std:: mem_fun

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

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 adaptor-compatible function objects from member functions.

Parameters

Return value

A function object wrapping f .

Exceptions

May throw implementation-defined exceptions.

Notes

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

Example

#include <functional>
#include <iostream>
 
struct S
{
    int get_data() const { return data; }
    void no_args() const { std::cout << "void S::no_args() const\n"; }
    void one_arg(int) { std::cout << "void S::one_arg()\n"; }
    void two_args(int, int) { std::cout << "void S::two_args(int, int)\n"; }
#if __cplusplus > 201100
    int data{42};
#else
    int data;
    S() : data(42) {}
#endif
};
 
int main()
{
    S s;
 
    std::const_mem_fun_t<int, S> p = std::mem_fun(&S::get_data);
    std::cout << "s.get_data(): " << p(&s) << '\n';
 
    std::const_mem_fun_t<void, S> p0 = std::mem_fun(&S::no_args);
    p0(&s);
 
    std::mem_fun1_t<void, S, int> p1 = std::mem_fun(&S::one_arg);
    p1(&s, 1);
 
#if __cplusplus > 201100
//  auto p2 = std::mem_fun(&S::two_args); // Error: mem_fun supports only member functions
                                          // without parameters or with only one parameter.
                                          // Thus, std::mem_fn is a better alternative:
    auto p2 = std::mem_fn(&S::two_args);
    p2(s, 1, 2);
 
//  auto pd = std::mem_fun(&S::data); // Error: pointers to data members are not supported.
                                      // Use std::mem_fn instead:
    auto pd = std::mem_fn(&S::data);
    std::cout << "s.data = " << pd(s) << '\n';
#endif
}

s.get_data(): 42
void S::no_args() const
void S::one_arg(int)
void S::two_args(int, int)
s.data = 42

See also