空白基类最优化(empty base optimization, EBO) 详解

本文地址: http://blog.csdn.net/caroline_wendy/article/details/23423247

EBO, empty base optimization, 即空白基类最优化, 可以使派生类节省空间;

但是如果使用复合(composition)的方式, 因为定义了新对象, 所以编译器会进行填充(padding), 填充进一个int, 4位的空间;

代码:

/*************************************************
File: test.cpp
Copyright: C.L.Wang
Author: C.L.Wang
Date: 2014-04-11
Description: test
Email: morndragon@126.com
**************************************************/

/*eclipse cdt, gcc 4.8.1*/

#include <iostream>

using namespace std;

class Empty {};

class HoldsAnInt {
private:
	int x;
	Empty e;
};

class HoldsAnIntP : private Empty {
private:
	int x;
};

int main () {
	std::cout << "Int : " << sizeof(int) << std::endl;
	std::cout << "HoldsAnInt(class) : " << sizeof(HoldsAnInt) << std::endl;
	std::cout << "HoldsAnIntP(inheritance) : " << sizeof(HoldsAnIntP) << std::endl;
	return 0;
}

Int : 4
HoldsAnInt(class) : 8
HoldsAnIntP(inheritance) : 4

C++ - 空白基类最优化(empty base optimization, EBO) 详解,布布扣,bubuko.com

C++ - 空白基类最优化(empty base optimization, EBO) 详解