What is the purpose for the "const" keyword for a reference if the object it is referencing is not a const object? Is there any difference between what r1 and r2 does (below)?
int i = 42; // non const object
const int &r1 = i; // const reference to non const object
int j = 25; // non const object
int &r2 = j; // non const reference to non const object
Here's a quote from CPP Primer 5th:
"C++ programmers tend to abbreviate the phrase “reference to const” as “const reference.” This abbreviation makes sense—if you remember that it is an abbreviation. Technically speaking, there are no const references. A reference is not an object, so we cannot make a reference itself const. Indeed, because there is no way to make a reference refer to a different object, in some sense all references are const. Whether a reference refers to a const or nonconst type affects what we can do with that reference, not whether we can alter the binding of the reference itself."
I think this means that making a reference a "const" when it is referenced to a non const object does absolutely nothing. We may as well take that const keyword out when defining that reference.
Asking this question here for confirmation.
Edit: Looks like my initial conjecture is wrong. I understand now that a const reference to a non const object does have a purpose: to prevent the reference from modifying the object. The non const object can still be modified by other means but not by this const reference.
Thanks all.
"What is the purpose for the "const" keyword for a reference if the object it is referencing is not a const object?" The purpose is to prevent that reference being used to modify the object it is referencing.
int i = 42; // non const object
const int &r1 = i; // const reference to non const object
r1 = 6 * 9; // error, r1 cannot be used to modify i;