Constructors and Destructors - Advanced Programming - Lecture Slides, Slides of Computer Science

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Classes

Constructors & Destructors

Constructor

• Special Member Function used for Initialization -- Same Name as the Class Name
• Does NOT Return a Value
• Cannot be virtual and static
• Implicitly Invoked When Objects are Created or Copied
• Can Have Arguments
• Cannot be Explicitly Called
• Multiple Constructors are Allowed
• Default Constructor -- No Arguments -- Explicit or Implicit
• Copy Constructor -- Explicit or Implicit

Constructor – Example 1

• // date.cpp #include “date.h” //Default Constructor date::date() {day = 0; month = 0; year = 0; string_date = 0;} //First Constructor date::date(int ip_day, int ip_month, int ip_year){ day = ip_day; month = ip_month; year = ip_year; string_date = 0;} //Second Constructor date::date(char *ip_date){ day = 0; month = 0; year = 0; string_date = new char [size]; strcpy(string_date, ip_date);}

Constructor – Example 1

• // client.cpp #include “date.h” main() { //"default_day" is an object of "date". //Default Constructor is invoked. date default_day; // "today" is an object of "date". //First Constructor is invoked. date today(02, 02, 2004); // "string_today" is an object of "date". //Second Constructor is invoked. date string_today(“February 2, 2004"); }

Constructor – Example 2 (cont)

• // student.cpp #include “student.h” /* Member functions of the “Student" class */ Student::Student(){ name = new char[size]; id = new char[size]; email = new char[size];}

Student::Student(char *studentName, char *studentId, char *studentEmail){ name = new char[size]; strcpy(name, studentName); id = new char[size]; strcpy(id, studentId); email = new char[size]; strcpy(email, studentEmail); }

Constructor – Example 2 contd….

• // client.cpp

#include “student.h”

/* “csStudent" is an instance of “Student" */

main(){

Student csStudent1;

Student csStudent2 ("Susie Creamchese“,

"[email protected]");

Destructor – Example 1

• // date.h

/* A Simple Date Class With a Destructor */ #define size 50 class date{ private: int day, month, year; char *string_date; public: date(char *ip_date); ~date(); //Destructor };

Destructor – Example 1

• // date.cpp

#include “date.h”

//Constructor

date::date(char *ip_date){

day = 0; month = 0; year = 0;

string_date = new char [size];

strcpy(string_date, ip_date);}

//Destructor

date::~date() {delete[] (string_date);}

Destructor - Example 2

• // student.h /* A Simple Class to Represent a Student */ #define size 50

class Student{ private: char *name; char *id; char *email; public: Student(); //Default Student(char *, char *, char *); ~Student(); };

Destructor – Example 2 (cont)

• // student.cpp #include “student.h” /* Member functions of the “Student" class */ Student::Student(){ name = new char[size]; id = new char[size]; email = new char[size];} Student::Student(char *studentName, char *studentId, char *studentEmail){ name = new char[size]; strcpy(name, studentName); id = new char[size]; strcpy(id, studentId); email = new char[size]; strcpy(email, studentEmail);} Student::~Student(){ delete [] name; delete [] id; delete [] email; }