std::function<R(Args...)>::target

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< cpp‎ | utility‎ | functional‎ | function
 
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(until 哋它亢++17*)(until 哋它亢++17*)

(until 哋它亢++17*)
(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)(until 哋它亢++17*)
(until 哋它亢++20*)
(until 哋它亢++20*)
 
std::function
 
template< class T >
T* target() noexcept;
 (1) (since 哋它亢++11)
template< class T >
const T* target() const noexcept;
 (2) (since 哋它亢++11)

Returns a pointer to the stored callable function target.

Parameters

(none)

Return value

A pointer to the stored function if target_type() == typeid(T), otherwise a null pointer.

Example

Run this code
#include <functional>
#include <iostream>
 
int f(int, int) { return 1; }
int g(int, int) { return 2; }
void test(std::function<int(int, int)> const& arg)
{
    std::cout << "test function: ";
    if (arg.target<std::plus<int>>())
        std::cout << "it is plus\n";
    if (arg.target<std::minus<int>>())
        std::cout << "it is minus\n";
 
    int (*const* ptr)(int, int) = arg.target<int(*)(int, int)>();
    if (ptr && *ptr == f)
        std::cout << "it is the function f\n";
    if (ptr && *ptr == g)
        std::cout << "it is the function g\n";
}
 
int main()
{
    test(std::function<int(int, int)>(std::plus<int>()));
    test(std::function<int(int, int)>(std::minus<int>()));
    test(std::function<int(int, int)>(f));
    test(std::function<int(int, int)>(g));
}

Output: 

test function: it is plus
test function: it is minus
test function: it is the function f
test function: it is the function g

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2591 哋它亢++11 the behavior is undefined if T is not Callable behavior is defined (always returns nullptr)

See also

 obtains the typeid of the stored target
(public member function)
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