c# ean 13 generator Visual Basic Code That Avoids gotos by Using a Status Variable in C#.NET

Encoding EAN13 in C#.NET Visual Basic Code That Avoids gotos by Using a Status Variable

Visual Basic Code That Avoids gotos by Using a Status Variable
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' This routine purges a group of files. Sub PurgeFiles( ByRef errorState As Error_Code ) Dim fileIndex As Integer Dim fileToPurge As Data_File Dim fileList As File_List Dim numFilesToPurge As Integer MakePurgeFileList( fileList, numFilesToPurge ) errorState = FileStatus_Success fileIndex = 0 While ( fileIndex < numFilesToPurge ) And ( errorState = FileStatus_Success ) fileIndex = fileIndex + 1 If Not FindFile( fileList( fileIndex ), fileToPurge ) Then errorState = FileStatus_FileFindError End If If ( errorState = FileStatus_Success ) Then If Not OpenFile( fileToPurge ) Then errorState = FileStatus_FileOpenError
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2 The While test has been changed to add a test for errorState.
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0 The status variable is tested.
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17. Unusual Control Structures
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End If End If If ( errorState = FileStatus_Success ) Then If Not OverwriteFile( fileToPurge ) Then errorState = FileStatus_FileOverwriteError End If End If If ( errorState = FileStatus_Success ) Then If Not Erase( fileToPurge ) Then errorState = FileStatus_FileEraseError End If End If Wend DeletePurgeFileList( fileList, numFilesToPurge ) End Sub
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6 The status variable is tested.
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2 The status variable is tested.
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The advantage of the status-variable approach is that it avoids the deeply nested if-then-else structures of the first rewrite and is thus easier to understand. It also places the action following the if-then-else test closer to the test than the nestedif approach did and completely avoids else clauses. Understanding the nested-if version requires some mental gymnastics. The status-variable version is easier to understand because it closely models the way people think about the problem. You find the file. If everything is OK, you open the file. If everything is still OK, you overwrite the file. If everything is still OK,... The disadvantage of this approach is that using status variables isn t as common a practice as it should be. Document their use fully, or some programmers might not understand what you re up to. In this example, the use of well-named enumerated types helps significantly.
Rewrite with try-finally Some languages, including Visual Basic and Java, provide a try-finally statement that can be used to clean up resources under error conditions.
To rewrite using the try-finally approach, enclose the code that would otherwise need to check for errors inside a try block, and place the cleanup code inside a finally block. The try block specifies the scope of the exception handling, and the finally block performs any resource cleanup. The finally block will always be called regardless of whether an exception is thrown and regardless of whether the PurgeFiles() routine Catches any exception that s thrown.
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17. Unusual Control Structures
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Visual Basic Code That Avoids gotos by Using Try-Finally
' This routine purges a group of files. Exceptions are passed to the caller. Sub PurgeFiles() Dim fileIndex As Integer Dim fileToPurge As Data_File Dim fileList As File_List Dim numFilesToPurge As Integer MakePurgeFileList( fileList, numFilesToPurge ) Try fileIndex = 0 While ( fileIndex < numFilesToPurge ) fileIndex = fileIndex + 1 FindFile( fileList( fileIndex ), fileToPurge ) OpenFile( fileToPurge ) OverwriteFile( fileToPurge ) Erase( fileToPurge ) Wend Finally DeletePurgeFileList( fileList, numFilesToPurge ) End Try End Sub
This approach assumes that all function calls throw exceptions for failures rather than returning error codes. The advantage of the try-finally approach is it achieves the visual simplicity of the goto approach without the use of gotos. It also avoids the deeply nested ifthen-else structures. The limitation of the try-finally approach is that it must be implemented consistently throughout a code base. If the code above was part of a code base that used both error codes and exceptions, the code would be required to set an error code for each possible error, and that requirement would make the code above about as complicated as the other approaches. In that context, the tryfinally structure wouldn t be decisively more attractive than the other approaches. A final limitation of this approach is that the try-finally statement is not available in all languages.
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