[GLUT] Pointers to class methods

This is a discussion on [GLUT] Pointers to class methods within the C++ Programming forums, part of the General Programming Boards category; I've created a little class which basically wraps up a little demo type thing I've written while following various GLUT ...

  1. #1
    Supermassive black hole cboard_member's Avatar
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    [GLUT] Pointers to class methods

    I've created a little class which basically wraps up a little demo type thing I've written while following various GLUT tutorials and I need to make the calls to the "glutXFunc" (eg. glutDisplayFunc) but I'm stumped on how to give it a class method as a parameter.

    Here's the function - initGLUT () - which attempts to do this:

    Code:
    void initGLUT ()
    {
            glutInitDisplayMode (GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
            glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
    
            glutInitWindowPosition (0, 0);
            glutInitWindowSize (640, 480);
            glutCreateWindow ("Engine Demo");
            glEnable (GL_DEPTH_TEST);
    
            glutDisplayFunc (engineDemo::render);  // problem line
    
            // haven't tackled these yet so ignore them
            glutReshapeFunc (reshape);
            glutIdleFunc (render);
            glutKeyboardFunc (normalKeys);
            glutSpecialFunc (specialKeys);
            glutMouseFunc (mousePress);
            glutPassiveMotionFunc (mousePassiveMotion);
    }
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  2. #2
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    The syntax is pretty tortured:
    Code:
    #include <iostream>
    #include <string>
    using namespace std;
    
    class Dog
    {
    public:
    	string bark(int num)
    	{
    		for(int i = 0; i<num; i++)
    			cout<<"Woof!";
    
    		cout<<endl;
    		
    		return "I finished barking.";
    	}
    };
    
    void someFunc(const Dog& aDog, string(Dog::*pDogFunc)(int) )
    {
    	string result = (aDog.*pDogFunc)(3);
    	cout<<result<<endl;
    }
    
    int main()
    {
    	Dog myDog;
    	string(Dog::*pFunc)(int) = Dog::bark;
    	someFunc(myDog, pFunc);
    
    	return 0;
    }
    Last edited by 7stud; 02-15-2006 at 02:51 PM.

  3. #3
    Supermassive black hole cboard_member's Avatar
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    Ok I've given it my best shot:

    Code:
    void initGLUT ()
    {
            void (engineDemo::*p_Render) (void) = engineDemo::render;
    
            glutInitDisplayMode (GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
            glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
    
            glutInitWindowPosition (0, 0);
            glutInitWindowSize (640, 480);
            glutCreateWindow ("Engine Demo");
            glEnable (GL_DEPTH_TEST);
    
            glutDisplayFunc (p_Render);
            glutReshapeFunc (reshape);
            glutIdleFunc (render);
            glutKeyboardFunc (normalKeys);
            glutSpecialFunc (specialKeys);
            glutMouseFunc (mousePress);
            glutPassiveMotionFunc (mousePassiveMotion);
    }
    EDIT: Oh yeah, the errors:

    Code:
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(283) : error C2664: 'glutDisplayFunc' : cannot convert parameter 1 from 'void (__thiscall engineDemo::* )(void)' to 'void (__cdecl *)(void)'
            There is no context in which this conversion is possible
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  4. #4
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    If you make the function inside the render class static you should be able to send it to glutDisplayFunc.

  5. #5
    Supermassive black hole cboard_member's Avatar
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    Ok I'll try that quick.
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  6. #6
    Supermassive black hole cboard_member's Avatar
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    It sort of worked. There were probs except I've had to make everything in the class static and the linker threw up unresolved externals because I forgot to type static in front of all the definitions, but when I did that I now get these:

    Code:
    ------ Build started: Project: glutProj, Configuration: Debug Win32 ------
    
    Compiling...
    glutProj.cpp
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(98) : error C2724: 'engineDemo::renderString' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(107) : error C2724: 'engineDemo::playSound' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(118) : error C2724: 'engineDemo::setOrthoProjection' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(143) : error C2724: 'engineDemo::resetPerspectiveProjection' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(151) : error C2724: 'engineDemo::render' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(188) : error C2724: 'engineDemo::reshape' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(208) : error C2724: 'engineDemo::normalKeys' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(221) : error C2724: 'engineDemo::specialKeys' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(243) : error C2724: 'engineDemo::mousePress' : 'static' should not be used on member functions defined at file scope
    c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(265) : error C2724: 'engineDemo::mousePassiveMotion' : 'static' should not be used on member functions defined at file scope
    
