std::ref, std::cref

From cppreference.com

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.

#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)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

std::ref, std::cref

Contents

[edit] Parameters

[edit] Return value

[edit] Exeptions

[edit] Example

[edit] See also