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<title>10.4 CDatabase类</title>
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</center></div><font FACE="Times New Roman" SIZE="3"><b><p ALIGN="CENTER"></b></font><font color="#3973DE" FACE="Times New Roman" size="4">10.4 CDatabase</font><font color="#3973DE" size="4">类</font><font FACE="Times New Roman" size="4"></p>
</font><font size="4"><p ALIGN="JUSTIFY"></font><font SIZE="3">要建立与数据源的连接，首先应构造一个</font><font FACE="Times New Roman" SIZE="3">CDatabase</font><font SIZE="3">对象，然后再调用</font><font FACE="Times New Roman" SIZE="3">CDatabase</font><font SIZE="3">的</font><font FACE="Times New Roman" SIZE="3">Open</font><font SIZE="3">成员函数．</font><font FACE="Times New Roman" SIZE="3">Open</font><font SIZE="3">函数负责建立连接，其声明为</font><font FACE="Times New Roman" SIZE="3"></p>
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<p ALIGN="JUSTIFY">virtual BOOL Open( LPCTSTR lpszDSN, BOOL bExclusive = FALSE, BOOL
bReadOnly = FALSE, LPCTSTR lpszConnect = </font><font SIZE="3">“</font><font FACE="Times New Roman" SIZE="3">ODBC;</font><font SIZE="3">”</font><font FACE="Times New Roman" SIZE="3">, BOOL bUseCursorLib = TRUE ); throw( CDBException,
CMemoryException );</p>
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<p><font SIZE="3"> </p>
<p ALIGN="JUSTIFY">参数</font><font FACE="Times New Roman" SIZE="3">lpszDSN</font><font SIZE="3">指定了数据源名（构造数据源的方法将在后面介绍），在</font><font FACE="Times New Roman" SIZE="3">lpszConnect</font><font SIZE="3">参数中也可包括数据源名，此时</font><font FACE="Times New Roman" SIZE="3">lpszDSN</font><font SIZE="3">必需为</font><font FACE="Times New Roman" SIZE="3">NULL</font><font SIZE="3">，若在函数中未提供数据源名且使</font><font FACE="Times New Roman" SIZE="3">lpszDSN</font><font SIZE="3">为</font><font FACE="Times New Roman" SIZE="3">NULL</font><font SIZE="3">，则会显示一个数据源对话框，用户可以在该对话框中选择一个数据源．参数</font><font FACE="Times New Roman" SIZE="3">bExclusive</font><font SIZE="3">说明是否独占数据源，由于目前版本的类库还不支持独占方式，故该参数的值应该是</font><font FACE="Times New Roman" SIZE="3">FALSE</font><font SIZE="3">，这说明数据源是被共享的．参数</font><font FACE="Times New Roman" SIZE="3">bReadOnly</font><font SIZE="3">若为</font><font FACE="Times New Roman" SIZE="3">TRUE</font><font SIZE="3">则对数据源的连接是只读的．参数</font><font FACE="Times New Roman" SIZE="3">lpszConnect</font><font SIZE="3">指定了一个连接字符串，连接字符串中可以包括数据源名、用户帐号</font><font FACE="Times New Roman" SIZE="3">(ID)</font><font SIZE="3">和口令等信息，字符串中的＂</font><font FACE="Times New Roman" SIZE="3">ODBC</font><font SIZE="3">＂表示要连接到一个</font><font FACE="Times New Roman" SIZE="3">ODBC</font><font SIZE="3">数据源上．参数</font><font FACE="Times New Roman" SIZE="3">bUseCursorLib</font><font SIZE="3">若为</font><font FACE="Times New Roman" SIZE="3">TRUE</font><font SIZE="3">，则会装载光标库，否则不装载，快照需要光标库，动态集不需要光标库．
若连接成功，函数返回</font><font FACE="Times New Roman" SIZE="3">TRUE</font><font SIZE="3">，若返回</font><font FACE="Times New Roman" SIZE="3">FALSE</font><font SIZE="3">，则说明用户在数据源对话框中按了</font><font FACE="Times New Roman" SIZE="3">Cancel</font><font SIZE="3">按钮。若函数内部出现错误，则框架会产生一个异常。</font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY"></font><font SIZE="3">下面是一些调用</font><font FACE="Times New Roman" SIZE="3">Open</font><font SIZE="3">函数的例子。</font><font FACE="Times New Roman" SIZE="3"></p>
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<p ALIGN="JUSTIFY">CDatabase m_db; //</font><font SIZE="3">在文档类中嵌入一个</font><font FACE="Times New Roman" SIZE="3">CDatabase</font><font SIZE="3">对象</font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY"></font><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY">//</font><font SIZE="3">连接到一个名为＂</font><font FACE="Times New Roman" SIZE="3">Student Registration</font><font SIZE="3">＂的数据源</font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY">m_db.Open("Student Registration"); </p>
<p ALIGN="JUSTIFY"></font><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY">//</font><font SIZE="3">在连接数据源的同时指定了用户帐号和口令</p>
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</font><font FACE="Times New Roman" SIZE="3"><p ALIGN="JUSTIFY">m_db.Open(NULL,FALSE,FALSE,"ODBC;DSN=Student
Registration;UID=ZYF;PWD=1234");</p>
<p ALIGN="JUSTIFY">m_db.Open(NULL); //</font><font SIZE="3">将弹出一个数据源对话框</font></p>
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<p><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p ALIGN="JUSTIFY"></font><font SIZE="3">要从一个数据源中脱离，可调用函数</font><font FACE="Times New Roman" SIZE="3">Close</font><font SIZE="3">。在脱离后，可以再次调用</font><font FACE="Times New Roman" SIZE="3">Open</font><font SIZE="3">函数来建立一个新的连接．调用</font><font FACE="Times New Roman" SIZE="3">IsOpen</font><font SIZE="3">可判断当前是否有一个连接，调用</font><font FACE="Times New Roman" SIZE="3">GetConnect</font><font SIZE="3">可返回当前的连接字符串。函数的声明为</p>
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</font><font FACE="Times New Roman" SIZE="3"><p ALIGN="JUSTIFY">virtual void Close( );</p>
<p ALIGN="JUSTIFY">BOOL IsOpen( ) const; //</font><font SIZE="3">返回</font><font FACE="Times New Roman" SIZE="3">TRUE</font><font SIZE="3">则表明当前有一个连接</p>
</font><font FACE="Times New Roman" SIZE="3"><p ALIGN="JUSTIFY">const CString&
GetConnect( ) const;</p>
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<p ALIGN="JUSTIFY">CDatabase</font><font SIZE="3">的析构函数会调用</font><font FACE="Times New Roman" SIZE="3">Close</font><font SIZE="3">，所以只要删除了</font><font FACE="Times New Roman" SIZE="3">CDatabase</font><font SIZE="3">对象就可以与数据源脱离。</font><font FACE="Times New Roman" SIZE="3"></p>
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<p align="center"></font><font size="2" color="#000000">本教程由<a href="http://vcdynasty.yeah.net">Visual C++王朝（Where programmers come together）</a>协助制作<br>
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