 29 30 cout << "counter.x after instantiation: "; counter.print(); 31 cout << "counter.x after call to setX friend function: "; 32 setX( counter, 8 ); 33 counter.print();

34 return 0; // set x with a friend 35 } counter.x after instantiation: 0 counter.x after call to setX friend function: 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

28 29 30 31 // Fig. 7.6: fig07_06.cpp // Non-friend/non-member functions cannot access // private data of a class. #include using std::cout; using std::endl; // Modified Count class class Count { public: Count() { x = 0; } // constructor void print() const { cout << x << endl; } // output private: int x; // data member }; // Function tries to modify private data of Count, // but cannot because it is not a friend of Count. void cannotSetX( Count &c, int val ) { c.x = val; // ERROR: 'Count::x' is not accessible } int main() { Count counter; cannotSetX( counter, 3 ); // cannotSetX is not a friend return 0; } Compiling... Fig07_06.cpp D:\books\2000\cpphtp3\examples\Ch07\Fig07_06\Fig07_06.cpp(22) : error C2248: 'x' : cannot access private member declared in class 'Count' D:\books\2000\cpphtp3\examples\Ch07\Fig07_06\

Fig07_06.cpp(15) : see declaration of 'x' Error executing cl.exe. test.exe - 1 error(s), 0 warning(s) Program Output Using the this Pointer this pointer Allows objects to access their own address Not part of the object itself Implicit first argument on non-static member function call to the object Implicitly reference member data and functions The type of the this pointer depends upon the type of the object and whether the member function using this is const In a non-const member function of Employee, this has type Employee * const Constant pointer to an Employee object In a const member function of Employee, this has type const Employee * const Constant pointer to a constant Employee object Using the this Pointer Examples using this For a member function print data member x, either this->x or ( *this ).x Cascaded member function calls Function returns a reference pointer to the same object { return *this; } Other functions can operate on that pointer Functions that do not return references must be called last Using the this Pointer Example of cascaded member function calls Member functions setHour, setMinute, and setSecond all return *this (reference to an object)

For object t, consider t.setHour(1).setMinute(2).setSecond(3); Executes t.setHour(1), returns *this (reference to object) and the expression becomes t.setMinute(2).setSecond(3); Executes t.setMinute(2), returns reference and becomes t.setSecond(3); Executes t.setSecond(3), returns reference and becomes t; 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

25 26 27 28 29 30 31 32 // Fig. 7.7: fig07_07.cpp // Using the this pointer to refer to object members. #include using std::cout; using std::endl; class Test { public: Test( int = 0 ); void print() const; private: int x; }; Test::Test( int a ) { x = a; } // default constructor // constructor void Test::print() const // ( ) around *this required { cout << " x = " << x << "\n this->x = " << this->x << "\n(*this).x = " << ( *this ).x << endl; } int main() { Test testObject( 12 ); testObject.print();

return 0; } x = 12 this->x = 12 (*this).x = 12 All three methods have the same result. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

30 31 32 33 // Fig. 7.8: time6.h // Cascading member function calls. // Declaration of class Time. // Member functions defined in time6.cpp #ifndef TIME6_H #define TIME6_H class Time { public: Time( int = 0, int = 0, int = 0 ); // set functions Time &setTime( int, int, Time &setHour( int ); Time &setMinute( int ); Time &setSecond( int ); int ); // set // set // set // default constructor // set hour, minute, second hour minute second // get functions (normally declared const) int getHour() const; // return hour int getMinute() const; // return minute int getSecond() const; // return second

// print functions (normally declared const) void printMilitary() const; // print military time void printStandard() const; // print standard time private: int hour; // 0 - 23 int minute; // 0 - 59 int second; // 0 - 59 }; #endif Notice the Time & - function returns a reference to a Time object. Specify object in function definition. 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 58 59 60 61 62 63 64 // Fig. 7.8: time.cpp // Member function definitions for Time class. #include using std::cout; #include "time6.h" // Constructor function to initialize private data. // Calls member function setTime to set variables. // Default values are 0 (see class definition). Time::Time( int hr, int min, int sec ) { setTime( hr, min, sec ); } // Set the values of hour, minute, and second. Time &Time::setTime( int h, int m, int s ) Returning *this enables { cascading function calls setHour( h ); setMinute( m ); setSecond( s ); return *this; // enables cascading } // Set the hour value Time &Time::setHour( int h ) { hour = ( h >= 0 && h < 24 ) ? h : 0; return *this; }

// enables cascading 65 // Set the minute value 66 Time &Time::setMinute( int m ) 67 { 68 69 70 71 } minute = ( m >= 0 && m < 60 ) ? m : 0; return *this; // enables cascading 72 73 // Set the second value 74 Time &Time::setSecond( int s ) 75 { 76 77 78 79 } second = ( s >= 0 && s < 60 ) ? s : 0; return *this; // enables cascading 80 81 // Get the hour value 82 int Time::getHour() const { return hour; } 83 84 // Get the minute value 85 int Time::getMinute() const { return minute; } 86 87 // Get the second value 88 int Time::getSecond() const { return second; } 89

