function template
<functional>
std::cref
| reference (1) |
template <class T>
reference_wrapper<const T> cref (const T& elem) noexcept;
|
|---|
| copy (2) |
template <class T>
reference_wrapper<const T> cref (reference_wrapper<const T>& x) noexcept;
|
|---|
| move (3) |
template <class T>
void cref (const T&&) = delete; |
|---|
Construct reference_wrapper to const
Constructs an object of the appropriate reference_wrapper type to hold a const T reference to elem.
If the argument is itself a reference_wrapper to a const T (2), it creates a copy of x instead.
The function calls the proper reference_wrapper constructor.
Parameters
- elem
- An lvalue reference, whose const reference is stored in the object.
- x
- A reference_wrapper object to
const T, which is copied.
Return Value
A reference_wrapper object of the appropriate type to hold an element of type const T.
Example
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
|
// cref example
#include <iostream> // std::cout
#include <functional> // std::ref
int main () {
int foo (10);
auto bar = std::cref(foo);
++foo;
std::cout << bar << '\n';
return 0;
}
|
Output:
Data races
The initialization version (1) does not access elem, but the returned object can be used to access it.
The copying version (2) accesses its argument (x), returning an object that which can be used to access its referred element.
Exception safety
No-throw guarantee: never throws exceptions.