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Passing a member function pointer

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Passing a member function pointer

Sep 6th, 2008

Normally I call this function like this

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void MouseButton(int button, int state, int x, int y);
...
glutMouseFunc(MouseButton);
void MouseButton(int button, int state, int x, int y);
...
glutMouseFunc(MouseButton);

But now I would like to pass a member function instead of a "real" (non-member? whats the word for this?) function.

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class Plot
{
  void Plot::MouseButton(int button, int state, int x, int y);
  ...
  Plot() { glutMouseFunc(MouseButton); }
}
class Plot
{
  void Plot::MouseButton(int button, int state, int x, int y);
  ...
  Plot() { glutMouseFunc(MouseButton); }
}

But I get this error:

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/home/dave/Plot/src/Plot.h:81: error: argument of type 'void (Plot::)(int, int, int, int)' does not match 'void (*)(int, int, int, int)'
/home/dave/Plot/src/Plot.h:81: error: argument of type 'void (Plot::)(int, int, int, int)' does not match 'void (*)(int, int, int, int)'

What do I have to do differently to get this to work?

Thanks!
Dave

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Re: Passing a member function pointer

Sep 6th, 2008

Assuming you have control over glutMouseFunc, you need to overload it to accept a pointer to a member function:

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class Plot {
public:
  void MouseButton();
};
 
void glutMouseFunc ( void (Plot::*pmf)() )
{
  //...
 
  Plot p;
  (p.*pmf)();
 
  //...
}
class Plot {
public:
  void MouseButton();
};

void glutMouseFunc ( void (Plot::*pmf)() )
{
  //...

  Plot p;
  (p.*pmf)();

  //...
}

I'm here to prove you wrong.

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Re: Passing a member function pointer

Sep 6th, 2008

I actually don't have control over glutMouseFunc (I mean I suppose I could edit the glut source, but that sounds like a bad idea)

Why is it so much different to pass a member function than a normal function?

Is there no way to do this without overloading glutMouseFunc?

Thanks!

Dave

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Re: Passing a member function pointer

Sep 6th, 2008

•

Originally Posted by daviddoria

I actually don't have control over glutMouseFunc (I mean I suppose I could edit the glut source, but that sounds like a bad idea)

Why is it so much different to pass a member function than a normal function?

Is there no way to do this without overloading glutMouseFunc?

Thanks!

Dave

You could just overload the function to accept a pointer-to-member function.

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Re: Passing a member function pointer

Sep 6th, 2008

As I mentioned, I can't overload the function because it is not mine, it is in the glut library!

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Re: Passing a member function pointer

Sep 6th, 2008

Non-static member function always called for the object, not in itself. The glutMouseFunc does not know, which object used for member function call. So it's no sense to pass a member function pointer to glutMouseFunc: it can't use such a pointer.

In other words, a pointer to a function is an address but a pointer to a member function is (roughly speaking) an offset in a class member functions table. The gkutMouseFunc wants address only.

Last edited by ArkM; Sep 6th, 2008 at 3:51 pm.

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Re: Passing a member function pointer

Sep 6th, 2008

I see, that makes sense.

What I was trying to do was this:

make a Plot class that would have all mouse selection routines (like rotation and zooming) defined and have everything else for opengl setup but then have a virtual Display() function so the user can override what actually gets plotted.

How else would I go about doing this since I have to provide glutMouseFunc and glutDisplayFunc with function pointers to be used when those callbacks are called?

Thanks,
Dave

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Narue

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Re: Passing a member function pointer

Sep 6th, 2008

>How else would I go about doing
Use a static member function, or provide a non-member helper that does what you want.

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Re: Passing a member function pointer

Sep 6th, 2008

ok cool, i'll give it a try

thanks everyone

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Re: Passing a member function pointer

#10

Sep 10th, 2008

Hi all!
I have exactly the same problem! How can I solve it?
I tried to change the member function in a static member function, or to move the member function outside the class, or to use a global wrapper, or to use a delegate function, but I can not reach to a solution :-(

here is my simple code (using the static member function option):

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 C++ Syntax (Toggle Plain Text) 
class OGL {
   ...
   void init(void) {
      ...
      glutMouseFunc(mouse);
      ...
   }
   static void mouse(int button, int state, int x, int y) {
      ...
   }
   ...
}
class OGL {
   ...
   void init(void) {
      ...
      glutMouseFunc(mouse);
      ...
   }
   static void mouse(int button, int state, int x, int y) {
      ...
   }
   ...
}