virtual function specifier

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[editar] Sintaxe

[editar] Explicação

Aqui nos referimos à função primordial como Derived::f() e para a função de substituído como Base::f()

Original:

Here we refer to the overriding function as Derived::f() and to the overridden function as Base::f()

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• ambos os tipos são ponteiros ou referências a classes. Multi-nível ponteiros ou referências não são permitidos.

  Original:

  both types are pointers or references to classes. Multi-level pointers or references are not allowed.

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• a classe do tipo de retorno de Base::f() deve ser uma classe base inequívoca e acessível direta ou indireta da classe do tipo de retorno de Derived::f().

  Original:

  the class of the return type of Base::f() must be a unambiguous and accessible direct or indirect base class of the class of the return type of Derived::f().

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• o tipo de retorno deve ser Derived::f() cv-qualificados igual ou menor do que o tipo de retorno de Base::f().

  Original:

  the return type of Derived::f() must be equally or less cv-qualificados than the return type of Base::f().

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[editar] Exemplo

class Parent {
public:
    void functionA();
    virtual void functionB();   //Note the keyword virtual
    void functionC();
};
 
class Child : public Parent {
public:
    void functionA();
    virtual void functionB();   //Note the keyword virtual
};
 
int main()
{
    Parent* p1 = new Parent;
    Parent* p2 = new Child;
    Child* c = new Child;
 
    p1->functionA();   //Calls Parent::functionA
    p1->functionB();   //Calls Parent::functionB
    p1->functionC();   //Calls Parent::functionC
 
    p2->functionA();   //Calls Parent::functionA because p2 points to a Parent
    p2->functionB();   //Calls Child::functionB even though p2 points 
                       // to a Parent because functionB is virtual
    p2->functionC();   //Calls Parent::functionC
 
    c->functionA();   //Calls Child::functionA
    c->functionB();   //Calls Child::functionB
    c->functionC();   //Calls Parent::functionC
 
    return 0;
}

[editar] Veja também

• substituir especificador (desde C++11)
• final de especificador (desde C++11)