Question

The most common way to declare a destructor explicitly is to use an identifier that consists of a tilde followed by the class name.

1. Please explain the purpose of a constructor method. Note that constructors typically provide initial values for the fields of an object.
2. Discuss the use of the default constructor that takes no arguments and contrast it with a non-default constructor, otherwise known as a parameterized constructor that requires arguments.
3. Describe the purpose of a destructor method. Explain when destructors are called, and note that a default destructor is provided automatically.

Answer 1

Constructor

• Constructor is the special method whose name is  same as the class name which called automatically when objects are created.
• They are used to initialize an instance variables of object.When objects are created, its instance variable must gets some valid value.This is done by the constructor.

Default constructors

• These are the constructors taking no parameters.
• Programmer can define default constructor without providig parameters and using these, instance varibles can be initialized with some default values.
• When the programmer writes no constructor,the compiler itself provide a default constructor
• The purpose of default constructor is to assign same default values to all objects which are created by without providing any values(parameters)
• On contrast, parameterized constructor takes parameters and initialize instance variables using these parameters.
• The purpose of parameterized constructor is to provide user wanted specific values to the variables of different objects

Destructor

• Destructors are the method whose name is same as the class name but preceeded by tilde(~) symbol
• This method called automatically when objects are destructed
• It is used to de allocating or deleting the resources such as heap memory,network connections,files after usage

Example

Class sample
{
   int *ptr;
   ifstram f;
   Sample()
   {
       ptr=new int[50];
       f.open("student.txt")
   }
   ~Sample()
   {
       delete [] ptr;
       f.close();
   }
}

• In the above example,inside the constructor resources are acquired and inside the destructor heap memory is deallocated and file is closed.