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

 

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integer_sequence (C++14)

 

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.

Run this code

#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

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