警告分配运算符类参考

Question

i have this code:

class ABC{
    public:

        ABC(std::ostream& os) : _os(os) {}
        void operator() (const Stud* course) {
        Stud->print(_os);

        }

        ABC& operator=(const ABC& other); //Declaration of operator=

    private:
        std::ostream& _os;
    };

befor i define assignment operator i get warning "assignment operator could not be generated". i want assignment between object this class do nothing, its just class print in for_each algorithm.

i try write :

ABC& operator=(const ABC& other){
     return *this;
  }

but still get warning the other not use. how can i define assignment operator do nothing. (no Use the #pragma warning statement to suppress the warning).

thanks!

Answer 1

Few problems in your code...

 class ABC
 {
    public:
        ABC(std::ostream& os) : _os(os) {}

        void operator() (const Stud* course) 
        {
           //Stud->print(_os);   // you can't use Stud here - this is wrong
           course->print(_os);
        }

        ABC& operator=(const ABC& other); //Declaration of operator=

    private:
        std::ostream& _os;
    };

Additionally, as operator() defines course as const Stud* the print method in Stud class should be defined as const as well.

other than that, the code compiles perfercly.

Answer 2

To get rid of the warning about an unused argument, just don't name it:

ABC& operator=(const ABC&){
    return *this;
}

The reason that the compiler can't generate an assignment operator for your class is that it has a reference variable, and these can only be initialised, never re-assigned.

If you don't need an assignment operator, but only added one to make the compiler happy, you can declare it private and then not provide an implementation.