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std::ptr_fun

From cppreference.com
< cpp‎ | utility‎ | functional
 
 
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Defined in header <functional>
template< class Arg, class Result >

std::pointer_to_unary_function<Arg,Result>

    ptr_fun( Result (*f)(Arg) );
(1) (deprecated in C++11)
(removed in C++17)
template< class Arg1, class Arg2, class Result >

std::pointer_to_binary_function<Arg1,Arg2,Result>

    ptr_fun( Result (*f)(Arg1, Arg2) );
(2) (deprecated in C++11)
(removed in C++17)

Creates a function wrapper object (either std::pointer_to_unary_function or std::pointer_to_binary_function), deducing the target type from the template arguments.

1) Effectively calls std::pointer_to_unary_function<Arg,Result>(f).
2) Effectively calls std::pointer_to_binary_function<Arg1,Arg2,Result>(f).

This function and the related types are deprecated as of C++11 in favor of the more general std::function and std::ref, both of which create callable adapter-compatible function objects from plain functions.

Contents

[edit] Parameters

f - pointer to a function to create a wrapper for

[edit] Return value

A function object wrapping f.

[edit] Exceptions

May throw implementation-defined exceptions.

[edit] Example

#include <iostream>
#include <algorithm>
#include <functional>
#include <string_view>
 
constexpr bool is_vowel(char c)
{
    return std::string_view{"aeoiuAEIOU"}.find(c) != std::string_view::npos;
}
 
int main()
{
    std::string_view s = "Hello, world!";
    std::ranges::copy_if(s, std::ostreambuf_iterator<char>(std::cout),
        std::not1(std::ptr_fun(is_vowel)));
#if 0
// C++11 alternatives:
        std::not1(std::cref(is_vowel)));
        std::not1(std::function<bool(char)>(is_vowel)));
        [](char c){ return !is_vowel(c); });
// C++17 alternatives:
        std::not_fn(is_vowel));
#endif
}

Output:

Hll, wrld!

[edit] See also

(C++11)
wraps callable object of any type with specified function call signature
(class template) [edit]
(C++17)(C++23)
invokes any Callable object with given arguments and possibility to specify return type (since C++23)
(function template) [edit]
(C++17)
Creates a function object that returns the complement of the result of the function object it holds
(function template) [edit]