Thread: problem: passing `xx' as `this' argument of `int xx::accessor()' discards qualifiers

Hi, I wrote a simplified version of a program I was having a problem with, to better illustrate my questions:
1. How do I bypass this error?
2. What is the exact cause?

Code:

#include <iostream>

using namespace std;

class Stuff {
        public:
                Stuff();
                Stuff(int);
                Stuff(const Stuff&);
                int accessor();
                void mutator(int);
        private:
                int mystery;
};

Stuff::Stuff(): mystery(0) {}
Stuff::Stuff(int b): mystery(b) {}
Stuff::Stuff(const Stuff& b)
{
        mystery = b.accessor();
}
int Stuff::accessor() { return mystery; }
void Stuff:: mutator(int b) { mystery = b; }

int main()
{
        Stuff fool;
        cout << fool.accessor() << endl;
        return 0;
}

and the error that spits out:

Code:

bash-3.00$ !g
g++ test.c
test.c: In copy constructor `Stuff::Stuff(const Stuff&)':
test.c:20: error: passing `const Stuff' as `this' argument of `int Stuff::accessor()' discards qualifiers
bash-3.00$

Thanks dudes.