VC++怎么取得父窗口变量的东西

父窗口dlg1 中打开 dlg2 时，dlg2 能修改 dlg1 中的成员变量

//dlg1.cpp
#include "dlg2.h"
CDlg1::OnButton1()
{
CDlg2 dlg2;
dlg2.m_pDlg1 = this;
dlg2.DoModal();
}

//dlg2.h
class CDlg1;//添加dlg1类的声明
class CDlg2 : public CDialog
{
...
public:
CDlg1 *m_pDlg1;
}

BOOL CDlg2 ::OnInitDialog()
{
  …

//初始化
 dlg = (CDlg1*)this->GetParent();

 …

}

//dlg2.cpp
#include "dlg1.h"