std::function<R(Args...)>::target
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std::function
template< class T >
T* target() noexcept;
(1)
(since C++11)
T* target() noexcept;
template< class T >
const T* target() const noexcept;
(2)
(since C++11)
const T* target() const noexcept;
Returns a pointer to the stored callable function target.
[edit] Parameters
(none)
[edit] Return value
A pointer to the stored function if target_type() == typeid(T), otherwise a null pointer.
[edit] 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
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2591 | C++11 | the behavior is undefined if T is not Callable
|
behavior is defined (always returns nullptr)
|