std::function
STD：功能
| Defined in header | | |
|---|---|---|
| template< class > class function; /* undefined */ | | (since C++11) |
| template< class R, class... Args > class function<R(Args...)>; | | (since C++11) |
类模板std::function是一个通用的多态函数包装器。实例std::function可以存储、复制和调用任何Callable目标-职能，Lambda表达式，，，绑定表达式，或者其他函数对象，以及指向成员函数和数据成员的指针。
存储的可调用对象称为目标成std::function.如果std::function不包含目标，则调用空空调用目标一种空空std::function结果std::bad_function_call异常被抛出。
std::function满足…的要求CopyConstructible和CopyAssignable...
成员类型
| Type | Definition |
|---|---|
| result_type | R |
| argument_type(deprecated in C++17) | T if sizeof...(Args)==1 and T is the first and only type in Args... |
| first_argument_type(deprecated in C++17) | T1 if sizeof...(Args)==2 and T1 is the first of the two types in Args... |
| second_argument_type(deprecated in C++17) | T2 if sizeof...(Args)==2 and T2 is the second of the two types in Args... |
成员函数
| (constructor) | constructs a new std::function instance (public member function) |
|---|---|
| (destructor) | destroys a std::function instance (public member function) |
| operator= | assigns a new target (public member function) |
| swap | swaps the contents (public member function) |
| assign (until C++17) | 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) |
目标访问
目标[医]类型获得存储目标%28公共成员函数%29的类型
获取指向存储目标%28公共成员函数%29的指针。
非会员职能
| std::swap(std::function) (C++11) | specializes the std::swap algorithm (function template) |
|---|---|
| operator==operator!= | compares an std::function with nullptr (function template) |
帮助者类
| std::uses_allocator | specializes the std::uses_allocator type trait (class template specialization) |
|---|
例
二次
#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
// 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
}
二次
产出：
二次
-9
42
31337
314160
num_: 314159
314161
314162
18
二次
另见
| 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) |
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