C + +: Blank base class optimization (empty base optimization, EBO) detailed

EBO, empty base optimization, which is the optimization of the blank base class, can make the derived class space-saving;

But if you use a composite (composition) method, because the new object is defined, the compiler fills (padding) and fills in an int, 4-bit space;

Code:

/************************************************* 
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;  
}

Output:

Int:4  
Holdsanint (Class): 8  
holdsanintp (inheritance): 4

Author: csdn Blog spike_king

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