    Build Time 0:00
    Build log was saved at "file://c:\Documents and Settings\lee\Desktop\glutProj\Debug\BuildLog.htm"
    glutProj - 10 error(s), 0 warning(s)
    
    
    ---------------------- Done ----------------------
    
        Build: 0 succeeded, 1 failed, 0 skipped
    I've never had these before.
    Oh yeah I don't understand how making them static 'makes it work'?
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  7. #7
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    Ok I guess that what it looks like now is something like this:
    Code:
    class Foo
    {
    public:
    	static void Test();
    };
    
    static void Foo::Test()
    {
    	// Bla bla bla bla
    }
    if so change it to this:
    Code:
    class Foo
    {
    public:
    	static void Test();
    };
    
    void Foo::Test()  // Note that static is not preceeding void here
    {
    	// Bla bla bla bla
    }

  8. #8
    Supermassive black hole cboard_member's Avatar
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    OK so now the linker can't see the class member data:

    Code:
    ------ Build started: Project: glutProj, Configuration: Debug Win32 ------
    
    Compiling...
    glutProj.cpp
    Linking...
    glutProj.obj : error LNK2001: unresolved external symbol "private: static class FMOD::Sound * engineDemo::m_Sound" (?m_Sound@engineDemo@@0PAVSound@FMOD@@A)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static enum FMOD_RESULT engineDemo::m_Result" (?m_Result@engineDemo@@0W4FMOD_RESULT@@A)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static class FMOD::System * engineDemo::m_FMOD_System" (?m_FMOD_System@engineDemo@@0PAVSystem@FMOD@@A)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static char * engineDemo::m_FPS" (?m_FPS@engineDemo@@0PADA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static char * engineDemo::m_Buffer" (?m_Buffer@engineDemo@@0PADA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static int engineDemo::m_Timebase" (?m_Timebase@engineDemo@@0HA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static int engineDemo::m_Time" (?m_Time@engineDemo@@0HA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static int engineDemo::m_Frame" (?m_Frame@engineDemo@@0HA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static int engineDemo::m_Height" (?m_Height@engineDemo@@0HA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static int engineDemo::m_Width" (?m_Width@engineDemo@@0HA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static float engineDemo::m_Blue" (?m_Blue@engineDemo@@0MA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static float engineDemo::m_Green" (?m_Green@engineDemo@@0MA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static float engineDemo::m_Red" (?m_Red@engineDemo@@0MA)
    glutProj.obj : error LNK2001: unresolved external symbol "private: static float engineDemo::m_Angle" (?m_Angle@engineDemo@@0MA)
    Debug/glutProj.exe : fatal error LNK1120: 14 unresolved externals
    
    Build Time 0:00
    Build log was saved at "file://c:\Documents and Settings\lee\Desktop\glutProj\Debug\BuildLog.htm"
    glutProj - 15 error(s), 0 warning(s)
    
    
    ---------------------- Done ----------------------
    
        Build: 0 succeeded, 1 failed, 0 skipped
    EDIT: Here's the class:

    Code:
    class engineDemo {
            static float   m_Angle;
            static float   m_Red;
            static float   m_Green;
            static float   m_Blue;
            static char    m_Buffer[30];
            static int     m_Width;
            static int     m_Height;
            static int     m_Frame;
            static int     m_Time;
            static int     m_Timebase;
            static char    m_FPS[10];
    
            static FMOD_RESULT     m_Result;
            static FMOD::System    *m_FMOD_System;
            static FMOD::Channel   *m_Channel;
            static FMOD::Sound     *m_Sound;
    
    public:
            engineDemo ();
            ~engineDemo ();
    
            static void    renderString (float x, float y, void *font, char *str);
            static void    playSound ();
            static void    setOrthoProjection ();
            static void    resetPerspectiveProjection ();
            static void    render ();
            static void    reshape (int w, int h);
    
            // GLUT handler functions
            static void    normalKeys (unsigned char key, int x, int y);
            static void    specialKeys (int key, int x, int y);
            static void    mousePress (int button, int state, int x, int y);
            static void    mousePassiveMotion (int x, int y);
    
    };
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  9. #9
    carry on JaWiB's Avatar
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    Sounds like you need to define them outside the class:
    Code:
    float engineDemo::m_angle;
    float engineDemo::m_Red  = 10; //you can initialize them as well
    Still, it seems bad design to me to have a class full of static members. Maybe (and take what I say with a grain of salt because I'm no design expert) you want to use the singleton design pattern instead. In that case, you could have a single static instance of the class as a member, which would be used to access the data
    Code:
    class engineDemo
    {
    float m_Angle;
    //etc
    static engineDemo m_instance;
    public:
      static engineDemo* Instance() { return &m_instance; }
      static void render();
      //other methods could be non-static if they don't need to be
      //passed as arguments to functions
    }
    If you do a google search you'll find plenty of information on singletons
    "Think not but that I know these things; or think
    I know them not: not therefore am I short
    Of knowing what I ought."
    -John Milton, Paradise Regained (1671)

