From: hofmann@anvil-soft.com   
      
   "Seungbeom Kim"  schrieb im Newsbeitrag   
   news:iudq83$9hm$1@usenet.stanford.edu...   
      
   > It seems that you have something like this in mind:   
   >   
   >    struct X { ... };   
   >    struct Y { ... };   
   >    struct Z : X, Y { ... };   
   >   
   >    Y* py = new Z;   
   >    void* pv = dynamic_cast(py);   
   >    assert(pv != py);   
   >    assert(pv == dynamic_cast(py));   
      
   You are relying on a certain memory layout of the X and Y subobjects within   
   Z. For your example, a compiler is likely to structure a Z object like this:   
      
   [Storage for X's data]   
   [Storage for Y's data]   
   [Storage for Z's data]   
      
   Let's see what this means for the casts in your example. The first line of   
   code makes a pointer-to-Y point to a new Z object:   
      
   [Storage for X's data]   
   [Storage for Y's data] <- py   
   [Storage for Z's data]   
      
   The second line performs a dynamic_cast from pointer-to-Y to   
   pointer-to-void, which yields the address of the complete object:   
      
   [Storage for X's data] <- pv   
   [Storage for Y's data] <- py   
   [Storage for Z's data]   
      
   For this reason, pv and py do not compare equal indeed in the third line.   
   The dynamic_cast from pointer-to-Y to pointer-to-X in the fourth line yields   
   the address of the X subobject within Z, which does indeed compare equal to   
   pv.   
      
   However, as far as I know, there is no requirement for a compiler to use the   
   layout shown above. If the positions of the areas of storage for the X and Y   
   subobjects are switched, both asserts will fail.   
      
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   Anvil-Soft, CEO   
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