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Help w/ Funcuntion Pointers

Started by gandolf1212 Dec 13, 2001 at 1:21 AM 6 replies 350+ views

Original Post

Dec 13, 2001 at 1:21 AM

Okay, basically what i''m trying to do is delare a function pointer in a class that points to a function in the same class. Something like this...

class Creature{
 public: 
  int X;

  void (*Move)();

  void Walk();
  void Run();
};

void Creature::Walk(){ // Normal movement
  X += 1;
};

void Creature::Run(){ // Fast movement
  X += 5;
};

void Main(){
  Creature C1;

  C1.Move = C1.Run; // Now i try to set the pointer to my
                    // function and it crashes
};

If anyone knows how to do this please tell me, this has been bothering me for weeks. Thanks!

Oluseyi

Dec 13, 2001 at 1:51 AM

Pointers to member functions.

[ GDNet Start Here | GDNet FAQ | MS RTFM | STL | Google ]
Thanks to Kylotan for the idea!

LyLFox

Dec 13, 2001 at 2:19 AM

The reason why you''re getting error is because void (*Move)() is a pointer to a function, and when you declare C1.Move = C1.Run you are forcing C1.Move to point to a member function. A pointer to function is different from a pointer to member function. If you want that to work, you''ll have to declare C1.Move() to be a pointer to a member function - although I agree with AP''s suggestion since that it''s much simpler and less overhead.

gandolf1212

Dec 13, 2001 at 1:45 PM

quote:
Original post by LyLFox
you''ll have to declare C1.Move() to be a pointer to a member function

Could you please tell me the syntax to do that?

Also, the reason I''m trying to do this is because I want to create a game with a very large amount of moves and a big gaint switch statement seems a little messy compared to a function pointer array, plus you loose some cool array/matrix math tricks.

Thanks alot for the help guys,
Gandolf

gandolf1212

Dec 13, 2001 at 2:03 PM

Oluseyi, i went to the sight you gave me but i can''t figure out what to do. I put in the line:

void (Creature::*Move)();

and set move to Walk and Run (plus a few other changes) but much crashing occured. Thanks anyway though.

Oluseyi

Dec 13, 2001 at 4:20 PM

The point (pun not intended) is that your pointer to methods should be outside the class definition. If it''s inside the class, why not have the user set a flag ro have the method do some additional logic?

Outside class:

void (*Creature::Move)();
Creature c1;
// assume object has been initialized
Move = c1.Run();
...
c1.Move(); // <- this is how you use the method pointer

[ GDNet Start Here | GDNet FAQ | MS RTFM | STL | Google ]
Thanks to Kylotan for the idea!

Rube

Dec 13, 2001 at 4:34 PM

Hrms, I don''t know exactly what you mean...but how about this:

Create an array of all your movement rate values you want to store as a property of your class

Then create a function ::SetMovementRate(unsigned int array_index)

Then within your function, edit a value for your movement rate

current_move_rate += movement_array(array_index);

or whatever you are doing.

It''ll preserve your array tricks?

R.

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