[英]Is there any way to make a class function only callable from another class function?
我正在开发一个小的 2D“渲染器”,它使用从屏幕上的类读取的参数来绘制事物。 绘图动作由大型渲染器 class 完成。 因此 ObjectParameters class 和 MainDrawing class 之间存在数据转换。 我用来声明一个公共 function 以使来自 MainDrawing 的调用成为可能。 但它也可以由其用户调用,并使 class object不安全。
那么有什么方法可以使声明的 class function只能由另一个 class 调用(但是方法是公共的、私有的或受保护的)?
class ObjectParameters {
public:
COORD position;
int Width;
int Height;
COLORREF elemColor;
private:
int _zIndex;
public:
ObjectParameters();
~ObjectParameters();
/* This line is the code which won't be called by the user,
/* but MainDrawing class needs it for setting the layers.
/* I don't want to make it callable from user,
/* because it can occur errors. */
void Set_ZIndex(int newValue);
};
class MainDrawing {
public:
MainDrawing();
~MainDrawing();
/* Here will change the object's z-index to order the draw sequence,
/* so it calls the Set_ZIndex() function */
void AddThingsToDraw(ObjectParameters& object);
private:
/* OTHER CODES */
};
使用friend
关键字: https://en.cppreference.com/w/cpp/language/friend
// Forward declaration. So that A knows B exists, even though it's no been defined yet.
struct B;
struct A {
protected:
void foo() {}
friend B;
};
struct B {
void bar(A& a) {
a.foo();
}
};
int main()
{
A a; B b;
b.bar(a);
//a.foo(); Not allowed
}
您可以将私有 function 设为嵌入式 class 的私有成员,如下所示:
class MyOuterClass
{
public:
class MyInnerClass
{
private:
void MyPrivateFunction () {}
public:
void MyPublicFuncton ()
{
MyPrivateFunction ();
}
};
};
我得到的是您希望继承的 class 无法访问父 class 变量。 为此,您只需将变量设为私有并将 function 设为公开即可。 并继承 class 作为保护,以便只有子 class 可以访问和使用 function。 如果您想要代码,我也可以提供帮助。 第一种方法是声明它受保护并继承 class。
class ObjectParameters {
public:
int Width;
int Height;
private:
int _zIndex
;
public:
ObjectParameters();
~ObjectParameters();
/* This line is the code which won't be called by the user,
/* but MainDrawing class needs it for setting the layers.
/* I don't want to make it callable from user,
/* because it can occur errors. */
protected:
void Set_ZIndex(int newValue);
};
class MainDrawing:ObjectParameters {
public:
MainDrawing();
~MainDrawing();
Set_ZIndex(5);
/* Here will change the object's z-index to order the draw sequence,
/* so it calls the Set_ZIndex() function */
private:
/* OTHER CODES */
};
第二种方法是在 ObjectParameters 中将 MainDrawing 声明为友元
friend class MainDrawing
并将Set_ZIndex()
私有,因此只有朋友 class 可以访问它
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