The override Keyword

While always a logic error for a derived class to redefine a non-virtual function, it is not a syntax error. C++ 11 added new contextual keywords that allow the compiler to catch such logic errors that previously were often hidden, and turn them into syntax errors that can be caught at compile time.

To tell the compiler that you intend to override a base class function, add the contextual keyword override to the end of the member function declaration like this:

std::string toString() const override;

Now, if you were to forget the virtual in the base class, trying to (incorrectly) override a non-virtual inherited member function, or misspell the name of the member function, or provide the wrong arguments, the compiler catches those errors and warns you when you compile, like this:

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