C++ - 指向对象的指针数组，什么存储在 STACK 中，什么存储在 HEAP 中？

Question

我是 C++ 的新手，我想澄清一些关于使用运算符“new ...”和运算符“delete ...”进行内存管理的要点。

我会发布一些我的代码，如果我的评论有误，请您指正。

我也在处理虚函数和接口(interface)，通过阅读代码就很清楚了，我也问你我是否以正确的方式接近它们。

那么我有一个更直接的问题，什么时候应该使用“new[] ...”或“delete[] ...”，又该如何正确使用呢？

PS:下面代码的输出是:

car built
motorcycle built
car has 4 wheels
motorcycle has 2 wheels
car destroyed
motorcycle destroyed

这是 main.cpp 的来源:

#include <iostream>

using namespace std;

class vehicle
{
    public:
        virtual
        ~vehicle()
        {
        }

        virtual void
        wheelNum() = 0;
};

class car : public vehicle
{
    public:
        car()
        {
            cout << "car built" << endl;
        }

        ~car()
        {
            cout << "car destroyed" << endl;
        }

        void
        wheelNum()
        {
            cout << "car has 4 wheels" << endl;
        }

};

class motorcycle : public vehicle
{
    public:
        motorcycle()
        {
            cout << "motorcycle built" << endl;
        }

        ~motorcycle()
        {
            cout << "motorcycle destroyed" << endl;
        }

        void
        wheelNum()
        {
            cout << "motorcycle has 2 wheels" << endl;
        }

};

int
main()
{
    // motorVehicle[2] is allocated in the STACK and has room for 2 pointers to vehicle class object

    // when I call "new ...", I allocate room for an object of vehicle class in the HEAP and I obtain its pointer, which is stored in the STACK

    vehicle* motorVehicle[2] = { new (car), new (motorcycle) };

    for (int i = 0; i < 2; i++)
    {
        // for every pointer to a vehicle in the array, I access the method wheelNum() of the pointed object

        motorVehicle[i] -> wheelNum();
    }

    for (int i = 0; i < 2; i++)
    {
        // given that I allocated vehicles in the HEAP, I have to eliminate them before terminating the program

        // nevertheless pointers "motorVehicle[i]" are allocated in the STACK and therefore I don't need to delete them

        delete (motorVehicle[i]);
    }

    return 0;
}

谢谢大家

Answer 1

用 new 分配的内存在 HEAP 上，其他所有东西都在堆栈上。所以在你的代码中，你有

vehicle* motorVehicle[2] = { new (car), new (motorcycle) };

栈上有两个指针 vehicle*[2] 的数组，堆上有两个对象，car 和 motocycle.

然后你有两个循环

for (int i = 0; i < 2; i++)

在循环期间，每一个都在堆栈上创建一个整数。