devxlogo

Performance of typeid vs. dynamic_cast<>

Performance of typeid vs. dynamic_cast<>

As far as design is concerned, dynamic_cast should be preferred to typeid because the former enables more flexibility and extensibility. Notwithstanding that, the runtime overhead of typeid can be less expensive than dynamic_cast, depending on the operands. An invocation of operator typeid is a constant time operation–it takes the same length of time to retrieve the runtime type information of every polymorphic object, regardless of the object’s derivational complexity.On the other hand, dynamic_cast is not a constant time operation. It has to traverse the derivation tree of the operand until it has located the target object in it. The worst case scenario is when the operand is a deeply derived object and the target is a non-related class type. Then, dynamic_cast has to traverse the entire derivation tree before it can confidently decide that requested cast cannot be done.

devx-admin

Share the Post: