c++ - Why can I assign a new value to a reference, and how can I make a reference refer to something else?

Question

I have couple of questions related to usage of references in C++.

1. In the code shown below, how does it work and not give a error at line q = "world";?

   #include <iostream>
   
   using namespace std;
   
   int main()
   {
     char *p = "Hello";
     char* &q = p;
     cout <<p <<' '<<q <<"
   ";
     q = "World"; //Why is there no error on this line
     cout <<p <<' '<<q <<"
   ";
   }
   

   1. How can a reference q be reinitialized to something else?

   2. Isn't the string literal, p = "Hello", a constant or in read-only space? So if we do,

      q = "World";
      

      wouldn't the string at p which is supposed to be constant be changed?

2. I have read about C++ reference type variables as they cannot be reinitialized or reassigned, since they are stored 'internally' as constant pointers. So a compiler would give a error.

   But how actually a reference variable can be reassigned?

   int i;
   
   int &j = i;
   
   int k;
   
   j = k; //This should be fine, but how we reassign to something else to make compiler flag an error?
   

   I am trying to get hold of this reference, and in that maybe missed some key things related, so these questions.

So any pointers to clear this up, would be useful.

Answer 1

1. • a) It cannot, the line you quote doesn't change the reference q, it changes p.
   • b) No the literal is constant, but p is a pointer which points at a literal. The pointer can be changed, what is being pointed to cannot. q = "world"; makes the pointer p point to something else.

2. You seem to think that this code

   int i;
   int &j = i;
   int k;
   j = k;
   

   is reassigning a reference, but it isn't. It's assigning the value of k to i, j still refers to i. I would guess that this is your major misunderstanding.