What is the operator precedence order in VB6?

Question

In particular, for the logical operators

Answer 1

Logical Operation Precedence Order

1. Not
2. And
3. Or
4. Xor
5. Eqv
6. Imp

Comparison Operation Precedence Order

1. =
2. ><
3. <
4. >
5. <=
6. >=
7. Like, Is

Arithmetic Operation Precedence Order

1. ^
2. -
3. *, /
4. \
5. Mod
6. +, -
7. &

Source: Sams Teach Yourself Visual Basic 6 in 24 Hours — Appendix A: Operator Precedence

Found via a Google search for visual basic 6 logical operator precedence.

Answer 2

It depends on whether or not you're in the debugger. Really. Well, sort of.

Parentheses come first, of course. Then comparisons (>, <, =, etc). Then the logical operators. The trick is that the order of execution is not defined. That means given the following expression:

If A < B And B < C Then

you are guaranteed that the < operators will both be executed before the logical And comparison. But you are not guaranteed which comparison will be executed first.

IIRC, the debugger executes left to right, but the compiled application executes right to left. I could have them backwards (it's been a long time), but the important thing is that they're different. So the actual precedence doesn't change, but the order of execution might.

Answer 3

Joel,

does this mean that an OR operation will not (ever) be able to skip the right hand side if the left evaluates to true, and the same for AND and false?

Answer 4

@[Oskar]: Yes. VB.Net defines the execution order and has the AndAlso and OrElse logical operators to do short circuit evaluation. But VB6 will always evaluate both sides of an expression. You have to simulate it with additional If/Else statements.

Answer 5

Yes, VB6 always evaluates both sides of an Or or And operator.

For example, the following will always throw an error:

Dim a as Form
If a is Nothing Or Not a.Visible Then
    MsgBox "VB6 will never reach here and will instead throw an error."
End If

Answer 6

Use parentheses

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EDIT: That's my advice for new code! But Oscar is reading someone else's code, so must figure it out somehow. I suggest the VB6 manual topic Operator Precedence. Unfortunately this topic doesn't seem to be in the MSDN online VB6 manual, so I will paste the logical operator information here. If you installed the VB6 help (the MSDN library) you will have it on your machine.

Logical operators are evaluated in the following order of precedence:

Not   
And   
Or   
Xor   
Eqv   
Imp   

The topic also explains precedence for comparison and arithmetic operators.

I would suggest once you have figured out the precendence, you put in parentheses unless there is some good reason not to edit the code.