Referencing in VB.NET

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I'm trying to reference an intptr to value (integer, for example), but I don't
find the solution

VB

Dim a As Integer = 100 (a = 100)
Dim b As IntPtr = a (b = 100)
a = 50 (a = 50)
b = 100 (b = 100)

I want to be 50, but I can't find the solution.

If I try that, in the first case b is really a, but not in the second case.

Is there any way to track the variables or do something like that?

Thanks in advance

What I have tried:

I have tried with events, wrappers, and even so I can't find the solution.

Could anyone help me?

Newly, thanks in advance

Posted 29-Apr-19 9:39am

EdwardCarnby

Updated 29-Apr-19 20:22pm

Maciej Los

v2

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phil.o 30-Apr-19 2:34am

You cannot really mimic the C language with pointers in Vb.net or any other managed language. Here you should assign to b the address of variable a, not the value of variable a. But I don't know how to do it in vb.net. I know c# can understand unsafe blocks, but i'm not sure vb.net has an equivalent functionality. Managed code induces tge fact that you should not care about memory addresses, at all.

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Maciej Los · Accepted Answer · 2019-04-29T20:22:00

Solution 1

I'm not sure i understand you well, but seems you want to track variable changes.

1. Tracking variables is messy for set of reason...
2. If you want to be informed about variable changes, use Class and call event in setter, for example:

VB.NET

Public Class myVar
    Private mValue As Integer
    Public Event VariableChanged(ByVal mvalue As Integer)

    Public Property Variable() As Integer
        Get
            Variable = mValue
        End Get
        Set(ByVal value As Integer)
            mValue = value
            RaiseEvent VariableChanged(mValue)
        End Set
    End Property
End Class

Usage:

VB.NET

Public Class Form1
    Private WithEvents test As New myVar
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        test.Variable = CInt(TextBox1.Text)
    End Sub
    Private Sub VariableChanged(ByVal NewValue As Integer) Handles test.VariableChanged
        MessageBox.Show(NewValue)
    End Sub
End Class

Above code comes from: vb.net - Detect variable change. [SOLVED] | DaniWeb[^]

If i'm wrong and you want to track variables while debugging, use breakpoints, see: Set a watch on variables - Visual Studio | Microsoft Docs[^]

Posted 29-Apr-19 20:22pm

Maciej Los

Updated 29-Apr-19 20:57pm

v2

Comments

phil.o 30-Apr-19 2:41am

My 5 :)
Didn't you mean breakpoints instead of brakepoints?

Maciej Los 30-Apr-19 2:55am

Oh yeah! The level of cafe in my body is too low... I need to fill in...
[EDIT]
Thanks! Changed ;)

EdwardCarnby 30-Apr-19 3:03am

It worked, but I have to track manually the change. The thing is:
I'm trying to emulate a C-Like expression.
int a = 100;
int *p;
p = &a;
Something like this. I studied C many years ago, and I don't remember it very well,
but think that, in this way you obtained the adress of memory and when a changed, I obtained a value in p, with no matter the times a changed.
Is there any way?. Thanks, newly

Maciej Los 30-Apr-19 3:15am

Even if i'm not sure what you mean by "track manually the change", the shortest answer is: No. Why? VB.NET is not a C.

Ralf Meier 30-Apr-19 3:44am

What Maciej means here when he asks 'Why' :
Perhaps there is a possible Solution for you if we understand what you REALLY try to achieve ...

Maciej Los 30-Apr-19 3:52am

Holy true!
Thanks, Ralf.

EdwardCarnby 30-Apr-19 4:36am

In vb.net, intptr acts as a pointer and value.gethashcode as address. The problem is that gethashcode changes constaintly. That's I want track, the hashcode of the variable.

phil.o 30-Apr-19 5:38am

GetHashCode() method has nothing to do with memory addresses :)

EdwardCarnby 30-Apr-19 4:42am

The solution you gave me before works if I change the type of the variables (for example a to wrapper, and b to wrapper), but I want a variable untouched.

EdwardCarnby 30-Apr-19 4:43am

Pardon, I meant 'a' variable untouched

Maciej Los 30-Apr-19 5:54am

IntPtr Struct (System) | Microsoft Docs[^] can act as a pointer or handle. Sorry, but i still can't get what you mean.

EdwardCarnby 30-Apr-19 6:09am

dim a as integer = 100
dim p as intptr
p = marshal.sizeof(a)
p = a.gethashcode or p = a (at the effects it's the same)
Now, a = 100 and p = 100
a = 50
Now, a = 50 and p = 100

That's I mean when referring to tracking variables. I want p be 50, not 100.

class Wrapper
public property value as integer
end class

dim a as new Wrapper, b as new Wrapper
a.value = 100
b.value = a
If I write so, it works, but I want that variable 'a' be the native type (integer, in this case) not a wrapper. Ah, and forgot it (I'm not sure if that occurs int c pointers) If I write this with wrappers, changing b changes a. I'm trying to discover that variable b change when variable a change, but not variable a change when variable b change.

Thanks

Thanks in advance

Ralf Meier 30-Apr-19 6:39am

Each way you showed to us says the same :
You directly or indirectly assign the value from "a" to "p" - but only in the moment of the instruction.
What you want to have is something like a binding - each time "a" changes it's value the same should happen to "p" - p automaticly gets the value from "a".
But ... for what do you need that ? What is the hidden sense of it ...?
Please understand - because I didn't understand the sense I'm not able to give a helpful answer ...

Maciej Los 30-Apr-19 7:08am

To be honest i understand that you want to use 'p' as a pointer (an address of 'a' variable in a memory), but(!) i've already mentioned that VB.NET is not a C. And striclty saying VB.NET doesn't have pointers (and certainly not like C pointers).
At this moment the closest think that came to my mind is to use Delegates (Visual Basic)[^], which are sometimes described as type-safe function pointers because they are similar to function pointers used in other programming languages. But unlike function pointers, Visual Basic delegates are a reference type based on the class System.Delegate. Delegates can reference both shared methods — methods that can be called without a specific instance of a class — and instance methods.
Sorry, but i do not see other solution...

EdwardCarnby 30-Apr-19 7:00am

I just had an Idea that can help me. But need help for the return.

Public Class Form1
Dim a As Integer = engine(100, a.GetType, p)
Dim p As IntPtr = New IntPtr(a)

Private Sub Form1_Click(sender As Object, e As System.EventArgs) Handles Me.Click
Debug.Print("First pass")
Debug.Print("a: " & a)
Debug.Print("b: " & p.ToString)
a = engine(50, a.GetType, p)
Debug.Print("Second pass")
Debug.Print("a: " & a)
Debug.Print("b: " & p.ToString)
End Sub
Private Function engine(ByVal o As Object, ByVal t As Type, ByVal p As IntPtr)
p = ctype(o, t)
Return o
End Function
End Class

I think it will work, and I had the variable untouched, but I don't know how to return it. It gives me a mistake in ctype. Could be need some changes

Maciej Los 30-Apr-19 7:15am

Please, read my previous comment and follow this link: Relaxed Delegate Conversion (Visual Basic) | Microsoft Docs[^]

EdwardCarnby 30-Apr-19 7:18am

Sorry, I had not read the previous post. Thanks

Maciej Los 30-Apr-19 7:19am

Don't worry. Take a look at time of publishing ;)