Archive for October, 2010

I often get confused about the different types of C++ casts:

• dynamic_cast can be used for “upcasting” or “downcasting”

  • Upcasting:    A* pA = dynamic_cast<A*>(pB)  when B inherits from A
    

  • Downcasting:  B* pB = dynamic_cast<B*>(pA)  when B inherits from A
    

• static_cast
  • static_cast conversions are not as safe as dynamic_cast conversions, because static_cast does no run-time type check, while dynamic_cast does.
  • A dynamic_cast to an ambiguous pointer will fail, while a static_cast returns as if nothing were wrong; this can be dangerous.
  • Although dynamic_cast conversions are safer, dynamic_cast only works on pointers or references, and the run-time type check is an overhead. (http://msdn.microsoft.com/en-us/library/5f6c9f8h%28v=VS.100%29.aspx)
• reinterpret_cast
  • Allows any pointer to be converted into any other pointer type. Also allows any integral type to be converted into any pointer type and vice versa. (http://msdn.microsoft.com/en-us/library/e0w9f63b.aspx)