Are there any subtleties in using both the virtual and override keywords in C++11?

Question

Is it dangerous to use both virtual and override on a function in C++? Does that open you up for ambiguity with overloading?

Obviously virtual must be used in the base class and it would be silly to not use override in the derived class, but is it actually problematic to use virtual with override in the derived class?

Trying to determine if this is an issue of style or correctness.

Example:

class Widget {   virtual void transmogrify() = 0; }  class Gadget : public Widget {   virtual void transmogrify() override {} } 

Answer 1

The virtual keyword has no effect when you are overriding. A derived function that is a signature match for a virtual function defined in a base class will override the base definition, and the override will be entered in the vtable, whether the virtual keyword is used in the derived class or not.

Because the override keyword will cause a compile error if overriding is not happening, the virtual keyword is useless in combination.

Here, have a cheatsheet:

| Keyword used | Matching virtual function in base class | Result                   | |--------------|-----------------------------------------|--------------------------| | Neither      | No                                      | New non-virtual function | | Neither      | Yes                                     | Override                 | | virtual      | No                                      | New virtual function     | | virtual      | Yes                                     | Override                 | | override     | No                                      | Compile error            | | override     | Yes                                     | Override                 | | Both         | No                                      | Compile error            | | Both         | Yes                                     | Override                 |