std::add_cv,std::add_const,std::add_volatile (3) - Linux Manuals

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

NAME

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