Undefined symbols of the architechture x86_64 [closed]

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ok I am learning c++ and I got this error

Undefined symbols for architecture x86_64:
  "Point::set(int, int)", referenced from:
      Point::Point(int, int)in ccHkya9E.o
  "Point::add(Point const&)", referenced from:
      Point::operator+(Point const&)in ccHkya9E.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

here is my code

#include<iostream>

 using namespace std;

 class Point {
 private:
   int x, y;
 public:
   Point() {}
   Point(int new_x, int new_y) {set(new_x, new_y);}
   Point (const Point & src) {set(src.x, src.y);}

 //Operations
   Point add (const Point &pt);
   Point sub (const Point &pt);
   Point operator+(const Point &pt) {return add(pt);}
   Point operator-(const Point &pt) {return sub(pt);}
 //other member functions
   void set(int new_x, int new_y);
   int get_x() const {return 开发者_如何学运维x;}
   int get_y() const {return y;}
 };

 int main() {
   Point point1(20,20);
   Point point2(0,5);
   Point point3(-10, 25);
   Point point4=point1+point2+point3;

   cout<<"the point is"<<point4.get_x();
   cout<<","<<point4.get_y()<<"."<<endl;
   return 0;
 }

any help is appreciated!

---

You only declared the functions:

void set(int new_x, int new_y);
Point add (const Point &pt);

But You did not provide definitions for them. So the linker cannot find their definitions and complains about it, The compiler tells you to provide a definition for those two functions, and you should.

An empty(which does nothing) definition of the functions look like:

void set(int new_x, int new_y)
{

}
Point add (const Point &pt)
{
    Point temp;
    return temp;
}

Disclaimer: You should replace these definitions with your actual implementation, The above shall just let you compile and link sucessfully(not work as you want to)