基类析构函数声明为虚函数，继承关系的内存分布如何实现？

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1，基本结构函数不为虚函数+

1，基类析构函数不为虚函数

#include "pch.h" #include <iostream> class CBase { public: CBase() { m_one = 0; printf("this is CBase construct\n"); } ~CBase() { printf("this is ~CBase deconstruct\n"); } void setNumOne(int n) { m_one = n; } int getNumOne() { return m_one; } private: int m_one; }; class CDrived:public CBase { public: CDrived() { m_two = 0; printf("this is CDrived construct\n"); } ~CDrived() { printf("this is ~CDrived deconstruct\n"); } void setNumTwo(int n) { m_two = n; } int getNumTwo() { return m_two; } private: int m_two; }; int main() { CBase *p = new CDrived; delete p; std::cout << "Hello World!\n"; }

输出：

this is CBase construct this is CDrived construct this is ~CBase deconstruct Hello World!

可以发现继承类析构函数没有调用，若继承类中有一些资源需要释放，则不能释放，故需要将基类析构函数声明为虚函数。

#include "pch.h" #include <iostream> class CBase { public: CBase() { m_one = 0; printf("this is CBase construct\n"); } virtual ~CBase() { printf("this is ~CBase deconstruct\n"); } void setNumOne(int n) { m_one = n; } int getNumOne() { return m_one; } private: int m_one; }; class CDrived:public CBase { public: CDrived() { m_two = 0; printf("this is CDrived construct\n"); } ~CDrived() { printf("this is ~CDrived deconstruct\n"); } void setNumTwo(int n) { m_two = n; } int getNumTwo() { return m_two; } private: int m_two; }; int main() { CBase *p = new CDrived; delete p; std::cout << "Hello World!\n"; }

输出：

this is CBase construct this is CDrived construct this is ~CDrived deconstruct this is ~CBase deconstruct Hello World!

2，

#include "pch.h" #include <iostream> class CBase { public: CBase() { m_one = 0; printf("this is CBase construct\n"); } virtual ~CBase() { printf("this is ~CBase deconstruct\n"); } virtual void setNumOne(int n) { m_one = n; } virtual int getNumOne() { return m_one; } private: int m_one; }; class CDrived:public CBase { public: CDrived() { m_two = 0; printf("this is CDrived construct\n"); } ~CDrived() { printf("this is ~CDrived deconstruct\n"); } void setNumTwo(int n) { m_two = n; } int getNumTwo() { return m_two; } private: int m_two; }; int main() { CDrived *p = new CDrived; printf("sizeof(CDrived) = %d\n", sizeof(CDrived)); // 12 delete p; std::cout << "Hello World!\n"; }