运算符（==）重载错误

Question

So, I'm working on a flowchart project(OOP), and I need to implement a condition for the GUI to let the user DrawConnector, but the "Connector" has a condition is to be drawn only when you have 2 other "Shapes" (Diamond/Rectangl/Etc.).

So this is the Connector Class.h

    class Connector
{
protected :
    Point start;
    Point end;
    Statement *St;
    bool DrawCondition;
    bool DelCondition;
public :
    Connector();
    virtual void setStart(Point S); //Not a condition to be virtuals
    virtual void setEnd(Point E);
    virtual void DrawConnector(Output* pOut);
    //virtual bool setDrawCondition ();
    friend bool operator == (Point P, Point T);
};

I actually want to "setStart" and "setEnd" by the values user "Clicks" on mouse -during runtime- and check after that if these points are to be on a shape, so it draws the connector, if not, then nothing happens.

void Connector::setStart(Point S)
{
    if (S == St->getPoint())
        {start = S;}
    else return;
}

void Connector::DrawConnector(Output *pOut)
{
    /*if (DrawCondition == true)*/
        pOut->DrawConnector(start.x,start.y,end.x,end.y);
}

You can notice I overloaded the operator " == " to check for the points if they're EVEN read ... but it ends up giving me this compilation error !

Error 3 error LNK2019: unresolved external symbol "bool __cdecl operator==(struct Point,struct Point)" (??8@YA_NUPoint@@0@Z) referenced in function "public: virtual void __thiscall Connector::setStart(struct Point)" (?setStart@Connector@@UAEXUPoint@@@Z) C:\\Users\\Cereal Killer\\Downloads\\Phase1-Code\\Phase1-Code\\Connector.obj

EDIT

Sorry guys, I forgot to mention I ALREADY defined the overloading in another file but I guess that was the problem, but why, isn't it a "GLOBAL FUNCTION" ?

Here's the def. :

bool operator == (Point P, Point T)
{
    if ( (P.x == T.x) && (P.y == T.y) )
        return true;
    else return false;
}

One more thing, if I want to check that the given POINT is ON the SHAPE from the GUI shapes "DrawRectangle, DrawCircle, etc." How can I "trace the points that drawed the shape" ? Or is there another way ?

Answer 1

You have declared

friend bool operator == ( Point P, Point T);

but have not defined it.

You need a definition of

bool operator == ( Point P, Point T) {
    //...
}

Answer 2

You need give a definition of the operator like any function, not just the declarations. The lack thereof will generate this error. Since it's a friend, it's just a global function, and you need to define this external to the class. Either in the header, or in the appropriate .cpp file.

bool operator==(Point P, Point T) {
  return P.x == T.x && P.y == T.y;
}

You might also consider passing the points by const reference rather than value.