🔒 Locked

dynamic_cast

Started by peter86 Jan 6, 2003 at 4:03 AM 3 replies 200+ views

Original Post

peter86

Jan 6, 2003 at 4:03 AM

How does dynamic_cast differentiate from static_cast and reinterpret_cast?

Fruny

203

Fruny

Jan 6, 2003 at 4:22 AM

reinterpret_cast is used to ... reinterpret the bit pattern as another type, without modification. While using static_cast to convert a float to an int would truncate, reinterpret_cast would just transfer the bits an read them as if it had been an int all along.

static_cast is a close relative of the C cast, with the exception that C casts can be reinterpret_casts in some cases. It is used when the actual types are known at compile-time.

dynamic_cast is used to safely downcast from a polymorphic Base (must have a virtual function) to a Derived type when you''re not sure the object really is of the Derived type. See below.


Base *pBase = new Base;       // pointer to Base, Base object
Base *pDerived = new Derived; // pointer to Base, Derived object

Derived* pD0 = static_cast(pBase); 
// BOOM ! pBase doesn''t point to a Derived object

Derived* pD1 = static_cast(pDerived):
// Ok. pDerived really pointed to a Derived object

Derived* pD0 = dynamic_cast(pBase); 
// pD0 will be set to NULL, you can test for it.

Derived* pD1 = dynamic_cast(pDerived):
// Ok. pDerived really pointed to a Derived object