Re: Button error

// 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 at the location :
      pDoc->m_dmaxA=m_dmaxA=dlg.m_dmaxA;
it said that :
Unhandled exception in GAS. exe :0xC0000005 ; Access Violation