Constructor and Destructor.pdf

Constructor and Destructor.pdf

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  Constructor and Destructor
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  Constructor • In C++,constructor is a special method which is invoked automatically at the time of object creation. • It is used to initialize the data members of new object generally. • The constructor in C++ has the same name as class or structure. • There can be two types of constructors in C++. 1. Default constructor 2. Parameterized constructor
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  Default Constructor • Aconstructor which has no argument is known as default constructor. • It is invoked at the time of creating object.
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  Default Constructor class Employee { public: Employee() { cout<<"DefaultConstructor Invoked"<<endl; } }; int main(void) { Employee e1; //creating an object of Employee Employee e2; return 0; }
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  Parameterized Constructor • Aconstructor which has parameters is called parameterized constructor. • It is used to provide different values to distinct objects.
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  Parameterized Constructor class Employee{ public: int id;//data member (also instance variable) string name;//data member(also instance variable) float salary; Employee(int i, string n, float s) { id = i; name = n; salary = s; } void display() { cout<<id<<" "<<name<<" "<<salary<<endl; } }; int main(void) { Employee e1 =Employee(101, "Sonoo", 890000); //creating an object of Employee Employee e2=Employee(102, "Nakul", 59000); e1.display(); e2.display(); return 0; }
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  int main() { int a=10,*c; int*p; p=&a; c=p; cout<<a<<endl; cout<<p<<endl; cout<<c<<endl; cout<<*c<<endl; } Pointer Basic
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  Copy Constructor • ACopy constructor is an overloaded constructor used to declare and initialize an object from another object. Copy Constructor is of two types: • Default Copy constructor: The compiler defines the default copy constructor. If the user defines no copy constructor, compiler supplies its constructor. • User Defined constructor: The programmer defines the user-defined constructor.
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  Syntax of User-definedCopy Constructor: Class_name(const class_name &old_object);
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  class A { public: int x; A(inta) // parameterized constructor. { x=a; } A(A &i) // copy constructor { x = i.x; } }; int main() { A a1(20); // Calling the parameterized constructor. A a2(a1); // Calling the copy constructor. cout<<a2.x; return 0; }
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  When Copy Constructoris called • Copy Constructor is called in the following scenarios: • When we initialize the object with another existing object of the same class type. • For example, Student s1 = s2, where Student is the class. • When the object of the same class type is passed by value as an argument. • When the function returns the object of the same class type by value. • Two types of copies are produced by the constructor: ❖Shallow copy ❖Deep copy https://www.javatpoint.com/cpp-copy-constructor
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  Copy constructor andAssignment operator(=) • https://www.javatpoint.com/cpp-copy-constructor
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  Destructor • A destructorworks opposite to constructor; • it destructs the objects of classes. • It can be defined only once in a class. • Like constructors, it is invoked automatically. • A destructor is defined like constructor. • It must have same name as class. • But it is prefixed with a tilde sign (~).
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  Constructor and DestructorExample class Employee { public: Employee() { cout<<"Constructor Invoked"<<endl; } ~Employee() { cout<<"Destructor Invoked"<<endl; } }; int main(void) { Employee e1; //creating an object of Employee Employee e2; //creating an object of Employee return 0; } Output: Constructor Invoked Constructor Invoked Destructor Invoked Destructor Invoked