std::mem_fn

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Defined in header `<functional>`

template< class R, class T > /unspecified/ mem_fn(R T::* pm); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...)); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) volatile); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const volatile); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) &); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const &); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) volatile &); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const volatile &); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) &&); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const &&); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) volatile &&); template< class R, class T, class... Args > /unspecified/ mem_fn(R (T::* pm)(Args...) const volatile &&);		(since C++11)

Function template std::mem_fn generates wrapper objects for pointers to member functions, which can store, copy, and invoke a pointer to member function. Both references and pointers (including smart pointers) to an object can be used when invoking a std::mem_fn..

#include <iostream>
#include <functional>
#include <iterator>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
int main()
{
    std::vector<std::string> words = {"This", "is", "a", "test"};
    std::vector<std::unique_ptr<std::string>> words2;
    words2.emplace_back(new std::string("another"));
    words2.emplace_back(new std::string("test"));
    std::vector<std::size_t> lengths;
    std::transform(words.begin(),
                   words.end(),
                   std::back_inserter(lengths),
                   std::mem_fn(&std::string::size)); // uses references to strings
    std::transform(words2.begin(),
                   words2.end(),
                   std::back_inserter(lengths),
                   std::mem_fn(&std::string::size)); // uses unique_ptr to strings
    std::cout << "The string lengths are ";
    for(auto n : lengths) std::cout << n << ' ';
    std::cout << '\n';
}

Output:

The string lengths are 4 2 1 4 7 4

[edit] See also


function (C++11)	wraps callable object of any type with specified function call signature (class template)

bind (C++11)	binds one or more arguments to a function object (function template)


type	definition

`result_type`	`R`

`argument_type`	`T*`, possibly cv-qualified, if sizeof...(Args}==0

`first_argument_type`	`T*` if sizeof...(Args}==1

`second_argument_type`	`T1` if sizeof...(Args}==1 and `T1` is the only type in `Args...`

std::mem_fn

From Cppreference

Contents

[edit] Parameters

[edit] Return value

[edit] Member types

[edit] Member functions

[edit] Execptions

[edit] Example

[edit] See also


operator()	invokes the target of an std::mem_fn (public member function)