Question

我正在尝试按特定顺序输出对象的创建和删除。默认情况下，首先使用构造函数的析构函数会创建第一个对象，依此类推，然后析构函数会从最后创建的对象开始删除。我正在尝试更改输出顺序，类似于以下内容：

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;
};

为此，我发现我可以使用指针，指向创建的对象，并删除，当我们需要时，可以通过这种方式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;

    }

现在，它仅创建3个对象，并在创建后立即删除第三个对象，而我正在尝试删除第三个对象之后删除第二个对象。

Answer 1

您使用delete是无效的，从而导致未定义的行为，因为您没有使用new创建对象。您正在尝试销毁堆栈上存在的对象，这些对象在超出范围时会被自动销毁，您无权手动销毁它们。

如果要使用delete控制销毁顺序，则必须使用new，如下所示：

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;
}

Live Demo

或者，在您的特定示例中，可以通过简单地更多地控制对象的范围而完全不使用new和delete来获得相同的输出：

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!

Live Demo

如何在对象上使用指针；构造函数和析构函数。 C ++

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