Question

So do these two functions accomplish the same thing in C++?

void MYCLASS::clear() {
classSize = 0;
class_ptr = NULL;
}

void MYCLASS::clear() {
classSize = 0;
*class_ptr = NULL;
}

Where int *class_ptr is declared in my header file. When I hover my mouse over Visual Studio shows class_ptr as the same type.

I believe that they are both pointing class_ptr at NULL. However, I want to make sure that they are indeed both doing this.

Answer 1

I believe that they are both pointing class_ptr at NULL.

Nope…

class_ptr = NULL;

Sets the pointer’s value to NULL, i.e., class_ptr == NULL.

*class_ptr = NULL;

Sets what class_ptr refers (points) to to NULL, which is 0. class_ptr itself retains its value.

A pointer’s value is an address. What resides at that address is (should be) a representation of the type of the pointer itself, i.e.,

int *p = new int(10);
/* ... */
 p  <-- an address, let's say, 0x0000F8BE
*p  <-- an int, 10

Note that, if there existed no implicit conversion from int (NULL has a value of 0) to whatever type class_ptr refers to, the code wouldn’t even compile (which leads me to believe that this particular pointer is poorly named).

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EDIT: I liked @Mooing Duck’s analogy so much that I stole it (he has not posted an answer, so I don’t think he’ll mind).

It’s like the difference between destroying directions to a house, and destroying the house.