What are the differences between pointers and references in C++?

By | September 8, 2013

Pointers and references look very different (pointers use * and ->, while references use .), but they seem to have the same function: both can be used to indirectly point to another object. So when should you use pointers vs. references?

  • The most important thing you should always remember is that, reference can never be assigned NULL directly. A reference has always to refer to an object. Therefore, if you need a variable that needs to point to nothing sometimes, then this variable should be declared as a pointer, not a reference. The fact that reference should always refer to an object makes the program more effective, because it doesn’t need to be tested null before usage.

  • A pointer can be re-assigned to another object, but a reference cannot. A reference must be assigned at initialization.

  • A pointer can points to a 2nd pointer, which points to a 3rd pointer, … This offers extra levels of indirection. Whereas a reference only offers one level of indirection.

  • Pointers can iterate over an array, you can use ++ to go to the next item, and +n to go to the (n+1)th element. This is no matter what size the object is that the pointer points to.

  • The last situation is that when you need to overload an operator, you should use references rather than pointers. A typical overloaded operator is [], by which an object should be returned. For example

    vector<int> v(10);
    v[5] = 10;
    

    If the operator [] returns a pointer, the last line would be

    *v[5] = 10;
    

    This would make v look like a vector of pointers.

Also, a pointer has its own memory address and size on the stack, whereas a reference shares the same memory address with the original variable. So it is safe to think of a reference as another name for the same variable. This difference is important, but I don’t think it is a reason when choosing references vs pointers.

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