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

 

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Supported operations
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is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)
is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11)
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)
has_virtual_destructor (C++11)
is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17)
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Type modifications
remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11)	remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11)
Type transformations
aligned_storage (C++11) aligned_union (C++11) decay (C++11) remove_cvref (C++20) enable_if (C++11) void_t (C++17)	conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) result_ofinvoke_result (C++11)(until C++20)(C++17) type_identity (C++20)

 

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 <iostream>
#include <type_traits>
 
int main() {
    typedef std::remove_cv<const int>::type type1;
    typedef std::remove_cv<volatile int>::type type2;
    typedef std::remove_cv<const volatile int>::type type3;
    typedef std::remove_cv<const volatile int*>::type type4;
    typedef std::remove_cv<int * const volatile>::type type5;
 
    std::cout << "test1 " << (std::is_same<int, type1>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test2 " << (std::is_same<int, type2>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test3 " << (std::is_same<int, type3>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test4 " << (std::is_same<const volatile int*, type4>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test5 " << (std::is_same<int*, type5>::value
        ? "passed" : "failed") << '\n';
}

Output:

test1 passed
test2 passed
test3 passed
test4 passed
test5 passed

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 or/and volatile specifiers to the given type (class template)
remove_cvref (C++20)	combines std::remove_cv and std::remove_reference (class template)