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<tr><td width="100%" colspan="2" height="454">　<p align="center">[<a href="index.htm">回到开始</a>][<a href="7.htm">上一层</a>][<a href="140.htm">下一篇</a>]
<hr><p align="left"><small>发信人: strayli (stray), 信区: Delphi <br>

标  题: How to Circumvent the 'index not found' Exception <br>

发信站: BBS 水木清华站 (Fri Sep 18 13:11:43 1998) <br>

  <br>

  <br>

KEYWORDS: dbase dbf mdx index not found delphi AREA: All <br>

  <br>

Q: How do I open a dBASE table without the required MDX file? <br>

   I keep getting an "Index not found..." exception. <br>

  <br>

A: When you create a dBASE table with a production index (MDX), a <br>

   special byte is set in the header of the DBF file.  When you <br>

   subsequently attempt to re-open the table, the dBASE driver <br>

   will read that special byte, and if it is set, it will also <br>

   attempt to open the MDX file.  When the MDX file cannot be <br>

   opened, an exception is raised. <br>

  <br>

   To work around this problem, you need to reset the byte (byte <br>

   28 decimal) in the DBF file that causes the MDX dependency <br>

   to zero. <br>

  <br>

   The following unit is a simple example of how to handle the <br>

   exeption on the table open, reset the byte in the DBF file, <br>



   and re-open the table. <br>

  <br>

unit Fixit; <br>

  <br>

interface <br>

  <br>

uses <br>

  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, <br>

  Controls, Forms, Dialogs, StdCtrls, DB, DBTables, Grids, DBGrids; <br>

  <br>

type <br>

  TForm1 = class(TForm) <br>

    Table1: TTable; <br>

    Button1: TButton; <br>

    procedure Button1Click(Sender: TObject); <br>

  private <br>

    { Private declarations } <br>

  public <br>

    { Public declarations } <br>

  end; <br>

  <br>

var <br>

var <br>

  Form1: TForm1; <br>

  <br>

implementation <br>

  <br>

{$R *.DFM} <br>

  <br>

const <br>

  TheTableDir = 'c:\temp\'; <br>

  TheTableName = 'animals.dbf'; <br>

  <br>

procedure RemoveMDXByte(dbFile: String); <br>

{ This procedure accepts a DBF file as a parameter.  It will patch} <br>

{ the DBF header, so that it no longer requires the MDX file } <br>

const <br>

  Value: Byte = 0; <br>

var <br>

  F: File of byte; <br>

begin <br>

  AssignFile(F, dbFile); <br>

  Reset(F); <br>

  Seek(F, 28); <br>

  Write(F, Value); <br>



  CloseFile(F); <br>

end; <br>

  <br>

procedure TForm1.Button1Click(Sender: TObject); <br>

{ This procedure is called in response to a button click.  It    } <br>

{ attempts to open a table, and, if it can't find the .MDX file, } <br>

{ it patches the DBF file and re-execute the procedure to        } <br>

{ re-open the table without the MDX  } <br>

begin <br>

  try <br>

    { set the directory for the table } <br>

    Table1.DatabaseName := TheTableDir; <br>

    { set the table name } <br>

    Table1.TableName := TheTableName; <br>

    { attempt to open the table } <br>

    Table1.Open; <br>

  except <br>

    on E:EDBEngineError do <br>

      { The following message indicates the MDX wasn't found: } <br>

      if Pos('Index does not exist. File', E.Message)>0 then begin <br>

        { Tell user what's going on. } <br>

        MessageDlg('MDX file not found.  Attempting to open <br>

Attempting to open <br>

                    without index.', mtWarning, [mbOk], 0); <br>

        { remove the MDX byte from the table header } <br>

        RemoveMDXByte(TheTableDir + TheTableName); <br>

        { Send the button a message to make it think it was } <br>

        { pressed again.  Doing so will cause this procedure to } <br>

        { execute again, and the table will be opened without } <br>

        { the MDX } <br>

        PostMessage(Button1.Handle, cn_Command, bn_Clicked, 0); <br>

      end; <br>

  end; <br>

end; <br>

  <br>

end. <br>

  <br>

  <br>

  <br>

-- <br>

※ 来源:·BBS 水木清华站 bbs.net.tsinghua.edu.cn·[FROM: gps.auto.ustc.e] <br>

</small><hr>
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