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std::is_const

STD：：是[医]康斯特

Defined in header ​​
template< class T > struct is_const;​(since C++11)

如果T是Const-合格类型%28，即，const，或const volatile%29，提供成员常量。value平等true.对于任何其他类型，value是false...

模板参数

T-a type to check

辅助变量模板

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

继承自STD：积分[医]常量

成员常数

value statictrue if T is a const-qualified type , 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]Const：STD：：false[医]类型{}；模板<class T>结构是[医]康斯特<const T>*STD：：真[医]{}型；

*。

例

二次

#include <iostream>
#include <type_traits>
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_const<int>::value << '\n'; // false
    std::cout << std::is_const<const int>::value  << '\n'; // true
    std::cout << std::is_const<const int*>::value  << '\n'; // false
    std::cout << std::is_const<int* const>::value  << '\n'; // true
    std::cout << std::is_const<const int&>::value  << '\n'; // false
}

二次

产出：

二次

false
true
false
true
false

二次

另见

is_volatile (C++11)checks if a type is volatile-qualified (class template)
as_const (C++17)obtains a reference to const to its argument (function template)

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在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/type/is[医]康斯特

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