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std::ref, std::cref

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Template:ddcl list begin <tr class="t-dsc-header">

<td>
Defined in header <functional>
</td>

<td></td> <td></td> <tr class="t-dcl ">

<td >
template< class T >
std::reference_wrapper<T> ref(T& t);
</td>

<td > (1) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template< class T >
std::reference_wrapper<T> ref( std::reference_wrapper<T> t );
</td>

<td > (2) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template <class T>
void ref(const T&&) = delete;
</td>

<td > (3) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template< class T >
std::reference_wrapper<const T> cref( const T& t );
</td>

<td > (4) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template< class T >
std::reference_wrapper<const T> cref( std::reference_wrapper<T> t )
</td>

<td > (5) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template <class T>
void cref(const T&&) = delete;
</td>

<td > (6) </td> <td > (since C++11) </td> </tr> Template:ddcl list end

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.

Contents

Parameters

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

Return value

2) ref(t.get())
4) std::reference_wrapper<const T>(t)
5) cref(t.get())

Exeptions

noexcept specification:  
noexcept
  

Example

#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

See also

CopyConstructible and CopyAssignable reference wrapper
(class template) [edit]