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

From cppreference.net
C++
Utilities library
Function objects
Function invocation
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Identity function object
(C++20)
Old binders and adaptors
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( until C++17* )
( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
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( until C++17* )
( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
( until C++20* )
( until C++20* )
std::function
template < class T >
T * target ( ) noexcept ;
(1) (自 C++11 起)
template < class T >
const T * target ( ) const noexcept ;
(2) (自 C++11 起)

返回指向存储的可调用函数目标的指针。

目录

参数

(无)

返回值

若 target_type ( ) == typeid ( T ) 则返回指向存储函数的指针，否则返回空指针。

示例

运行此代码 
#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));
}

输出： 

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

缺陷报告

下列行为变更缺陷报告被追溯应用于先前发布的 C++ 标准。

缺陷报告 应用于 发布时行为 正确行为
LWG 2591 C++11 若 T 不满足 Callable 要求则行为未定义 行为已定义（始终返回 nullptr ）

参见

获取存储目标的 typeid
(公开成员函数)