std::mem_fun_ref

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.

Parameters

pointer to a member function to create a wrapper for

Return value

A function object wrapping f.

Exceptions

(none).

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.

Example

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

#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