C++ dynamic_cast vs typeid for class comparison [duplicate]

Answer 1

There is an important difference between the two methods:

if(A* test = dynamic_cast<A*>(&someClassCVar)) {
    // someClassCVar is A or publicly derived from A
}

Whereas:

if(typeid(someClassCVar) == typeid(A)) {
   // someClassCVar is of class A, not a derived class
}

Answer 2

it depends if post type identification processing needs a pointer on A or not.

cheking typeid will surely be faster (since they're compiler generated constant identifiers) but won't provide any A instance to manipulate so will oblige you to perform a dynamic_cast to get a A instance.