c++ - 能够访问类定义之外的私有(private)对象成员

Question

看来我的代码违反了不能在类定义之外访问对象的私有(private)成员的规则。

我有一个这样定义的类

class Test{
private:
    int x;
public:
    const Test& operator=(const Test &other){
        this->x = other.x;
        return *this;
    }
    void addX(int);
    void getX();
};

这里让我感到困惑的是，我能够访问类 Test 的对象“other”的私有(private)成员

这似乎不对，或者如果是，那一定是我遗漏了一些基本的东西

Answer 1

对于相同类型，您可以访问任何实例的私有(private)(和 protected )成员。这包括静态成员以及私有(private)或 protected 继承基。

几个例子:

class Base {
protected:
    int y;
private:
    int z;
};
class Sub;
class Test : private Base {
private:
    int x;
public:
    const Test& operator=(const Test &other) {
        this->x = other.x; // Can access private members for any instance
        this->y = other.y; // Can access a protected member of a base type
        this->z = other.z; // ERROR: Neither side is OK, can't access a private member of a base
        return *this;
    }
    void foo(Sub &sub);
};
class Sub : public Test
{
private:
    int w;
};
inline void Test::foo(Sub &sub) {
    int a = sub.x; // Still OK, as x is a member of Test
    a += sub.w; // ERROR: Can't access privates of subtypes however
}