Question

C++

1. The copy constructor is used for one the following scenarios: I. Initialize one object from another of the same type. II. Copy an object to pass it as argument to a function. III. Copy an object to return it from a function. Read the following program and answer questions (20 points) #include <iostream> using namespace std; class Line public: int getLength( void); Line( int len // simple constructor Line( const Line &obj) 1/ copy constructor Line (); // destructor private: int ptr; // Member functions definitions including constructor Line: :Line (int len) cout <<"Normal constructor allocating ptr" << endl; // allocate memory for the pointer; ptr new int; *ptr = len; Line: :Line (const Line &obj) cout << "Copy constructor allocating ptr." << endl; ptr = new int; *ptrobj.ptri // copy the value Line: :~Line (void) cout << "Freeing memory!" << endl; delete ptri int Line: :getLength( void) f return *ptr; void display(Line obj) t cout <<"Length of line "<< obj.getLength) <<endl;

Answer 1

1. Copy constructor is used for one of the following scenarios:
I. Initialize one object from another of the same type:
Solution:
A copy constructor is a member function which initializes an object using another object of the same class. A copy constructor initialize the members of an object with same values as that of some previously created object. The object must be of same class. A copy constructor in the program has the following function prototype
Line( const Line &obj); // copy constructor
A copy constructor it creates a new object, which is exact copy of the existing copy, hence it is called copy constructor.
In above copy constructor where Line is the name of the class. obj is a reference to an object that is being used to initialize another object. The argument to the copy constructor is the object to be copied. The copy constructor should copy the values of each of the parameter object's data members to each of the class's data members. Reference parameter should be const to avoid potential for data corruption
Then the copy constructor should look something like:
Line::Line(const Line &obj) {
cout << "Copy constructor allocating ptr." << endl;
ptr = new int;
*ptr = *obj.ptr; // copy the value
}

p = new int; // creates a new int object.
*ptr = *obj.ptr; // copy data from obj
II. Copy an object to pass it as an argument to a function
Solution: passing a object of class as an argument by value to a function display() but it calling copy constructor and then control is hitting the display() function.Because passing by value to a function means the function has its own copy of the object.
Line line(10);
display(line); //calling copy constructor & display function

void display(Line obj) {
cout << "Length of line : " << obj.getLength() <<endl;
}

III. Copy an object to return it from a function
Solution: copy constructor is called whenever we return a object from a function
int Line::getLength( void ) {
return *ptr;
}
In above code *ptr is an return object from the function getLength this makes to call copy constructor.
2. Given declarations,
Money baseAmount(100,60);
Money fullAmount;
Which of the following operations are legal? If so why?
Solution: a) is the answer : BaseAmount + 25;
Because integer 25 converted to type Money so it can be added to BaseAmount. The compiler looks BaseAmount + 25,it first look for an overloaded + operator to perform addition operation i.e. Money object + integer.