计算类型大小的宏

#include <iostream>

using namespace std;

//两个指针相减，得到的是相隔几个元素
//char* 相隔几个元素，就是相隔几个字节
#define sizeof_v(x)	(char*)(&x+1) - (char*)(&x)
#define sizeof_t(t)	((size_t)((t*)0 + 1))

//对齐，内存池中，内存块大小是规则的。产生空隙碎片
#define ALIGN(v,b)	((v+b-1) & ~(b-1))

class Empty {
};


int main(void ) {
	Empty e;
	int n;
	cout << sizeof_v(e) << endl;
	cout << sizeof_v(n) << endl;
	cout << sizeof_t(Empty) << endl;
	cout << sizeof_t(int) << endl;
	
	cout << ALIGN(0, 16) <<endl;	
	cout << ALIGN(2, 16) <<endl;	
	cout << ALIGN(16, 16) <<endl;	
	cout << ALIGN(31, 16) <<endl;	
	return 0;
}