90 // Display military format time: HH:MM 91 void Time::printMilitary() const 92 { 93 94 cout << ( hour < 10 ? "0" : "" ) << hour << ":" << ( minute < 10 ? "0" : "" ) << minute; Returning *this enables cascading function calls 95 } 96 97 // Display standard format time: HH:MM:SS AM (or PM) 98 void Time::printStandard() const 99 { 100 cout << ( ( hour == 0 || hour == 12 ) ? 12 : hour % 12 ) 101 << ":" << ( minute < 10 ? "0" : "" ) << minute 102 << ":" << ( second < 10 ? "0" : "" ) << second 103 << ( hour < 12 ? " AM" : " PM" ); 104 } 105 // Fig. 7.8: fig07_08.cpp 106 // Cascading member function calls together 107 // with the this pointer 108 #include 109 110 using std::cout; 111 using std::endl; 112 Notice cascading 113 #include "time6.h" 114 115 int main() 116 {

117 Time t; 118 119 t.setHour( 18 ).setMinute( 30 ).setSecond( 22 ); 120 cout << "Military time: "; 121 t.printMilitary(); 122 cout << "\nStandard time: "; 123 t.printStandard(); 124 125 cout << "\n\nNew standard time: "; 126 t.setTime( 20, 20, 20 ).printStandard(); function calls. 127 cout << endl; 128 129 return 0; 130 } Military time: 18:30 Standard time: 6:30:22 PM New standard time: 8:20:20 PM Dynamic Memory Allocation with Operators new and delete new and delete

Used for dynamic memory allocation Superior to Cs malloc and free new Creates an object of the proper size, calls its constructor and returns a pointer of the correct type delete Destroys object and frees space Examples of new TypeName *typeNamePtr; Creates pointer to a TypeName object typeNamePtr = new TypeName; new creates TypeName object, returns pointer (which typeNamePtr is set equal to) Dynamic Memory Allocation with Operators new and delete Examples of delete delete typeNamePtr; Calls destructor for TypeName object and frees memory Delete [] arrayPtr; Used to dynamically delete an array Initializing objects double *thingPtr = new double( 3.14159 ); Initializes object of type double to 3.14159 int *arrayPtr = new int[ 10 ]; Creates a ten element int array and assigns it to arrayPtr static Class Members

static class members Shared by all objects of a class Normally, each object gets its own copy of each variable Efficient when a single copy of data is enough Only the static variable has to be updated May seem like global variables, but have class scope only accessible to objects of same class Initialized at file scope Exist even if no instances (objects) of the class exist Both variables and functions can be static Can be public, private or protected static Class Members static variables Static variables are accessible through any object of the class public static variables Can also be accessed using scope resolution operator(::) Employee::count private static variables When no class member objects exist, can only be accessed via a public static member function To call a public static member function combine the class name, the :: operator and the function name Employee::getCount() static Class Members Static functions static member functions cannot access nonstatic data or functions

There is no this pointer for static functions, they exist independent of objects 1 // Fig. 7.9: employ1.h 2 // An employee class 3 #ifndef EMPLOY1_H 4 #define EMPLOY1_H 5 6 class Employee { 7 public: 8 Employee( const char*, const char* ); // constructor 9 ~Employee(); // destructor 10 const char *getFirstName() const; // return first name 11 const char *getLastName() const; // return last name 12 13 // static member function

14 static int getCount(); // return # objects instantiated 15 16 private: 17 char *firstName; 18 char *lastName; 19 20 // static data member 21 static int count; 22 }; 23 24 #endif // number of objects instantiated 25 26 27 28 29 30 31 32

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 // Fig. 7.9: employ1.cpp // Member function definitions for class Employee #include using std::cout; using std::endl; #include #include #include "employ1.h" static data member count and function getCount( ) initialized at file scope (required). // Initialize the static data member

int Employee::count = 0; // Define the static member function that // returns the number of employee objects instantiated. int Employee::getCount() { return count; } // Constructor dynamically allocates space for the // first and last name and uses strcpy to copy // the first and last names into the object Employee::Employee( const char *first, const char *last ) { firstName = new char[ strlen( first ) + 1 ]; assert( firstName != 0 ); // ensure memory allocated strcpy( firstName, first ); static data member count changed when a constructor/destructor called. lastName = new char[ strlen( last ) + 1 ]; assert( lastName != 0 ); // ensure memory allocated strcpy( lastName, last ); ++count; // increment static count of employees 57 58 59 60 61 62 63 64 65 66 67 68 69

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 cout << "Employee constructor for " << firstName << ' ' << lastName << " called." << endl; } // Destructor deallocates dynamically allocated memory Employee::~Employee() { cout << "~Employee() called for " << firstName << ' ' << lastName << endl; delete [] firstName; // recapture memory delete [] lastName; // recapture memory --count; // decrement static count of employees } // Return first name of employee const char *Employee::getFirstName() const { // Const before return type prevents client from modifying // private data. Client should copy returned string before // destructor deletes storage to prevent undefined pointer. return firstName;

