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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 <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> &&
    same<std::remove_cv_t<const int>, int> &&
    same<std::remove_cv_t<volatile int>, int> &&
    same<std::remove_cv_t<const volatile int>, int> &&
    // remove_cv only works on types, not on pointers
    not same<std::remove_cv_t<const volatile int*>, int*> &&
    same<std::remove_cv_t<const volatile int*>, const volatile int*> &&
    same<std::remove_cv_t<const int* volatile>, const int*> &&
    same<std::remove_cv_t<int* const volatile>, int*>
);
 
int main() {}

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 and/or 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