std::is_const
std::is_const
Defined in header <type_traits> | ||
|---|---|---|
template< class T > struct is_const; | (since C++11) |
If T is a const-qualified type (that is, const, or const volatile), provides the member constant value equal true. For any other type, value is false.
Template parameters
| T | - | a type to check |
Helper variable template
template< class T > inline constexpr bool is_const_v = is_const<T>::value; | (since C++17) |
Inherited from std::integral_constant
Member constants
| value
[static] | true if T is a const-qualified type , false otherwise (public static member constant) |
Member functions
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
Member types
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
Possible implementation
template<class T> struct is_const : std::false_type {};
template<class T> struct is_const<const T> : std::true_type {}; |
Example
#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
}Output:
false true false true false
See also
|
(C++11) | checks if a type is volatile-qualified (class template) |
|
(C++17) | obtains a reference to const to its argument (function template) |
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