Std::add_cv,std::add_const,std::add_volatile (3) Linux Manual Page

std::add_cv,std::add_const,std::add_volatile – std::add_cv,std::add_const,std::add_volatile

Synopsis

Defined in header<type_traits>

    template <class T>
    (1)(since C++ 11)

        struct add_cv;

template <class T>
(2)(since C++ 11)

    struct add_const;

template <class T>
(3)(since C++ 11)

    struct add_volatile;

Provides the member typedef type which is the same as T, except it has a cv-qualifier added (unless T is a function, a reference, or already has this cv-qualifier)
1) adds both const and volatile
2) adds const
3) adds volatile

Member types

Name Definition
type the type T with the cv-qualifier

Helper types

template< class T > (since C++14)
using add_cv_t = typename add_cv<T>::type;
template< class T > (since C++14)
using add_const_t = typename add_const<T>::type;
template< class T > (since C++14)
using add_volatile_t = typename add_volatile<T>::type;

Possible implementation

template< class T >
struct add_cv { typedef const volatile T type; };

template< class T> struct add_const { typedef const T type; };

template< class T> struct add_volatile { typedef volatile T type; };

Example

// Run this code

#include <iostream>

#include <type_traits>
struct foo

{
    void m()
    {
        std::cout << "Non-cv\n";
    }
    void m() const
    {
        std::cout << "Const\n";
    }
    void m() volatile
    {
        std::cout << "Volatile\n";
    }
    void m() const volatile
    {
        std::cout << "Const-volatile\n";
    }
};
int main()

{
    foo{}.m();
    std::add_const<foo>::type{}.m();
    std::add_volatile<foo>::type{}.m();
    std::add_cv<foo>::type{}.m();
}

Output:

  Non-cv
  Const
  Volatile
  Const-volatile

std::add_cv,std::add_const,std::add_volatile (3) Linux Manual Page