C++ Programming

Answer1

Virtual destructors:

If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.

There is a simple solution to this problem declare a virtual base-class destructor.

This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called. Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error.

Answer2

Virtual destructors: If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base-class destructor function (matching the pointer type) is called on the object.

There is a simple solution to this problem – declare a virtual base-class destructor. This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called.

Answer1

Array is collection of homogeneous elements.

List is collection of heterogeneous elements.

For Array memory allocated is static and continuous.

For List memory allocated is dynamic and Random.

Array: User need not have to keep in track of next memory allocation.

List: User has to keep in Track of next location where memory is allocated.

Answer2

Array uses direct access of stored members, list uses sequencial access for members.

//With Array you have direct access to memory position 5

Object x = a[5]; // x takes directly a reference to 5th element of array

//With the list you have to cross all previous nodes in order to get the 5th node:

list mylist;

list::iterator it;

for( it = list.begin() ; it != list.end() ; it++ )

{

if( i==5)

{

x = *it;

break;

}

i++;

}

Answer1

constructor is a member function of the class, with the name of the function being the same as the class name. It also specifies how the object should be initialized.

Ways of calling constructor:

1) Implicitly: automatically by complier when an object is created.

2) Calling the constructors explicitly is possible, but it makes the code unverifiable.

Answer2

class Point2D{

int x; int y;

public Point2D() : x(0) , y(0) {} //default (no argument) constructor

};

main(){

Point2D MyPoint; // Implicit Constructor call. In order to allocate memory on stack, the default constructor is implicitly called.

Point2D * pPoint = new Point2D(); // Explicit Constructor call. In order to allocate memory on HEAP we call the default constructor.

Answer1

1.) “new and delete” are preprocessors while “malloc() and free()” are functions. [we dont use brackets will calling new or delete].

2.) no need of allocate the memory while using “new” but in “malloc()” we have to use “sizeof()”.

3.) “new” will initlize the new memory to 0 but “malloc()” gives random value in the new alloted memory location [better to use calloc()]

Answer2

new() allocates continous space for the object instace

malloc() allocates distributed space.

new() is castless, meaning that allocates memory for this specific type,

malloc(), calloc() allocate space for void * that is cated to the specific class type pointer.

class Point2D{

int x; int y;

public int color;

protected bool pinned;

public Point2D() : x(0) , y(0) {} //default (no argument) constructor

};

Point2D MyPoint;

You cannot directly access private data members when they are declared (implicitly) private:

MyPoint.x = 5; // Compiler will issue a compile ERROR

//Nor yoy can see them:

int x_dim = MyPoint.x; // Compiler will issue a compile ERROR

On the other hand, you can assign and read the public data members:

MyPoint.color = 255; // no problem

int col = MyPoint.color; // no problem

With protected data members you can read them but not write them: MyPoint.pinned = true; // Compiler will issue a compile ERROR

bool isPinned = MyPoint.pinned; // no problem