VBScript checks all OR conditions?

Question

Perhaps I'm missing something, but it annoys me that VBScript seems to read all OR condtions. For example, I'd like to do something like this:

If (oFS.FileExists(sFileLoc) = False) Or (sNewText <> oFS.OpenTextFile(sFileLoc).ReadAll) Then

Now I get an error that the file doesn't exist because of the second condition. I was hoping that if the file doesn't exist VBScript would skip immediately to the result, and if it does, it checks the second condition.

Am I right and is this normal behavior?

Answer 1

As M. Harris already said in 2003 and the docs for the logical operators (e.g. Or) state explicitly, VBScript does not short-circuit the evaluation of conditionals. You must use nested Ifs or a slightly fancy Select Case

Answer 2

You can use inline nested IF's to achieve short-circuiting in VBScript. For example, you could rewrite your statement like this:

If oFS.FileExists(sFileLoc) Then If sNewText = oFS.OpenTextFile(sFileLoc).ReadAll Then

But your Then condition must be specified on the same line as this statement. So if you need to perform multiple operations as a result of this condition, you must separate the statements with a colon (:), which is the single-line statement separator in VBScript.

If oFS.FileExists(sFileLoc) Then If sNewText = oFS.OpenTextFile(sFileLoc).ReadAll Then x = 1 : y = 2

You could also just move your logic into a Sub or Function and make a call instead:

If oFS.FileExists(sFileLoc) Then If sNewText = oFS.OpenTextFile(sFileLoc).ReadAll Then DoStuff

Note, too, that if you need to specify an Else clause, it must be specified on this line as well.

If oFS.FileExists(sFileLoc) Then If sNewText = oFS.OpenTextFile(sFileLoc).ReadAll Then x = 1 Else x = 2