common_type (Clase)
Determina el tipo común de uno o más tipos.
Sintaxis
template <class... T>
struct common_type;
template <class T>
struct common_type<T> {
typedef typename decay<T>::type type;
};
template <class T, class U>
struct common_type<T, U> {
typedef typename decay<decltype(true declval<T>() :
declval<U>())>::type type;
};
template <class T, class U, class... V>
struct common_type<T, U, V...> {
typedef typename common_type<typename common_type<T, U>::type, V...>::type type;
};
Parámetros
Lista de tipos que son tipos completos o nulos.
Comentarios
El miembro type es el tipo común al que se pueden convertir todos los tipos de la lista de parámetros.
Ejemplo
El programa siguiente muestra algunos escenarios de uso correctos y realiza pruebas para obtener resultados.
// Compile using cl.exe /EHsc
// common_type sample
#include <iostream>
#include <type_traits>
struct Base {};
struct Derived : Base {};
int main()
{
typedef std::common_type<unsigned char, short, int>::type NumericType;
typedef std::common_type<float, double>::type FloatType;
typedef std::common_type<const int, volatile int>::type ModifiedIntType;
typedef std::common_type<Base, Derived>::type ClassType;
std::cout << std::boolalpha;
std::cout << "Test for typedefs of common_type int" << std::endl;
std::cout << "NumericType: " << std::is_same<int, NumericType>::value << std::endl;
std::cout << "FloatType: " << std::is_same<int, FloatType>::value << std::endl;
std::cout << "ModifiedIntType: " << std::is_same<int, ModifiedIntType>::value << std::endl;
std::cout << "ClassType: " << std::is_same<int, ClassType>::value << std::endl;
std::cout << "---------------------------" << std::endl;
std::cout << "Test for typedefs of common_type double" << std::endl;
std::cout << "NumericType: " << std::is_same<double, NumericType>::value << std::endl;
std::cout << "FloatType: " << std::is_same<double, FloatType>::value << std::endl;
std::cout << "ModifiedIntType: " << std::is_same<double, ModifiedIntType>::value << std::endl;
std::cout << "ClassType: " << std::is_same<double, ClassType>::value << std::endl;
std::cout << "---------------------------" << std::endl;
std::cout << "Test for typedefs of common_type Base" << std::endl;
std::cout << "NumericType: " << std::is_same<Base, NumericType>::value << std::endl;
std::cout << "FloatType: " << std::is_same<Base, FloatType>::value << std::endl;
std::cout << "ModifiedIntType: " << std::is_same<Base, ModifiedIntType>::value << std::endl;
std::cout << "ClassType: " << std::is_same<Base, ClassType>::value << std::endl;
return 0;
}
Output
Test for typedefs of common_type int
NumericType: true
FloatType: false
ModifiedIntType: true
ClassType: false
---------------------------
Test for typedefs of common_type double
NumericType: false
FloatType: true
ModifiedIntType: false
ClassType: false
---------------------------
Test for typedefs of common_type Base
NumericType: false
FloatType: false
ModifiedIntType: false
ClassType: true
Requisitos
Encabezado:<type_traits>
Espacio de nombres: std