深度探索c++對象模型（四）補充

1. 普通成員變量的存儲順序按照在類中定義的順序

class A
{
public:
	int m_i;
	static int m_si;

	int m_j;
	static int m_sj;

	int m_k;
	static int m_sk;
};

int main()
{
	A a;
	a.m_i = 2;
	a.m_k = 5;
	a.m_j = 3;

	return 0;
}

• 對應的內存地址
  

打印成員變量的偏移地址

class A
{
public:
	int m_i;
	static int m_si;

	int m_j;
	static int m_sj;

	int m_k;
	static int m_sk;

public:
	//法2：
	void printMemberOffect()
	{
		printf("%d\n", &A::m_j);
	}
};

int main()
{

	A a;
	a.m_i = 2;
	a.m_k = 5;
	a.m_j = 3;
	
	//法1：
	int A::* p = &A::m_j;
	printf("%d\n", p);

	//
	a.printMemberOffect();

	return 0;
}

• 結果
  

2. 引入繼承關係後，可能會增加類的內存空間（字節對齊）

• 沒引入繼承關係

class A
{
public:
	int m_i;
	char m_j;
	char m_k;
	char m_l;
};

int main()
{
	cout << sizeof(A) << endl;
	
	return 0;
}

結果：

• 引入繼承關係

class A
{
public:
	int m_i1;
	char m_j1;
};

class B :public A
{
public:
	char m_k2;
};

class C :public B
{
public:
	char m_l3;
};

int main()
{
	cout << sizeof(A) << endl;
	cout << sizeof(B) << endl;
	cout << sizeof(C) << endl;

	return 0;
}

結果：