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std::remove_cv, std::remove_const, std::remove_volatile

Defined in header <type_traits> 
template< class T >
struct remove_cv;
 (1) (since C++11) 
template< class T >
struct remove_const;
 (2) (since C++11) 
template< class T >
struct remove_volatile;
 (3) (since C++11)

Provides the member typedef type which is the same as T, except that its topmost cv-qualifiers are removed.

1) removes the topmost const, or the topmost volatile, or both, if present.
2) removes the topmost const
3) removes the topmost volatile

The behavior of a program that adds specializations for any of the templates described on this page is undefined.

Member types

Name Definition
type the type T without cv-qualifier

Helper types

template< class T >
using remove_cv_t       = typename remove_cv<T>::type;
 (since C++14) 
template< class T >
using remove_const_t    = typename remove_const<T>::type;
 (since C++14) 
template< class T >
using remove_volatile_t = typename remove_volatile<T>::type;
 (since C++14)

Possible implementation

template< class T > struct remove_cv                   { typedef T type; };
template< class T > struct remove_cv<const T>          { typedef T type; };
template< class T > struct remove_cv<volatile T>       { typedef T type; };
template< class T > struct remove_cv<const volatile T> { typedef T type; };
 
template< class T > struct remove_const                { typedef T type; };
template< class T > struct remove_const<const T>       { typedef T type; };
 
template< class T > struct remove_volatile             { typedef T type; };
template< class T > struct remove_volatile<volatile T> { typedef T type; };

Example

Removing const/volatile from const volatile int * does not modify the type, because the pointer itself is neither const nor volatile.

#include <iostream>
#include <type_traits>
 
template<typename U, typename V> constexpr bool same = std::is_same_v<U, V>;
 
static_assert(
        same< std::remove_cv_t< int >, int >
    and same< std::remove_cv_t< const int >, int >
    and same< std::remove_cv_t< volatile int >, int >
    and same< std::remove_cv_t< const volatile int >, int >
    and same< std::remove_cv_t< const volatile int* >, const volatile int* >
    and same< std::remove_cv_t< const int* volatile >, const int* >
    and same< std::remove_cv_t< int* const volatile >, int* >
);
 
int main() {
    std::cout << std::boolalpha;
 
    using type1 = std::remove_cv<const int>::type;
    using type2 = std::remove_cv<volatile int>::type;
    using type3 = std::remove_cv<const volatile int>::type;
    using type4 = std::remove_cv<const volatile int*>::type;
    using type5 = std::remove_cv<int* const volatile>::type;
 
    std::cout << std::is_same<type1, int>::value << "\n";
    std::cout << std::is_same<type2, int>::value << "\n";
    std::cout << std::is_same<type3, int>::value << "\n";
    std::cout << std::is_same<type4, int*>::value << " "
              << std::is_same<type4, const volatile int*>::value << "\n";
    std::cout << std::is_same<type5, int*>::value << "\n";
}

Output:

true
true
true
false true
true

See also

(C++11)
 checks if a type is const-qualified
(class template)
(C++11)
 checks if a type is volatile-qualified
(class template)
(C++11)(C++11)(C++11)
 adds const or/and volatile specifiers to the given type
(class template)
(C++20)
 combines std::remove_cv and std::remove_reference
(class template)

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https://en.cppreference.com/w/cpp/types/remove_cv