C++ making an array of pointers to const objects

Question

I'm trying to make a non-constant array of non-constant pointers to constant objects. The idea is that I should be able to change what the pointers in the array point to, but what they point to is a constant object.

I'm having problem defining this array (it's an array of pointers to objects of type Person - a custom class). I'm currently declaring the array like so:

Person* people[10];

Also that's not explicitly saying that the pointers point to const Persons. So when I do something like this:

people[i] = &p;

where p is a reference to an object of type const Person, it fails.

@NeilKirk, does this not make the array itself const? Or the pointers const? It seems there would be three different ways to declare it depending on which part you want const. — user83643
– user83643, Commented Oct 1, 2014 at 13:04
@user83643: Only two different ways, since a const array is the same thing as an array of const elements. An array of const pointers to mutable Person would be Person* const people[10];. — aschepler
– aschepler, Commented Oct 1, 2014 at 13:05
const Person * cannot change the person, but can point to other people. Person *const can change the person, but can't point to anyone else. I feel I could make a joke here, but one eludes me. Putting the pointer into an array doesn't change that property of the pointer. const Person * == Person const * — Neil Kirk
– Neil Kirk, Commented Oct 1, 2014 at 13:05
@kotlomoy: Yes and no. 3.9.3/2: "Any cv-qualifiers applied to an array type affect the array element type, not the array type." but 3.9.3/5: "Cv-qualifiers applied to an array type attach to the underlying element type, so the notation "cv T," where T is an array type, refers to an array whose elements are so-qualified. An array type whose elements are cv-qualified is also considered to have the same cv-qualifications as its elements." — aschepler
– aschepler, Commented Oct 2, 2014 at 12:49

utnapistim · Accepted Answer · 2014-10-01 13:13:01Z

10

When in doubt ... use typedef (because it's explicit, adds more specialized semantics and avoids the confusion completely):

typedef const Person* PersonCPtr;
PersonCPtr people[10];

edited Oct 1, 2014 at 13:13

answered Oct 1, 2014 at 13:07

utnapistim

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2 Comments

Neil Kirk Over a year ago

I prefer not to be in doubt!

utnapistim Over a year ago

@NeilKirk, I know (so do I). I still think it's a good idea to use a typedef, because when a declaration looks ugly/long/complicated it requires effort to understand (and this will probably hold true for other developers looking at the code in the future).

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