急！MFC 文本读写的问题

我想只改写文本的第一行数据

 void EditView::WriteInTitle(CString strName, CString lpsz)
{
    CFile WriteFile;
    WriteFile.Open(strName, CFile::modeWrite | CFile::modeRead | CFile::typeBinary);

    CString subStr = "\r";   //要被删除的子串
    int index = lpsz.Find(subStr);
    while (index!= -1)
    {
       lpsz.Delete(index, subStr.GetAllocLength());
       index = lpsz.Find(subStr);
    }

    lpsz = lpsz + "\r\n";
    LPCTSTR s = lpsz.GetBuffer(lpsz.GetLength());
    WriteFile.Write(s, lpsz.GetLength()*sizeof(CHAR));
    WriteFile.Close();
}

但是我覆盖了第一行后，后面就乱码了。。
目测是写入长度出问题了。。应该是覆盖到了第二行的文字。
但是这里长度不对吗？为什么会超出第一行的文字长度？

 CString ReplaceFirstLine(CString s, CString newline)
{
    if (s.IsEmpty()) return newline;
    LPCTSTR sc = (LPCTSTR)s;
    int i;
    int p = -1; 
    for (i = 0; i < strlen(sc) - 1; i++)
    {
        if (sc[i] == '\r' && sc[i + 1] == '\n')
        {
            p = i;
            break;
        }
    }
    if (p == -1) return newline;
    return CString(newline + CString(sc + i));
}

void CApp2Dlg::OnButton1() 
{
    // TODO: Add your control notification handler code here
    CString str;
    CString t = "title";
    m_edit.GetWindowText(str);
    str = ReplaceFirstLine(str, t);
    m_edit.SetWindowText((LPCTSTR)str);
}

    CString subStr = "\r";   //要被删除的子串
    int index = lpsz.Find(subStr);
    while (index!= -1)
    {
       lpsz.Delete(index, subStr.GetAllocLength());
       index = lpsz.Find(subStr);
    }

这段代码是把数据内的换行符去掉，只在末尾加换行符。（因为每写入一次末尾都会加一个换行符）

代码没有考虑 \r 和 \r\n，如果 \r\n只Delete掉\r就破坏文本内容 了
Remarks

Call this member (CString::Delete) function to delete a character or characters from a string starting with the character at nIndex.