std::is_placeholder

 

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Enlazar Original: Bind The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
bind (C++11)
is_bind_expression (C++11)
is_placeholder (C++11)
_1, _2, _3, ... (C++11)
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plus minus negate multiplies divides modulus logical_and logical_or logical_not	equal_to not_equal_to greater less greater_equal less_equal bit_and bit_or bit_xor
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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>
template< class T > struct is_placeholder;		(ya que C + +11)

Si T es el tipo de un marcador de posición estándar (_1, _2, _3, ...), a continuación, esta plantilla se deriva de std::integral_constant<int,1>, std::integral_constant<int,2>, std::integral_constant<int,3>, respectivamente. Si T no es un tipo de marcador de posición estándar, esta plantilla se deriva de std::integral_constant<int,0> .

Original:

If T is the type of a standard placeholder (_1, _2, _3, ...), then this template is derived from std::integral_constant<int,1>, std::integral_constant<int,2>, std::integral_constant<int,3>, respectively. If T is not a standard placeholder type, this template is derived from std::integral_constant<int,0>.

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La plantilla puede ser especializado para cualquier tipo definido por el usuario que debe ser tratado por std::bind como si fuera un marcador de posición para los argumentos no unidos .

Original:

The template may be specialized for any user-defined type which should be treated by std::bind as if it was a placeholder for unbound arguments.

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Inherited from std::integral_constant

Member constants

value [estático]	placeholder value or 0 for non-placeholder types (público miembro constante estática)

Member functions

operator int	convierte el objeto a int, devuelve value Original: converts the object to int, returns value The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (miembro público función)

Member types

Tipo Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition
value_type	int
type	std::integral_constant<int, value>

Ejemplo

#include <iostream>
#include <type_traits>
#include <functional>
 
struct My_2 {
} my_2;
 
namespace std {
    template<>
    struct is_placeholder<My_2> : public integral_constant<int, 2> {};
}
 
int f(int n1, int n2)
{
    return n1+n2;
}
 
int main()
{
    std::cout << "Standard placeholder _5 is for the argument number "
              << std::is_placeholder<decltype(std::placeholders::_5)>::value
              << '\n';
 
    auto b = std::bind(f, my_2, 2);
    std::cout << "Adding 2 to 11 selected with a custom placeholder gives " 
              << b(10, 11) 
              << '\n';
}

Output:

Standard placeholder _5 is for the argument number 5
Adding 2 to 11 selected with a custom placeholder gives 13

Ver también

bind (C++11)	se une uno o más argumentos a un objeto de función Original: binds one or more arguments to a function object The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (función de plantilla)
_1, _2, _3, _4, ... (C++11)	marcadores de posición para los argumentos no unidos en una expresión std::bind Original: placeholders for the unbound arguments in a std::bind expression The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (constante)