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 (Click here for a personal note from Marshall Cline.) |
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Section 19:
| 19.1 | Is inheritance important to C++? |
| 19.2 | When would I use inheritance? |
| 19.3 | How do you express inheritance in C++? |
| 19.4 | Is it OK to convert a pointer from a derived class to its base class? |
| 19.5 | What's the difference between public, private, and protected? |
| 19.6 | Why can't my derived class access private things from my base class? |
| 19.7 | How can I protect derived classes from breaking when I change the internal parts of the base class? |
| 19.8 | Protected data vs. private data with protected access functions? |
| 19.9 | Okay, so exactly how should I decide whether to build a "protected interface"? |
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[19.4] Is it OK to convert a pointer from a derived class to its base class?
Yes.
An object of a derived class is a kind of the base class. Therefore the conversion from a derived class pointer to a base class pointer is perfectly safe, and happens all the time. For example, if I am pointing at a car, I am in fact pointing at a vehicle, so converting a Car* to a Vehicle* is perfectly safe and normal:
void f(Vehicle* v);
void g(Car* c) { f(c); } // Perfectly safe; no cast
(Note: this FAQ has to do with public inheritance;
private and protected
inheritance are different.)