Error Handling In Vba Function
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Error Handling In Vba Excel
just like you, helping each other. Join them; it only takes a minute: Sign up VBA Excel Error Handling - especially in functions - Professional Excel Development Style up vote 5 down vote favorite 4 I
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got the book "Professional Excel Development" by Rob Bovey and it is opening up my eyes. I am refitting my code with error handling. However, there is a lot I don't understand. I especially need to know how to correctly use it in functions. I use Bovey's rethrow version of the error handler (at bottom). When I started, I was using the basic boolean (non-rethrow) method and turned my subroutines into boolean functions. (P.S. vba error handling best practices I am switching back to the boolean method based on the answer.) I need guidance on how to fit functions into this scheme. I want them to return their real values (a string or double, e.g., or -1 if they fail in some cases) so I can nest them in other functions and not just return an error handling boolean. This is what a typical subroutine call to bDrawCellBorders(myWS) would look like within an entry point. Sub calls seem to be working well. (I.e. it is a subroutine that was turned into a function only so it can return a boolean to the error handling scheme.) Sub UpdateMe() ' Entry Point Const sSOURCE As String = "UpdateMe()" On Error GoTo ErrorHandler Set myWS = ActiveCell.Worksheet Set myRange = ActiveCell myWS.Unprotect ' lots of code If Not bDrawCellBorders(myWS) Then ERR.Raise glHANDLED_ERROR ' Call subroutine ' lots of code ErrorExit: On Error Resume Next Application.EnableEvents = True myWS.Protect AllowFormattingColumns:=True Exit Sub ErrorHandler: If bCentralErrorHandler(msMODULE, sSOURCE,,True) Then ' Call as Entry Point Stop Resume Else Resume ErrorExit End If End Sub However, I don't know how to extend this to real functions. This is based off an example in the book that was drawn up for a subroutine, and I just switched it to a function. Questions: * How do I call it?
a full version of Access, while a run-time version just crashes. For a more detailed approach to error handling, see vba error handling exit sub FMS' article on Error Handling and Debugging. The simplest approach is to vba error handling display message display the Access error message and quit the procedure. Each procedure, then, will have this format (without vba error handling line number the line numbers): 1 Sub|Function SomeName() 2 On Error GoTo Err_SomeName ' Initialize error handling. 3 ' Code to do something here. 4 Exit_SomeName: ' Label to resume after http://stackoverflow.com/questions/19042604/vba-excel-error-handling-especially-in-functions-professional-excel-developm error. 5 Exit Sub|Function ' Exit before error handler. 6 Err_SomeName: ' Label to jump to on error. 7 MsgBox Err.Number & Err.Description ' Place error handling here. 8 Resume Exit_SomeName ' Pick up again and quit. 9 End Sub|Function For a task where several things could go wrong, lines 7~8 will be replaced with more detail: Select Case http://allenbrowne.com/ser-23a.html Err.Number Case 9999 ' Whatever number you anticipate. Resume Next ' Use this to just ignore the line. Case 999 Resume Exit_SomeName ' Use this to give up on the proc. Case Else ' Any unexpected error. Call LogError(Err.Number, Err.Description, "SomeName()") Resume Exit_SomeName End Select The Case Else in this example calls a custom function to write the error details to a table. This allows you to review the details after the error has been cleared. The table might be named "tLogError" and consist of: Field Name Data Type Description ErrorLogID AutoNumber Primary Key. ErrNumber Number Long Integer. The Access-generated error number. ErrDescription Text Size=255. The Access-generated error message. ErrDate Date/Time System Date and Time of error. Default: =Now() CallingProc Text Name of procedure that called LogError() UserName Text Name of User. ShowUser Yes/No Whether error data was displayed in MsgBox Parameters Text 255. Optional. Any parameters you wish to record. Below is a procedure for writing to this table. It optionally allows recording the value of any variables/parameters at the time
- Macro Comments VBA - Message Box VBA - Input Box VBA - Variables VBA - Constants VBA - Operators VBA - Decisions VBA - Loops VBA - Strings VBA - Date and Time VBA - Arrays VBA - Functions VBA - https://www.tutorialspoint.com/vba/vba_error_handling.htm SubProcedure VBA - Events VBA - Error Handling VBA - Excel Objects VBA - Text http://excelatfinance.com/xlf/xlf-vba-function-error-handler.php Files VBA - Programming Charts VBA - Userforms VBA Useful Resources VBA - Quick Guide VBA - Useful Resources VBA - Discussion Selected Reading Developer's Best Practices Questions and Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who VBA - Error Handling Advertisements Previous Page Next Page There are three types of errors in programming: (a) Syntax Errors and error handling (b) Runtime Errors (c) Logical Errors. Syntax errors Syntax errors, also called parsing errors, occur at interpretation time for VBScript. For example, the following line causes a syntax error because it is missing a closing parenthesis: Function ErrorHanlding_Demo() dim x,y x = "Tutorialspoint" y = Ucase(x End Function Runtime errors Runtime errors, also called exceptions, occur during execution, after interpretation. For example, the following line causes a runtime error because here syntax is correct but at runtime it is vba error handling trying to call fnmultiply, which is a non-existing function: Function ErrorHanlding_Demo1() Dim x,y x = 10 y = 20 z = fnadd(x,y) a = fnmultiply(x,y) End Function Function fnadd(x,y) fnadd = x+y End Function Logical errors Logic errors can be the most difficult type of errors to track down. These errors are not the result of a syntax or runtime error. Instead, they occur when you make a mistake in the logic that drives your script and you do not get the result you expected. You can not catch those errors, because it depends on your business requirement what type of logic you want to put in your program. For example, dividing a number by zero or a script that is written which enters into infinite loop. Err Object Assume if we have a runtime error, then the execution stops by displaying the error message. As a developer, if we want to capture the error, then Error Object is used. Example In the below example, Err.Number gives the error number and Err.Description gives error description. Err.Raise 6 ' Raise an overflow error. MsgBox "Error # " & CStr(Err.Number) & " " & Err.Description Err.Clear ' Clear the error. Error Handling VBA Enables an error-handling routine and can also be used to disable an error-handling routine. Without an On Error statement, any run-time error that occurs is fatal: an error message is displayed, and execution
a number, with the error raised when divide by zero occurs. Three variations of the function are developed in Code panes 1, 2, and 3. Without any specific error handling, all three return a #VALUE! error when used as worksheet functions. The analyst wants to replace the #VALUE! error with a #DIV/0! error. Code 1 In Code 1, the divide by zero condition is tested by the If statement in line 4 . If Number = 0 is TRUE, then the CVErr(xlErrDiv0) value is assigned to the function name xlfReciprocal_1 in line 5. Execution then skips to line 8. Code 1: Function xlfReciprocal_1 the reciprocal of Number: 1 / Number Function xlfReciprocal_1(Number As Double) As Variant '' Return the reciprocal of Number: 1 / Number If Number = 0 Then xlfReciprocal_1 = CVErr(xlErrDiv0) Else xlfReciprocal_1 = 1 / Number End If End Function The #DIV/0! error is code value 2007 (see the Cell Error Values table below) with an enumeration of xlErrDiv0. This value is converted to an error with the VBA CVErr function. CVErr returns a Variant with subtype Error, thus the function name is set to type Variant to allow this return type. Code 2 This example uses formal error handling. In code 2 line 3, the VBA On Error Goto