NAME

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

Synopsis

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

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

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 <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