c++ reference/pointer

Question

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Difference between pointer variable and reference variable in C++

I saw this simple code the other day, and I consider myself a beginner with pointers, although I have about a year and half experience with c++. Anyways...

Whats the difference between

int a = 0; 
int &b = a;

and

int a = 0
int *p = &a;

Obviously, p holds the address of a, but b is a reference to a, meaning I can change the value of a with b. But I can also do the same thing with p. So what are advantages or disadvantages?

score 2 · Accepted Answer · edited Dec 06 '10 at 20:13

2

A reference must always be initialized
A reference can't be null
Once initialized, a reference can't be changed to be an alias of a different object.

edited Dec 06 '10 at 20:13

Brent Writes Code

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answered Dec 06 '10 at 20:10

Cătălin Pitiș

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A reference can be null. int *a=0; int &b = *a; – Benoit Thiery Dec 06 '10 at 20:18
1

If you put it this way, the reference can refer to an invalid object, too. But you can't initialize something like int& b = NULL; – Cătălin Pitiș Dec 06 '10 at 20:26
1

@Benoit: A reference can *not* be null. 8.3.2/4: "a reference shall be initialized to refer to a valid object or function. [...] a null reference cannot exist in a well-defined program" – John Dibling Dec 06 '10 at 21:08

score 0 · Answer 2 · answered Dec 06 '10 at 20:13

I think it comes down to how you plan to use the variables afterwards in your program. Both statements appear to do the same thing (in this limited scope).

The first approach seems to be (in my opinion) poor programming practice since it may not be obvious later in the program that changing the value of b also changes the value of a. In the second, at least it is known that p is a pointer, so you should expect the side effects that come with changing the value to which it points.

c++ reference/pointer

2 Answers2