Problem with eval

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Hi
I’ve got some code-testing code that needs to use the eval command to evaluate strings as code.
I’ve narrowed it down to actions that use array types. Here’s a one liner that fails:

b = Eval(“ubound(Array(1, 2, 3))”)

It throws run-time error 2425 – “The expression you entered has a function name that Microsoft Access can’t find”
Of course, this works fine in Interactive mode:
? ubound(Array(1, 2, 3))
2

Strangley, if I use Evaluate I get a slightly different error:

b = Evaluate(“ubound(Array(1, 2, 3))”)
? b
Error 2029

What’s the difference between eval and Evaluate?

It’s in Access 2002; don’t know whether it’s a problem in other versions or other applications.
Any ideas welcomed.

Peter

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If you highlight the function name Eval (or Evaluate) and press F1, do you get a specific page or the dialog indicating that it exists in multiple libraries, or an error?

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If you highlight the function name Eval (or Evaluate) and press F1, do you get a specific page or the dialog indicating that it exists in multiple libraries, or an error?

F1 on Eval takes me to Microsoft Visual Basic Help – Eval Method – You can use the Eval function to evaluate an expression that results in a text string or a numeric value. Variant.
F1 on Evaluate takes me to Microsoft Visual Basic Help – Evaluate Method – Converts a Microsoft Excel name to an object or a value.

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Eval is a method of the Access Application, Evaluate is a method of the Excel (and possibly others) application. Neither can be used to evaluate VBA like that.

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OK, looks like I’ve got two problems.

I don’t think Access works the way I want to, but for anyone else that’s ever wanted to know, here’s my findings.

1. The eval method has it’s own scoping rules.
eval can’t ‘see’ variables outside it’s scope. This isn’t a big problem, you can just build up the string. Consider the str function if you don’t have a string type.

num = 2
i = Eval(“5 + num * 2”) ‘FAILS

i = Eval(“5 + ” & str(num) & ” * 2″)
Debug.Print i ‘Prints 9

2. eval doesn’t work with arrays.
It just looks like there’s no support for arrays from within eval.

Debug.Print Array(1, 2, 3)(2) ‘Prints 3
Debug.Print Eval(“Array(1, 2, 3)(2)”) ‘Error

Peter

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As I mentioned, neither Eval nor Evaluate can be used to evaluate VBA.

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Thanks Rory.
What do you mean eval can’t be used to evaluate VBA?
I’m using it all the time to do just that – it’s just I’m having trouble using eval with arrays.
For example, this works fine:

Code:

num = 2
i = Eval("5 + " & str(num) & " * 2")    'Prints 9

Pete

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Array(arg1,arg2,arg3,…) is a VBA function and eval cannot handle VBA functions or methods. It can do the regular math operations however.

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Array(arg1,arg2,arg3,…) is a VBA function and eval cannot handle VBA functions or methods. It can do the regular math operations however.

Not true. Access VBA can handle some (most?) functions, but not all. So this works fine:

Code:

Debug.Print eval("chr(65)")     'Prints A

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What you are evaluating there is a straight expression (which would work in a query for example), not VBA.

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What you are evaluating there is a straight expression (which would work in a query for example), not VBA.

Sorry, I still don’t understand.
Here’s some plain VBA using Eval, which works fine in Access 2002 and 2007:

Code:

Sub test()
    Dim num As Integer
    num = 2
    i = Eval("5 + " & Str(num) & " * 2")
    MsgBox i    'Displays 9
End Sub

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Your Eval statement there is not evaluating the str function, it is only evaluating “5 + 2 * 2” which is an expression (such as you can use in a query), not VBA.

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Your Eval statement there is not evaluating the str function, it is only evaluating “5 + 2 * 2” which is an expression (such as you can use in a query), not VBA.

True. But this example has eval evaluating a VBA function:

Code:

Debug.Print eval("chr(65)")     'Prints A

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You are quite right! I was foolishly assuming that Eval and Evaluate work the same way, but they are actually VERY different.

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