The keyword inline is used as a function specifier only in function declarations. The inline specifier is a hint to the compiler that inline substitution of the function body isto be preferred to the usual function call implementation.

The advantage of using inline member functions are: 

1. The size of the object code is considerably reduced. 
2. It increases the execution speed
3. The inline member functions are compact functions calls.

The general form is:
 
 class user_name 
 {
  //data variables;
  public:
   inline return_type function name (parameters);
   //other member functions;
 }


Whenever a function is declared with inline specifier, the C++compiler merely
replaces it with the code itself so the overhead of the transfer of control between the
calling portion of a program and a function is reduced.  
// demonstration of inline function
# include <iostream.h>
class sample
{
 int x; 
 public:
  inline void getdata( );
  inline void display ( );
}
inline void sample :: getdata ( )
{
 cout<<" enter a number"<<endl;
 cin>>x; 
}
inline void sample:: display ( )
{ 
 cout<<"entered number is = "<<x<<endl;
}
void main( )
{
 sample ob;
 ob.getdata ( );
 ob.display ( );
}