C++ 错误 : Not declared in scope; Member function

Question

我有一个错误，“结果 vector ”未在此范围内声明。我不确定在哪里或如何申报？ Result Vector 的目的是显示 vector 的 X 和每个 vector 的 Y 相加的结果，然后返回 result_vector

#include <iostream>
#include <vector>
using namespace std;

class vector{
private:
    double x;
    double y;
public:
    //Constructor - default
    vector() : x(0), y(0) {}
    //Constructor - Custom
    vector(double xx, double yy) : x(xx), y(yy) {}
    //Get X & Y Coordinates
    double get_x() { return x;
    }
    double get_y() { return y;
    }
    //Set X & Y Coordinates
    void set_x( double xx) { x = xx;
    }
    void set_y( double yy) { y = yy;
    }
    //Adding Vectors
    vector add_vector( vector v1, vector v2){ 
        result_vector.x = v1.x + v2.x;
        result_vector.y = v1.y + v2.y;
        return result_vector; 
    }
    //Subtracting Vectorsed
    vector subtract_vector( vector v1, vector v2){
        result_vector.x = v1.x - v2.x;
        result_vector.y = v1.y - v2.y;
        return result_vector;
    }
};

int main() {
    //Default
    vector test;
    cout <<"Default \n" test.get_x().get_y() << "\n";
    //Customer
    vector test2(10, 12);
    cout <<"Custom \n" test2.get_x().get_y() << "\n";
    //Adding
    vector add = vector.add_vector(vector test1&, vector test2&);
    cout <<"Adding \n" add.get_x().get_y() <<"\n";
    //Subtracting
    vector sub = vector.subtract_vector(vector test1&, vector test2&);
    cout <<"Subtracting \n" sub.get_x().get_y() <<"\n";

    return 0;


}

Answer 1

错误是不言自明的。

• 您需要在首次使用之前声明 result_vector。
• 您不能将类名和对象名一起作为参数传递。
• 假设这个声明cout <<"Default \n" test.get_x().get_y() << "\n";应该打印 vector 的 x 和 y 值，你将不得不调用 get_x()和 get_y()分别。

• 另外正如 Andreas DM 所提到的，您不能使用 using namespace std;因为修正后与现有类vector.vector类冲突

  #include <iostream>
  #include <vector>
  
  class vector{
  private:
      double x;
      double y;
  public:
      //Constructor - default
      vector() : x(0), y(0) {}
      //Constructor - Custom
      vector(double xx, double yy) : x(xx), y(yy) {}
      //Get X & Y Coordinates
      double get_x() { return x;
      }
      double get_y() { return y;
      }
      //Set X & Y Coordinates
      void set_x( double xx) { x = xx;
      }
      void set_y( double yy) { y = yy;
      }
      //Adding Vectors
      vector add_vector( vector v2){ 
          vector result_vector;
          result_vector.x = x + v2.x;
          result_vector.y = y + v2.y;
          return result_vector; 
      }
      //Subtracting Vectorsed
      vector subtract_vector( vector v2){
          vector result_vector;
          result_vector.x = x - v2.x;
          result_vector.y = y - v2.y;
          return result_vector;
      }
  };
  
  int main() {
      //Default
      vector test;
      std::cout <<"Default \n" <<test.get_x()<<test.get_y() << "\n";
      //Customer
      vector test2(10, 12);
      std::cout <<"Custom \n" <<test2.get_x()<<test2.get_y() << "\n";
      //Adding
      vector add;
      add = test.add_vector(test2);
      std::cout <<"Adding \n" <<add.get_x()<<add.get_y() <<"\n";
      //Subtracting
      vector sub ;
      sub = test.subtract_vector(test2);
     std::cout <<"Subtracting \n"<< sub.get_x()<<sub.get_y() <<"\n";
  
      return 0;
  
  
  }