没有使用虚析构函数可能会出现的问题：
#include <iostream>
#include <string>
using namespace std;
class A {
public:
A() { cout << "
A constructor
" << endl; }
~A() { cout << "
A destructor
" << endl; }
};
class B: public A {
char
*buf;
public:
B() { buf = new
char
[10]; cout << "
B constructor
" << endl; }
~B() { cout << "
B destructor
" << endl; }
};
int
main()
{
A *p = new B;
delete p; // p是基类类型指针，仅调用基类析构函数，造成B中申请的10字节内存没被释放。
return
0;
}
输出：
A constructor
B constructor
A destructor
解决：将基类中的析构函数定义为虚析构函数
#include <iostream>
#include <string>
using namespace std;
class A {
public:
A() { cout << "
A constructor
" << endl; }
virtual ~A() { cout << "
A destructor
" << endl; }
};
class B: public A {
char
*buf;
public:
B() { buf = new
char
[10]; cout << "
B constructor
" << endl; }
~B() { cout << "
B destructor
" << endl; }
};
int
main()
{
A *p = new B;
delete p; //A中的析构函数说明为虚析构函数后，B中析构函数自动成为虚析构函数，由于P
//指向派生类对象，因此会调用派生类B的析构函数。
return
0;
}
输出：
A constructor
B constructor
B destructor
A destructor
