如何在C++中调用虚拟析构函数？

Question

我试图看到调用属于长层次结构的类的虚拟析构函数的影响:类A到类E.

奇怪的是,析构函数不会向控制台写任何内容.我首先想到也许它正在发生,因为主要也在退出.因此,我将所有测试代码放在一个名为test()的函数中,并从main()中调用,这样当测试返回时,我会看到析构函数的脚印.但是,没有!控制台上没有"cout"标志出现!

#include <iostream>

using namespace std;

//A constructor cannot be virtual but a destructor can.
class A {
public:
A() {
    cout << "A constructor" << endl;
}
virtual ~A() {cout << "A destructor" << endl;}
};

class B :public A {
public:
    B() {
    cout << "B constructor" << endl;
    }
    virtual ~B() {cout << "B destructor" << endl;}
};

class C :public B {
public:
    C() {
    cout << "C constructor" << endl;
    }
    virtual ~C() {cout << "C destructor" << endl;}
};

class D :public C {
public:
    D() {
    cout << "D constructor" << endl;
    }
    ~D() {cout << "D destructor" << endl;}
};

class E :public D {
public:
    E() {
     cout << "E constructor" << endl;
      }
     ~E() {cout << "E destructor" << endl;}
};

void test() {
   cout << "Test1 begins..." << endl;
   A* a1 = new D();
   cout << "Test2 begins..." << endl;
   A* a2 = new E();
}

int main() {
 test();
 return 0;
}

Answer 1

嗯......你真的泄漏了那些.

new关键字创建的每个对象必须具有等效性delete:

void test() {
   cout << "Test1 begins..." << endl;
   A* a1 = new D();
   cout << "Test2 begins..." << endl;
   A* a2 = new E();
   delete a1;
   delete a2;
}

开发人员(仅在您的情况下)总是忘记删除动态分配的对象,因此引入了智能指针:

void test() {
   cout << "Test1 begins..." << endl;
   std::unique_ptr<A> a1(new D());
   cout << "Test2 begins..." << endl;
   std::unique_ptr<A> a2(new E());
}

无需担心泄漏,因为unique_ptr当它们超出范围时自动删除它们的指针.