Déclaration d'une union — cppreference.com

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Une union est un type de classe spéciale qui stocke l'ensemble de ses membres de données dans le même emplacement mémoire.

Original:

A union is a special class type that stores all of its data members in the same memory location.

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Les unions ne peuvent pas avoir de fonctions virtuelles, ne peuvent être héritées ou hériter d'autres classes.

Original:

Unions cannot have virtual functions, be inherited or inherit other classes.

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Les unions (avant C++11) ne peuvent contenir que les types BVD (bonnes vieilles données) .

Original:

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(depuis C++11) Si une union contient un élément non-BVD, qui a une fonction particulière définie par l'utilisateur (constructeur, destructeur, constructeur par copie ou affectation par copie) cette fonction est supprimée par défaut dans l' union et doit être explicitement définie par l'utilisateur .

Original:

(depuis C++11) If a union contains a non-POD member, which has a user-defined special function (constructor, destructor, copy constructor or copy assignment) that function is deleted by default in the union and needs to be defined explicitly by the user.

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Syntaxe


`union` name `{` member_declarations `}` object_list (en option) `;`	(1)

`union` `{` member_declarations `}` `;`	(2)

Explication

# Union nomée

Original:

#Named union

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# Union anonyme

Original:

#Anonymous union

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Unions anonymes

Les membres d'une union anonyme sont accessibles à partir de la portée englobante comme des simples variables.

Original:

Members of an anonymous union are accessible from the enclosing scope as single variables.

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Les unions anonymes ont d'autres restrictions: elles doivent seulement comporter des membres publiques et ne peuvent pas avoir des fonctions membres.

Original:

Anonymous unions have further restrictions: they must have only public members and cannot have member functions.

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Les unions dans la portée d'un espace de noms doivent être statiques.

Original:

Namespace-scope anonymous unions must be static.

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Exemple

union foo
{
  int x;
  signed char y;
};

int main()
{
  foo.x = 128 + 896;
  std::cout << "comme int: "  << (int)foo.x << '\n';
  std::cout << "comme char: " << (int)foo.y << '\n';
  return 0;
}

Résultat :

comme int: 1024
comme char: 128

(Pour processeurs petit-boutistes)

Original:

(for little-endian processors)

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