关于析构

最新推荐文章于 2023-11-12 11:04:37 发布

原创最新推荐文章于 2023-11-12 11:04:37 发布 · 368 阅读

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#delete #class #null #struct

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struct IBase { virtual Release() = NULL; }; class CDerive:public IBase { public: ~CDerive() { printf("CDerive destraction/n"); }; virtual Release() { delete this; }; }; class CDerive2:public CDerive { public: ~CDerive2() { printf("CDerive2 destraction/n"); }; };

int _tmain(int argc, _TCHAR* argv[]) { IBase *pBase1 = new CDerive(); IBase *pBase2 = new CDerive2(); CDerive *pDerive = new CDerive(); CDerive2 *pDerive2 = new CDerive2(); pBase1->Release(); //(1)正确 pBase2->Release(); //(2)错误 pDerive->Release(); //(3)正确 pDerive2->Release(); //(4)错误 // delete pBase1; //(5)错误 // delete pBase2; //(6)错误 // delete pDerive; //(7)正确 // delete pDerive2; //(8)正确 return 0; }

这段代码中，Release为virtual，析构函数没有被声明称virtual，这时：

(1)(2)调用CDerive的Release，析构CDerive。

(3)能够正确调用CDerive的Release，析构CDerive。

(4)CDerive2没有实现自己的Release，这时调用的是CDerive的Release，析构CDerive。

输出：

(1)CDerive destraction
(2)CDerive destraction
(3)CDerive destraction
(4)CDerive destraction

(5)(6)析构IBase

(7)析构CDerive

(8)析构CDerive2，之后析构CDerive

输出：

(5)CDerive destraction
(6)CDerive2 destraction

(6)CDerive destraction

struct IBase { virtual Release() = NULL; }; class CDerive:public IBase { public: virtual ~CDerive() { printf("CDerive destraction/n"); }; virtual Release() { delete this; }; }; class CDerive2:public CDerive { public: virtual ~CDerive2() { printf("CDerive2 destraction/n"); }; };

int _tmain(int argc, _TCHAR* argv[]) { IBase *pBase1 = new CDerive(); IBase *pBase2 = new CDerive2(); CDerive *pDerive = new CDerive(); CDerive2 *pDerive2 = new CDerive2(); pBase1->Release(); //(1)正确 pBase2->Release(); //(2)正确 pDerive->Release(); //(3)正确 pDerive2->Release(); //(4)正确 // delete pBase1; //(5)错误 // delete pBase2; //(6)错误 // delete pDerive; //(7)正确 // delete pDerive2; //(8)正确 return 0; }

这里析构函数全部被声明为virtual：

(1)(3)调用CDerive的Release，析构CDerive。

(2)(4)调用CDerive的Release，析构CDerive2，析构CDerive。

输出：

(1)CDerive destraction
(2)CDerive2 destraction
(2)CDerive destraction
(3)CDerive destraction
(4)CDerive2 destraction
(4)CDerive destraction

(5)(6)析构IBase。

(7)析构CDerive。

(8)析构CDerive2，析构CDerive。

输出：

(7)CDerive destraction
(8)CDerive2 destraction
(8)CDerive destraction

如果利用virtual Release销毁对象时，析构函数如果非virtual，那么需要每个类都实现自己的virtual Release()。如果析构函数是virtual，那么只要基类实现一个virtual Release()就可以了。

如果用delete基类指针销毁对象，则需要基类和派生类都有virtual析构。