Invalid use of null?

[l)ragon]

Code Select Expand

    Dim HWND As Long, PiD As Long, phandle As Long
   
    HWND = FindWindow(windowclass, windowcaption)
    If (HWND <> 0) Then
        GetWindowThreadProcessId HWND, PiD
        phandle = OpenProcess(PROCESS_ALL_ACCESS, False, PiD)
        If (phandle <> 0) Then
            WriteProcessMemory phandle, ByVal Address&, Value, 1, 0&
        End If
        CloseHandle phandle
    End If
This is how I use those calls from something I built quite some time ago and it still works aswell.

The way you have yours set up looks right.
Your PROCESS_ALL_ACCESS is the right value also.

So what are you useing this on?

[warz]

The problem has been fixed. The visual basic version of my class now works. The definition of VirtualAllocEx was incorrect.

[UserLoser]

Don't use Null keyword at all in VB...it's rather pointless.  Btw, second parameter should be 0 not False.  There's a difference.  A BOOL isn't same as a boolean in Visual Basic.  NULL isn't same as Null keyword in VB.  Don't use it.  NULL as defined on MSDN would be 0 in Visual Basic (or in anything really).  #define NULL (void*)0 or something to that affect.  MSDN prototypes are all C++ syntaxish based.

Well, false and 0 should be interpreted the same way. Either way, it doesn't change the result of the call.

False and 0 in Visual Basic is not the same as the Null keyword in Visual Basic at all.  If anything needs to be passed as a null parameter, use 0 (same thing as passing vbNullString aka "")

[warz]

Well, this is fairly old, but I wasn't talking about the Null keyword. I was only talking about the False keyword, and 0.

[l2k-Shadow]

the way i interpret it is that False and 0 are the same, however, Null is more like the idea of nothing, while 0 is still a value of a defined variable.

[Joe[x86]]

As far as Java is concerned, false and 0 are values, that of a boolean or an int. As for null, it's a 0x0000000000000000 pointer to a java.lang.Object, I believe.

[MyndFyre]

I realize that this is the VB forum, but I couldn't let misinformation go.

As for null, it's a 0x0000000000000000 pointer to a java.lang.Object, I believe.

Well, it's only 0x00000000 on 32-bit platforms.  And it's not pointing to anything, that's why it's null.  0x00000000 is usually an invalid memory reference.

null can be assigned to any reference of which the type is derived from Object.  This should be more or less any reference, since all Java classes derive from java.lang.Object. 

I'm not sure whether null in Java is implicitly typed.  In C#, there are implicit null typing rules, such as:

Code Select Expand


string str = "abc";
IPAddress addr = Dns.Resolve("forum.valhallalegends.com").AddressList[0];
str = addr = null;

Line 3 would cause a compile-time error because, even though null is being assigned to addr, addr's type is IPAddress, and even as it's null, it can't be assigned to str.

In Visual Basic .NET, the keyword Nothing should be used instead of Null when you are referring to a null reference.

[Joe[x86]]

In Java, if I understand correctly, line three would also provide you with a nice error, but (again, I think) when null is passed or assigned it's assumed that it's a java.lang.Object, so replacing line three with something along the lines of addr = (IPAddress)null; would be allowed by the syntax (it may be incomptable types, but that's a different story).

But this is a nice topic and I don't want to kill it, so if someone wants to add to the java aspect, could you split it? Thanks.

[warz]

yeaah yeaah yeahh jav-WAH?

[Joe[x86]]

Jawa!

[K]

the way i interpret it is that False and 0 are the same, however, Null is more like the idea of nothing, while 0 is still a value of a defined variable.

I believe that the value of False in visual basic 6 is actual -1, strangely enough.  I don't have it installed, so I can't test it, but I seem to recall this being true.

Code Select Expand


' I hope this is valid Visual Basic syntax
Dim b as Boolean
Dim i as Integer
b = False
i = CInt(b)
MessageBox CStr(i)


[FrOzeN]

the way i interpret it is that False and 0 are the same, however, Null is more like the idea of nothing, while 0 is still a value of a defined variable.

I believe that the value of False in visual basic 6 is actual -1, strangely enough.  I don't have it installed, so I can't test it, but I seem to recall this being true.

Code Select Expand


' I hope this is valid Visual Basic syntax
Dim b as Boolean
Dim i as Integer
b = False
i = CInt(b)
MessageBox CStr(i)


In VB6, False is "0". True is everything else, but default it's "-1". Also with your code, it's right except MessageBox is "MsgBox"

[Adron]

False and 0 in Visual Basic is not the same as the Null keyword in Visual Basic at all.  If anything needs to be passed as a null parameter, use 0 (same thing as passing vbNullString aka "")

vbNullString is actually not "", and it can be important to separate the two. Use the right one at the right time.

[FrOzeN]

vbNullString is actually not "", and it can be important to separate the two. Use the right one at the right time.

I've read about vbNullString hundreds of times but forget the reasoning behind it. But my understanding of it, is that as a value it's the same as "" but Visual Basic handles it different and is a preferred method as it provides some slightly more proficient capabilities over "" (non of which I can remember).

Can you tell me a case of where you would ever use "" instead of vbNullString? (Just as reference, I'm trying to grasp a full understanding of all the minor things in VB6 that tutorials don't touch up on)

[warz]

This entire thread is easily answered by MSDN.

Constant: vbNullString
Equiv: String having value 0
Desc: Not the same as a zero-length string (""); used for calling external procedures.

NullChar
Constant: vbNullChar
Equiv: Chr(0)
Desc: Character having value 0

Null
Constant: vbNull
Desc: Null object.

False
Desc: False. The numeric value of this member is 0.