Derived Classes

A function in a derived class can look like it was written to replace a virtual function in a base class. But a similar-looking name is not proof that the functions are connected. To decide whether overriding occurs, compare the declared name and type exactly.

A derived function overrides a base class virtual function only when its name and type match exactly. Do not decide from how similar the declarations look at a glance. A near match may have been intended as an override, or it may be a separate function; appearance alone does not tell you which.

The first comparison passes because both the name and type match. The second fails because the type differs, even though the name is the same. The type check covers the declared function type: a difference in a parameter type is enough to make the function a near match rather than an override.

The override keyword lets a programmer state explicitly that a derived class function is meant to override a base class virtual function. The explicit form is described as equivalent to writing the function without the keyword; its value is making the programmer’s intent visible, not changing what the function does.

This clarity is especially useful when a class hierarchy is large and contains many functions with similar names. A reader may not know whether a near match was intended to replace an inherited virtual function or to add a separate function. Stating the intent helps remove that uncertainty. The keyword does not make a mismatched name or type satisfy the exact-match test.