sizeof操作符关于类相关使用

首先，看一个题目：以下代码使用VC编译成32位可执行程序，请问：nLenA、nLenAObject、nLenB、nLenAObject、nLenC、nLenCObject的值分别为

#include<iostream>#include<stdlib.h>using namespace std;class t_classA{public:t_classA(){};~t_classA(){};};class t_classB{public:t_classB(){};virtual ~t_classB(){};};class t_classC:public t_classA,public t_classB{public:t_classC(){};virtual ~t_classC(){};};int main(){int nLenA = sizeof(t_classA);cout<<"nLenA: "<<nLenA<<endl;t_classA oA;int nLenAObject = sizeof(oA);cout<<"nLenAObject: "<<nLenAObject<<endl;int nLenB = sizeof(t_classB);cout<<"nLenB: "<<nLenB<<endl;t_classB oB;int nLenBObject = sizeof(oB);cout<<"nLenBObject: "<<nLenBObject<<endl;int nLenC = sizeof(t_classC);cout<<"nLenC: "<<nLenC<<endl;t_classC oC;int nLenCObject = sizeof(oC);cout<<"nLenCObject: "<<nLenCObject<<endl;}

下面进行全面的分析：

1、空类

#include<iostream>#include<stdlib.h>using namespace std;class A//1{};int main(){A a;cout<<sizeof(A)<<endl;//1cout<<sizeof(a)<<endl;//1}

2、一般非空

#include<iostream>#include<stdlib.h>using namespace std;class A{int a;//4int *p;//4char c;//1};int main(){A a;cout<<sizeof(A)<<endl;//12cout<<sizeof(a)<<endl;//12}

3.有虚函数

#include<iostream>#include<stdlib.h>using namespace std;class A{public:    A(){};virtual ~A(){};//4private:    int b;//4    int *p;//4    char c;//1};int main(){A a;cout<<sizeof(A)<<endl;//16cout<<sizeof(a)<<endl;//16}

4.虚函数继承

#include<iostream>#include<stdlib.h>using namespace std;class A//16{public:    A(){};virtual ~A(){};private:    int b;    int *p;    char c;};class B:public A{public:B(){};~B(){};private:     int b;//4};int main(){B b;cout<<sizeof(B)<<endl;//20cout<<sizeof(b)<<endl;//20}

5.静态成员函数

#include<iostream>#include<stdlib.h>using namespace std;class A//1{static int n;//0};int main(){A a;cout<<sizeof(A)<<endl;//1cout<<sizeof(a)<<endl;//1}

6.普通成员函数

#include<iostream>#include<stdlib.h>using namespace std;class A//1{func();//0};int main(){A a;cout<<sizeof(A)<<endl;//1cout<<sizeof(a)<<endl;//1}

所以结果如下：

nLenA=1 nLenAObject=1 nLenB=4 nLenAObject=4nLenC=4nLenCObject=4

参考：http://blog.csdn.net/zzhongcy/article/details/38361755