class template
<type_traits>
std::add_volatile
template <class T> struct add_volatile;
Add volatile qualification
Obtains the type T with volatile qualification.
The transformed type is aliased as member type add_volatile::type.
If T is not already volatile-qualified, and is neither a reference nor a function (which cannot be volatile-qualified), this is the same type as T volatile. Otherwise, it is T unchanged.
Notice that this class merely obtains a type using another type as model, but it does not transform values or objects between those types. To explicitly add volatile-qualification to an object, const_cast can be used.
Template parameters
- T
- A type.
Member types
| member type | definition |
|---|
| type | If T is not volatile-qualified, and is neither a reference nor a function, the same type as T but volatile-qualified.
Otherwise, T |
Example
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// add_volatile example
#include <iostream>
#include <type_traits>
int main() {
typedef std::add_volatile<int>::type A; // volatile int
typedef std::add_volatile<volatile int>::type B; // volatile int (unchanged)
typedef std::add_volatile<int* volatile>::type C; // int* volatile (unchanged)
typedef std::add_volatile<volatile int*>::type D; // volatile int* volatile
typedef std::add_volatile<volatile int&>::type E; // volatile int& (unchanged)
std::cout << std::boolalpha;
std::cout << "checking volatileness:" << std::endl;
std::cout << "A: " << std::is_volatile<A>::value << std::endl;
std::cout << "B: " << std::is_volatile<B>::value << std::endl;
std::cout << "C: " << std::is_volatile<C>::value << std::endl;
std::cout << "D: " << std::is_volatile<D>::value << std::endl;
std::cout << "E: " << std::is_volatile<E>::value << std::endl;
return 0;
}
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Output:
checking volatileness:
A: true
B: true
C: true
D: true
E: false
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