8.4. Subobjetos duplicados

//: C09:Offset.cpp
// Illustrates layout of subobjects with MI.
#include <iostream>
using namespace std;

class A { int x; };
class B { int y; };
class C : public A, public B { int z; };

int main() {
  cout << "sizeof(A) == " << sizeof(A) << endl;
  cout << "sizeof(B) == " << sizeof(B) << endl;
  cout << "sizeof(C) == " << sizeof(C) << endl;
  C c;
  cout << "&c == " << &c << endl;
  A* ap = &c;
  B* bp = &c;
  cout << "ap == " << static_cast<void*>(ap) << endl;
  cout << "bp == " << static_cast<void*>(bp) << endl;
  C* cp = static_cast<C*>(bp);
  cout << "cp == " << static_cast<void*>(cp) << endl;
  cout << "bp == cp? " << boolalpha << (bp == cp) << endl;
  cp = 0;
  bp = cp;
  cout << bp << endl;
}
/* Output:
sizeof(A) == 4
sizeof(B) == 4
sizeof(C) == 12
&c == 1245052
ap == 1245052
bp == 1245056
cp == 1245052
bp == cp? true
0
*/ ///:~

Listado 8.10. C09/Offset.cpp


//: C09:Duplicate.cpp
// Shows duplicate subobjects.
#include <iostream>
using namespace std;

class Top {
  int x;
public:
  Top(int n) { x = n; }
};

class Left : public Top {
  int y;
public:
  Left(int m, int n) : Top(m) { y = n; }
};

class Right : public Top {
  int z;
public:
  Right(int m, int n) : Top(m) { z = n; }
};

class Bottom : public Left, public Right {
  int w;
public:
  Bottom(int i, int j, int k, int m)
  : Left(i, k), Right(j, k) { w = m; }
};

int main() {
  Bottom b(1, 2, 3, 4);
  cout << sizeof b << endl; // 20
} ///:~

Listado 8.11. C09/Duplicate.cpp