c++ - 为什么使用赋值时不调用堆栈变量的析构函数？

Question

这段愚蠢的代码已经花了我两个小时，我不明白为什么第一个元素的析构函数，即大小为 7 的元素，没有被调用？为 new uint16_t[7] 分配的内存会发生什么情况？

#include <iostream>

using namespace std;

struct Node
{
    Node(uint16_t n) : p(new uint16_t[n]) {
        cout<<"Constructed with size= "<<n<<", memory addr: "<<(p)<<endl;
        for(uint16_t i=0; i<n; i++) p[i] = n;
    }

    ~Node() {
        cout<<"Destructor for p[0] = "<< *p <<" with memory addr: "<<p<<endl;
        delete[] p;
    }

    uint16_t *p;
};

int main()
{
    {
        Node nd1(7);
        {
            nd1 = Node(3);
            cout << "1st place holder" << endl;
        }
        cout << "2nd place holder" << endl;
    }

    return 0;
}

输出为

Constructed with size= 7, memory addr: 0x158cc20                                                                                                                                   
Constructed with size= 3, memory addr: 0x158cc40                                                                                                                                   
Destructor for p[0] = 3 with memory addr: 0x158cc40                                                                                                                                
1st place holder                                                                                                                                                                   
2nd place holder                                                                                                                                                                   
Destructor for p[0] = 0 with memory addr: 0x158cc40                                                                                                                                
*** Error in `./a.out': double free or corruption (fasttop): 0x000000000158cc40 ***                                                                                                
Aborted (core dumped) 

Answer 1

I cannot figure out why the destructor of the first element, the one with size 7, not called?

它被称为。事实上，正是该析构函数导致了程序崩溃。程序的行为是未定义的，因为析构函数删除了先前由临时对象的析构函数删除的相同指针值。在此之前，它通过该无效指针进行间接访问。

<小时/>

What happens to the memory allocated for new uint16_t[7]?

当您对对象进行分配时，指向内存的指针丢失了。这称为内存泄漏。