CString类型转换为long类型

CShanLingDlg *maindlg=(CShanLingDlg *)AfxGetApp()->m_pMainWnd;
int sel = maindlg->m_MySearch.m_GridSearch.GetSelectionMark();
CString m_FileSize;
m_FileSize = maindlg->m_MySearch.m_GridSearch.GetItemText(sel,1);
long filesize;
filesize=atol(m_FileSize.GetBuffer(m_FileSize.GetLength()));