| Defined in header <type_traits> | ||
|---|---|---|
template< class T > struct add_cv; | (1) | (since C++11) |
template< class T > struct add_const; | (2) | (since C++11) |
template< class T > struct add_volatile; | (3) | (since C++11) |
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 > using add_cv_t = typename add_cv<T>::type; | (since C++14) | |
template< class T > using add_const_t = typename add_const<T>::type; | (since C++14) | |
template< class T > using add_volatile_t = typename add_volatile<T>::type; | (since C++14) |
Possible implementation
template< class T >
struct add_cv {
typedef typename std::add_volatile<typename std::add_const<T>::type>::type type;
};
template< class T> struct add_const { typedef const T type; };
template< class T> struct add_volatile { typedef volatile T type; }; |
Example
#include <iostream>
#include <type_traits>
struct foo
{
void m() { std::cout << "Non-cv\n"; }
void m() const { std::cout << "Const\n"; }
};
template <class T>
void call_m()
{
T().m();
}
int main()
{
call_m<foo>();
call_m<std::add_const<foo>::type>();
}Output:
Non-cv Const
See also
| (C++11) | checks if a type is const-qualified (class template) |
| (C++11) | checks if a type is volatile-qualified (class template) |
| (C++11)(C++11)(C++11) | removes const or/and volatile specifiers from the given type (class template) |
| (C++17) | obtains a reference to const to its argument (function template) |
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