When is using a reference better than a pointer? [duplicate] - c++

Question

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What are the differences between pointer variable and reference variable in C++?
When to pass by reference and when to pass by pointer in C++?
Seems to me that a pointer is more flexible and basically the same as a reference. References can't be null, but what happens if you have a reference of a pointer that you then make null? Doesn't that case then negate the 'can't be null' advantage?. And is it really an advantage anyway?
Why not just always use pointers? (I'm genuinely asking, I honestly haven't made up my mind on this)

Answer 1

A reference cannot be null, as you said.
A reference is always initialized. A non-null pointer can still be not initialized at all.
A reference is stable. You cannot make the reference point first to A, and then to B. Once initialized, it is an alias of one and the same object
The syntax of references is somewhat neater.

Answer 2

A reference to a pointer that can be null is not the same as a reference to the actual value or object. The pointer's value can be null, but the actual pointer is not!
Using references gives you peace of mind knowing that you are safe and weird stuff won't happen. So when you don't need the features of actual pointers, you should always use references. In general (and there are always exceptions) use pointers only if:
a. you need dynamic allocation of memory during execution.
b. you actually need pointer arithmetic (p++)
c. you need to save allocated objects inside containers, but in this case it's a generally good practice to wrap your pointers with something like shared_ptr.

Answer 3

By using a reference you are explicitly stating that it cannot be 0. It makes sense when some value in code cannot be uninitialised. On the other hand pointers are useful when value can be either initialised or uninitialised. You can check it by comparing to 0.

Answer 4

When in doubt, go to the source (Stroustrup): http://www2.research.att.com/~bs/bs_faq2.html#pointers-and-references
References are good for operator overloading and copy constructors.
References are guaranteed to not be null and to be initialized.
Using pointers as arguments works well when you want to have arguments that are optional or that can be ignored when the value is NULL.

Answer 5

The flexibility of pointers comes with a price: every time you see one, you have to consider that you may be using that flexibility somewhere. That's more to have to watch out for...more to debug..etc. References, being simpler and less featurish, carry less mental baggage.
Add to that, the syntax is less cluttered with *s and ->s. :)

Answer 6

Dereferencing a null pointer to create a reference will result in undefined behavior.
See also Is there a platform or situation where dereferencing (but not using) a null pointer to make a null reference will behave badly?
and What are the differences between a pointer variable and a reference variable in C++?

Answer 7

Usually, references are just syntactic sugar of pointers which means whereever you use one, can be used other as well (well, not always, though). But sometimes, references make more sense than pointers, especially when you define a function whose argument(s) cannot be null, or checking for null argument is that elegant. In such cases, you simply make them references. One such example is swap function:
template<typename T>
void swap(T & a, T & b)
{
T temp(a);
a = b;
b = temp;
}
If one uses pointers, then it would become this:
template<typename T>
void swap(T * a, T * b)
{
//do you want to check for null here?
T temp(*a);
*a = *b;
*b = temp;
}
I think, most C++ programmers will find the first solution using reference elegant, and the second solution unnecessarily cumbersome.