1:-Initalisation: A pointer can be initalised in this way:
int a = 10;
int *p = &a;
OR
int *p;
p = &a;
we can declare and initalise pointer at same step or in multiple line.
While in refrences,
int a=10;
int &p=a; //it is correct
but
int &p;
p=a; // it is incorrect as we should declare and initialise references at single step.
2:-Reassignment: A pointer can be re-assigned. This property is useful for implementation of data structures like linked list, tree, etc. See the following examples:
int a = 5;
int b = 6;
int *p;
p = &a;
p = &b;
On the other hand, a reference cannot be re-assigned, and must be assigned at initialization.
int a = 5;
int b = 6;
int &p = a;
int &p = b; //At this line it will show error as "multiple declaration is not allowed".
However it is valid statement,
int &q=p;
3:-Memory Address: A pointer has its own memory address and size on the stack whereas a reference shares the same memory address (with the original variable) but also takes up some space on the stack.
int &p = a;
cout << &(&p);
4:-NULL value: Pointer can be assigned NULL directly, whereas reference cannot. The constraints associated with references (no NULL, no reassignment) ensure that the underlying operations do not run into exception situation.
5:-Indirection: You can have pointers to pointers offering extra levels of indirection. Whereas references only offer one level of indirection.I.e,
In Pointers,
int a = 10;
int *p;
int **q; //it is valid.
p = &a;
q = &p;
Whereas in refrences,
int &p = a;
int &&q = p; //it is reference to reference, so it is an error.
Arithmetic operations: Various arithmetic operations can be performed on pointers whereas there is no such thing called Reference Arithmetic.(but you can take the address of an object pointed by a reference and do pointer arithmetics on it as in &obj + 5).)
