Compiler-generated copy/assignment functions for classes with reference and const members

Question

The book I'm reading says that when your class contains a member that's a reference or a const, using the compiler-generated copy constructor or assignment operators won't work. For instance,

#include <iostream>
#include <string>
using namespace std;

class TextBlock
{
    public:
        TextBlock (string str) : s(str) {
            cout << "Constructor is being called" << endl;
        }
        string& s;
};


int main () {
    TextBlock p("foo");
    TextBlock q(p);

    q = p;

    cout << "Q's s is " << q.s << endl;

    return(0);
}

According to my book, both the lines TextBlock q(p); and q = p; should return compiler errors. But using the g++ compiler for Linux, I'm only getting an error for the line q = p; When I comment that out, this works fine and the code compiles. The correct s is output for Q, so it's apparently being copied by the compiler-generated copy constructor. I get the same results when I change the line string& s; to const string s.

Have there been some changes to C++ that now allow the copy constructor to be generated automatically for reference and const objects, but not the assignment operator? Or maybe I'm just not understanding the book correctly? Any thoughts?

Answer 1

The book is wrong. A const member or a reference member will inhibit generation of the default copy assignment operator, but doesn't prevent the compiler from generating a copy constructor.