c++ - std::binary_function - 调用不匹配？

Question

包括

#include <functional>

using namespace std;

int main() {
  binary_function<double, double, double> operations[] = {
    plus<double>(), minus<double>(), multiplies<double>(), divides<double>() 
  };
  double a, b;
  int choice;
  cout << "Enter two numbers" << endl;
  cin >> a >> b;
  cout << "Enter opcode: 0-Add 1-Subtract 2-Multiply 3-Divide" << endl;
  cin >> choice;
  cout << operations[choice](a, b) << endl;
}

我得到的错误是:

Calcy.cpp: In function ‘int main()’:
Calcy.cpp:17: error: no match for call to ‘(std::binary_function<double, double, double>) (double&, double&)’

谁能解释为什么我会收到此错误以及如何消除它？

Answer 1

std::binary_function 仅包含参数和返回类型的类型定义。它从未打算充当多态基类(即使是，您仍然会遇到切片问题)。

作为替代方案，您可以像这样使用 boost::function(或 std::tr1::function):

boost::function<double(double, double)> operations[] = {
  plus<double>(), minus<double>(), multiplies<double>(), divides<double>() 
};