error with function

This is a discussion on error with function within the C++ Programming forums, part of the General Programming Boards category; Hi, I am trying to write a function but keep getting an error when I try to build. I'm not ...

  1. #1
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    error with function

    Hi,

    I am trying to write a function but keep getting an error when I try to build. I'm not very experienced with c++ so I can't really figure out what the error means. The funcion is called like this:

    Code:
    nMarkerCount = netClient.GetMarkerCount();
    and it looks like this:

    Code:
    int BMLClient::GetMarkerCount(void)
    {
    	if (!m_bConnected) return 0; //??
    
    	long cmd = 3;
    	if (!Send(&cmd, sizeof(cmd)))
    	{
    		std::cout << "Unable to send <get marker data> command" << std::endl;
    		return false;
    	}
    	long count;
    	if (!Recv(&count,sizeof(count)))
    	{
    		std::cout << "Unable to get marker count" << std::endl;
    		return false;
    	}
    	m_nMarkerCount = count;
    	m_buffer = new double[count*3];
    	m_bConnected = true;
    	return m_nMarkerCount;
    }
    I have declared it as public in the header file like this:

    Code:
    int GetMarkerCount(void);
    The error that I get says: error C2662: 'BMLClient::GetMarkerCount' : cannot convert 'this' pointer from 'const BMLClient' to 'BMLClient &'


    Can anyone tell from what I've posted what this error means? Thanks!

  2. #2
    Cat without Hat CornedBee's Avatar
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    If the line in the header file is within a class, you're probably calling the function on a const object. How is netClient declared?
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  3. #3
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    This probably isn't causeing that error but I can see two places where you're returning a bool instead of an int.

  4. #4
    System Novice siavoshkc's Avatar
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    Send the class definition code if possible.
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  5. #5
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    netClient is declared as:

    Code:
    protected:
    	BMLClient netClient;
    in this class:
    Code:
    class BMLDrawable: public osg::Drawable
    i'm not sure what you mean by the class definition code....what else do i need to post?

  6. #6
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    Post your .h where your class is defined.

    If your GetMarkerCount(void) function is defined within the BMLDrawable class you need to say...

    Code:
    int BMLDrawable::GetMarkerCount(void)
    {
    // stuff
    }
    Last edited by Peter5897; 07-26-2006 at 01:05 PM.

  7. #7
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    ok hopefully this is the one

    Code:
    #pragma once
    #include <winsock2.h>
    #include "Vector3.h"
    
    class BMLClient
    {
    public:
    	BMLClient(void);
    	virtual ~BMLClient(void);
    
    	bool Connect(void);
    	void Disconnect(void);
    	bool isConnected(void) const { return m_bConnected; }
    	int GetMarkerCount(void);
    	void GetFrame(CVector3* buf) const;
    
    protected:
    	bool m_bConnected;				// true when connection to server established successfully
    	int m_nMarkerCount;				// number of targets being tracked
    	SOCKET m_socket;				// network socket connection to BML server
    	double *m_buffer;				// buffer for frame data
    
    	bool Send(void* buf, long size) const;
    	bool Recv(void* buf, long size) const;
    };

  8. #8
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    >> nMarkerCount = netClient.GetMarkerCount();

    The place that the function call above is made is probably inside a BMLDrawable member function, right? If so, then is that member function const? Show the declaration of the function that contains the line above.

  9. #9
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    yup it's a const....here it is:

    Code:
    void BMLDrawable::drawImplementation (osg::State& state) const
    {
    	if (!netClient.isConnected()) return;
    
    	nMarkerCount = netClient.GetMarkerCount();
    
    	// draw a sphere at each joint
    	glColor3fv(red);
    	glEnable(GL_LIGHTING);
    	for (int m=0; m<nMarkerCount; m++)
    		GenSphere(frameData[m],BALL_RADIUS);
    	
    	// get next batch of frame data
    	netClient.GetFrame(frameData);
    }

  10. #10
    (?<!re)tired Mario F.'s Avatar
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    There you go!
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  11. #11
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    ok maybe this is stupid but i'm still not really sure how to fix this

  12. #12
    (?<!re)tired Mario F.'s Avatar
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    Well.. what is happening, and Daved so cleverly guessed at, is that you are calling GetMarkerCount() which alters data members of your class from within a const member function named drawImplementation(). So...

    drawImplementation() is really not a const function is it?

    remove the const from both the declaration and definition and it should be ok
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  13. #13
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    hmmm yea that's the first thing i tried but it's giving me more errors in this class:

    Code:
    class BMLDrawable: public osg::Drawable {
    public:
    	BMLDrawable();
    	virtual ~BMLDrawable();
    
    	virtual osg::Object* cloneType() const
    	{
    		return new BMLDrawable();
    	}
    
    	virtual osg::Object* clone(const osg::CopyOp&) const
    	{
    		return new BMLDrawable();
    	}
    
    	bool computeBound() const;
    	virtual void drawImplementation(osg::State& state);
    
    protected:
    	BMLClient netClient;
    	CVector3 *frameData;
    	int nMarkerCount;
    	GLuint nSphere;
    	void GenSphere (CVector3 &center, GLfloat radius) const;
    };
    the errors say "error C2259: 'BMLDrawable' : cannot instantiate abstract class"

    any clue what that means?

  14. #14
    (?<!re)tired Mario F.'s Avatar
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    I think that instead you just solved a problem and it is now detecting another.

    Does osg::Object have any pure virtual functions? And if so... are all of them being defined in BMLDrawable?
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  15. #15
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    i'm not really sure what a pure virtual function is...how would i know?

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