memory layout of inherited class

Question

I\'m keen to know exactly how the classes will be arranged in memory esp. with inheritance and virtual functions.

I know that this is not defined by the c++ language st

Answer 1

Create an object of class, cast pointer to it to your machine's word, use sizeof to find the size of the object, and examine the memory at the location. Something like this:

#include 

class A
{
 public:
  unsigned long long int mData;
  A() :
   mData( 1 )
  {
  }      
  virtual ~A()
  {
  }
};
class B : public A
{
 public:
  unsigned long long int mData1;
  B() :
   A(), mData1( 2 )
  {
  }
};

int main( void )
{
 B lB;

 unsigned long long int * pB = ( unsigned long long int * )( &lB );

 for( int i = 0; i < sizeof(B) / 8; i++ )
 {
  std::cout << *( pB + i ) << std::endl;
 }

 return ( 0 );
}


Program output (MSVC++ x86-64):

5358814688 // vptr
1          // A::mData
2          // B::mData1

On a side note, Stanley B. Lippman has excellent book "Inside the C++ Object Model".