Question

const int &ra=3;

1. As I know, making ra const will extends the lifetime of the temporary r-value which is in this case 3. This is a little bit confusing, as I know ra should have the same address as r-value which is here 3, but 3 is not a real variable and it does not have a memory where it’s stored. So how can this be possible?

2. what is the difference between:

   const int& ra=a;
   

   and

   int& const ra=a;
   

Answer 1

but 3 is not a real variable and it does not have a memory where it’s stored. so how can this be possible ?

Actually a temporary object gets created out of the literal 3, and then that temporary is bound to the const reference. That is how it becomes possible.

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Now your next question: the difference between these two

const int& ra=a;
int& const ra=a;

is that the second statement is illegal.