Espacios de nombres
Variantes
Acciones

auto specifier (desde C++11)

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< cpp‎ | language

 
 
Lenguaje C++
Los temas generales
Original:
General topics
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Control de flujo
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Flow control
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Sentencias condicionales ejecución
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Conditional execution statements
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Instrucciones de iteración
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Iteration statements
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Ir declaraciones
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Jump statements
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Funciones
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Functions
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declaración de la función
lambda declaración de la función
función de plantilla
especificador inline
especificaciones de excepción (obsoleto)
noexcept especificador (C++11)
Excepciones
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Exceptions
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Los espacios de nombres
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Namespaces
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Tipos
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Types
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decltype specifier (C++11)
Los especificadores
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Specifiers
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cv especificadores
almacenamiento duración especificadores
constexpr especificador (C++11)
auto especificador (C++11)
alignas especificador (C++11)
Inicialización
Original:
Initialization
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Los literales
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Literals
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Expresiones
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Expressions
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representaciones alternativas
Utilidades
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Utilities
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Tipos
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Types
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typedef declaration
alias de tipo de declaración (C++11)
atributos (C++11)
Lanza
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Casts
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conversiones implícitas
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-cast estilo y funcional
De asignación de memoria
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Memory allocation
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Clases
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Classes
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Clase propiedades específicas de la función
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Class-specific function properties
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Funciones especiales miembro
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Special member functions
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Plantillas
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Templates
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clase de plantilla
función de plantilla
plantilla de especialización
paquetes de parámetros (C++11)
Varios
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Miscellaneous
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Montaje en línea
 
Especifica que el tipo de la variable que se está declarando será automáticamente deducida de su inicializador. Para las funciones, especifica que el tipo de retorno es un tipo de retorno posterior .
Original:
Specifies that the type of the variable that is being declared will be automatically deduced from its initializer. For functions, specifies that the return type is a trailing return type.
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Contenido

[editar] Sintaxis

auto variable initializer (desde C++11)
auto function -> return type (desde C++11)

[editar] Explicación

1)
Cuando la declaración de variables en el ámbito de bloque, en el ámbito de espacio de nombres, en los estados de inicialización de bucles, etc, el tipo de la variable puede ser omitido y la palabra clave auto lugar, puede utilizarse .
Original:
When declaring variables in block scope, in namespace scope, in init statements of for loops, etc, the type of the variable may be omitted and the keyword auto may be used instead.
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Una vez que el tipo del inicializador ha sido determinada, el compilador determina el tipo que reemplazará la palabra clave auto como si estuviera utilizando las reglas de deducción plantilla argumento de una llamada de función. El auto palabra clave puede estar acompañado por modifica, tal como const o &, que participarán en la deducción tipo. Por ejemplo, dada const auto& i = expr;, el tipo de i es exactamente el tipo de la u argumento en un template<class U> void f(const U& u) plantilla imaginaria si el f(expr) llamada de función se compiló .
Original:
Once the type of the initializer has been determined, the compiler determines the type that will replace the keyword auto as if using the rules for template argument deduction from a function call. The keyword auto may be accompanied by modifies, such as const or &, which will participate in the type deduction. For example, given const auto& i = expr;, the type of i is exactly the type of the argument u in an imaginary template template<class U> void f(const U& u) if the function call f(expr) was compiled.
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2)
En un declaración de la función, el auto palabra clave no realizar la detección automática del tipo. Sólo sirve como una parte de la sintaxis tipo de retorno posterior .
Original:
In a declaración de la función, the keyword auto does not perform automatic type detection. It only serves as a part of the trailing return type syntax.
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[editar] Notas

Hasta C + +11, auto tenido la semántica de una almacenamiento duración especificador .
Original:
Until C++11, auto had the semantic of a almacenamiento duración especificador.
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[editar] Ejemplo

#include <iostream>
#include <cmath>
#include <typeinfo>
 
template<class T, class U>
auto add(T t, U u) -> decltype(t + u) // the return type of add is the type of operator+(T,U)
{
    return t + u;
}
 
auto get_fun(int arg)->double(*)(double) // same as double (*get_fun(int))(double)
{
    switch (arg) {
        case 1: return std::fabs;
        case 2: return std::sin;
        default: return std::cos;
    }
}
 
int main()
{
    auto a = 1 + 2;
    std::cout << "type of a: " << typeid(a).name() << '\n';
    auto b = add(1, 1.2);
    std::cout << "type of b: " << typeid(b).name() << '\n';
    //auto int c; //compile-time error
    auto d = {1, 2};
    std::cout << "type of d: " << typeid(d).name() << '\n';
 
    auto my_lambda = [](int x) { return x + 3; };
    std::cout << "my_lambda: " << my_lambda(5) << '\n';
 
    auto my_fun = get_fun(2);
    std::cout << "type of my_fun: " << typeid(my_fun).name() << '\n';
    std::cout << "my_fun: " << my_fun(3) << '\n';
}

Output:

type of a: int
type of b: double
type of d: std::initializer_list<int>
my_lambda: 8
type of my_fun: double (*)(double)
my_fun: 0.14112