##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# std::ref, std::cref

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class T > std::reference_wrapper<T> ref(T& t); | (1) | (since C++11)
template< class T > std::reference_wrapper<T> ref( std::reference_wrapper<T> t ); | (2) | (since C++11)
template <class T> void ref(const T&&) = delete; | (3) | (since C++11)
template< class T > std::reference_wrapper<const T> cref( const T& t ); | (4) | (since C++11)
template< class T > std::reference_wrapper<const T> cref( std::reference_wrapper<T> t ); | (5) | (since C++11)
template <class T> void cref(const T&&) = delete; | (6) | (since C++11)

Function templates `ref` and `cref` are helper functions that generate an object of type std::reference_wrapper, using template argument deduction to determine the template argument of the result.

### [edit] Parameters

t | - | lvalue reference to object that needs to be wrapped or an instance of std::reference_wrapper

### [edit] Return value

1) std::reference_wrapper<T>(t)
2) ref(t.get())
4) std::reference_wrapper<const T>(t)
5) cref(t.get())
3,6) rvalue reference wrapper is deleted.

### [edit] Exceptions

`noexcept` specification:
noexcept

### [edit] Example

Run this code

    #include <functional>
    #include <iostream>

    void f(int& n1, int& n2, const int& n3)
    {
        std::cout << "In function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
        ++n1; // increments the copy of n1 stored in the function object
        ++n2; // increments the main()'s n2
        // ++n3; // compile error
    }

    int main()
    {
        int n1 = 1, n2 = 2, n3 = 3;
        std::function<void()> bound_f = std::bind(f, n1, std::ref(n2), std::cref(n3));
        n1 = 10;
        n2 = 11;
        n3 = 12;
        std::cout << "Before function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
        bound_f();
        std::cout << "After function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';
    }

Output:

    Before function: 10 11 12
    In function: 1 11 12
    After function: 10 12 12

### [edit] See also

reference_wrapper (C++11) | `CopyConstructible` and `CopyAssignable` reference wrapper (class template) [edit]

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=cpp/utility/functional/ref&oldid=91876"
Category:

- unconditionally noexcept

Hidden categories:

- Pages with unreviewed unconditional noexcept template
- Pages with unreviewed noexcept template