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Every LabVIEW programmer has their own approach to handling errors.  In fact, those with multiple personalities probably have several different approaches to handling errors.  As an example, consider the producer-consumer diagram shown in '''Figure 8'''.


[[Image:Producer-consumer.PNG|center|thumb|600px|'''Figure 8''':  producer-consumer diagram with error handling in the top loop]]
This entire section of WIKI about "Error Handling" could benefit from a deep reading of the online help for the General Error Handler.vi. That VI has more facilities than folks typically know. FOR EXAMPLE:  
 
The “event loop” (bottom) produces enumerated commands that are processed by the “cmd loop” (top).  The outer case structure in the top loop traps for errors that are placed on the lower shift register.  The corresponding error case (not shown) allows error handling by “code” with different methods of notification.  For example, a user interface application based on this design pattern might employ the '''General Error Handler.vi''' shown in '''Figure 3''' to display a dialog for particular errors.  However, this method would not work for applications that run continuously without user interaction.
 
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| For continuously running applications, an error dialog (or any other kind of dialog for that matter) would disrupt execution, causing data loss or some other event you are being paid to avoid.  Logging error information to file is a useful notification method for such applications.  This approach requires an error description, which is provided by the '''Error Code Database.vi''' (see '''Figure 9''') for specified error codes in LabVIEW.
 
[[Image:Error_code_database_connector.jpg|frame|center|'''Figure 9''':  connector for the '''Error Code Database.vi''']]
 
This locked VI, located in the library <labview\vi.lib\Utility\error.llb>, is easily found as a subVI of the '''General Error Handler.vi'''.  You could extend this database to handle user defined error codes and provide some type of error log.  For example, some Windows applications log errors to the '''Event Viewer''' (right-click on '''My Computer''' and select '''Manage''' from the popup menu) shown in '''Figure 10''' and '''Figure 11'''.  The '''eventcreate''' command can be used in Windows to log events to this application.  A VI [http://forums.lavag.org/downloads.html&showfile=86 log event error] for logging errors to the '''Event Viewer''' is available.
 
|This entire section of WIKI about "Error Handling" could benefit from a deep reading of the online help for the General Error Handler.vi. That VI has more facilities than folks typically know. FOR EXAMPLE:  


The General Error Handler.vi includes an input parameter for the type of dialog, one option is "no dialog." I would STRONGLY recommended instead of calling "Error Code Database.vi". The primary reason for the recommendation is that the translation of error code cluster into human readable strings involves much more than just looking up text in the database. The '''source''' string itself may include information to override or extend the database, and the text in either the '''source''' string or the database may include formatting commands, such as HTML tags for bold face. Encoding information in the '''source''' string is a technique that will become more common in the future.  
The General Error Handler.vi includes an input parameter for the type of dialog, one option is "no dialog." I would STRONGLY recommended instead of calling "Error Code Database.vi". The primary reason for the recommendation is that the translation of error code cluster into human readable strings involves much more than just looking up text in the database. The '''source''' string itself may include information to override or extend the database, and the text in either the '''source''' string or the database may include formatting commands, such as HTML tags for bold face. Encoding information in the '''source''' string is a technique that will become more common in the future.  


You may desire to display the text, fully formatted, in a string indicator of your own instead of in any dialog. Use the function of General Error Handler CORE.vi (found on the block diagram of General Error Handler.vi) to do this.  
You may desire to display the text, fully formatted, in a string indicator of your own instead of in any dialog. Use the function of General Error Handler CORE.vi (found on the block diagram of General Error Handler.vi) to do this.  
|}
[[Image:Event_viewer.JPG|frame|center|'''Figure 10''':  '''Event Viewer''' in Windows]]
[[Image:Event_properties.jpg|frame|center|'''Figure 11''':'''Event Properties''' in Windows]]
<!-- Bill VanArsdale, 21:17, 3 May 2007 (CDT) -->


[[category:LabVIEW fundamentals]]
[[category:LabVIEW fundamentals]]

Revision as of 14:38, 14 October 2007

This article or section is currently being developed or reviewed.
Some statements may be disputed, incorrect, unverified, biased or otherwise objectionable. Please read the discussion thread before making substantial changes.

This entire section of WIKI about "Error Handling" could benefit from a deep reading of the online help for the General Error Handler.vi. That VI has more facilities than folks typically know. FOR EXAMPLE:

The General Error Handler.vi includes an input parameter for the type of dialog, one option is "no dialog." I would STRONGLY recommended instead of calling "Error Code Database.vi". The primary reason for the recommendation is that the translation of error code cluster into human readable strings involves much more than just looking up text in the database. The source string itself may include information to override or extend the database, and the text in either the source string or the database may include formatting commands, such as HTML tags for bold face. Encoding information in the source string is a technique that will become more common in the future.

You may desire to display the text, fully formatted, in a string indicator of your own instead of in any dialog. Use the function of General Error Handler CORE.vi (found on the block diagram of General Error Handler.vi) to do this.

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