Using Pointers

[thebarslider]

Dear All,

I have a problem with pointers. I have a pointer to a class that is used to call a function. Within the called function i wish to access a pointer that is declared in the class that contains the called function.

For example i have called the pointer to the class and this runs the following method:

void COneDlg::ChangeRecordingFrequency(double RecordingFrequency)
{
m_pWinTV->SetFrequency(RecordingFrequency);

}

Using the debugger i know that the function is called but my program breaks when i attempt to use the m_pWinTV pointer.

The following error is given on the break:

Unhandled exception at 0x00414c1e in One.exe: 0xC0000005: Access violation reading location 0xcdcdce41.

I know that the error comes from using the m_pWinTV pointer. Although this pointer is used by other functions in the method so i know it works.

I have tried calling the functions within the class and i still get the same problem. Therefore does the computer know that i'm trying to access this pointer from another pointer?

Does anyone know how i get around this problem?

Thank you again to anyone who helps.

Mark.

 

[palbano]

I know that the error comes from using the m_pWinTV pointer. Although this pointer is used by other functions in the method so i know it works.

I have tried calling the functions within the class and i still get the same problem. Therefore does the computer know that i'm trying to access this pointer from another pointer?

I just don't follow most of that,
this pointer is used by other functions in the method
is really confusing. What is the "value" of m_pWinTV at the time the error occurs?

certainly if m_pWinTV is NULL or even worse, invalid, you would get the error you are seeing.

-pete

 

[thebarslider]

Hey there,

Sorry, my post is really confusing. I have redesigned my code since i posted on here.

My program works like this: A thread is calling a function which executes at a given time. In the (thread called) function i wish to change a variable of an ActiveX control that is inserted into my dialog. I access functions in the ActiveX control i using the m_pWinTV pointer.

This pointer is initialised when the dialog is created. It is possible to set handler functions in the dialog class to access functions of the ActiveX control when a button is pressed.

For example:

void COneDlg::OnBnClickedButton4()
{
m_pWinTV->SetFrequency(105.8);

}

All i wish to do is execute the same function with a given parameter to SetFrequency when the thread tells me the time is correct to change the frequency.

I have attempted to do this by getting a pointer to OneDlg then passing the SetFrequency function a parameter.

Therefore the thread executes when the time is correct and runs a given function. The function includes a pointer to OneDlg and runs a function in OneDlg that attempts to excute code similar to the code given above. i.e. SetFrequency method.

I know the SetFrequency method is executed but i recieve an assertion failure error farer into the method. I dont understand why this is happening as i am able to change the Frequency with a button press (in the above example) using the same code.

I originally thought the problem arouse due to the thread calling member functions accross thread boundaries. So i changed the code so it posted a message to OneDlg instead but still recieved the same error.

Hope this makes it a little clearer, it is quite hard to explain i hope you understand.

Mark.

 

[thebarslider]

Hey everyone,

I have solved this problem so require no further help.

Thanks anyway to everyone.

Good luck with your programming.

Mark.