CFile 深入研究之 CFile::modeNoTruncate

原文：CFile 深入研究之 CFile::modeNoTruncate

即时通讯爱好者 NanShan 最近专注于研究 CFile 的各种问题，今天主要是 CFile::modeNoTruncate 相信研究。

CFile::modeNoTruncate Combine this value with modeCreate. If the file being created already exists, it is not truncated to 0 length. Thus the file is guaranteed to open, either as a newly created file or as an existing file. This might be useful, for example, when opening a settings file that may or may not exist already. This option applies to CStdioFile as well.

1. ////////////////////////////////////////////////////////
   
2. //读取注册文件。
   
3.     CString username;
   
4.     CFile file;
   
5.     file.Open(_T("user.dat"), CFile::modeRead|CFile::modeCreate|CFile::modeNoTruncate, NULL);//保留源文件内容。
   
6.     if (file.GetLength() == 0)
   
7.     {
   
8.         
   
9.         GetDlgItem(IDC_ENTER)->EnableWindow(FALSE);
   
10.         GetDlgItem(IDC_REGISTER)->EnableWindow(TRUE);
    
11.         MessageBox("您还没有注册，请点击注册按钮进行注册。");
    
12.     }
    
13.     else
    
14.     {
    
15.         GetDlgItem(IDC_ENTER)->EnableWindow(TRUE);
    
16.         GetDlgItem(IDC_REGISTER)->EnableWindow(FALSE);
    
17.     }
    
18.     file.Close();

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