Doubt about Polymorphism and fixes in C ++

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Doubt about Polymorphism and fixes in C ++

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#1 by (1 votes)

1

I have a question about the use of arrays with polymorphism, the subject is like this: I have a class Article that inherit two classes Book and CD.

class Articulo {

   protected:

     string nom;
   public:

     Articulo();
     virtual void mostrar() = 0;
}

class Libro : public Articulo{

   private:

     string autor;

   public:

     Libro();
     void mostrar();
     void verAutor();

}

class Cd : public Articulo{

   private:

     string compositor;

   public:

      Libro();
      void mostrar();
      void verCompositor();
}

Then I have a Business class that manages a vector of articles loaded with instances of book and CD.

class Negocio {

   private

     std::vector<Articulo*> vArticulos;

   public:

     Negocio();

     std::vector<Libro*> buscarPorAutor();
     std::vector<Cd*> buscarPorComp();

}

Within Business I have two methods of searching for articles by author (which returns books) and another by composer (returns cds) . As much in book as in cd I have methods to see the author and the composer, How I can know Of what instance is each element of the vector of articles?

c++ poo polimorfismo arreglos

asked by pepexito 31.10.2017 в 22:56

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1 answer

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score 1 · Accepted Answer

You need to use dynamic_cast . I give you an example to extract the books:

std::vector<Libro*> seleccionarLibros()
{
  std::vector<Libro*> libros;
  for( size_t i=0; i<vArticulos.size(); i++ )
  {
    if( Libro* libro = dynamic_cast<Libro*>(vArticulos[i]) )
    {
      // Una vez obtenido el puntero puedes utilizarlo con normalidad
      libro->verAutor(); 
      libros.push_back(libro);
  }
  return libros;
}

dynamic_cast works as follows:

Can only be used with classes that have some type of inheritance. Otherwise, it fails at compile time.
Compile with RTTI enabled (usually a default option). Otherwise, it fails at compile time.
Can not be used to convert from an inherited type to another base (compile error). This conversion is automatic and does not require additional operations.
If the base pointer can be converted to the inherited type, it converts it, otherwise it returns a null pointer.