73 lines
1.2 KiB
C++
73 lines
1.2 KiB
C++
/**
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* @file geninhe.cpp
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* @brief 1.普通单继承,继承就是基类+派生类自身的大小(注意字节对齐)
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* 注意：类的数据成员按其声明顺序加入内存，无访问权限无关，只看声明顺序。
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* 2.虚单继承，派生类继承基类vptr
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* @author 光城
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* @version v1
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* @date 2019-07-21
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*/
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#include<iostream>
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using namespace std;
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class A
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{
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public:
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char a;
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int b;
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};
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/**
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* @brief 此时B按照顺序：
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* char a
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* int b
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* short a
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* long b
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* 根据字节对齐4+4+8+8=24
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*
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* 或编译器优化
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* char a
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* short a
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* int b
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* long b
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* 根据字节对齐2+2+4+8=16
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*/
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class B:A
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{
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public:
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short a;
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long b;
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};
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/**
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* 把A的成员拆开看，char为1，int为4，所以是1+（3）+4+1+（3）=12，（）为字节补齐
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*/
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class C
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{
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A a;
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char c;
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};
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class A1
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{
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virtual void fun(){}
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};
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class C1:public A
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{
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};
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int main()
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{
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cout<<sizeof(A)<<endl; // 8
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cout<<sizeof(B)<<endl; // 16
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cout<<sizeof(C)<<endl; // 12
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/**
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* @brief 对于虚单函数继承，派生类也继承了基类的vptr，所以是8字节
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*/
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cout<<sizeof(C1)<<endl; // 8
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return 0;
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}
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