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# std::mem_fun_ref

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class Res, class T > std::mem_fun_ref_t<Res,T> mem_fun_ref( Res (T::*f)() ); | (1) | (until C++17) (deprecated since C++11)
template< class Res, class T > std::const_mem_fun_ref_t<Res,T> mem_fun_ref( Res (T::*f)() ); | (1) | (until C++17) (deprecated since C++11)
template< class Res, class T, class Arg > std::mem_fun1_ref_t<Res,T,Arg> mem_fun_ref( Res (T::*f)(Arg) ); | (2) | (until C++17) (deprecated since C++11)
template< class Res, class T, class Arg > std::const_mem_fun1_ref_t<Res,T,Arg> mem_fun_ref( S (T::*f)(Arg) ); | (2) | (until C++17) (deprecated since C++11)

Creates a member function wrapper object, deducing the target type from the template arguments. The wrapper object expects a reference to an object of type `T` as the first parameter to its operator().

1) Effectively calls std::mem_fun_ref_t<S,T>(f) or std::const_mem_fun_ref_t<S,T>(f).

2) Effectively calls std::mem_fun1_ref_t<S,T>(f) or std::const_mem_fun1_ref_t<S,T>(f).

This function and the related types were deprecated in C++11 and removed in C++17 in favor of the more general std::mem_fn and std::bind, both of which create callable adapter-compatible function objects from member functions.

### [edit] Parameters

f | - | pointer to a member function to create a wrapper for

### [edit] Return value

A function object wrapping `f`.

### [edit] Exceptions

(none)

### [edit] Notes

The difference between std::mem_fun and std::mem_fun_ref is that the former produces an function wrapper that expects a pointer to an object, whereas the latter -- a reference.

### [edit] Example

uses std::mem_fun_ref to bind std::string's member function .size()

Run this code

    #include <functional>
    #include <vector>
    #include <string>
    #include <iterator>
    #include <algorithm>
    #include <iostream>

    int main()
    {
        std::vector<std::string> v = {"once", "upon", "a", "time"};
        std::transform(v.begin(), v.end(),
                       std::ostream_iterator<std::size_t>(std::cout, " "),
                       std::mem_fun_ref(&std::string::size));
    }

Output:

    4 4 1 4

### [edit] See also

mem_fun (until C++17) | creates a wrapper from a pointer to member function, callable with a pointer to object (function template) [edit]

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