[shoorik@devproxy-test-v ~]$ cat a.cpp
#include <stdio.h>

struct T1 {
  char a;
  int b;
};

class T2 {
public:
  char a;
  int b;
};

class T3 {
public:
  char a;
  int b;
  virtual void foo() {
  }
};

struct __attribute__ ((__packed__)) T4 {
  char a;
  int b;
};

int main () {
  return printf ("%d %d %d %d\n", sizeof(T1), sizeof(T2), sizeof(T3), sizeof(T4));
}
[shoorik@devproxy-test-v ~]$ g++ a.cpp
[shoorik@devproxy-test-v ~]$ ./a.out
8 8 16 5
[shoorik@devproxy-test-v ~]$