Tip 20: Define constants using a TypeLib or an Enum.

When you create error values try not to use the so-called Magic Numbers. Thirteen is such a number, as in Err.Raise Number:=13. What does 13 mean? Basically it's a pain to resolve, so attempt always to use more meaningful names.

Visual Basic doesn't come with a set of symbolic constants defined for its own errors so I thought I'd put one together for you. Here's a snippet:

Public Enum vbErrorCodes
VBErrReturnWithoutGoSub = 3
VBErrInvalidProcedureCall = 5
VBErrOverflow = 6
VBErrOutOfMemory = 7
VBErrSubscriptOutOfRange = 9
VBErrThisArrayIsFixedOrTemporarilyLocked = 10
VBErrDivisionByZero = 11
VBErrTypeMismatch = 13
VBErrOutOfStringSpace = 14
VBErrExpressionTooComplex = 16
VBErrCantPerformRequestedOperation = 17
VBErrUserInterruptOccurred = 18
VBErrResumeWithoutError = 20
VBErrOutOfStackSpace = 28
VBErrSubFunctionOrPropertyNotDefined = 35
.
.
.
End Enum

Once you've added it to your project, this snippet is browsable via Visual Basic's Object Browser. You'll find the code on the companion CD. To see how you might define constants using a type library, see Chapter 7.