A constructor that accepts no parameter is called default constructor. For example in the class data program Data :: Data ( ) is the default constructor. Using this constructor. objects are created similar to the way the variables of other data types are created.
Example
int num; // ordinary variable declaration
Data d1; // object declaration

The member functions are created and placed in the memory space only when they are defined as a part of the class specification. Since all the objects belonging to that class use the same member function, no separate space is allocated for member functions when the objects are created. Memory space required for the member variable are only allocated separately for each object because the member variables will hold different data values for different objects.

Inside the class definition:
When a member function is defined inside a class, it behaves like inline functions. These are called Inline member functions.
Outside the class definition:
When Member function defined outside the class just like normal function definition (Function definitions you are familiar with) then it is be called as outline member function or non-inline member function.

A copy constructor is called
(i) When an objects is passed as a parameter to any of the member functions.
Example void simple::tputdata(simple x);
(ii) When a member function returns an object
Example simple getdata( ) { }
(iii) When an object is passed by reference to an instance of its own class.
For example: simples1, s2(s1); // s2(s1) calls copy constructor

Implicit call: In this method, the parameterized constructor is invoked automatically whenever an object is created. For example simple s1(10,20); in this for creating the object s 1 parameterized constructor is automatically invoked.
Explicit call: In this method, the name of the constructor is explicitly given to invoke the parameterized constructor so that the object can be created and initialized.For example: simple s1=simple(10,20); //explicit call.