Question

我的班级/指针有问题。我有两个课程FirstClass和SecondClass。 FirstClass有两个指点：

MyClass *character1;
MyClass *character2;

我稍后在我的代码中分配给这些指针，但现在我有SecondClass我还有2个指针：

 MyClass *oldChar1;
 MyClass *oldChar2;

我想将oldChar设置为与character所指示的相同。我在SecondClass中使用friend子句在FirstClass中创建了一个函数。

void SecondClass::setChars()
{
    *oldChar1 = FirstClass::character1;
    *oldChar2 = FirstClass::character2;
}

结果： illegal reference to non-static member 'FirstClass::character1' 我不明白：/有人可以帮助我吗？

Answer 1

有几种方法可以做到这一点。

在两个班级（source）中共享的朋友功能。

友元函数可以访问类MyFirstClass和MySecondClass的数据成员，但仍然需要告诉友元函数使用哪些类的实例（参见this），例如

class MyClass {

};

class MySecondClass; //forward declaration for later

class MyFirstClass {

private:
  MyClass *character1;
  MyClass *character2;

public:
  //friend function
  friend void setChars(MyFirstClass& c1, MySecondClass& c2); //<---- friend function

};

class MySecondClass {

private:
  MyClass *oldChar1;
  MyClass *oldChar2;

public:
  //friend function
  friend void setChars(MyFirstClass& c1, MySecondClass& c2);

};

//define the friend function
void setChars(MyFirstClass& c1, MySecondClass& c2) {
  c2.oldChar1 = c1.character1;
  c2.oldChar2 = c1.character2;
}

int main() {

  MyFirstClass c1;
  MySecondClass c2;

  setChars(c1,c2);

}

朋友类。使MySecondClass成为MyFirstClass的朋友。 MySecondClass将有方法setChars，它将MyFirstClass的一个实例作为参数。 e.g。

class MyClass {

};

class MySecondClass;

class MyFirstClass {

private:
  MyClass *character1;
  MyClass *character2;

public:   
  friend MySecondClass; //<----- friend class

};

class MySecondClass {

private:
  MyClass *oldChar1;
  MyClass *oldChar2;

public:

  void setCharsUsingFriendClass(MyFirstClass& c1) {
    oldChar1 = c1.character1;
    oldChar2 = c1.character2;
  }


};

int main() {

  MyFirstClass c1;
  MySecondClass c2;

  c2.setCharsUsingFriendClass(c1);

}

最后使用2个getter方法。我认为这种方法更好，因为它允许类隐藏它们的实现细节（encapsulation）。

class MyClass {

};

class MySecondClass;

class MyFirstClass {

private:
  MyClass *character1;
  MyClass *character2;

public:

  //define getters to access the private members
  MyClass* GetCharacter1() {return character1;}
  MyClass* GetCharacter2() {return character2;}
};

class MySecondClass {

private:
  MyClass *oldChar1;
  MyClass *oldChar2;

public:

  void setCharsUsingGetters(MyFirstClass& c1) {
    oldChar1 = c1.GetCharacter1();
    oldChar2 = c1.GetCharacter2();
  }
};

int main() {

  MyFirstClass c1;
  MySecondClass c2;

 c2.setCharsUsingGetters(c1);

}

非法引用2个类中的非静态成员

1 个答案: