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.
Contents |
[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())
[edit] Exeptions
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
| (C++11)
|
CopyConstructible and CopyAssignable reference wrapper (class template) |