My basic question here is: Is the following code doing what I think its doing?

class Thing
{
private:
    std::vector<int> numbers;

public:
    Thing(const Thing& thing2)
    {
        numbers = thing2.numbers;
    }
}

class Some_Other_Class
}
private:
    Thing &second;

public:
    Some_Other_Class(Thing &thisThing)
        :   second(thisThing);
    {
    }
}

int main()
{
    Thing first;
    Some_Other_Class(first);
}

Sorry if this is overly complex but I wanted to replicate the structure of things in my program to make sure I'm asking the right question. Long story short, I want to have a reference to a "Thing" object that is passed into another (temporary) object. I don't want a copy, and I think I'm doing that much correctly, however, am I copying "numbers" or does the second instance of Thing contain a reference to "numbers" (which is my intent)?

However, the second declaration is, in fact, not a temporary object where you pass the previously defined object named first to its constructor. It is another default constructed object named first, and that is an error both because it is a conflicting redefinition of the name first, and because the type does not have a default constructor.

In that case, there will only be one instance of class "Thing", sitting on the stack of "main". "main" will have a reference to it and "Some_Other_Class" will have a reference to it.
Since there's only one "Thing", there's only one "numbers".

These two things seem to contradict unless I'm missing something...

And yes, your assumption is correct, first is supposed to be named Thing (Edited), that's just a mix up.

Perhaps you can advise me on this... I was attempting to make it work this way rather than with pointers primarily because I've heard the advice "Use references when you can and pointers when you have to" quite a few times. Is that not good advice when it comes to data members?

Reference members can only be shallow copied which is a big restriction, you probably want to disable copying (EDIT: and assignment) of classes with reference members. With pointers you can create a new object of the appropriate type and copy all the members.

Both pointer and reference members have the problem that if you hold a pointer/reference to an object which has been destroyed it is undefined behaviour (hopefully undefined in the sense it will crash immediately on access, but usually you just get hard to track down bugs).

Rattenhirn is probably overlooking the mistake you likely made in your code where Some_Other_Class(first); does not create an unnamed temporary object, but a default constructed named object called first. I don't believe that is what you intended, and what Ratthenhirn assumed.

Under the assumption that you intended to create a second object with a reference to the first object, then his explanation is correct.

I've not heard of that before, are you saying

Some_Other_Class(first);

is essentially the same as

Some_Other_Class first;

?

I think what the OP wanted to do was create a Some_Other_Class instance as a copy of first, somthing like

Some_Other_Class myOtherClass(first);

which should be OK despite the non const reference in the copy constructor (is it even a copy constructor with a non-const reference?).

EDIT: Whoops

Lulz then, that's not just mad it is BONKERS mad. Why would they implement it like that? Is it a template thing?