Class X {} sizeof(X) // = 1 ?

[arunkumar_gona]

Class X
{

}

Class Y
{
char c;
}

class Z
{
int i;
}

Now:

sizeof(X) // == 1
sizeof(Y) // == 1
sizeof(Z) // == 4

Why is the size of class X is 1 when it is empty ?
I understand that sizeof(Y) & sizeof(Z) to be 1 and 4 because of the member variables.

Can someone enlighten me on this.