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C++ In a Nutshell
book

C++ In a Nutshell

by Ray Lischner
May 2003
Intermediate to advanced content levelIntermediate to advanced
808 pages
32h 24m
English
O'Reilly Media, Inc.
Content preview from C++ In a Nutshell

Name

virtual specifier — Polymorphic function specifier or shared base class

Synopsis

               function-specifier := virtual
base-modifiers ::= virtual [access-specifier] | access-specifier [virtual]

The virtual keyword has two unrelated uses; it is used in virtual functions and virtual base classes:

  • As a function specifier, virtual can be used only with a nonstatic member function. It makes the function and class polymorphic. A virtual function can be declared with = 0 after the function header, which means the function is abstract. You cannot create an instance of a class with an abstract function; instead, a derived class must override the function. You can create an instance of the derived class.

  • Using virtual as a base-class modifier means the base class subobject is shared when it is used more than once in an inheritance graph.

Example

struct shape {virtual void draw(canvas&) = 0;
  virtual void debug(  );
};
struct square : virtual shape {
  virtual void draw(canvas&);
  virtual void debug(  );
};

See Also

class, declaration, Chapter 6

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Publisher Resources

ISBN: 059600298XSupplemental ContentErrata Page