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

The operating system provides an abstraction of the physical machine to your program (i.e. your program runs in a virtual machine). Thus, your program does not have access to any physical resource of your computer, be it CPU time, memory, etc; it merely has to ask the OS for these resources.

In the case of memory, your program works in a virtual address space, defined by the operating system. This address space has multiple regions, such as stack, heap, code, etc. The value of your pointers represent addresses in this virtual address space. Indeed, 2 pointers to consecutive addresses will point to consecutive locations in this address space.

However, this address space is splitted by the operating system into pages and segments, which are swapped in and out from memory as required, so your pointers may or may not point to consecutive physical memory locations and is impossible to tell at runtime if that is true or not. This also depends on the policy used by the operating system for paging and segmentation.

Bottom line is that pointers are memory addresses. However, they are addresses in a virtual memory space and it is up to the operating system to decide how this is mapped to the physical memory space.

As far as your program is concerned, this is not an issue. One reason for this abstraction is to make programs believe they are the only users of the machine. Imagine the nightmare you'd have to go through if you would need to consider the memory allocated by other processes when you write your program - you don't even know which processes are going to run concurrently with yours. Also, this is a good technique to enforce security: your process cannot (well, at least shouldn't be able to) access maliciously the memory space of another process since they run in 2 different (virtual) memory spaces.