Difference between revisions of "cpp/utility/functional/function"
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Revision as of 03:36, 8 June 2019
| 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, as well as pointers to member functions and pointers to data members.
The stored callable object is called the target of std::function. If a std::function contains no target, it is called empty. Invoking the target of an empty std::function results in std::bad_function_call exception being thrown.
std::function satisfies the requirements of CopyConstructible and CopyAssignable.
Contents |
Member types
| Type | Definition |
result_type
|
R
|
argument_type(deprecated in C++17)(removed in C++20)
|
T if sizeof...(Args)==1 and T is the first and only type in Args...
|
first_argument_type(deprecated in C++17)(removed in C++20)
|
T1 if sizeof...(Args)==2 and T1 is the first of the two types in Args...
|
second_argument_type(deprecated in C++17)(removed in C++20)
|
T2 if sizeof...(Args)==2 and T2 is the second of the two types in Args...
|
Member functions
constructs a new std::function instance (public member function) | |
destroys a std::function instance (public member function) | |
| assigns a new target (public member function) | |
| swaps the contents (public member function) | |
| (removed in C++17) |
assigns a new target (public member function) |
| checks if a target is contained (public member function) | |
| invokes the target (public member function) | |
Target access | |
| obtains the typeid of the stored target (public member function) | |
| obtains a pointer to the stored target (public member function) | |
Non-member functions
| (C++11) |
specializes the std::swap algorithm (function template) |
| (removed in C++20) |
compares a std::function with nullptr (function template) |
Helper classes
| (C++11) (until C++17) |
specializes the std::uses_allocator type trait (class template specialization) |
Deduction guides(since C++17)
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'; } struct PrintNum { void operator()(int i) const { 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; const Foo foo(314159); f_add_display(foo, 1); f_add_display(314159, 1); // store a call to a data member accessor std::function<int(Foo const&)> f_num = &Foo::num_; std::cout << "num_: " << f_num(foo) << '\n'; // store a call to a member function and object using std::placeholders::_1; std::function<void(int)> f_add_display2 = std::bind( &Foo::print_add, foo, _1 ); f_add_display2(2); // store a call to a member function and object ptr std::function<void(int)> f_add_display3 = std::bind( &Foo::print_add, &foo, _1 ); f_add_display3(3); // store a call to a function object std::function<void(int)> f_display_obj = PrintNum(); f_display_obj(18); }
Possible output:
-9 42 31337 314160 314160 num_: 314159 314161 314162 18
See also
| (C++11) |
the exception thrown when invoking an empty std::function (class) |
| (C++11) |
creates a function object out of a pointer to a member (function template) |
