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std::is_null_pointer

STD：：是[医]零[医]指针

Defined in header ​​
template< class T > struct is_null_pointer;​(since C++14)

检查是否T类型std::nullptr_t...

提供成员常量。value等于true，如果T类型std::nullptr_t，，，conststd::nullptr_t，，，volatilestd::nullptr_t，或constvolatilestd::nullptr_t...

否则，value等于false...

模板参数

T-a type to check

辅助变量模板

template< class T > inline constexpr bool is_null_pointer_v = is_null_pointer::value;​(since C++17)

继承自STD：积分[医]常量

成员常数

value statictrue if T is the type std::nullptr_t (possibly cv-qualified) , false otherwise (public static member constant)

成员函数

operator boolconverts the object to bool, returns value (public member function)
operator() (C++14)returns value (public member function)

成员类型

TypeDefinition
value_typebool
typestd::integral_constant<bool, value>

可能的实施

模板<class T>结构是[医]零[医]指针：std：：is[医]相同<std：：nullptr[医]t，type Name std：：Remove[医]CV<T>*类型>{}；

*。

注记

std::is_pointer是false为std::nullptr_t因为它不是内置的指针类型。

例

二次

#include <iostream>
#include <type_traits>
 
int main()
{
    std::cout << std::boolalpha
              << std::is_null_pointer< decltype(nullptr) >::value << ' '
              << std::is_null_pointer< int* >::value << '\n'
              << std::is_pointer< decltype(nullptr) >::value << ' '
              << std::is_pointer<int*>::value << '\n';
}

二次

产出：

二次

true false
false true

二次

另见

is_void (C++11)checks if a type is void (class template)
is_array (C++11)checks if a type is an array type (class template)
is_pointer (C++11)checks if a type is a pointer type (class template)
is_enum (C++11)checks if a type is an enumeration type (class template)
is_union (C++11)checks if a type is an union type (class template)
is_class (C++11)checks if a type is a non-union class type (class template)
is_function (C++11)checks if a type is a function type (class template)
is_object (C++11)checks if a type is object type (class template)

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