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Error Handling (2)
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Visual Basic 6 -Error handling and Debugging and File Input/Output

Error Handling enables programmers to write clearer, more robust, more fault-tolerant programs. Error handling enables the programmer to attempt to recover (i.e., continue executing) from infrequent fatal errors rather than letting them occur and suffering the consequences (such as loss of application data). If an error is severe and recovery is not possible, the program can be exited "gracefully"-all files can be closed and notification can be given that the program is terminating. The recovery code is called an error handler.

Error handling is designed for dealing with synchronous errors such as an attempt to divide by 0 (that occurs as the program executes the divide instruction). Other common examples of synchronous errors are memory exhaustion, an out-of-bound array index, and arithmetic overflow. Error handling provides the programmer with a disciplined set of capabilities for dealing with these types of errors.

Error-handling code varies in nature and amount among software systems depending on the application and whether or not the software is a product for release. Products tend to contain much more error-handling code than is contained in "casual" software.

Usually, error-handling code is interspersed throughout a program's code. Errors are dealt with the places in the code where errors are likely to occur. The advantage of this approach is that a programmer reading the code can see the error handling in the immediate vicinity of the code and determine if the proper error handling has been implemented.

The problem with the scheme is that code in a sense becomes "polluted" with error handling. It becomes difficult for a programmer concerned with the application itself to read the code and determine if the code is working is correctly. Error handling often makes the code more difficult to understand and maintain.

When Error Handling should be used

Error handling should be used to process only exceptional situations, despite the fact that there is nothing to prevent that programmer from using errors as an alternate form of program control.

This lesson explains about error handling and debugging in easy steps with quick examples. For more in-depth lessons in Error Handling click here

Contents

Error Types

Run-Time Error Trapping and Handling

General Error Handling Procedure

             Example - Simple Error Trapping

Debugging Visual Basic Programs

             Example - Debugging Example

Using the Debugging Tools

Debugging Strategies

Sequential Files

Sequential File Output (Variables)

             Quick Example: Writing Variables to Sequential Files

Sequential File Input (Variables)

             Quick Example: Reading Variables from Sequential Files

Writing and Reading Text Using Sequential Files

Random Access Files

User-Defined Variables

Writing and Reading Random Access Files

Using the Open and Save Common Dialog Boxes

             Example - Note Editor - Reading and Saving Text Files

Exercise - Information Tracking

Exercise - ‘Recent Files’ Menu Option


  

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