存储指向方法的派生指针

时间:2013-11-30 12:10:46

标签: c++ inheritance function-pointers

我想创建一个类,它具有指向其某个方法的指针作为属性。然后应该有一个方法,用于设置这个指针。

class A {
    private:
        void (A::*curr_f)();
    public:

        void set(void (A::*f)()) {
            curr_f = f;
        }
};

当我尝试创建继承的类并将指针设置为其方法之一时,问题就开始了。

class B : A {
    public:
        void main() {
            set(&B::new_function);
        };
        void new_function() {};
};

我得到的错误非常简单,但我仍然不知道如何解决这个问题。

error: no matching function for call to ‘B::set(void (B::*)())’
note: candidate is:
note: void A::set(void (A::*)())
note: no known conversion for argument 1 from ‘void (B::*)()’ to ‘void (A::*)()’

2 个答案:

答案 0 :(得分:6)

你做不到。 A没有方法new_function而且您对编译器撒谎。你有三种方式

1

new_function移至A并传递A::new_function(首选virtual)。

class A
{
    void (A::*curr_f)();
public:
    void set(void (A::*f)())
    {
        curr_f = f;
    }
    virtual void new_function() {};
};

class B : A
{
public:
    void main()
    {
        set(&A::new_function);
    };
    void new_function() {};
};

2

转发B声明并将B::*存储在A

class B;

class A
{
    void (B::*curr_f)();
public:
    void set(void (B::*f)())
    {
        curr_f = f;
    }
};

class B : A
{
public:
    void main()
    {
        set(&B::new_function);
    }
    void new_function() {}
};

3

您可以尝试基于模板的方式,例如the curiously recurring template pattern (CRTP)

template <typename D>
class A
{
    void (D::*curr_f)();
public:
    void set(void (D::*f)())
    {
        curr_f = f;
    }
};

class B : public A<B>
{
public:
    void main()
    {
        set(&B::new_function);
    }
    void new_function() {}
};

答案 1 :(得分:0)

You can have the code like this:


   #include <iostream>

using namespace std;

template<class T>
class A {
  protected:
    void (T::*curr_f)();
  public:

    virtual void set(void (T::*f)()) {
      curr_f = f;
      cout<<"Set in A"<<endl;
      T obj;
      (obj.*curr_f)();
    }

    virtual void new_function() {cout<<"in A"<<endl;};

};


class B :public A<B> {

  public:
    void func() {
      set(&B::new_function);
    };
    void new_function() {cout<<"in B"<<endl;};

};

int main()
{

  B obj;
  obj.func();

}