Question

I was thinking along the lines of using typeid() but I don’t know how to ask if that type is a subclass of another class (which, by the way, is abstract)

Answer 1

You really shouldn’t. If your program needs to know what class an object is, that usually indicates a design flaw. See if you can get the behavior you want using virtual functions. Also, more information about what you are trying to do would help.

I am assuming you have a situation like this:

class Base; class A : public Base {...}; class B : public Base {...};  void foo(Base *p) {   if(/* p is A */) /* do X */   else /* do Y */ } 

If this is what you have, then try to do something like this:

class Base {   virtual void bar() = 0; };  class A : public Base {   void bar() {/* do X */} };  class B : public Base {   void bar() {/* do Y */} };  void foo(Base *p) {   p->bar(); } 

Edit: Since the debate about this answer still goes on after so many years, I thought I should throw in some references. If you have a pointer or reference to a base class, and your code needs to know the derived class of the object, then it violates Liskov substitution principle. Uncle Bob calls this an ‘anathema to Object Oriented Design‘.