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std::function

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< cpp‎ | utility‎ | functional
Revision as of 15:44, 14 October 2013 by 121.99.33.183 (Talk)

 
 
 
Function objects
Function wrappers
function
(C++11)
(C++11)
Bind
(C++11)
Reference wrappers
(C++11)(C++11)
Operator wrappers
Negators
Deprecated binders and adaptors
(deprecated)
(deprecated)
(deprecated)
(deprecated)
(deprecated)(deprecated)(deprecated)(deprecated)
(deprecated)
(deprecated)(deprecated)(deprecated)(deprecated)
(deprecated)(deprecated)
(deprecated)(deprecated)
 
 
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.

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 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...

Member functions

constructs a new std::function instance
(public member function) [edit]
destroys a std::function instance
(public member function) [edit]
assigns a new target
(public member function) [edit]
swaps the contents
(public member function) [edit]
assigns a new target
(public member function) [edit]
checks if a valid target is contained
(public member function) [edit]
invokes the target
(public member function) [edit]
Target access
obtains the typeid of the stored target of a std::function
(public member function) [edit]
obtains a pointer to the stored target of a std::function
(public member function) [edit]

Non-member functions

specializes the std::swap algorithm
(function template) [edit]
compares an std::function with std::nullptr
(function template) [edit]

Helper classes

specializes the std::uses_allocator type trait
(class template specialization) [edit]

Example

#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;
    Foo foo(314159);
    f_add_display(foo, 1);
 
    // store a call to a function object
    std::function<void(int)> f_display_obj = PrintNum();
    f_display_obj(18);
}

Output:

-9
42
31337
314160
18

See also

the exception thrown when invoking an empty std::function
(class) [edit]
(C++11)
creates a function object out of a pointer to a member
(function template) [edit]