std::mem_fun
Defined in header <functional> |
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template< class Res, class T > std::mem_fun_t<Res,T> mem_fun( Res (T::*f)() ); |
(1) | (deprecated in C++11) (removed in C++17) |
template< class Res, class T > std::const_mem_fun_t<Res,T> mem_fun( Res (T::*f)() const ); |
(1) | (deprecated in C++11) (removed in C++17) |
template< class Res, class T, class Arg > std::mem_fun1_t<Res,T,Arg> mem_fun( Res (T::*f)(Arg) ); |
(2) | (deprecated in C++11) (removed in C++17) |
template< class Res, class T, class Arg > std::const_mem_fun1_t<Res,T,Arg> mem_fun( Res (T::*f)(Arg) const ); |
(2) | (deprecated in C++11) (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.
Parameters
| f | - | pointer to a member function to create a wrapper for |
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 an function wrapper that expects a pointer to an object, whereas the latter -- a reference.
Example
demonstrates std::mem_fun usage and compares it with std::mem_fn. C++11/14 compatible compilation mode might be necessary (e.g. g++/clang++ with -std=c++11, cl with /std:c++11).
#include <iostream>
#include <functional>
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"; }
int data{42};
};
int main() {
S s;
auto p = std::mem_fun(&S::get_data);
std::cout << "s.get_data(): " << p(&s) << '\n';
auto p0 = std::mem_fun(&S::no_args);
p0(&s);
auto p1 = std::mem_fun(&S::one_arg);
p1(&s, 1);
// 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';
}
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
See also
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(C++11)
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creates a function object out of a pointer to a member (function template) |
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(deprecated in C++11)(removed in C++17)
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creates a wrapper from a pointer to member function, callable with a reference to object (function template) |
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