Espacios de nombres
Variantes
Acciones

std::placeholders::_1, std::placeholders::_2, ..., std::placeholders::_N

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Utilidades de la biblioteca
Escriba apoyo (basic types, RTTI, type traits)
Gestión de memoria dinámica
Gestión de errores
Programa de servicios públicos
Funciones variadic
Fecha y hora
Objetos Function
initializer_list(C++11)
bitset
hash(C++11)
Operadores relacionales
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Pares y tuplas
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Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Cambiar, hacia adelante y mover
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Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
Objetos Function
Envoltorios de función
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Function wrappers
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function(C++11)
mem_fn(C++11)
bad_function_call(C++11)
Enlazar
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Bind
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bind(C++11)
is_bind_expression(C++11)
is_placeholder(C++11)
_1, _2, _3, ...(C++11)
Envolturas de referencia
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Reference wrappers
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reference_wrapper(C++11)
ref
cref
(C++11)
(C++11)
Envoltorios Operador
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Operator wrappers
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Negadores
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Negators
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Desaprobado aglutinantes y adaptadores
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Deprecated binders and adaptors
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unary_function(obsoleto)
binary_function(obsoleto)
ptr_fun(obsoleto)
pointer_to_unary_function(obsoleto)
pointer_to_binary_function(obsoleto)
mem_fun(obsoleto)
mem_fun_t
mem_fun1_t
const_mem_fun_t
const_mem_fun1_t
(obsoleto)
(obsoleto)
(obsoleto)
(obsoleto)
mem_fun_ref(obsoleto)
mem_fun_ref_t
mem_fun1_ref_t
const_mem_fun_ref_t
const_mem_fun1_ref_t
(obsoleto)
(obsoleto)
(obsoleto)
(obsoleto)
binder1st
binder2nd
(obsoleto)
(obsoleto)
bind1st
bind2nd
(obsoleto)
(obsoleto)
 
Defined in header <functional>
extern /*unspecified*/ _1;

extern /*unspecified*/ _2;
.
.

extern /*unspecified*/ _N;
El espacio de nombres std::placeholders contiene los objetos de marcador de posición [_1, . . . _N] donde N es una aplicación definida número máximo .
Original:
The std::placeholders namespace contains the placeholder objects [_1, . . . _N] where N is an implementation defined maximum number.
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Cuando se utiliza como un argumento en una expresión std::bind, los objetos de marcador de posición se almacenan en el objeto de la función generada, y cuando ese objeto se invoca la función con argumentos no consolidados, cada _N marcador de posición se sustituye por el argumento no unida enésima correspondiente .
Original:
When used as an argument in a std::bind expression, the placeholder objects are stored in the generated function object, and when that function object is invoked with unbound arguments, each placeholder _N is replaced by the corresponding Nth unbound argument.
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Los tipos de los objetos de marcador de posición son DefaultConstructible y CopyConstructible, su copia por omisión / move constructores no producen excepciones, y para cualquier _N marcador de posición, la std::is_placeholder<decltype(_N)> tipo se define y se deriva de std::integral_constant<int, N> .
Original:
The types of the placeholder objects are DefaultConstructible and CopyConstructible, their default copy/move constructors do not throw exceptions, and for any placeholder _N, the type std::is_placeholder<decltype(_N)> is defined and is derived from std::integral_constant<int, N>.
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[editar] Ejemplo

El siguiente código muestra la creación de objetos de función con un argumento marcador de posición .
Original:
The following code shows the creation of function objects with a placeholder argument.
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#include <functional>
#include <string>
#include <iostream>
 
void goodbye(const std::string& s)
{
    std::cout << "Goodbye " << s << '\n';
}
 
class Object {
public:
    void hello(const std::string& s)
    {
        std::cout << "Hello " << s << '\n';
    }
};
 
int main(int argc, char* argv[])
{
    typedef std::function<void(const std::string&)> ExampleFunction;
    Object instance;
    std::string str("World");
    ExampleFunction f = std::bind(&Object::hello, &instance, 
                                  std::placeholders::_1);
 
    // equivalent to instance.hello(str)
    f(str);
    f = std::bind(&goodbye, std::placeholders::_1);
 
    // equivalent to goodbye(str)
    f(str);    
    return 0;
}

Output:

Hello World
Goodbye World

[editar] Ver también

(C++11)
se une uno o más argumentos a un objeto de función
Original:
binds one or more arguments to a function object
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(función de plantilla) [edit]
indica que un objeto es un marcador de posición estándar o se puede usar como una
Original:
indicates that an object is a standard placeholder or can be used as one
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(clase de plantilla) [edit]