vcg18.htm

Visual C++与数据库的连接经典实例

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<FONT COLOR="#000080"><B>Table 18.4. Access macro actions that have exact Visual C++ counterparts.</B></FONT></CENTER>

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<CENTER><TABLE  BORDERCOLOR=#000040 BORDER=1 CELLSPACING=2 CELLPADDING=3 >

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

<I>Access Action</I>

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

<I>Purpose</I>

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

<I>Visual C++ Substitute</I>

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

Hourglass

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

Turns the mouse pointer into the hourglass shape.

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

Use the CCmdTarget::BeginWaitCursor() function.

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

MsgBox

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

Displays a message box with an optional title.

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

Use either AFXMessageBox() or ::MessageBox().

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

Quit

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

Exits the Access application.

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

Send a message to the application to quit. Typical AFX programs send a WM_COMMAND message with the ID_APP_EXIT parameter to simulate the selection of eXit from the main menu.

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

RunApp

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

Runs another Windows application.

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

Use LoadModule() to do this.

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

SendKeys

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

Sends keystrokes to the application that has the focus.

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

Send a WM_CHAR message.

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

Beep

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

Sounds the standard Windows message beep.

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

Use ::MessageBeep().</FONT>

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<FONT SIZE=4 COLOR="#FF0000"><B>Actions with No Direct Counterpart in Visual C++</B></FONT></CENTER></H4>

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<P>Table 18.5 lists the Access macro actions that have no direct equivalents in Visual C++. Some of the actions listed, such as RunMacro, StopMacro, and StopAllMacros, aren't applicable to Visual C++ because you convert all Access macros to Visual C++ functions. Menus you create in Visual C++'s resource edit menu windows substitute for Access menus created by the AddMenu action. There is no need to use the Echo False and Echo True actions in Visual C++ applications, because you don't need to inhibit screen repainting.

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<P>In cases where a macro action listed in Table 18.5 is applicable to Visual C++ programming methodology, a workaround usually exists or can be created with Visual C++ code. Some workarounds are simpler than others. You can use flags to selectively execute event-handling code to duplicate the effect of the CancelEvent action. On the other hand, a substantial amount of code and programming expertise are required to write a workaround for Visual C++'s lack of Access's TransferSpreadsheet action. However, you can use OLE Automation to export data to an Excel worksheet object and then save the worksheet.

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<FONT COLOR="#000080"><B>Table 18.5. Access macro actions with no direct Visual C++ counterparts.</B></FONT></CENTER>

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<CENTER><TABLE  BORDERCOLOR=#000040 BORDER=1 CELLSPACING=2 CELLPADDING=3 >

<TR>

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

<I>Access Action</I>

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

<I>Purpose</I>

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

<I>Visual C++ Workaround</I>

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

AddMenu

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

Adds a menu or submenu choice to a form and specifies the macro or function to execute.

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

Use the CMenu member functions such as InsertMenu().

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

ApplyFilter

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

Applies a WHERE clause filter to a Table or QueryDef object.

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Use CRecordSet::Close(), modify m_strFilter to specify the WHERE clause, and then use CRecordSet::Open() to reopen the recordset with the new query value.

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

CancelEvent

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

Cancels the event that initiated the macro execution.

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

End the function.

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

DoMenuItem

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

Executes a menu choice.

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

Call the OnItem() menu Item handler.

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

Echo

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

Halts repainting of most visible objects.

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

Not applicable. Ignore Echo actions.

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

GoToPage

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

Sets the focus to the first control of the specified page of a multipage form.

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

Not applicable. Multipage forms aren't supported.

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

Print (except forms)

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

Prints the specified datasheet.

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

Not applicable. Create your own printing code or use a report generator.

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

RunCode

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

Runs a specified Visual Basic for Applications function from a macro.

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

Not applicable. The closest equivalent is to call a function.

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

RunMacro

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

Runs a designated macro.

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

Not applicable. Macros aren't supported.

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

SelectObject,

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

Selects, copies, or

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

Not applicable to Visual

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

CopyObject, Rename

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

renames database objects.

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

Basic database objects.

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

SetWarnings

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

Enables or disables Access warning messages primarilyrelated to manipulating database objects.

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

Not applicable. Access warning messages don't appear.

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

ShowAllRecords

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

Removes filters applied to a Table or QueryDef object.

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

Use CRecordSet::Close(), modify m_strFilter to specify the WHERE clause, and then use CRecordSet::Open() to reopen the recordset with the new query value.

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

StopMacro, StopAllMacros

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

Stops execution of the current macro or all macros.

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

Not applicable. Macros aren't supported.

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

Transfer Database, Transfer Spreadsheet, TransferText

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

Imports data from or exports data to database tables, worksheets, or text files.

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

Must be accomplished with code. Use Visual C++'s file I/O instructions or OLE Automation.</FONT>

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<FONT SIZE=5 COLOR="#FF0000"><B>Importing Visual Basic for Applications Code into Visual C++ Modules</B></FONT></CENTER></H3>

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<P>Access's Visual Basic for Applications, the successor to Access Basic originally called Embedded Basic, is a direct descendant of Visual Basic. Visual Basic inherited most of its data-access functions from Access 1.0 (although much has been added since then), along with Access's Jet database engine. Visual C++, however, shares nothing significant with either Visual Basic for Applications or Visual Basic. The not-so-close relationship of the two languages makes importing Visual Basic for Applications code into Visual C++ modules a rather difficult task that often involves a significant amount of time and energy. The following sections describe the alterations to Visual Basic for Applications code that are necessary when you import Access functions into Visual C++ modules.

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<NOTE><B>NOTE</B>

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<BR>I don't want to imply by the preceding statements that it isn't feasible to convert Access's Visual Basic for Applications to Visual C++ code. I only want to point out that you should also consider the feasibility of rewriting the entire application from scratch.</NOTE>

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