std::mem_fun - cppreference.com (original) (raw)

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 #include   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

| | creates a function object out of a pointer to a member (function template) [edit] | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | (deprecated in C++11)(removed in C++17) | creates a wrapper from a pointer to member function, callable with a reference to object (function template) [edit] |