What are the differences between pointer variable and reference variable in C++?

   Differences Between Pointer Variable and Reference Variable

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1) A pointer can be re-assigned:
int x = 5;
int y = 6;
int *p;
p =  &x;
p = &y;
*p = 10;
assert(x == 5);
assert(y == 10);
 A reference cannot, and must be assigned at initialization:
int x = 5;
int y = 6;
int &r = x;

 2) A pointer has its own memory address and size on the stack (4 bytes on x86), whereas a reference shares the same memory address but also takes up some space on the stack. Since a reference has the same address as the original variable itself, it is safe to think of a reference as another name for the same variable. Note: What a pointer points to can be on the stack or heap. Ditto a reference. My claim in this statement is not that a pointer must point to the stack. A pointer is just a variable that holds a memory address. This variable is on the stack. Since a reference has its own space on the stack, and since the address is the same as the variable it references. More on stack vs heap. This implies that there is a real address of a reference that the compiler will not tell you.
int x = 0;
int &r = x;
int *p = &x;
int *p2 = &r;
assert(p == p2);

 3) You can have pointers to pointers to pointers offering extra levels of indirection. Whereas references only offer one level of indirection.
int x = 0;
int y = 0;
int *p = &x;
int *q = &y;
int **pp = &p;
pp = &q;//*pp = q
**pp = 4;
assert(y == 4);
assert(x == 0);

 4) Pointer can be assigned NULL directly, whereas reference cannot. If you try hard enough, and you know how, you can make the address of a reference NULL. Likewise, if you try hard enough you can have a reference to a pointer, and then that reference can contain NULL.
int *p = NULL;
int &r = NULL; <--- compiling error

 5) Pointers can iterate over an array, you can use ++ to go to the next item that a pointer is pointing to, and + 4 to go to the 5th element. This is no matter what size the object is that the pointer points to.

6) A pointer needs to be dereferenced with * to access the memory location it points to, whereas a reference can be used directly. A pointer to a class/struct uses -> to access it's members whereas a reference uses a ..

7) A pointer is a variable that holds a memory address. Regardless of how a reference is implemented, a reference has the same memory address as the item it references.

8) References cannot be stuffed into an array, whereas pointers can be .

9) Const references can be bound to temporaries. Pointers cannot (not without some indirection):
const int &x = int(12); //legal C++
int *y = &int(12); //illegal to dereference a temporary.
 This makes const& safer for use in argument lists and so forth.