35

On every site that talks about VBScript, the '&' operator is listed as the string concatenation operator. However, in some code that I have recently inherited, I see the '+' operator being used and I am not seeing any errors as a result of this. Is this an accepted alternative?

Jeremy Cron
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4 Answers4

45

The & operator does string concatenation, that is, forces operands to be converted to strings (like calling CStr on them first). +, in its turn, forces addition if one of the expressions is numeric. For example:

1 & 2

gives you 12, whereas

1 + 2
"1" + 2
1 + "2"

give you 3.

So, it is recommended to use & for string concatenation since it eliminates ambiguity.

Helen
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    +1 for specifying string number + number. Accepted answer doesn't mention vbscript converting numeric strings to numbers. – baacke Jan 21 '14 at 17:22
43

The + operator is overloaded, whereas the & operator is not. The & operator only does string concatenation. In some circles the & operator is used as a best practice because it is unambiguous, and therefore cannot have any unintended effects as a result of the overloading.

Robert Harvey
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  • *`The + operator is overloaded`* -- *overloaded* in what sense? – Wolf Dec 08 '16 at 13:50
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    @wolf in VB the + operator can do both addition and concatenation, depending on context. – Robert Harvey Dec 08 '16 at 15:32
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    Well, I already read this. I found the word *overloaded* itself so overloaded that I wished, the answer could be a little bit more precise in this point. – Wolf Dec 08 '16 at 23:00
7

+ operator might backfire when strings can be interpreted as numbers. If you don't want nasty surprises use & to concatenate strings.

EFraim
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2

In some cases the + will throw an exception; for example the following:

Sub SimpleObject_FloatPropertyChanging(fvalue, cancel)
   'fvalue is a floating point number
   MsgBox "Received Event: " + fvalue
End Sub

You will get an exception when the COM object source fires the event - you must do either of the following:

MsgBox "Received Event: " & fvalue

or

MsgBox "Received Event: " + CStr(fvalue)

It may be best in either case to use CStr(value); but using & per above comments for string concatenation is almost always best practice.

Wai Ha Lee
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Neal Davis
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