Difference between pointer initializations

Question

While I was reading C++ Primer, found this example that i don't understand

double dval;
double *pd = &dval; //ok:initializer is the address of a double
double *pd2 = pd; // ok:initializer is a pointer to double

Shouldn't *pd2 be a pointer to pointer since *pd is a pointer aswell? Could somebody explain what happens in the background with the memory addresses( what is assigned to pd2 )?

Answer 1

pd2的值是分配给它的值，即dval的地址，该地址存储为pd值并分配给前者。

Answer 2

Shouldn't *pd2 be a pointer to pointer since *pd is a pointer aswell?

No. pd2 is being assigned the value that pd is currently holding. Thus pd2 ends up pointing at dval . You would only use a pointer-to-pointer if you want pd2 to point at pd itself, not what pd is pointing at, eg:

double dval;
double *pd = &dval;
double **pd2 = &pd;

Could somebody explain what happens in the background with the memory addresses( what is assigned to pd2)?

A pointer is just a number that happens to be a memory address. If you think of pointers as integers, the code you provided is not much different than the following behind the scenes:

double dval;
uintptr_t pd = address of dval;
uintptr_t pd2 = pd;

You are just assigning one pointer value (a number) as-is to another pointer (number) variable.

Answer 3

A pointer is a memory address. double *pd2 = pd; assigns one pointer to another pointer. No magic, just a simple assignment operation. Both pointers are pointing at the same memory address.

The value in pd2 is the same value as in pd . if you were to dereference either pd or pd2 you would get the value stored in dval .

Assigning &pd would require a pointer to a pointer since you are taking the address of a pointer.

Answer 4

First you declare a double dval , then you declare a pointer, that points on that double (because its set by the doubles adress &dval ). Then the second pointer is set equal to the first pointer. So finally, you have:

pd = pd2 = &dval

Which are two pointers, pointing to the same adress, not a pointer pointing to another pointer.