c++ references appear reassigned when documentation suggests otherwise

Question

According to this question you can\'t change what a reference refers to. Likewise the C++ Primer 5th Edition states

Once we have defined a reference,

Answer 1

You are not reassigning a reference. A reference acts as an alias for a variable. In this case, ref is an alias for a, so

ref = b;

is the equivalent of

a = b;

You can easily check that by printing out the value of a:

std::cout << a << std::endl; // prints 4

Answer 2

You can understand how references work by comparing their behavior to that of a pointer. A pointer can be thought of as the name of the address of a variable; however a reference is just the name of the variable itself--it is an alias. An alias, once set, can never be changed whereas you can assign a pointer a new address if you want. So you have:

int main(void)
{
    int a = 2;
    int b = 4;
    int* ptr_a = &a;
    int& ref_a = a;

    ptr_a = &b;  //Ok, assign ptr_a a new address
    ref_a = &b;  //Error--invalid conversion.  References are not addresses.
    &ref_a = &b; //Error--the result of the `&` operator is not an R-value, i.e. you can't assign to it.

    return 0;
}