深度探索c++對象模型（四）

1. 單一繼承下數據成員佈局

引入繼承關係後，可能會帶來內存空間的額外增加（字節對齊）

class A
{
public:
	int a;
	int b;
	char c;
	char d;
};


int main() {

	cout << sizeof(A) << endl;

	return 0;
}

結果：

class A
{
public:
	int a;
	int b;
};

class B:public A
{
public:
	char b;
};

class C :public B
{
public:
	char c;
};

int main() {

	cout << sizeof(A) << endl;
	cout << sizeof(B) << endl;
	cout << sizeof(C) << endl;

	return 0;
}

結果：

2. 單一繼承（父類帶、不帶虛函數）的成員佈局

class A
{
public:
	int m_a;
	virtual void funA() {};
};

class B : public A
{
public:
	int m_b1;
	int m_b2;
	virtual void funB() {};
};

int main()
{


	B b;
	cout << sizeof(B) << endl;
	printf("A::m_a= %d\n", &A::m_a);
	printf("B::m_b1= %d\n", &B::m_b1);
	printf("B::m_b2= %d\n", &B::m_b2);

	b.m_a = 1;
	b.m_b1 = 2;
	b.m_b2 = 3;


	return 0;
}

結果：

地址佈局：

3. 多層繼承數據佈局

class A
{
public:
	int m_a;
	virtual void funA() {};
};

class B
{
public:
	int m_b;
	virtual void funB() {};
};

class C :public A, public B
{
public:
	int m_c;
	virtual void funC() {};
};

int main()
{


	C c;
	cout << sizeof(C) << endl;
	printf("A::m_a= %d\n", &C::m_a);
	printf("B::m_b= %d\n", &C::m_b);
	printf("C::m_c= %d\n", &C::m_c);

	c.m_a = 1;
	c.m_b = 2;
	c.m_c = 3;


	return 0;
}