如何对对象使用指针； 构造函数和析构函数。 C++

Question

我正在尝试按特定顺序创建和删除对象的输出。 默认情况下，首先使用构造函数析构函数创建第一个对象，依此类推，析构函数从最后创建的对象开始删除。 我正在尝试更改类似于此的输出顺序：

Object 1 is created, we've got 1 object(s) now!

Object 2 is created, we've got 2 object(s) now!

Object 3 is created, we've got 3 object(s) now!

Object 3 is deleted, we've got 2 object(s) now!

Object 2 is deleted, we've got 1 object(s) now!

Object 4 is created, we've got 2 object(s) now!

Object 4 is deleted, we've got 1 object(s) now!

Object 1 is deleted, we've got 0 object(s) now!  

代码：

class Object {
public:
    Object(int i) {
        id = i;
        count++;
        cout<<"Object "<<id<<" is created, we've got "<<count<<" object(s) now!"<<endl;
    }
    ~Object() {
        count--;
        cout<<"Object "<<id<<" is deleted, we've got "<<count<<" object(s) now!"<<endl;
    }
private: 
    int id;
    static int count;
};  

为了做到这一点，我发现我可以使用指针，指向创建的对象并在需要时删除它，这样我们就可以控制创建和删除的顺序。

#include"Object.h"
extern void TestObjects()
    {

    Object *a;
    Object obj1(1),obj2(2),obj3(3);

    a = &obj3;
    delete a;

    Object *c;
    c = &obj2;
    delete c;

    }

到目前为止，它只创建了 3 个对象，并在创建后立即删除了第三个对象，我试图在删除第三个对象后立即删除第二个对象。

Answer 1

您使用delete无效，导致未定义行为，因为您没有使用new创建对象。 您正在尝试销毁堆栈中存在的对象，并且当它们超出范围时会自动销毁，您无权手动销毁它们。

如果你想使用delete来控制销毁顺序，你必须使用new ，像这样：

void TestObjects()
{
    Object *obj1 = new Object(1);
    Object *obj2 = new Object(2);
    Object *obj3 = new Object(3);

    delete obj3;
    delete obj2;

    Object *obj4 = new Object(4);
    delete obj4;

    delete obj1;
}

现场演示

或者，在您的特定示例中，只需更多地控制对象的范围并且根本不使用new和delete ，就可以获得相同的输出：

void TestObjects()
{
    Object obj1(1);

    {
    Object obj2(2);
    Object obj3(3);
    } // <-- obj3 and obj2 are destroyed here, in that order!

    Object obj4(4);
} // <-- obj4 and obj1 are destroyed here, in that order!

现场演示