What is the difference between VBScript's + and & operator?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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

Answer 4

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.