[SOLVED] Function pointers to class members, cpp

brazilnut · 05-23-2010, 02:22 PM

Hi, i'm a bit stuck playing with the following class setup for glut. The actual issue is with the function pointers.

Basically the following code is the opengl redbook cube example slightly modified...

Quote:

/*
* Copyright (c) 1993-1997, Silicon Graphics, Inc.
* ALL RIGHTS RESERVED
*/

Code:

#include <GL/glut.h>
#include <stdlib.h>

using namespace std;

class myApp
{

public:
	
	myApp(int argc, char** argv)
	{
		glutInit(&argc, argv);
		glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
		glutInitWindowSize (500, 500); 
		glutInitWindowPosition (100, 100);
		glutCreateWindow (argv[0]);
		init ();
		glutDisplayFunc(display); 
		glutReshapeFunc(reshape);
		glutKeyboardFunc(keyboard);
		glutMainLoop();
	}
	
	void init(void) 
	{
		glClearColor (0.0, 0.0, 0.0, 0.0);
		glShadeModel (GL_FLAT);
	}
	
	void display(void)
	{
		glClear (GL_COLOR_BUFFER_BIT);
		glColor3f (1.0, 1.0, 1.0);
		glLoadIdentity();
		gluLookAt(0.0,0.0,5.0,0.0,0.0,0.0,0.0,1.0,0.0);
		glScalef (1.0, 2.0, 1.0);
		glutWireCube (1.0);
		glFlush ();
	}
	
	void reshape (int w, int h)
	{
		glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
		glMatrixMode (GL_PROJECTION);
		glLoadIdentity ();
		glFrustum (-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
		glMatrixMode (GL_MODELVIEW);
	}
	
	void keyboard(unsigned char key, int x, int y)
	{
		switch (key) {
			case 27:
				exit(0);
				break;
		}
	}

};

int main(int argc, char** argv)
{
	myApp app(&argc, argv);
	
	return 0;
}

Thanks...

oops...

Code:

g++ -Wall -I/usr/include/ -L/usr/X11R6/lib -lX11 -lXi -lXmu -lglut -lGL -lGLU -lm cube.cpp -o cube

johnsfine · 05-23-2010, 05:39 PM

Non static member functions of a class cannot be called without using an object of that class.

So the address of such a function is not the same data type as the address of an ordinary function whose signature looks the same.

If you don't want to involve an object of the class, then you can make the functions static class members, then the data type of the address of the function would be the same as the data type as that of an ordinary (non member) function with the same signature.

If you do want to involve an object of the class, things get a bit more complicated. You would need to think through the desired behavior before it would make any sense to start digging into the tricky syntax of bind member function.

brazilnut · 05-26-2010, 10:18 AM

Hi,

Thanks for your reply (I have thanked, even though it doesn't seem to work for me)...

I did try the static method before posting but it didn't work, I kept on getting the same errors. After your post I tried statics again (using above demo) and hey it worked, so I expanded out into properly defined classes (h + cpp) and I got the errors again...

After a little more searching I see that you don't use the static keyword on the function body, only the declaration.

So yes, learnt something new...

Thanks again :-)