Array and strings; If statement

[dRsrb]

Hello!

I have two general problems which I don't understand:

#include <array.au3>

_1_Array_Problem()
_2_If_Problem()

Func _1_Array_Problem()
    
    Local $aTest[3]
    
    $aTest[0] = 'Test'
    $aTest[1] = 'Test|String'
    $aTest[2] = 'String'

    _ArrayDisplay($aTest)
    
EndFunc

Func _2_If_Problem()
    
    Local $vTest
    
    If $vTest = '' Then MsgBox(0, '1: $vTest is empty', $vTest)
    If $vTest == '' Then MsgBox(0, '2: $vTest is empty', $vTest)
    
    $vTest = 0
    
    If $vTest = '' Then MsgBox(0, '3: $vTest is empty', $vTest)
    If $vTest == '' Then MsgBox(0, '4: $vTest is empty', $vTest)
    
    $vTest = ''
    
    If $vTest = '' Then MsgBox(0, '5: $vTest is empty', $vTest)
    If $vTest == '' Then MsgBox(0, '6: $vTest is empty', $vTest)
    
EndFunc

1.

Why is everything behind the '|'-char cropped? The '|'-char is part of the string, so I don't understand this behavior. Could it be a possible bug or is there a way to escape the vertical line? 'Chr(124)' doesn't work as well.

2.

Firstly I used '==' in statements until I noticed, that this method doesn't work with MsgBox(). So I started to use in general only one '=' in my script to not mix them all the time.

Today I came across this behavior: If '$vTest' is '0' then 'If $vTest = '' Then ...' evaluates to true. But '$vTest' is zero and not empty. Now I'm forced to mix '==' and '='.

And I'm confused. Why does this not work as expected? Why are there two methods at all?

Bye

Edited April 8, 2009 by dRsrb

[bo8ster]

dRsrb

Some good questions

1. I tried using escape characters like \| and ||. Searching the forum I can only suggest looking here..

I also wondering if anyone else can get it going. I found nothing in the help file not much searching. I did find this. Any suggestions?

2. I have seen this around. I would say, just because AutoIt allows you to be a little lazy, don't be. I would tread == and = like you would in C. Running your program shows me that '==' holds true in all situations. With the first test, I would recommend you initialize that var before you use it like any good programmer. This will stop you having unexpected bugs.

[exodius]

The first situation only happens because of _ArrayDisplay displaying things as a ListView (which uses the "|" to delimit column info).

If you do:

MsgBox (0, "", $aTest[1])

after you define $aTest[1] then it works just fine.

Edited April 9, 2009 by exodius

[Ascend4nt]

$vTest = 0

If $vTest = '' Then MsgBox(0, '3: $vTest is empty', $vTest)

If $vTest == '' Then MsgBox(0, '4: $vTest is empty', $vTest)

Valik recently enlightened me that '==' *forces* a string comparison (and makes it case-sensitive). But the whole bit of '' equals 0 confuses me (unless '' basically means a null pointer, but how it would work in an actual string comparison I wouldn't have a clue).

A test for 'If Not $vTest' would make more sense for my code...

Edited April 9, 2009 by ascendant

[bo8ster]

That would make sense. C/C++ == usually goes for the memory address and you have to use a string compare method to compare strings.

Ideally you would get a compile error as you are comparing two different data types, as you say 0 could be seen as null. Generally NULL = 0.

[Ascend4nt]

Actually, in C/C++, == is just a regular 'is equals' operation. [and can't be used to compare strings]

'=' in C/C++ on the other hand is an assignment operator.

Regarding the == string comparison, I just realized that its pretty much the same as doing:

StringCompare($vTest,0)

0 is converted to '0', so null or an empty string won't equal it, which is why this results in True (when $vTest=0):

If $vTest == '0'

Edited April 9, 2009 by ascendant

[bo8ster]

That's correct. It compares either the pointers or the first element in the array, if forget which, because a string var is a pointer to the start of the array.

Now if 0 is converted to a char, that makes things interesting. I would expect "Test = 0 - if Test == 0" to be true every time. That said, in my scripts you will often see int() in use.

Either way in summary I recommend using == not = for testing equality.

http://en.wikipedia.org/wiki/Equality_(relational_operator) holds some reasons why = is allowed.

[Ascend4nt]

The reason = is allowed is totally up to the language interpreter/compiler, it doesn't matter what Wikipedia says. However, it can make debugging easier if you can clearly see where the assignments vs. comparisons are - BUT there's a problem in using '==' in AutoIt, as it incurs a performance hit as Valik pointed out.

[bo8ster]

Thanks for the link ascendant - I learnt something here.

[dRsrb]

I learnt something here.

Me too! Absolutely important tips!

Thank you all very much!

[andybiochem]

Hello!

I have two general problems which I don't understand:

.......

1.

Why is everything behind the '|'-char cropped? The '|'-char is part of the string, so I don't understand this behavior. Could it be a possible bug or is there a way to escape the vertical line? 'Chr(124)' doesn't work as well.

The _ArrayDisplay documentation shows how to get around this:

#include <array.au3>

_1_Array_Problem()

Func _1_Array_Problem()
    
    Local $aTest[3]
    
    $aTest[0] = 'Test'
    $aTest[1] = 'Test|String'
    $aTest[2] = 'String'

    _ArrayDisplay($aTest,"",-1,0,"¬")
    
EndFunc

[dRsrb]

The _ArrayDisplay documentation shows how to get around this: ...

Thank you for the hint. I just edited the "Array.au3" and replaced the vertical line with an other default char.

Bye