Are array indexes 0-based in VB6?

Question

I'm reviewing an automatic translation of VB6 code to C# and the convertor translated someArray(3) to someArray[3]. But accordingly to the old code documentation it should pick the third element not the fourth as it is doing in the translated version.

Are array indexes 0-based in VB6? Or do they start at 1?

Solution 1

Yes - arrays are (generally) 0 based in VB6

The exceptions to this are when the explicit Dim someArray(1 To 10) as Int syntax has been used, or when Option Base 1 is declared at the top of the code module.

It's Collections that aren't - when you loop through Collection objects I'm pretty sure that they are 1 based.

Solution 2

The short answer is that array lower bounds are what you tell them to be.

The default is base 0 (unless overridden by Option Base 1), but you can declare lower bound to any value you want (Dim arr(-42 To 42) is as valid as Dim(3)).

Also, if an array is returned by some object, its lower bound is whatever that object sets it to. For example an Excel Range.Value reference will return a 1 based array.

Comments

[Matt Wilko]

"Unless Explicit Type Syntax has been used" Or Option Base 1 has been declared at the top of the code block

[Jader Dias]

@Matt Does this statement affect only the current file?

[Jon Egerton]

@XMLforDummies: Yes - in VB6 you have the Option statements at the top of each code file.

[Matt Wilko]

@XMLforDummies - Yes, so if say you have two modules and ModuleA has Option Base 1 declared then any array declared in ModuleA is 1 based.

[Cody Gray]

Unless explicitly specified otherwise at the moment of array declaration. It gets complicated. That's one of the reasons why they changed this for VB.NET.