MFC突然写入不了txt怎么回事

void CGzfDlg::Onzhuche()
{
CFile WriteFile;
WriteFile.Open("e://代码//3//xinxi.txt",CFile::modeRead);
CString username;
CString psd;
CString s;
GetDlgItemText(IDC_EDIT1,username);
GetDlgItemText(IDC_EDIT2,psd);
if(!(username.GetLength()*psd.GetLength()))
{
MessageBox("请输入完整信息!","通知");
}
else
{
s = "账户："+username + "密码：" + psd+"\r\n";
}
WriteFile.SeekToEnd();
WriteFile.Write((LPCTSTR)s, s.GetLength());
MessageBox("恭喜注册成功","通知");
WriteFile.Close();

// TODO: Add your control notification handler code here

}

题目中是对文件进行 写 操作

 WriteFile.Open("e://代码//3//xinxi.txt",CFile::modeRead); //换成CFile::modeReadWrite

用心回答每个问题，如果有帮助，请采纳答案好吗，谢谢~~~

 WriteFile.Open("e://代码//3//xinxi.txt",CFile::modeRead | CFile::modeReadWrite);