Why abstract class in c

The compiler generates code to implicitly call the destructor for class base after the derived destructor. Without it, the linker generates an unresolved external symbol error for the implicit call. It's also possible to call pure virtual functions explicitly by using a fully qualified member-function name. Such functions must have an implementation, or the call results in an error at link time. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services.

Privacy policy. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Is this page helpful? No objects of an abstract class can be created except for base subobjects of a class derived from it and no non-static data members of an abstract class can be declared.

Abstract types cannot be used as parameter types, as function return types, or as the type of an explicit conversion note this is checked at the point of definition and function call, since at the point of function declaration parameter and return type may be incomplete. The definition of a pure virtual function may be provided and must be provided if the pure virtual is the destructor : the member functions of the derived class are free to call the abstract base's pure virtual function using qualified function id.

Making a virtual call to a pure virtual function from a constructor or the destructor of the abstract class is undefined behavior regardless of whether it has a definition or not. Create account Log in. Namespaces Page Discussion. Views View Edit History. From cppreference. Keywords Escape sequences. Namespace declaration. Namespace aliases. Fundamental types Enumeration types Function types. Compound types Union types. Default initialization Value initialization Zero initialization Copy initialization Direct initialization.

Expressions Value categories Order of evaluation. Operators Operator precedence. Class declaration Constructors this pointer. Access specifiers friend specifier. Class template Function template. Inline assembly. Compiler support. Freestanding and hosted. In this example, the class Square must provide an implementation of GetArea because it derives from Shape :.

It is not possible to modify an abstract class with the sealed modifier because the two modifiers have opposite meanings. The sealed modifier prevents a class from being inherited and the abstract modifier requires a class to be inherited. A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.

Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation.

For example:. The implementation is provided by a method override , which is a member of a non-abstract class. It is an error to use the static or virtual modifiers in an abstract method declaration. Abstract properties behave like abstract methods, except for the differences in declaration and invocation syntax. An abstract inherited property can be overridden in a derived class by including a property declaration that uses the override modifier.

An abstract class that implements an interface might map the interface methods onto abstract methods.