Primer de C++, quinta edición: De structs a Tipos de Datos Abstractos

El viaje desde un struct hacia un Tipo de Datos Abstracto (TDA) marca la transición desde una "caja de vidrio", donde todos los cables internos son visibles, hacia una "caja negra" donde la interfaz está separada de la implementación. Este cambio garantiza encapsulamiento: los usuarios interactúan con funciones como leer o combinar sin necesidad de saber cómo se calcula o almacena el ingreso.

1. Arquitectura de Clases

Cada clase define una identidad única de tipo. Incluso si dos clases comparten miembros idénticos, C++ las trata como incompatibles. Usar typedef y declaraciones anticipadas (por ejemplo, class Pantalla;) nos permite diseñar relaciones complejas manteniendo la abstracción. A menudo usamos versiones sintetizadas de constructores, como Sales_data() = default;, para mantener la conveniencia de los tipos integrados ($$total = trans;$$).

2. Funciones de interfaz no miembro

Funciones como leer son Funciones relacionadas con la clase pero no miembro. Son parte de la interfaz pero no forman parte de la clase en sí, a menudo requiriendo amistad para acceder a datos privados.

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QUESTION 1

What is the result of the following code?
struct First { int i; }; struct Second { int i; }; First f; Second s = f;

Success: The members are identical.

Error: obj1 and obj2 have different types.

Success: C++ allows structural typing.

Warning: members should be private.

QUESTION 2

Which keyword is used to request the compiler to generate a synthesized default constructor?

= auto

= synthesized

= default

= virtual

✅ Correct!

= default can appear with the declaration inside the class or the definition outside.

❌ Incorrect

The specific syntax introduced in C++11 is = default.

QUESTION 3

Why is the read function typically not a member of the Sales_data class?

It requires access to private members.

Member functions cannot return stream references.

IO operations are often conceptually separate from the object's core state logic.

Nonmember functions are faster.

✅ Correct!

Nonmember functions like read and print are part of the interface but kept separate to maintain logical cohesion.

QUESTION 4

What is the default access level for a class vs a struct in C++?

Both are private by default.

class: private; struct: public.

class: public; struct: private.

Both are public by default.

✅ Correct!

The only technical difference between class and struct is the default access level for members and inheritance.

❌ Incorrect

Think of struct as 'data-first' (public) and class as 'logic-first' (private).

QUESTION 5

What does a 'forward declaration' like class Screen; allow you to do?

Define the full body of the class later.

Allocate an object of type Screen immediately.

Access the private members of Screen.

Inline all Screen member functions.