Variable/object validity check

 

　InGenerally, the ASSERT (x) macro is used to check the validity of variables in VC. The role of ASSERT is to check whether the expression is false or NULL. If the expression is false, an exception is thrown. In MFC, The ASSERT macro is widely used, for example:

BOOL CWnd: Attach (HWND hWndNew)
  

{
  

ASSERT (m_hWnd = NULL );// Only attach once, detach on
  

Destroy
  

//...
  

Return TRUE;
  

}
  

Void CString: AllocBuffer (int nLen)
  

{
  

ASSERT (nLen> = 0 );
  

ASSERT (nLen <= INT_MAX-1 );//
  

}
  

Void CDocument: AddView (CView * pView)
  

{
  

// Other code...
  

ASSERT (pView-> m_pDocument = NULL );
  

ASSERT (m_viewList.Find (pView, NULL) = NULL );
  

}
  

WhenWhen the ASSERT fails and an exception is thrown, a dialog box is displayed and the location where the ASSERT fails is reported. The error message is assertion failed in file <THIS_FILE> in line <__line __>.