即使该类已声明为友元类，数据成员也无法访问

Question

The data member is inaccessible even though the class has been declared as friend class. error: 'total' was not declared in this scope

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

class Produce
{
    private:
        float total;
    public:
        Produce()
        {
            total=0;
        }
        friend class Bill;
};
class Bill
{
    private:
        float grand_total;
    public:
    Bill()
    {
        grand_total=0;
    }
    Bill operator+=(const Produce &p)
    {
        return Bill(total+p.total);
    }
};

Answer 1

The error message is correct: there is no name total in the current scope. The code should either refer to grand_total , which is a member of the class Bill , which in turn defines the operator+= that's being written, or it should refer to p.total to access the total that's a member of the class Produce .

Answer 2

Making class A a friend of class B doesn't mean that you can just randomly name non-static members of B from within A , without naming an instance of B to use.

Which Produce::total (out of potentially infinite) do you want your program to use?