c++ 클래스의 sizeof

Empty Classes and Structs

In C, an empty struct like:

struct A {};

is invalid, whereas in C++, usage like:

struct A {};

or:

class B {};

is perfectly legal. This type of construct is useful when developing a skeleton or placeholder for a class.

An empty class has size greater than zero. Two class objects of empty classes will have distinct addresses, as in:

class A {};

void f()
{
A* p1 = new A;
A* p2 = new A;
// p1 != p2 at this point ...
}

There are still one or two C++ compilers that generate C code as their "assembly" language. To handle an empty class, they will generate a dummy member, so, for example:

class A {};

becomes:

struct A {
char __dummy;
};

in the C output.