template< class T > T* target() noexcept; | (1) | (since C++11) |
template< class T > const T* target() const noexcept; | (2) | (since C++11) |
Returns a pointer to the stored callable function target.
(none).
A pointer to the stored function if target_type() == typeid(T), otherwise a null pointer.
#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
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) |
| obtains the typeid of the stored target (public member function) |
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