Microsoft KB Archive/151321

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The information in this article applies to:


 * Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 5.0, 6.0
 * Visual FoxPro for Macintosh 3.0a
 * Microsoft FoxPro for Macintosh, version 2.6a
 * Microsoft FoxPro for UNIX, version 2.6
 * Microsoft FoxPro for Windows, version 2.6a
 * Microsoft FoxPro for MS-DOS, version 2.6a

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SUMMARY
FoxPro provides the ON ERROR command to allow programmers to trap for specific errors that occur within applications. This article describes how to use a generic error trapping routine and shows an example in the context of testing a table for exclusive use.

MORE INFORMATION
If certain FoxPro commands attempt to use a table that is not opened exclusively, these commands generate the error "Exclusive open of file is required." There are several Xbase commands that require the target table be opened exclusively. These commands include INDEX, INSERT [BLANK] (not INSERT SQL), PACK, REINDEX, MODIFY STRUCTURE, ALTER TABLE, and ZAP. The code example below illustrates a simple method of trapping this error and returning a custom message to the user. This basic example can be modified to handle other errors.

While the default FoxPro error contains useful information for a programmer, its appearance may be disconcerting to an end user. Since there is no command or function in FoxPro to report if a table is opened in shared mode by another machine, the user must attempt to open the table exclusively and trap for the error if the procedure is unsuccessful.

The following code example shows how to set up an ON ERROR routine to trap for error "110-Exclusive Open of File is Required", and report a more user- friendly error message. If the code runs on Microsoft Visual FoxPro for Windows, the MESSAGEBOX function returns the message to the user. If the code executes on FoxPro for Macintosh, MS-DOS, or UNIX, a WAIT WINDOW appears with the programmer's message. This example creates a table named Junk to demonstrate the concept, and then deletes it after trapping the error.

For more information on the options and parameters available with the MESSAGEBOX function, see the Visual FoxPro Help file.

Sample Code
  CREATE TABLE junk  (fld1 C(20)) FOR x = 1 to 2 INSERT INTO junk VALUES ("This is test data") ENDFOR

ON ERROR DO errhand WITH error &&  Activates ON ERROR routine

CLOSE ALL USE junk SHARE ZAP

PROCEDURE errhand PARAMETERS merror

IF merror =110 IF _windows=.t. and ATC("Visual",VERSION)>0 =MESSAGEBOX("This procedure requires exclusive use of the table. ;  Please try again ;   later.",48,"My Custom Messagebox Title") ELSE WAIT WINDOW "This procedure requires exclusive use of the table. ;  Try again later." ENDIF ENDIF

USE DELETE FILE Junk.dbf ON ERROR && Turns off ON ERROR routine The user can use the MESSAGEBOX function in FoxPro for Windows 2.x. However, the programmer must use the SET LIBRARY TO command to direct FoxPro to the FoxTools.fll file. Additionally, the user can use the FXALERT function to display the message on FoxPro for the Macintosh 2.x. For more information about the MESSAGEBOX and FXALERTfunctions in FoxPro 2.x versions, please see the following articles in the Microsoft Knowledge Base: "Q124717 HOWTO: Use the FXALERT Function in FOXTOOLS.MLB" "Q105006 HOWTO: Use the MsgBox Function in FOXTOOLS.FLL" Additional query words:

Keywords         : kbVFp300 kbVFp500 kbVFp600 kbVFP260 Version          : Platform         : Issue type       : kbhowto
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