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c++referenceconstants

What is a constant reference? (not a reference to a constant)


Why do constant references not behave the same way as constant pointers, so that I can actually change the object they are pointing to? They really seem like another plain variable declaration. Why would I ever use them?

This is a short example that I run which compiles and runs with no errors:

int main (){
    int i=0;
    int y=1;    
    int&const icr=i;
    icr=y;          // Can change the object it is pointing to so it's not like a const pointer...
    icr=99;         // Can assign another value but the value is not assigned to y...
    int x=9;
    icr=x;
    cout<<"icr: "<<icr<<", y:"<<y<<endl; 
}

Solution

  • The clearest answer. Does “X& const x” make any sense?

    No, it is nonsense

    To find out what the above declaration means, read it right-to-left: “x is a const reference to a X”. But that is redundant — references are always const, in the sense that you can never reseat a reference to make it refer to a different object. Never. With or without the const.

    In other words, “X& const x” is functionally equivalent to “X& x”. Since you’re gaining nothing by adding the const after the &, you shouldn’t add it: it will confuse people — the const will make some people think that the X is const, as if you had said “const X& x”.