To what extent is it acceptable to think of C++ pointers as memory addresses?

Question

When you learn C++, or at least when I learned it through C++ Primer, pointers were termed the \"memory addresses\" of the elements they point to. I\'m wondering to

Answer 1

I think this answer has the right idea but poor terminology. What C pointers provide are the exact opposite of abstraction.

An abstraction provides a mental model that's relatively easy to understand and reason about, even if the hardware is more complex and difficult to understand or harder to reason about.

C pointers are the opposite of that. They take possible difficulties of the hardware into account even when though the real hardware is often simpler and easier to reason about. They limit your reasoning to what's allowed by a union of the most complex parts of the most complex hardware regardless of how simple the hardware at hand may actually be.

C++ pointers add one thing that C doesn't include. It allows comparing all pointers of the same type for order, even if they're not in the same array. This allows a little more of a mental model, even if it doesn't match the hardware perfectly.

Answer 2

Somehow answers here fail to mention one specific family of pointers - that is, pointers-to-members. Those are certainly not memory addresses.

Answer 3

The particular example you give:

For example, do two elements *p1 and *p2 have the property p2 = p1 + 1 or p1 = p2 + 1 if and only if they are adjacent in physical memory?

would fail on platforms that do not have a flat address space, such as the PIC. To access physical memory on the PIC, you need both an address and a bank number, but the latter may be derived from extrinsic information such as the particular source file. So, doing arithmetic on pointers from different banks would give unexpected results.

Answer 4

Pointers are memory addresses, but you shouldn't assume they reflect physical address. When you see addresses like 0x00ffb500 those are logical addresses that the MMU will translate to the corresponding physical address. This is the most probable scenario, since virtual memory is the most extended memory management system, but there could be systems that manage physical address directly

Answer 5

Not at all.

C++ is an abstraction over the code that your computer will perform. We see this abstraction leak in a few places (class member references requiring storage, for example) but in general you will be better off if you code to the abstraction and nothing else.

Pointers are pointers. They point to things. Will they be implemented as memory addresses in reality? Maybe. They could also be optimised out, or (in the case of e.g. pointers-to-members) they could be somewhat more complex than a simple numeric address.

When you start thinking of pointers as integers that map to addresses in memory, you begin to forget for example that it's undefined to hold a pointer to an object that doesn't exist (you can't just increment and decrement a pointer willy nilly to any memory address you like).

Answer 6

Like other variables, pointer stores a data which can be an address of memory where other data is stored.

So, pointer is a variable that have an address and may hold an address.

Note that, it is not necessary that a pointer always holds an address. It may hold a non-address ID/handle etc. Therefore, saying pointer as an address is not a wise thing.

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Regarding your second question:

Pointer arithmetic is valid for contiguous chunk of memory. If p2 = p1 + 1 and both pointers are of same type then p1 and p2 points to a contiguous chunk of memory. So, the addresses p1 and p2 holds are adjacent to each other.