How to solve these error " First-chance exception at..."

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when i click on OK button of my model dialog box, this code through these exception

First-chance exception at 0x78a4a924 (mfc90ud.dll) in myproject.exe: 0xC0000005: Access violation reading location 0x00000020.

and then i click BREAK the debug, code goes to wincore.cpp UpdateData method ..
Thanks in advanced.

[EDIT by Jochen Arndt: Text posted as solution]

when i changed the TAB in my app, this method will get called.
And i just want to create Model dialog while switching the tab. But i create Modeless dlg its working fine with Create()(without error).. and i just wanna to create model dialog(using DoMdal())

My method is...

C++

void ParentClassName::OnSelchange(NMHDR* pNMHDR, LRESULT* pResult)
{
    // Get the number of the currently selected tab, and show it
    ShowWindowNumber(m_cTab.GetCurFocus()); 
    if(m_cTab.GetCurFocus() == 1){      
        CModeless m_pmodeless;
        m_pmodeless.DoModal();    
    }                   
    pNMHDR = NULL;
    pResult = NULL;
}

Posted 16-Apr-15 1:35am

Member 11482033

Updated 16-Apr-15 3:03am

Jochen Arndt

v3

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Comments

Black_Rose 16-Apr-15 7:46am

Without seeing code it's not possible to help you..

Member 11482033 16-Apr-15 8:24am

when i changed the TAB in my app, this method will get called.
And i just want to create Model dialog while switching the tab. But i create Modeless dlg its working fine with Create()(without error).. and i just wanna to create model dialog(using DoMdal())

My method is...

void ParentClassName::OnSelchange(NMHDR* pNMHDR, LRESULT* pResult)
{
// Get the number of the currently selected tab, and show it

ShowWindowNumber(m_cTab.GetCurFocus());
if(m_cTab.GetCurFocus() == 1){
CModeless m_pmodeless;
m_pmodeless.DoModal();
}
pNMHDR = NULL;
pResult = NULL;
}

barneyman 16-Apr-15 7:52am

i'd GUESS you're trying to access a member 32 bytes into the vtable/offset of a class, when the instance is NULL; look at the stack trace, and work back to your codebase - should stick out like a zit

Leo Chapiro 16-Apr-15 8:00am

lets look into your source code, dude!

Member 11482033 16-Apr-15 8:24am

when i changed the TAB in my app, this method will get called.
And i just want to create Model dialog while switching the tab. But i create Modeless dlg its working fine with Create()(without error).. and i just wanna to create model dialog(using DoMdal())

My method is...

void ParentClassName::OnSelchange(NMHDR* pNMHDR, LRESULT* pResult)
{
// Get the number of the currently selected tab, and show it

ShowWindowNumber(m_cTab.GetCurFocus());
if(m_cTab.GetCurFocus() == 1){
CModeless m_pmodeless;
m_pmodeless.DoModal();
}
pNMHDR = NULL;
pResult = NULL;
}

Jochen Arndt 16-Apr-15 9:12am

"when i click on OK button of my model dialog box, this code through these exception"

So the error is probably in your CModeless class (UpdataData is called by CDialog::OnOK).

I have copied the text from your "solution" to the question because the solution may be reported by others as "Not a solution".

Please use the green 'Improve question' link to add additional information to your question. You might do this now to add the code of your CModeless class (if it has not too many lines).

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KarstenK · Answer 1 · 2015-04-17T07:32:00

It is a usual MFC-problem: control-ID in the resoure arent matching the IDs in the code. Sometimes helps an "Rebuild all". If not you must fizzle through the ID or set break point in the DoDataExchange routines.

Tip: deactive one tab after the other so you better find the problematic page.