C++

參考

<functional>

function template
<functional>

std::ref

reference (1)
template <class T> reference_wrapper<T> ref (T& elem) noexcept;
複製 (2)
template <class T> reference_wrapper<T> ref (reference_wrapper<T>& x) noexcept;
移動 (3)
 template <class T> void ref (const T&&) = delete;
Construct reference_wrapper
Constructs an object of the appropriate reference_wrapper type to hold a reference to elem.

If the argument is itself a reference_wrapper (2), it creates a copy of x instead.

The function calls the proper reference_wrapper constructor.

引數

elem
An lvalue reference, whose reference is stored in the object.
x
A reference_wrapper object, which is copied.

返回值

A reference_wrapper object of the appropriate type to hold an element of type T.

示例

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
 
// ref example
#include <iostream>     // std::cout
#include <functional>   // std::ref

int main () {
  int foo (10);

  auto bar = std::ref(foo);

  ++bar;

  std::cout << foo << '\n';

  return 0;
}

輸出
11


資料競爭

The initialization version (1) does not access elem, but the returned object can be used to access or modify it.
The copying version (2) accesses its argument (x), returning an object that which can be used to access or modify its referred element.

異常安全

無異常保證： 絕不丟擲異常。

另見

reference_wrapper::reference_wrapper
構造引用包裝器 (public member function)
reference_wrapper::operator()
訪問元素（函式形式） (public member function)
cref
構造指向 const 的 reference_wrapper (函式模板)