WinExists function with empty text parameter

[hp38guser]

I'm converting my existing AutoIt script to Object Pascal (Inno Setup). I can access AutoIt functions and even the WinExists function works but I have to specify a text to search for. When using null I get an Acces Violation error: Read of Address 00000000. When I do specify a window text to search for it works, but how can I use null as a parameter? Other external dlls accept null parameters, but I need this to work with AutoItX.

function AU3_WinExists(
        title: string;
        text: string
        ): integer;
    external 'AU3_WinExists@files:autoitx3.dll';

    if AU3_WinExists('Notepad', '') <> 0 then
        MsgBox('AutoIt detected Notepad', mbError, mb_OK);

I tested using AutoItX 3.2.12.1 and 3.2.13.7 beta.

Edited August 22, 2008 by hp38guser

[Richard Robertson]

That looks more like a problem with Object Pascal. It's passing a null instead of a blank string. I don't know enough about the language to tell you how to make it do otherwise, but I'm guessing that is the problem.

[hp38guser]

That looks more like a problem with Object Pascal. It's passing a null instead of a blank string. I don't know enough about the language to tell you how to make it do otherwise, but I'm guessing that is the problem.

I'm still a novice programmer, but what's the difference between an empty string and null? I might be able to use SetLength(Str, 0) to create an empty string. Thanks anyway

[hp38guser]

I tried using Chr(0) as parameter and it seems to fix it. Thanks

[Richard Robertson]

The difference between an empty string and null is that the empty string is a value. It's a string with a length of 0 characters. A null on the other hand is a value given to a pointer to indicate that it doesn't contain any value.

Like, think of memory as a set of boxes. We've got a box for a string. The empty string won't have any letters in its "box." The null, doesn't even have a box. Does that make sense?

Chr(0) isn't exactly the right solution, but it will work.

Edited August 25, 2008 by Richard Robertson

[martin]

The difference between an empty string and null is that the empty string is a value. It's a string with a length of 0 characters. A null on the other hand is a value given to a pointer to indicate that it doesn't contain any value.

Like, think of memory as a set of boxes. We've got a box for a string. The empty string won't have any letters in its "box." The null, doesn't even have a box. Does that make sense?

Chr(0) isn't exactly the right solution, but it will work.

A String in Pascal is not a pointer to a char array as a string is in C so I think it should be converted to Pchar.

[Richard Robertson]

C++ doesn't handle Pchar, Martin. If the Pascal is going to make a call to the dll, it will have to be in a form that the dll will understand.

[Proph]

I could be wrong... but I got a simular issue in autoit.

Basically I had a loop that would wait until a Window does not exist and then ExitLoop... but it would never detect that the window did not exist anymore. Even though there were no windows with that name. I noticed that it would only work if I used a text in it.

Does not work when the window is closed:

While 1
    If Not WinExists('SUPERAntiSpyware') Then Exitloop
    Sleep(100)
WEnd

This does work (Thanks to the person who started this thread for the idea):

While 1
    If Not WinExists('SUPERAntiSpyware', chr(0)) Then Exitloop
    Sleep(100)
WEnd

This happens with the latest stable and Beta release of Autoit.

Can others test this and see what results they get? I really think there is a bug here.

[Richard Robertson]

This question doesn't belong in this forum.

I cannot say why that would happen, have you tried with other window titles? Are you 100% sure the window is actually closed and not just hidden? Many programs will hide the window instead of destroy it so it can be loaded again later.

[Proph]

Edit: Nevemind. You were right. It was a hidden window.

Edited November 12, 2008 by Proph