abstract (Visual C+)
abstract is a context sensitive keyword that can indicate:
A member can only be defined in a derived type.
A type cannot be instantiated (can only act as a base type).
Remarks
Marking a function abstract is the same as making it a pure virtual function. Making a member function abstract causes the enclosing class to also be marked abstract.
abstract is also valid when compiling for native targets (without /clr).
See Override Specifiers and Native Compilations for more information.
You can detect at compile time if a type is abstract with __is_abstract(type). For more information, see Compiler Support for Type Traits.
abstract is a context-sensitive keyword; see Context-Sensitive Keywords for more information.
Example
The following sample will generate an error because class X is marked abstract.
// abstract_keyword.cpp
// compile with: /clr
ref class X abstract {
public:
virtual void f() {}
};
int main() {
X ^ MyX = gcnew X; // C3622
}
The following code example generates an error because it instantiates a native class that is marked abstract. This error will occur with or without the /clr compiler option.
// abstract_keyword_2.cpp
class X abstract {
public:
virtual void f() {}
};
int main() {
X * MyX = new X; // C3622: 'X': a class declared as 'abstract'
// cannot be instantiated. See declaration of 'X'}
The following sample will generate an error because function f is marked abstract.
// abstract_keyword_3.cpp
// compile with: /clr
ref class X {
public:
virtual void f() abstract {} // C3634
virtual void g() = 0 {} // C3634
};
Requirements
Compiler option: /clr