    "Work hard and it might happen."
    -XSquared

  10. #10
    Supermassive black hole cboard_member's Avatar
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    Right I've found a couple of good articles thru google and I'm going to get this singletonised!
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  11. #11
    Supermassive black hole cboard_member's Avatar
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    Ok so how do I define the member functions? Here's what I've got so far:

    Code:
    class Demo {
            float   m_Angle;
            float   m_Red;
            float   m_Green;
            float   m_Blue;
            char    m_Buffer[30];
            int     m_Width;
            int     m_Height;
            int     m_Frame;
            int     m_Time;
            int     m_Timebase;
            char    m_FPS[10];
    
            FMOD_RESULT     m_Result;
            FMOD::System    *m_FMOD_System;
            FMOD::Channel   *m_Channel;
            FMOD::Sound     *m_Sound;
    
    public:
            static Demo     *Instance ();
    
            static void     renderString (float x, float y, void *font, char *str);
            void            playSound ();
            void            setOrthoProjection ();
            void            resetPerspectiveProjection ();
            static void     render ();
            static void     reshape (int w, int h);
    
            // GLUT Handler functions
            static void     normalKeys (unsigned char key, int x, int y);
            static void     specialKeys (int key, int x, int y);
            static void     mousePress (int button, int state, int x, int y);
            static void     mousePassiveMotion (int x, int y);
    
    
    protected:
            Demo ();
            Demo (const Demo &);
            Demo &operator= (const Demo &);
    };
    And this is as far as I've gotten with implementation:

    Code:
    // playSound
    void playSound ()
    {
            m_Result = m_FMOD_System->playSound (FMOD_CHANNEL_FREE, m_Sound, false, 0);
            if (m_Result != FMOD_OK) {
                    MessageBox (0, "Error playing sound", "FMOD Error",
                                    MB_OK | MB_ICONEXCLAMATION);
                    exit (1);
            }
    }
    Errors:

    Code:
    ------ Build started: Project: engineDemo, Configuration: Debug Win32 ------
    
    Compiling...
    Demo.cpp
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(31) : error C2065: 'm_Result' : undeclared identifier
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(31) : error C2065: 'm_FMOD_System' : undeclared identifier
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(31) : error C2227: left of '->playSound' must point to class/struct/union
            type is ''unknown-type''
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(31) : error C2065: 'm_Sound' : undeclared identifier
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(32) : error C2679: binary '!=' : no operator found which takes a right-hand operand of type 'FMOD_RESULT' (or there is no acceptable conversion)
    c:\Documents and Settings\lee\Desktop\engineDemo\Demo.cpp(32) : error C3861: 'm_Result': identifier not found, even with argument-dependent lookup
    Generating Code...
    Compiling...
    engineDemo.cpp
    Generating Code...
    
    Build Time 0:00
    Build log was saved at "file://c:\Documents and Settings\lee\Desktop\engineDemo\Debug\BuildLog.htm"
    engineDemo - 6 error(s), 0 warning(s)
    
    
    ---------------------- Done ----------------------
    
        Build: 0 succeeded, 1 failed, 0 skipped
    Sorry to dump all this on the reader but I'm completely stumped.
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  12. #12
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    Do you have a separate header file?

    (class.h)

    Code:
    class whatever {
    public:
    //your methods and data here
    };
    (class.cpp)

    Code:
    #include "class.h"
    
    // your method implementations here
    Hope this doesn't sound stupid.

  13. #13
    Supermassive black hole cboard_member's Avatar
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    Yes I do have it in a .h & .cpp but I'd be surprised to learn that this is the problem
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  14. #14
    carry on JaWiB's Avatar
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    Don't you want:
    Code:
    void Demo::playSound ()
    {
            m_Result = m_FMOD_System->playSound (FMOD_CHANNEL_FREE, m_Sound, false, 0);
            if (m_Result != FMOD_OK) {
                    MessageBox (0, "Error playing sound", "FMOD Error",
                                    MB_OK | MB_ICONEXCLAMATION);
                    exit (1);
            }
    }
    "Think not but that I know these things; or think
    I know them not: not therefore am I short
    Of knowing what I ought."
    -John Milton, Paradise Regained (1671)

    "Work hard and it might happen."
    -XSquared

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