当在 C++ 中重写一个类时（使用虚拟析构函数），我在继承类上再次将析构函数实现为虚拟，但我需要调用基析构函数吗？
如果是这样，我想它是这样的......
MyChildClass::~MyChildClass() // virtual in header
{
// Call to base destructor...
this->MyBaseClass::~MyBaseClass();
// Some destructing specific to MyChildClass
}
我说的对吗？
【问题讨论】：
标签： c++ destructor
不，析构函数会以与构造相反的顺序自动调用。 （最后是基类）。不要调用基类析构函数。
【讨论】：
delete 两次却会导致分段错误？
不，您不需要调用基析构函数，派生析构函数始终会为您调用基析构函数。 Please see my related answer here for order of destruction。
要了解为什么要在基类中使用虚拟析构函数，请查看以下代码：
class B
{
public:
virtual ~B()
{
cout<<"B destructor"<<endl;
}
};
class D : public B
{
public:
virtual ~D()
{
cout<<"D destructor"<<endl;
}
};
当你这样做时：
B *pD = new D();
delete pD;
如果你在 B 中没有虚拟析构函数，则只会调用 ~B()。但是由于你有一个虚拟析构函数，所以首先调用 ~D()，然后调用 ~B()。
【讨论】：
其他人所说的，但也请注意，您不必在派生类中声明析构函数 virtual 。一旦你声明了一个虚拟的析构函数，就像你在基类中所做的那样，所有派生的析构函数都将是虚拟的，无论你是否声明它们。换句话说：
struct A {
virtual ~A() {}
};
struct B : public A {
virtual ~B() {} // this is virtual
};
struct C : public A {
~C() {} // this is virtual too
};
【讨论】：
不，您从不调用基类析构函数，它总是像其他人指出的那样自动调用，但这里是概念证明和结果：
class base {
public:
base() { cout << __FUNCTION__ << endl; }
~base() { cout << __FUNCTION__ << endl; }
};
class derived : public base {
public:
derived() { cout << __FUNCTION__ << endl; }
~derived() { cout << __FUNCTION__ << endl; } // adding call to base::~base() here results in double call to base destructor
};
int main()
{
cout << "case 1, declared as local variable on stack" << endl << endl;
{
derived d1;
}
cout << endl << endl;
cout << "case 2, created using new, assigned to derive class" << endl << endl;
derived * d2 = new derived;
delete d2;
cout << endl << endl;
cout << "case 3, created with new, assigned to base class" << endl << endl;
base * d3 = new derived;
delete d3;
cout << endl;
return 0;
}
输出是：
case 1, declared as local variable on stack
base::base
derived::derived
derived::~derived
base::~base
case 2, created using new, assigned to derive class
base::base
derived::derived
derived::~derived
base::~base
case 3, created with new, assigned to base class
base::base
derived::derived
base::~base
Press any key to continue . . .
如果您将基类析构函数设置为虚函数，则情况 3 的结果将与情况 1 和 2 相同。
【讨论】：
C++ 中的析构函数自动被调用按照它们的构造顺序（Derived 然后 Base）仅当 Base 类析构函数声明为 virtual。
如果不是，则在删除对象时仅调用基类析构函数。
示例：没有虚拟析构函数
#include <iostream>
using namespace std;
class Base{
public:
Base(){
cout << "Base Constructor \n";
}
~Base(){
cout << "Base Destructor \n";
}
};
class Derived: public Base{
public:
int *n;
Derived(){
cout << "Derived Constructor \n";
n = new int(10);
}
void display(){
cout<< "Value: "<< *n << endl;
}
~Derived(){
cout << "Derived Destructor \n";
}
};
int main() {
Base *obj = new Derived(); //Derived object with base pointer
delete(obj); //Deleting object
return 0;
}
输出
Base Constructor
Derived Constructor
Base Destructor
示例：使用 Base 虚拟析构函数
#include <iostream>
using namespace std;
class Base{
public:
Base(){
cout << "Base Constructor \n";
}
//virtual destructor
virtual ~Base(){
cout << "Base Destructor \n";
}
};
class Derived: public Base{
public:
int *n;
Derived(){
cout << "Derived Constructor \n";
n = new int(10);
}
void display(){
cout<< "Value: "<< *n << endl;
}
~Derived(){
cout << "Derived Destructor \n";
delete(n); //deleting the memory used by pointer
}
};
int main() {
Base *obj = new Derived(); //Derived object with base pointer
delete(obj); //Deleting object
return 0;
}
输出
Base Constructor
Derived Constructor
Derived Destructor
Base Destructor
建议将基类析构函数声明为virtual，否则会导致未定义的行为。
【讨论】：
没有。与其他虚拟方法不同，您可以从 Derived 显式调用 Base 方法以“链接”调用，编译器生成代码以按照调用构造函数的相反顺序调用析构函数。
【讨论】：
没有。它是自动调用的。
【讨论】：