问一个关于C++多态中析构函数调用的问题
问题描述：
在跟着B站某视频学C++学到多态时敲代码，发现一个问题，先上代码（使用的是Visual Studio）
#include<iostream>
using namespace std;
#include<string>
class cpu {
public:
virtual void calculate() = 0;
};
class card {
public:
virtual void display() = 0;
};
class memory {
public:
virtual void store() = 0;
};
class IntelCPU :public cpu {
public:
void calculate() {
cout << "使用IntelCPU计算" << endl;
}
~IntelCPU() {
cout << "调用IntelCPU析构函数" << endl;
}
};
class IntelCARD :public card {
public:
void display() {
cout << "使用IntelCARD显示" << endl;
}
~IntelCARD() {
cout << "调用IntelCARD析构函数" << endl;
}
};
class IntelMEM :public memory {
void store() {
cout << "使用IntelMEM存储" << endl;
}
};
class computer {
public:
computer(cpu* cp, card* ca, memory* me) {
a = cp;
b = ca;
c = me;
}
void work() {
a->calculate();
b->display();
c->store();
}
~computer() {
if (a != NULL) {
delete a;
a = NULL;
}
if (b != NULL) {
delete b;
b = NULL;
}
if (c != NULL) {
delete c;
c = NULL;
}
cout << "调用computer析构函数" << endl;
}
private:
cpu* a;
card* b;
memory* c;
};
void dowork(computer* com) {
com->work();
}
int main() {
IntelCPU* cp= new IntelCPU;
IntelCARD* ca = new IntelCARD;
IntelMEM* me = new IntelMEM;
computer* a = new computer(cp, ca, me);
dowork(a);
delete a;
}
结果：
在main函数中，delete a后cp开辟的空间确实被释放了（在computer a的析构函数中释放），但此时却没有调用IntelCPU的析构函数：
class IntelCPU :public cpu {
public:
void calculate() {
cout << "使用IntelCPU计算" << endl;
}
~IntelCPU() {
cout << "调用IntelCPU析构函数" << endl;
}
};
而如果删去delete a，而加上delete cp，则会调用该析构函数:
但是如果同时写上：delete a和delete cp，此时编译器则会报错：
我估计原因是因为重复释放了内存，也就证明前面cp开辟的空间确实被释放了，但此时在computer中的析构函数：
~computer() {
if (a != NULL) {
delete a;
a = NULL;
}
if (b != NULL) {
delete b;
b = NULL;
}
if (c != NULL) {
delete c;
c = NULL;
}
cout << "调用computer析构函数" << endl;
}
中的delete a(就是delete cp，，写的没注意名称重复的问题。。)却并不会调用IntelCPU的析构函数。
想问问各位对此有什么看法？
（重点不是在cp已经被释放，而是没有调用析构函数，如果我IntelCPI* cp时，cp中有指针开辟了堆上数据，那不是这部分数据就不能释放而泄漏了吗？
ps：视频中还教了一种写法，即：computer* a = new computer(new IntelCPU,new IntelCARD,new IntelMEM);，此时就完全不能调用各个Intel的析构函数了，因为在main中连类型名都没有）；
答
你这是学的那个老是忘记STRING头文件的黑马程序员的例子吧，我也写过一个，刚才去试了下，删除computer类的时候也是没有调用intelcpu的析构函数。我也怀疑数据没有释放，但是你说----delete a后cp开辟的空间确实被释放了（在computer a的析构函数中释放），这是根据什么来的？？？
答
这是我写的代码，你试一下，也没有调用intelcpu的析构函数
#include<iostream>
using namespace std;
class CPU
{public:
virtual void calculate()=0;
};
class intelcpu:public CPU
{
public:
void calculate()
{
cout<<"intelcpu is working。"<<endl;
};
~intelcpu()
{
cout<<"intelcpu析构"<<endl;
}
};
class Videocard
{public:
virtual void display()=0;
};
class intelvideocard:public Videocard
{
public:
void display()
{
cout<<"intelvideocard is working。"<<endl;
};
};
class Memory
{
public:
virtual void storage()=0;
};
class intelmemory:public Memory
{
public:
void storage()
{
cout<<"intelmemory is working。"<<endl;
};
};
class computer
{
public:
computer(CPU*cpu,Videocard*vc,Memory*mem)
{
mcpu=cpu;
mvc=vc;
mmem=mem;
};
void work()
{
mcpu->calculate();
mvc->display();
mmem->storage();
};
~computer(){ if(mcpu!=NULL)
{
delete mcpu;
mcpu=NULL;
}
if(mvc!=NULL)
{
delete mvc;
mvc=NULL;
}
if(mmem!=NULL)
{
delete mmem;
mmem=NULL;
}
cout<<"computer析构"<<endl;
};
private:
CPU *mcpu;
Videocard *mvc;
Memory *mmem;
};
class AMDcpu:public CPU
{
public:
void calculate()
{
cout<<"AMDcpu is working。"<<endl;
};
};
class AMDvideocard:public Videocard
{
public:
void display()
{
cout<<"AMDvideocard is working。"<<endl;
};
};
class AMDmemory:public Memory
{
public:
void storage()
{
cout<<"AMDmemory is working。"<<endl;
};
};
void test01()
{
CPU *cpu=new intelcpu;
Videocard *vc=new intelvideocard;
Memory *mem=new intelmemory;
computer *computer1=new computer(cpu,vc,mem);
computer1->work();
delete computer1;
cout<<"----------------------------------------------------------"<<endl;
computer*computer2=new computer(new AMDcpu,new AMDvideocard,new AMDmemory );
computer2->work();
delete computer2;
};
int main()
{
test01();
}