wired: $someString = 0 is always true

[illuminon]

Hi there!

Some wired behavior (bug) of autoit3 cost me considerable time to debug. Here the core of the problem:

$string = "b"
If $string = 0 Then
MsgBox(0,"","weird, string is " & $string)
Else
MsgBox(0,"","all ok, string is " & $string)
EndIf

This shows: "weird, string is b"

Is this intentionally? I would have expected this statement to be false or at least cast some datatype error. But it seems to be true. The issue is solved when

$string == 0

is used. This behavior is devastating when for instance searching a value in a string array which has occasional gaps filled with zeroes by a data acquisition machine.

Any comments on this observation?

cheers

[Melba23]

illuminon,

Although not a Dev, I believe that you are running into a conflict of datatypes here. Remember that AutoIt has only one datatype - "Variant" - and so it is up to you to make sure you do the correct match.

In the case you post, you are asking AutoIt if a string variable is 0 - that means False or "". As the variable is not "", you get the result you do NOT expect.

If you were to use If $string = "0", you would get the expected response as the 2 strings would not match.

Having only a single datatype allows fantastic flexibility and is, in the opinion of most experienced users, worth the odd occasion where you need to take extra care - as here.

All clear?

M23

[illuminon]

Hi Melba

Having learned the ropes of programming with C and C++ I fully agree concerning the advantages of a single datatype. However, I ask whether $string is 0, or in other words, as you say, whether $string is "". Since it is not empty, it's "b", I expect the expression to be false and not true. As far as I understand your reasoning it still should be what I expected, no?

[Beege]

Wow this is kinda weird.

This returns all ok...

$string = "b"
If Not $string Then
MsgBox(0, "", "weird, string is " & $string)
Else
MsgBox(0, "", "all ok, string is " & $string)
EndIf

[BrewManNH]

When you try to compare a string to a 1 or 0 the string is converted to a number before it's compared, and strings evaluate to 0.

From the help file:

If a string is used as a number, an implicit call to Number() function is done. So if it doesn't contain a valid number, it will be assumed to equal 0.

[Beege]

But that says if a string is used AS a number. Not compared to a number. Its referring to something like this:

$string = '123'
If $string = 123 then MsgBox(0,'', 'String is 123')

Edited September 15, 2011 by Beege

[BrewManNH]

When you do a boolean compare with a string, it's either 1 or 0 (True or False), so it's comparing a string to a number. The keyword True is considered anything that's not 0, and a boolean compare is done the same way. Also from the same section of the help file:

If you use strings together with Boolean values, they will be converted as follows:

A Boolean true will be the string value "True"

A Boolean false will be the string value "False"

Example:

$Boolean1=true

$String1="Test is: "

$String2=$String1 & $Boolean1

This will result in $String2 being the string value "Test is: True"

The other way around however is different. When you use string comparisons with Boolean values, the following rules apply:

Only an empty string ("") will be a Boolean false

Any other string values (including a string equal "0") will be a Boolean true

[Beege]

Any other string values (including a string equal "0") will be a Boolean true

Now thats the key statement I was looking for.

[Beege]

Damn it... that statement didnt do it for me. So like you just, it's either 1 or 0 (True or False). So with that logic I always thought $string=0 and $string=false would evaluate the same. Same thing with the NOT keyword. Before now I thought "if $string=0" and "If Not $string" would return the same, but they dont.

$string = "b"
If $string = True Then
MsgBox(0,'','True')
EndIf
 
If $string = 1 Then
MsgBox(0,'','1')
EndIf
 
If $string = False Then
MsgBox(0,'', 'False')
EndIf
 
If $string = 0 Then
MsgBox(0,'', 'Zero')
EndIf
 
if Not $string then
MsgBox(0,'', 'not')
EndIf
 
if $string then
MsgBox(0,'', 'if $string')
EndIf

Edited September 15, 2011 by Beege

[illuminon]

That was enlightening :-) Thanks for untangelling,

cheers

[ChrisL]

Your after

If $String= "" then

;String is blank

Else

;String is not blank

Endif