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Safe Ubound And Lbound


imacul8

Ever wanted to use LBound and UBound to get arrays boundaries without jumping over error message when the array is empty? These functions will replace the ordinary LBound and UBound procedures so you dont need to worry about errors. I've also included a way to get the dimensions of an array. Just paste the following code into a module, and the problem is solved.

 

Inputs: SafeUBound and SafeLBound: [Address to the array], [What dimension you want to obtain]

ArrayDims: [Address To the array]

Returns: As expected from the ordinary functions, except that they will return -1 when the array is empty.

Assumes: You obtain the address to an array by passing it to the VarPtrArray API call. So if you want to get the boundaries of an array called aTmp, you need to call the functions like this:

lLowBound = SafeLBound(VarPtrArray(aTmp))

lHighBound = SafeUBound(VarPtrArray(aTmp))

lDimensions = ArrayDims(VarPtrArray(aTmp))

When dealing With String arrays that isn't allocated at design time, you *must* add the value 4 To the lpArray-paramenter:

lLowBound = SafeLBound(VarPtrArray(aString) + 4)

 

Side Effects: Since the return value is minus when the array is empty it's a big chance you will get problems with minus dimensioned arrays, but who use them anyway?

 

Option ExplicitDeclare Function VarPtrArray Lib "msvbvm50.dll" Alias "VarPtr" (Ptr() As Any) As LongDeclare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)Public Function SafeUBound(ByVal lpArray As Long, Optional Dimension As Long = 1) As Long Dim lAddress&, cElements&, lLbound&, cDims% If Dimension < 1 Then SafeUBound = -1 Exit Function End If CopyMemory lAddress, ByVal lpArray, 4 If lAddress = 0 Then ' The array isn't initilized SafeUBound = -1 Exit Function End If ' Calculate the dimensions CopyMemory cDims, ByVal lAddress, 2 Dimension = cDims - Dimension + 1 ' Obtain the needed data CopyMemory cElements, ByVal (lAddress + 16 + ((Dimension - 1) * 8)), 4 CopyMemory lLbound, ByVal (lAddress + 20 + ((Dimension - 1) * 8)), 4 SafeUBound = cElements + lLbound - 1End FunctionPublic Function SafeLBound(ByVal lpArray As Long, Optional Dimension As Long = 1) As Long Dim lAddress&, cElements&, lLbound&, cDims% If Dimension < 1 Then SafeLBound = -1 Exit Function End If CopyMemory lAddress, ByVal lpArray, 4 If lAddress = 0 Then ' The array isn't initilized SafeLBound = -1 Exit Function End If ' Calculate the dimensions CopyMemory cDims, ByVal lAddress, 2 Dimension = cDims - Dimension + 1 ' Obtain the needed data CopyMemory lLbound, ByVal (lAddress + 20 + ((Dimension - 1) * 8)), 4 SafeLBound = lLboundEnd FunctionPublic Function ArrayDims(ByVal lpArray As Long) As Integer Dim lAddress As Long CopyMemory lAddress, ByVal lpArray, 4 If lAddress = 0 Then ' The array isn't initilized ArrayDims = -1 Exit Function End If CopyMemory ArrayDims, ByVal lAddress, 2End Function

Hope this solves any problems u have of getting errors with empty arrays.

 

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Galahad

I was just about to write it was copied from PSC, but BuffaloHELP got here before me

Anyways, this code is good, since it uses Windows API, but this same code can be written in pure VB, with just a little error handling

Here it is:

Private Function SafeLBound() As LongOn Local Error GoTo SafeLBound_ErrSafeLBound = LBound(Niz)SafeLBound_Exit:Exit FunctionSafeLBound_Err:If Err.Number = 9 Then SafeLBound = -1Resume SafeLBound_ExitEnd FunctionPrivate Function SafeUBound() As LongOn Local Error GoTo SafeUBound_ErrSafeUBound = UBound(Niz)SafeUBound_Exit:Exit FunctionSafeUBound_Err:If Err.Number = 9 Then SafeUBound = -1Resume SafeUBound_ExitEnd Function
This code will work only with project-level, or form/module-level arrays, since building a function that checks arrays, would require a function for each data-type in Visual Basic, because useing arrays as function or procedure parameters, requires passinge them by refference (ByRef), so you can for example declare input parameter as array of variants, and pass array of strings... That would cause another run-time error


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