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📁 Visual C++与数据库的连接经典实例
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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the datasource name.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_DATATYPE

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_DataType

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the column's data type.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_NULLABLE

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Nullable

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control indicates whether the column supports nulls.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_OWNER

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Owner

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the table's owner.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_QUALIFIER

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Qualifier

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the table's qualifier.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_RADIX

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Radix

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the column's radix, if applicable.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_REMARKS

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Remarks

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows remarks on this column, if any.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_SCALE

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Scale

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the scale of the column, if applicable.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_TABLENAME

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_TableName

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the name of the table.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_TYPENAME

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_TypeName

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the column's data type, in character format.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_PRECISION

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Precision

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the precision of the column.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_LENGTH

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Length

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

int

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the length of the column.

</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

IDC_TABLE

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

m_Table

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

CString

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

This output control shows the name of the current table.</FONT>

</TABLE></CENTER><P>Although DOCDB can show information about columns in a table in a database, it's important to realize that not all ODBC drivers can return all the information. For example, in a text datasource (such as a CSV file), it isn't reasonable to have remarks, scale, or precision information. In fact, most ODBC drivers don't return all the information that DOCDB tries to display. Any information that is unavailable will be displayed as either a blank or a zero, depending on the variable's data type.

<BR>

<P>When Visual C++'s ClassWizard binds a variable to a control, it creates the code to initialize the variable and to actually transfer the variable's contents to the control. When there must be conversions (such as the conversion of integer variables to text for edit controls), the DDX_Text() macros take care of this conversion automatically.

<BR>

<P>In addition to binding variables to the controls (as described earlier), it's necessary to also have functions for the IDC_NEWDB button and the IDC_COLUMN combo box. Using ClassWizard (see Figure 22.2), create two functions. For the IDC_NEWDB button, create a function for the message BN_CLICKED. This function will be called each time the user clicks the New Database button. For the IDC_COLUMN button, create a function for the message CBN_SELCHANGE. This function will be called each time the user changes the current column in the table.

<BR>

<P><B><A HREF="22vcg02.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/22vcg02.gif">Figure 22.2. Functions bound to controls in DOCDB.</A></B>

<BR>

<P>The only changes you need to make to the code created by AppWizard are in DOCDBVW.CPP. You must add the functionality of the two functions created by ClassWizard. Listing 22.1 shows DOCDBVW.CPP. All the code that must be added appears in bold.

<BR>

<P>

<FONT COLOR="#000080"><B>Listing 22.1. DOCDBWV.CPP with added code.</B></FONT>

<BR>

<PRE>

<FONT COLOR="#000080">// docdbvw.cpp : implementation of the CDocdbView class

//

#include &quot;stdafx.h&quot;

#include &quot;docdb.h&quot;

#include &quot;docdbdoc.h&quot;

#include &quot;docdbvw.h&quot;

#include &quot;odbcmisc.h&quot;

#ifdef _DEBUG

#undef THIS_FILE

static char BASED_CODE THIS_FILE[] = __FILE__;

#endif

/////////////////////////////////////////////////////////////////////////////

// CDocdbView

IMPLEMENT_DYNCREATE(CDocdbView, CFormView)

BEGIN_MESSAGE_MAP(CDocdbView, CFormView)

    //{{AFX_MSG_MAP(CDocdbView)

    ON_BN_CLICKED(IDC_NEWDB, OnNewdb)

    ON_CBN_SELCHANGE(IDC_COLUMN, OnSelchangeColumn)

    //}}AFX_MSG_MAP

    // Standard printing commands

    ON_COMMAND(ID_FILE_PRINT, CFormView::OnFilePrint)

    ON_COMMAND(ID_FILE_PRINT_PREVIEW, CFormView::OnFilePrintPreview)

END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////

// CDocdbView construction/destruction

CDocdbView::CDocdbView()

    : CFormView(CDocdbView::IDD)

{

    //{{AFX_DATA_INIT(CDocdbView)

    m_Connect = &quot;&quot;;

    m_DataSource = &quot;&quot;;

    m_DataType = 0;

    m_Nullable = 0;

    m_Owner = &quot;&quot;;

    m_Qualifier = &quot;&quot;;

    m_Radix = 0;

    m_Remarks = &quot;&quot;;

    m_Scale = 0;

    m_TableName = &quot;&quot;;

    m_TypeName = &quot;&quot;;

    m_Precision = 0;

    m_Length = 0;

    m_Table = &quot;&quot;;

    m_DbmsVersion = &quot;&quot;;

    //}}AFX_DATA_INIT

    // TODO: Add construction code here

}

CDocdbView::~CDocdbView()

{

}
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