Re: Access Violation errors

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 25 May 2006 08:10:42 -0400

Message-ID:

<uobe4Q$fGHA.3916@TK2MSFTNGP04.phx.gbl>

liuerbin2000@163.com wrote:

// GASDoc.h : interface of the CGASDoc class
CGASDoc : public CDocument
{
public:
    int m_dmaxA;
.......
}

// A.h : header file
#include"GASDoc.h"
class CA: public CDialog
{
public:
    CGASDoc* pDoc;
    void someaction();
    int m_dmaxA;
}

// B.h : header file
class CB : public CDialog
{
// Dialog Data
    //{{AFX_DATA(CB)
    enum { IDD = IDD_B };
    int m_dmaxA;
    //}}AFX_DATA

//A.cpp
void CA::someaction()
{

    CB dlg;
    if(dlg.DoModal()==IDOK)
    {
          pDoc->m_dmaxA=m_dmaxA=dlg.m_dmaxA;
             }

}

its all right when compiling , but , when runing it has a wrong .
Usingthe debug tool , i find it stop in the location :
       pDoc->m_dmaxA=m_dmaxA=dlg.m_dmaxA;
it said that :
Unhandled exception in GAS. exe :0xC0000005 ; Access Violation

liuerbin:

If you must access the document from the dialog (not a good design in my
opinion) then pass the document pointer in the constructor:

//A.h

// #include "GASDoc.h" is not needed here
class CGASDoc; // forward declaration

class CA: public CDialog
{
public:
   DA(CGASDoc* pDoc);
private:
   CGASDoc* m_pDoc;
   void someaction();
   int m_dmaxA;
};

// A.cpp

CA::CA(CGASDoc* pDoc):
m_pDoc(pDoc)
{
}

Now you can use m_pDoc in your CA class.

Also, do not use public memmber variables in CGASDoc, but write a
method, e.g.

void CGASDoc::SetMaxA(int dmaxA)
{
   m_dmaxA = dmaxA;
   UpdateAllViews(NULL);
}

David Wilkinson