Initialization of Constant and Reference Data Members
Without using the member initialization list, it is not possible to initialize the const and reference data members.
For example,
class A
{
public :
A ( int n )
{
d2 = n ; // error3
r = v ;
}
private :
const int d1 = 15 ; // error2
const int d2 ;
int v ;
int & r ; // error1
} ;
The error1 is: the reference member ' r ' is not initialized, the error2 is: cannot initialize a classs member here and the error3 is: cannot modify a const object. These three errors can be removed by using the member initialization list.
class A
{
public :
A ( int n ) : d1 ( 15 ) , d2 ( n ) , r ( v )
{
}
private :
const int d1 ;
const int d2 ;
int v ;
int & r ;
} ;
An alternative to constant members is to use an anonymous enumerator containing the item like this:
class A
{
public :
enum { size = 10 } ;
int vector [ size ] ; // ok
// . . . . . .
} ;
Reference is a constant Reference
A reference variable is conceptually analogous to a pointer variable in that they both refer or point, to some other object. Unlike the pointer, however, a reference must be initialized and once initialized, a reference cannot be refer to other object. It implies that a reference is, in fact, a constant reference. There is no need to explicitly declare constant reference.
For example, the statement int & const m = v ;
is always equivalent to int & m = v ;