std::integral_constant - cppreference.com

Da cppreference.com.

Questa pagina è stata tradotta in modo automatico dalla versione in ineglese della wiki usando Google Translate.

La traduzione potrebbe contenere errori e termini strani. Muovi il puntatore sopra al testo per vedere la versione originale. Puoi aiutarci a correggere gli gli errori. Per ulteriori istruzioni clicca qui.

Click here for the English version of this page

Elemento definito nell'header `<type_traits>`

`template< class T, T v > struct integral_constant;`		(dal C++11)

std::integral_constant avvolge una costante statica del tipo specificato. E 'la classe base per il C + + caratteri morfologici.

Original:

std::integral_constant wraps a static constant of specified type. It is the base class for the C++ type traits.

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Due specializzazioni per la bool tipo sono previsti:

Original:

Two specializations for the type bool are provided:

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Definizione nell'header `<type_traits>`

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

`true_type`	`std::integral_constant<bool, true>`

`false_type`	`std::integral_constant<bool, false>`

Membri tipi


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`	`T`

`type`	`std::integral_constant<T,v>`

Membri costanti


Nome Original: Name The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Value

`value`	statica espressione costante di `T` tipo con `v` valore Original: static constant expression of type `T` with value `v` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

Membri funzioni


	converte l'oggetto in `value_type`, restituisce `value` Original: converts the object to `value_type`, returns `value` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (metodo pubblico)

Possibile implementazione

template<class T, T v>
struct integral_constant {
    static constexpr T value = v;
    typedef T value_type;
    typedef integral_constant type;
    constexpr operator value_type() const { return value; }
};

Esempio

#include <iostream>
#include <type_traits>

int main() 
{
    typedef std::integral_constant<int, 2> two_t;
    typedef std::integral_constant<int, 4> four_t;

//  static_assert(std::is_same<two_t, four_t>::value,
//                "two_t and four_t are not equal!"); 
//  error: static assertion failed: "two_t and four_t are not a same types"

    static_assert(two_t::value*2 == four_t::value,
       "2*2 != 4"
    );

    enum class my_e {
       e1,
       e2
    };
    typedef std::integral_constant<my_e, my_e::e1> my_e_e1;
    typedef std::integral_constant<my_e, my_e::e2> my_e_e2;

//  static_assert(my_e_e1::value == my_e::e2,
//               "my_e_e1::value != my_e::e2");
//  error: static assertion failed: "my_e_e1::value != my_e::e2"

    static_assert(std::is_same<my_e_e2, my_e_e2>::value,
                  "my_e_e2 != my_e_e2");
}