member function pointer to member function

Question

There is a lot of talk of pointers to member functions but I'm having trouble grasping the issue with the hidden const state of member functions. Can anyone give me a simpler answer what I'm doing wrong here?

class Entity
{
public:
    Entity();
    void(Entity::*update_function)();
private:
    void update_mode_1() {
    }
};

Entity::Entity()
{
    update_function = update_mode_1;
    //error C3867: 'Entity::update_mode1': non-standard syntax; use '&' to create a pointer to member
}

void test_init() {
    Entity obj;
    obj.update_function();
    //Error: Expression preceding parenthesis of apparent call must have (pointer-to-) function type
}

Answer 1

Here's the solutions how to solve the errors, anyway, it seems has nothing to do with "hidden const state of member functions".

error C3867: 'Entity::update_mode1': non-standard syntax; use '&' to create a pointer to member

As the error message said, use & to create a pointer to member.

update_function = &Entity::update_mode_1;

Error: Expression preceding parenthesis of apparent call must have (pointer-to-) function type

Use pointer-to-member access operator (such as the operator .*) to call it.

(obj.*(obj.update_function))();

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