C++ Library - <functional>

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Introduction

Function objects are objects specifically designed to be used with a syntax similar to that of functions. Instances of std::function can store, copy, and invoke any Callable target -- functions, lambda expressions, bind expressions, or other function objects, as well as pointers to member functions and pointers to data members.

Declaration

Following is the declaration for std::function.

 template<class > class function; 

C++11

 template< class R, class... Args > class function<R(Args...)> 

Parameters

• R − result_type.

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

Example

In below example for std::function.

 #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'; } struct PrintNum { void operator()(int i) const { std::cout << i << '\n'; } }; int main() { std::function<void(int)> f_display = print_num; f_display(-9); std::function<void()> f_display_42 = []() { print_num(42); }; f_display_42(); std::function<void()> f_display_31337 = std::bind(print_num, 31337); f_display_31337(); std::function<void(const Foo&, int)> f_add_display = &Foo::print_add; const Foo foo(314159); f_add_display(foo, 1); std::function<int(Foo const&)> f_num = &Foo::num_; std::cout << "num_: " << f_num(foo) << '\n'; using std::placeholders::_1; std::function<void(int)> f_add_display2= std::bind( &Foo::print_add, foo, _1 ); f_add_display2(2); std::function<void(int)> f_add_display3= std::bind( &Foo::print_add, &foo, _1 ); f_add_display3(3); std::function<void(int)> f_display_obj = PrintNum(); f_display_obj(18); } 

The sample output should be like this −

 -9 42 31337 314160 num_: 314159 314161 314162 18 

Member functions

Non-member functions

Operator classes