} // Return last name of employee const char *Employee::getLastName() const { // Const before return type prevents client from modifying // private data. Client should copy returned string before // destructor deletes storage to prevent undefined pointer. return lastName; } 88 // Fig. 7.9: fig07_09.cpp 89 // Driver to test the employee class 90 #include 91 92 using std::cout; 93 using std::endl; 94 95 #include "employ1.h" 96 97 int main() 98 { 99 cout << "Number of employees before instantiation is " 100 << Employee::getCount() << endl; // use class name 101 102 Employee *e1Ptr = new Employee( "Susan", "Baker" ); 103 Employee *e2Ptr = new Employee( "Robert", "Jones" ); of employees after instantiation is 2 Number 104 105 cout << "Number of employees after instantiation is " 106 << e1Ptr->getCount(); 107

108 cout << "\n\nEmployee 1: " 109 << e1Ptr->getFirstName() 110 << " " << e1Ptr->getLastName() 111 << "\nEmployee 2: " 112 << e2Ptr->getFirstName() 113 << " " << e2Ptr->getLastName() << "\n\n"; 114 115 delete e1Ptr; // recapture memory 116 e1Ptr = 0; 117 delete e2Ptr; // recapture memory 118 e2Ptr = 0; 119 120 121 cout << "Number of employees after deletion is " << Employee::getCount() << endl; 122 123 return 0; 124 } count back to zero.

Number of employees before instantiation is 0 Employee constructor for Susan Baker called. Employee constructor for Robert Jones called. Number of employees after instantiation is 2 Employee 1: Susan Baker Employee 2: Robert Jones ~Employee() called for Susan Baker ~Employee() called for Robert Jones Number of employees after deletion is 0 Example: Array Abstract Data Type Programmer can make an ADT array Could include Subscript range checking An arbitrary range of subscripts instead of having to start with 0 Array assignment Array comparison Array input/output Arrays that know their sizes Arrays that expand dynamically to accommodate more elements Example: String Abstract Data Type Strings in C++ C++ does not provide a built in string data type Maximizes performance Provides mechanisms for creating and implementing a string abstract data type string class available in ANSI/ISO standard Container Classes and Iterators Container classes (collection classes) Classes designed to hold collections of objects Provide services such as insertion, deletion, searching, sorting, or testing an item Examples:

Arrays, stacks, queues, trees and linked lists Iterator objects (iterators) Object that returns the next item of a collection (or performs some action on the next item) Can have several iterators per container Book with multiple bookmarks Each iterator maintains its own position information Proxy Classes Proxy class Used to hide implementation details of a class Class that knows only the public interface of the class being hidden Enables clients to use classs services without giving access to classs implementation Forward class declaration Used when class definition only uses a pointer to another class Prevents the need for including the header file Declares a class before it is referenced Format: class ClassToLoad; 1 // Fig. 7.10: implementation.h 2 // Header file for class Implementation 3 4 class Implementation { 5 public: 6 Implementation( int v ) { value = v; } 7

void setValue( int v ) { value = v; } 8 int getValue() const { return value; } 9 10 11 private: Forward class declaration. int value; 12 }; 13 // Fig. 7.10: interface.h 14 // Header file for interface.cpp 15 class Implementation; // forward class declaration 16 17 class Interface { 18 public: 19 Interface( int ); 20 void setValue( int ); // same public interface as

21 int getValue() const; // class Implementation 22 ~Interface(); 23 24 25 26 }; private: Implementation *ptr; // requires previous // forward declaration 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 // Fig. 7.10: interface.cpp // Definition of class Interface #include "interface.h" #include "implementation.h" Interface::Interface( int v ) : ptr ( new Implementation( v ) ) { } // call Implementation's setValue function void Interface::setValue( int v ) { ptr->setValue( v ); } // call Implementation's getValue function int Interface::getValue() const { return ptr->getValue(); } Interface::~Interface() { delete ptr; } // Fig. 7.10: fig07_10.cpp // Hiding a classs private data with a proxy class. #include using std::cout; using std::endl; #include "interface.h" int main() { Interface i( 5 ); cout << "Interface contains: " << i.getValue()

<< " before setValue" << endl; i.setValue( 10 ); cout << "Interface contains: " << i.getValue() << " after setValue" << endl; return 0; Interface contains: 5 before setVal Interface contains: 10 after setVal Program Output

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    the existence and direction of periodic trends. Plotting TrendsA Periodic Table Activity. Introduction. Materials. Calculator, at least 1 per student group: ... Each group chooses or is assigned one element property: atomic mass, atomic radius, ionization energy, electronegativity, electron ...
  • Scaling Out on Wall Street

    Scaling Out on Wall Street

    OpenFabrics driver for Windows includes support for Network Direct, Winsock Direct and IPoIB protocols. User Mode. Kernel Mode. TCP/Ethernet . Networking. Kernel By-Pass. MPI App. Socket-Based App. MS-MPI. Windows Sockets (Winsock + WSD) Networking Hardware.