sizeof: Empty class or empty structure body

A child Boots the day before yesterday to the ideal international company interview, came back in the dormitory discussed such a question:

VC + +, there is an empty class, did not declare any member variables or functions, I would like to ask this empty class accounted for how large byte space?

A, 0 B, 1 C, 4 D, 8

The 32bit and 64bit machines were considered, and the pointer address was int, 32bit accounted for 4 bytes or 64bit was 8 bytes, so C and D were selected.

After thinking again, this does not operate the pointer, also does not need the memory alignment (depending on VC + + compiler will automatically alignment optimization), excluding the C and D, selected a

At that time also considered the Houtie teacher translated the "Deep Exploration of C + + object Model", C + + inheritance and polymorphism in the compiler is how to distinguish between, so 0 bytes is not reliable

But it's not going to be a byte at all, so it's the first time to completely killed B.

The interview back, in VC6.0, VS2010, g++ (Linux 2.6.31-14) compiled, found that the results are: 1

First, I post the test code:

#include <iostream>     
using namespace std;

Empty class class
ClassA
{
};

Inherits the empty class class
Classb:public ClassA
{
};

Empty structure body
struct STRUCTC
{
};

Main function
int main (int argc, char **argv)
{
    cout<< "A:" <<sizeof (ClassA) <<endl;
    cout<< "B:" <<sizeof (CLASSB) <<endl;
    cout<< "C:" <<sizeof (STRUCTC) <<endl;

    return 0;
}

Then, compile on each compiler

The results were as follows:

VC6.0 (XP Professional sp2-32bit)

VS2010 (Win7 Ultimate Sp1-64bit)