binary_function 的使用向量。错误：与调用“(std::binary_function<int, int, int>) (int&, int&)

Question

我正在尝试使用binary_function向量进行变换调用。并出现错误。

代码：

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

int main(void) {
    vector<int> v1 = {1, 2, 10, 23, 13};
    vector<int> v2 = {10, 2, 4, -1, 3};
    vector<int> result(v1.size());

    plus<int> f1;
    minus<int> f2;
    multiplies<int> f3;

    vector<binary_function<int, int, int>> funcs = {f1, f2, f3};

    for (auto func: funcs) {
        transform(v1.begin(), v1.end(), v2.begin(), result.begin(), func);
        
        for (auto value: result) { cout << value << " "; }
        cout << endl;
    }


    return 0;
}

g++ 返回错误：

In file included from /usr/include/c++/8/algorithm:62,
                 from test.cpp:1:
/usr/include/c++/8/bits/stl_algo.h: In instantiation of ‘_OIter std::transform(_IIter1, _IIter1, _IIter2, _OIter, _BinaryOperation) [with _IIter1 = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; _IIter2 = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; _OIter = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; _BinaryOperation = std::binary_function<int, int, int>]’:
test.cpp:19:67:   required from here
/usr/include/c++/8/bits/stl_algo.h:4343:25: error: no match for call to ‘(std::binary_function<int, int, int>) (int&, int&)’
  *__result = __binary_op(*__first1, *__first2);
              ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

为什么？

我读了std::binary_function - 与调用不匹配？但我无法理解答案：

std::binary_function only contains typedefs for argument and return types. It was never intended to act as a polymorphic base class (and even if it was, you'd still have problems with slicing).

为什么？

Answer 1

替换 std::binary_function 的实例。这应该按预期工作，没有任何编译错误。

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

int main(void) {
    vector<int> v1 = {1, 2, 10, 23, 13};
    vector<int> v2 = {10, 2, 4, -1, 3};
    vector<int> result(v1.size());

    auto f1 = [](int a, int b) { return a + b; };
    auto f2 = [](int a, int b) { return a - b; };
    auto f3 = [](int a, int b) { return a * b; };

    vector<decltype(f1)> funcs = {f1, f2, f3};

    for (auto func : funcs) {
        transform(v1.begin(), v1.end(), v2.begin(), result.begin(), func);

        for (auto value : result) {
            cout << value << " ";
        }
        cout << endl;
    }

    return 0;
}