C++学习笔记(8)----C++类的大小

C++类的大小

(i)

如下代码：

#include<iostream>

using namespace std;

class CBase {

};

class CDerive :public CBase {

};

int main(int argc, char* argv[])

{

	CDerive p[3];

	cout << "sizeof(CBase)=" << sizeof(CBase) << endl

		<< "sizeof(CDerive)=" << sizeof(CDerive) << endl;

	cout << "sizeof(p)=" << sizeof(p) << endl;

	cout << "&p[0]=" << &p[0] << endl

		<< "&p[1]=" << &p[1] << endl

		<< "&p[2]=" << &p[2] << endl;

	return 0;

}

运行结果为：

S:\ComputerTech\VS2015\Release>Test.exe

sizeof(CBase)=1

sizeof(CDerive)=1

sizeof(p)=3

&p[0]=002CF7B8

&p[1]=002CF7B9

&p[2]=002CF7BA

(ii)

将上述代码中的CBase类重新声明如下：

class CBase {

	int num;

};

class CDerive :public CBase {

};

再次运行上述程序，结果如下：

S:\ComputerTech\VS2015\Release>Test.exe

sizeof(CBase)=4

sizeof(CDerive)=4

sizeof(p)=12

&p[0]=0023FD88

&p[1]=0023FD8C

&p[2]=0023FD90

(iii)

将(i)中的CBase类声明如下：

class CBase {

	int num;

	double d;

};

class CDerive :public CBase {

};

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe

sizeof(CBase)=16

sizeof(CDerive)=16

sizeof(p)=48

&p[0]=001DFA98

&p[1]=001DFAA8

&p[2]=001DFAB8

(iv)

将(i)中的CBase类和CDerive类声明如下：

class CBase {

	int num;

};

class CDerive :public CBase {

	int num2;

};

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe

sizeof(CBase)=4

sizeof(CDerive)=8

sizeof(p)=24

&p[0]=0032F734

&p[1]=0032F73C

&p[2]=0032F744

(v)

将(i)中的CBase类和CDerive类声明如下：

class CBase {

	int num;

};

class CDerive :public CBase {

	double d;

};

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe

sizeof(CBase)=4

sizeof(CDerive)=16

sizeof(p)=48

&p[0]=0041FE38

&p[1]=0041FE48

&p[2]=0041FE58