Thread: Weirdest error with '==' operator.

(WinXP, Borland C++ Free Command Line Compiler)
Well, it came down to the wire and I guess I need an '==' operator, so I built one. Theirs probably some trick to do this, but maybe not. So, I just did it the only logical way I know;

Code:

class Platform {
 private:
  SHORT Strength;
  SHORT SteppedOn;
  SHORT x;
  SHORT y;
 public:
  Platform() {Strength=1; SteppedOn=0; x=0; y=0;}
  Platform(SHORT str, SHORT Step, SHORT x_pos, SHORT y_pos) {Strength=str; SteppedOn=Step; x=x_pos; y=y_pos;}

  void Set(SHORT str, SHORT Step, SHORT x_pos, SHORT y_pos) {Strength=str; SteppedOn=Step; x=x_pos; y=y_pos;}

  SHORT GetX() {return x;}
  SHORT GetY() {return y;}
  SHORT GetStr() {return Strength;}
  SHORT GetWStatus() {return SteppedOn;}
  SHORT operator ==(Platform q);
};

SHORT Platform::operator ==(Platform q) {
 if(q.GetX() == this.GetX() && q.GetY() == this.GetY() && q.GetStr() == this.GetStr() && q.GetWStatus() == this.GetWStatus)
  return 1;

 return 0;
}

Ok. That should work. But my compiler doesnt seem to like how I called my '.' structures.

My errors:

Code:

C:\Borland\BCC55\Bin>BCC32 C:\MazeOfPain.cpp
Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
C:\MazeOfPain.cpp:
Error E2294 C:\PlatformClass.h 68: Structure required on left side of . or .* in function Platform::operator ==(Platform)
Error E2294 C:\PlatformClass.h 68: Structure required on left side of . or .* in function Platform::operator ==(Platform)
Error E2294 C:\PlatformClass.h 68: Structure required on left side of . or .* in function Platform::operator ==(Platform)
Error E2294 C:\PlatformClass.h 68: Structure required on left side of . or .* in function Platform::operator ==(Platform)
Warning W8057 C:\PlatformClass.h 72: Parameter 'q' is never used in function Platform::operator ==(Platform)
*** 5 errors in Compile ***

I'm not quite sure what this is asking? I tried calling my structure as if it was a pointer; "q->GetX()" it didint like that either. I'm quite confused... And why does it say 'q' is never used?

Also, is their a better way to do this? I doubt big classes use this method, it'd get way to big.

Anyways, why does my compiler hate me for this? -,-.

Thank you!

Code:

class Platform {
 private:
  SHORT Strength;
  SHORT SteppedOn;
  SHORT x;
  SHORT y;
 public:
  Platform() {Strength=1; SteppedOn=0; x=0; y=0;}
  Platform(SHORT str, SHORT Step, SHORT x_pos, SHORT y_pos) {Strength=str; SteppedOn=Step; x=x_pos; y=y_pos;}

  void Set(SHORT str, SHORT Step, SHORT x_pos, SHORT y_pos) {Strength=str; SteppedOn=Step; x=x_pos; y=y_pos;}

  SHORT GetX() {return x;}
  SHORT GetY() {return y;}
  SHORT GetStr() {return Strength;}
  SHORT GetWStatus() {return SteppedOn;}
  SHORT operator==(Platform q);
  SHORT IsNull();
};

SHORT Platform::operator==(Platform q) {
 if(q.GetX() == this->GetX() && q.GetY() == this->GetY() && q.GetStr() == this->GetStr() && q.GetWStatus() == this->GetWStatus)
  return 1;

 return 0;
}

SHORT Platform::IsNull() {
 static Platform K(-1, 0, 0, 0);

 if(this == K)
  return 1;

 return 0;
}

Still gives me:

Code:

C:\Borland\BCC55\Bin>BCC32 c:\MazeOfPain.cpp
Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
c:\MazeOfPain.cpp:
Error E2235 c:\PlatformClass.h 68: Member function must be called or its address taken in function Platform::operator ==(Platform)
Warning W8057 c:\PlatformClass.h 72: Parameter 'q' is never used in function Platform::operator ==(Platform)
Error E2096 c:\PlatformClass.h 77: Illegal structure operation in function Platform::IsNull()
*** 2 errors in Compile ***
C:\Borland\BCC55\Bin>

I still dont get the warnings either... And why is it still giving me an error when I use pointer dereferencing? And also, whats my problem with IsNull?

Thank you!

Code:

SHORT Platform::operator==(Platform q)
{
    if(q.GetX() == this->GetX() && q.GetY() == this->GetY() && q.GetStr() == this->GetStr() &&
       q.GetWStatus() == this->GetWStatus)
  return 1;

 return 0;
}

GetWStatus is a function, you need to use this->GetWStatus() and not this->GetWStatus.

Code:

SHORT Platform::IsNull() {
 static Platform K(-1, 0, 0, 0);

 if(this == K)
  return 1;

 return 0;
}

Again, you're forgetting that this is a pointer and not an object of type Platform. Coupled with how you have defined the operator (as a member function), you would need to say if( this->operator==(K) ). You should make your operators global friend functions as such:

Code:

class Platform
{
   ...
   friend bool operator==(const Platform&, const Platform&);
};

bool operator==(const Platform& lhs, const Platform& rhs)
{
    if(lhs.GetX() == rhs.GetX() && lhs.GetY() == rhs.GetY() && lhs.GetStr() == rhs.GetStr() &&
       lhs.GetWStatus() == rhs.GetWStatus())
        return true;

    else return false;
}

This will allow you to compare two Platform objects directly using == and say things like:

Code:

Platform foo(-1,0,0,0);
Platform bar(-1,0,0,0);

...

if( foo == bar )
...

... without needing the awkward syntax if( foo->operator==(bar) ) that wouild otherwise be required.


This will also require you make all your "get" member functions const correct as they should have been all along:

Code:

class Platform {
   ...
    SHORT GetX() const {return x;}
    SHORT GetY() const {return y;}
    SHORT GetStr() const {return Strength;}
    SHORT GetWStatus() const {return SteppedOn;}
};

O wow! I'm a mega-noob to classes I guess :P. Well, it works! Thank you very much!