Null character

[SlimShady]

Why are null/nil characters not supported in AutoIt3?

Is it because when AutoIt sees the char it stops because every string ends with a null char?

Did some tests just now so my theory may be incorrect.

What I tried?

This...

$val = "Some" & Chr(0) & "text"
MsgBox(64, "Test", "$val: " & @CRLF & $val)

and this...

$val = "Some"
$val = $val & Chr(0) & "text"
MsgBox(64, "Test", "$val: " & @CRLF & $val)

and this...

$val = Chr(0) & "Sometext"
MsgBox(64, "Test", "$val: " & @CRLF & $val)

*..Maybe you ignore the char when we're storing it in a variable..*

I'm really curious.

[Holger]

@SlimShady: toyour sample with Msgbox(), something from the MSDN-library:

"int MessageBox(

HWND hWnd, // handle of owner window

LPCTSTR lpText, // address of text in message box

LPCTSTR lpCaption, // address of title of message box

UINT uType // style of message box

);

Parameters

hWnd

Identifies the owner window of the message box to be created. If this parameter is NULL, the message box has no owner window.

lpText

Pointer to a null-terminated string containing the message to be displayed.

"

Edit: Ahhh, sorry, now I (hopefully) understand what you mean:

The text in the first sample should end after "some".

Hmmm...

Edited January 30, 2005 by Holger

[SlimShady]

@SlimShady: toyour sample with Msgbox(), something from the MSDN-library:

"int MessageBox(

  HWND hWnd,          // handle of owner window

  LPCTSTR lpText,    // address of text in message box

  LPCTSTR lpCaption,  // address of title of message box

  UINT uType          // style of message box

);

Parameters

hWnd

Identifies the owner window of the message box to be created. If this parameter is NULL, the message box has no owner window.

lpText

Pointer to a null-terminated string containing the message to be displayed.

"

<{POST_SNAPBACK}>

I have seen that mentioned many times before.

That's why I didn't expect to see the full string in my tests.

But the strings are completely visible!

So I have a strong feeling that AutoIt ignores the null char.

Please explain what you do or don't do with null chars in strings/variables.

[Holger]

@SlimShady: I never needed strings/vars in the past with a nul character...

Can you give a small example for what it could needed?

Thanks

[SlimShady]

I don't have any problems or requests or anything.

It's just a question I keep forgetting to ask.

And because Valik's RC4 Encrypt UDF is no 100% because AutoIt "can't handle" the null char.

So I wonder why AutoIt "can't handle" the null char.

BTW I did some more tests.

Check it out:

$val = "Sometext"
If StringInStr($val, "") Then MsgBox(64, "Test 1", "$val: " & @CRLF & $val)

$val = "Sometext"
If StringInStr($val, Chr(0)) Then MsgBox(64, "Test 2", "$val: " & @CRLF & $val)

$val = "Some" & Chr(0) & "text"
If StringInStr($val, Chr(0)) Then MsgBox(64, "Test 3", "$val: " & @CRLF & $val)

$val = "Some"
$val = $val & Chr(0) & "text"
If StringInStr($val, Chr(0)) Then MsgBox(64, "Test 4", "$val: " & @CRLF & $val)

$val = Chr(0) & "Sometext"
If StringInStr($val, Chr(0)) Then MsgBox(64, "Test 5", "$val: " & @CRLF & $val)

Edited January 30, 2005 by SlimShady

[Valik]

All AutoIt's internal string handling mechanisms are based on the C-style string approach. This means that the terminating character for a string is the NULL character. For example:

const char *szString = "This is a test\0";  // \0 is implicit, but can be manually specified.

This example won't print completely in AutoIt:

const char *szString2 = "This\0 is a test";  // Any C-string based function only sees "This"

Now, when you call Chr(0), this is the string thats built:

const char *szString3 = "\0";

Now, given that the \0 terminates the string, any C-string based approach reads up to but not including the NULL character. So that means its an empty string. In AutoIt, that's the equivalent of:

Local $sString = ""

Therefore, because all the internal string stuff uses a C style approach, the NULL character isn't being inserted into the string like you think it should be. If AutoIt did not use a C style approach, then it would be because some other method would be used to terminate strings.

And since I see the inevitable, "Well, why not use some other method?" Because its hard. When you read a C-string, you know to stop when you see \0. This prevents you from running past the end of the string and getting in something elses memory which would lead to a crash. This means that in order not to use a terminating character, the strings have to carry around extraneous information such as its own size and its potential size. It also means rewriting a bunch of functions to operate on these strings. In the end, its a lot of code and a major pain in the ass. It probably needs done someday, but its a lot of work and a lot of potential to break a lot of things.

[SlimShady]

Thanks for the info, Valik.

I was thinking and now I completely understand.

\0 (in C++) equals Chr(0) equals ""

The following explains the null character for me:

3 + 0 + 3

is like this:

$val = "Some" & Chr(0) & "text"

$val = "Some" & "" & "text"

That's why the null character is never visible and is only available for the programmer, the application and the computer.

Edited January 30, 2005 by SlimShady