Question

What I used to know about c++ references is that:

1. The reference should be initialized in the declaration statement
2. The reference cannot be re-defined once defined

The following piece of code perfectly run on g++ 4.6.1, although it breaks #2:

int a = 10, b = 30;
int& x = a;
x = b;

Answer 1

Jedi mindtrick:

What helped me better understand references is to think of them as names for your variables. int& x = a just means that when you say x, you actually mean a.

Think of references as an alias.

This is pretty clear:

int a = 10, b = 30;

Think of this not as x = 10, but as "x is a different name for a".

int& x = a;

So now, x will still reference a, so you give a the value of b (30).

x = b;

At this point, x is still bound to a, you just changed its value.

So, x == 30 and a == 30 at this point, but if you do:

a = 10;

x will also equal 10.