Question

I have a program following:

class INT {
public:
  INT(int ii = 0) : i(ii) {}
  operator int() { return i; }
private:
  int i;
};

int main()
{
  INT i;
  cin >> i;
}

the statement cin >> i is compiled error, but I don’t know the reason?

In my option, the compiler can find the function cin.operator>>(int&) for that statement, since INT can be converted to int through INT::operator int().

Answer 1

You operator int() returns a temporary, which can’t bind to a reference-to-non-const that the operator>> expects (since it needs to change that variable).

Change that to operator int&() and add a const overload as operator int const&() const.