编辑：

Question

我的朋友制作了这段代码，用于访问类的内存并更改私有变量的值。

#include <iostream>

using namespace std;

class has_private_variable
{
private:
    const int member1;
public:
    has_private_variable()
    : member1(5) //initializer list. In case you haven't seen that before
    {
    }
    int getMember1()
    {
        return member1;
    }
};

int main()
{
    has_private_variable hpv;
    int tmp = hpv.getMember1();
    cout << hpv.getMember1() << endl;
    char* ptr = (char*)&hpv; //Yeah this will generate all types of warnings hopefully
    //find the actual address of the member
    while (*(int*)ptr != tmp)
        ptr++;
    int* ptr_int = (int*)ptr;
    *ptr_int = 3;
    cout << hpv.getMember1() << endl;
    //There's a joke in here about hpv.vaccinate(), but I can't be bothered to find it
    return 0;
}

执行此操作的能力似乎破坏了拥有私有变量的整个过程。是否有一些方法可以阻止程序员访问这样的私有变量？

编辑：

从我收到的评论中，我的朋友正在调用C ++的未定义行为。但有没有它可以让程序员无法做到这一点？

Answer 1

可以使用专用的模板类，模板类创建一个私有成员并在隐藏的内存位置静态分配它：

template<typename type>
class true_private
{
public:
    ~true_private()
    {
       type local;
       get_set(-1, local);
    }

    true_private(type value)
    {
       type local = value;
       get_set(0, local);
    }

    void get_set(int op, type& value)
    {
        static type* var = 0;

        if( var == 0)
            var = new type();

        if( op == 0 ) // set
            *var = value;

        else if(op == 1) // get
            value = *var;
        else  // delete
            delete var;
    }

    type Get()
    {
        type local;
        get_set(1, local);
        return local;
    }

    void Set(type value)
    {
       type local = value;
       get_set(0, local);
    }
};

class has_private_variable
{
private:
     true_private<int> member1;
public:
    has_private_variable()
    :member1(5) //initializer list. In case you haven't seen that before
    {
    }
    int getMember1()
    {
        return member1.Get();
    }
};

这只是一个展示模板类功能的练习：）

C ++访问内存类和更改私有变量

编辑：

1 个答案: