[英]multiple protected inheritance with polymorphism
I have a question about multiple inheritance of protected function and polymorphism. 我有一个关于受保护函数和多态的多重继承的问题。 It's quite hard to describe it so I hope it will be clear enough.
描述它很难,所以我希望它足够清楚。
Say I have three classes: 说我有三个班:
class baseClass
{
protected:
virtual int function() = 0;
};
class derived_A:public baseClass
{
int function()
{
//implementation 1
};
};
class derived_B:public baseClass
{
int function()
{
//implementation 2
};
};
class derived_C:public derived_A, public derived_B
{
baseClass ** p_arr; //array of pointers of baseClass kind (polymorphism)
int x=0;
for (int i=0; i<arraySize; i++) // array size = many classes like derived_A, derived_B...
{
x = p_arr[i]->function(); //I already have function that builds this array
//it is not the question so I didn't put it here.
// process x
}
};
Finally my question is - how can I access that "protected" function()
from derived_C
class (inside the for loop)? 最后我的问题是 - 如何从
derived_C
类(for循环内function()
访问“protected” function()
)? I am a bit confused... and will be happy for explanation. 我有点困惑......并且很乐意解释。
Thanks. 谢谢。
When C++ permits access to protected
members, it's only to the members of this object (as mentioned here and here ). 当C ++允许访问
protected
成员时,它只对该对象的成员(如此处和此处所述 )。 The code x = p_arr[i]->function()
tries to call a method in another object, so the compiler complains. 代码
x = p_arr[i]->function()
尝试调用另一个对象中的方法,因此编译器会抱怨。
To fix your code, you can make function
public, or add a friend
declaration to baseClass
, like this: 要修复代码,可以将
function
public,或者向baseClass
添加一个friend
声明,如下所示:
class baseClass
{
public:
virtual int function() = 0;
};
Or 要么
class baseClass
{
protected:
friend class derived_C;
virtual int function() = 0;
};
However, to retain the protected
access and not mention the name of the derived class in the base class, you can fix your code by adding a static
accessor function to the base class: 但是,要保留
protected
访问权限而不提及基类中派生类的名称,可以通过向基类添加static
访问器函数来修复代码:
class baseClass
{
protected:
virtual int function() = 0;
static int call_the_function_on_object(baseClass& obj) {return obj.function();}
};
Use it (in a derived class) this way: 以这种方式使用它(在派生类中):
x = call_the_function_on_object(*p_arr[i]);
You can also give the accessor function the same name, but then, if your derived_C
overrides the virtual method, it will hide the accessor function. 您也可以为访问者函数指定相同的名称,但是,如果您的
derived_C
重写了虚方法,它将隐藏访问者函数。 You can fix that by referring to the base class explicitly: 您可以通过显式引用基类来解决这个问题:
class baseClass
{
protected:
virtual int function() = 0;
static int function(baseClass& obj) {return obj.function();}
};
...
class derived_C:public derived_A, public derived_B
{
...
x = baseClass::function(*p_arr[i]);
...
}
In this case your function()
is private in derived classes. 在这种情况下,您的
function()
在派生类中是私有的。 So, from derived_C
you cannot directly access that function. 因此,从
derived_C
您无法直接访问该函数。
However, if you are willing to make it public/protected
. 但是,如果您愿意将其
public/protected
。 Then you can use:- 然后你可以使用: -
derived_C dc;
dc.derived_A::function();
dc.derived_B::function();
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