std::mem_fun
<functional>
std::mem_fun_t <Res,T> mem_fun( Res (T::*f)() );
(removed in C++17)
std::const_mem_fun_t <Res,T> mem_fun( Res (T::*f)() const );
(removed in C++17)
std::mem_fun1_t <Res,T,Arg> mem_fun( Res (T::*f)(Arg) );
(removed in C++17)
std::const_mem_fun1_t <Res,T,Arg> mem_fun( Res (T::*f)(Arg) const );
(removed in C++17)
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.
[edit] Parameters
[edit] Return value
A function object wrapping f.
[edit] Exceptions
May throw implementation-defined exceptions.
[edit] 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.
[edit] Example
Demonstrates std::mem_fun usage and compares it with std::mem_fn . C++11/14 compatible compilation mode might be necessary: g++/clang++ with -std=c++11, cl with /std:c++11, etc. On recent compilers, e.g. gcc-12, might issue "deprecated declaration" warnings if not compiled in C++98 mode.
#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 }
Possible output:
s.get_data(): 42 void S::no_args() const void S::one_arg(int) void S::two_args(int, int) s.data = 42
[edit] See also
(function template) [edit]