std::function

From cppreference.com

Defined in header `<functional>`

template< class > class function; /* undefined */		(since C++11)

template< class R, class... Args > class function<R(Args...)>		(since C++11)

Class template std::function is a general-purpose polymorphic function wrapper. Instances of std::function can store, copy, and invoke any callable target -- functions, lambda expressions, bind expressions, or other function objects.


Type	Definition

`result_type`	`R`

`argument_type`	`T` if sizeof...(Args)==1 and `T` is the first and only type in `Args...`

`first_argument_type`	`T1` if sizeof...(Args)==2 and `T1` is the first of the two types in `Args...`

`second_argument_type`	`T2` if sizeof...(Args)==2 and `T2` is the second of the two types in `Args...`

[edit] Member functions


(constructor)	constructs a new std::function instance (public member function)

(destructor)	destroys a std::function instance (public member function)

operator=	assigns the contents (public member function)

swap	swaps the contents (public member function)

assign	assigns a new target (public member function)

operator bool	checks if a valid target is contained (public member function)

operator()	invokes the target (public member function)
Target access

target_type	obtains the typeid of the stored target of a std::function (public member function)

target	obtains a pointer to the stored target of a std::function (public member function)

[edit] Non-member functions


std::swap(std::function) (C++11)	specializes the std::swap algorithm (function template)

operator== operator!=	compares an std::function with std::nullptr (function template)

[edit] Helper classes


std::uses_allocator<std::function> (C++11)	specializes the std::uses_allocator type trait (class template specialization)

[edit] Example

run this code

#include <functional>
#include <iostream>
 
struct Foo {
    Foo(int num) : num_(num) {}
    void print_add(int i) const { std::cout << num_+i << '\n'; }
    int num_;
};
 
void print_num(int i)
{
    std::cout << i << '\n';
}
 
int main()
{
    // store a free function
    std::function<void(int)> f_display = print_num;
    f_display(-9);
 
    // store a lambda
    std::function<void()> f_display_42 = []() { print_num(42); };
    f_display_42();
 
    // store the result of a call to std::bind
    std::function<void()> f_display_31337 = std::bind(print_num, 31337);
    f_display_31337();
 
    // store a call to a member function
    std::function<void(const Foo&, int)> f_add_display = &Foo::print_add;
    Foo foo(314159);
    f_add_display(foo, 1);
}

Output:

[edit] See also


bad_function_call (C++11)	the exception thrown when invoking an empty std::function (class)

mem_fn (C++11)	creates a function object out of a pointer to a member (function template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

std::function

Contents

[edit] Member types

[edit] Member functions

Target access

[edit] Non-member functions

[edit] Helper classes

[edit] Example

[edit] See also