How to call a Procedure by Name.

[cafeenman]

I'm sure there's a way to do it and I even think I've done it in the past but I can't find it and an internet search gave me AddressOf and CallByName.

I use callbyname to recolor my forms at run-time per user preferences.

So this is what I'm trying to do.

I'm writing a thing that chooses a random thing to do. Let's say there's 20 choices of random things.

So I have this:

Sub Random00
End Sub

Sub Random01
End Sub

and so on.

To call it I do this:

Sub DoARandomThing
Dim nRnd as long

nRnd=int(rnd * 19)

Select Case nRnd

    Case 0

        Random00

    Case 1

     Random01

etc.

What I'd like to do is this:

Sub DoARandomThing
Dim nRnd as long

nRnd = int(rnd * 19)

CallSubroutineByName "Random" & format(nrnd, "00")

[VanGoghGaming]

Only public methods of classes can be called by their name. All other names are lost after compilation (they become memory addresses).

[cafeenman]

OK, so I have a create a cRandomThings Class?

That will make this sticky because at least some of the random things are with controls so I'd have to pass those subs the controls.

I'm not sure it's worth it to just get out of doing a long select case thing.

[cafeenman]

Does anyone know how to make the actual call?

[wqweto]

Only public methods of classes can be called by their name. All other names are lost after compilation (they become memory addresses).

This sounds logical but VB6 leaves some internal VBProject structures in final binary which allow traversing modules/procedures and finding offset/address is current process. Another thing is that friend/private methods of classes do end up in runtime VTable albeit not used by codegen to make actual calls from callsites but the addresses in current process are present.

[Schmidt]

Does anyone know how to make the actual call?

If your 20 procedures are defined in the Form itself, then just make them Public there.

Then calling (also from within the Form):

CallByName Me, "Random" & Format(Int(Rnd * 20), "00"), vbMethod

...should do it (also note the 20 instead of your 19 above).

Olaf

[cafeenman]

Thanks. I do know how rnd works. (add 1 if you want 1-based). Otherwise zero-based.

so all my six-sided die rolls are actually 0 to 5 just so I'm not swapping back and forth all the time between number bases. Just make it all base 0.

E.g Int(Rnd * 6) returns 0 to 5.

Thanks again.

Edit: OK, I see why you specified the 20. The 19 in my OP which was wrong.

[Schmidt]

I do know how rnd works. (add 1 if you want 1-based).
Otherwise zero-based.

No - just play that through for a "zerobased" Coin-Toss... (a 50:50 distribution between result 0 or 1).

For that case - your proposed Int(Rnd * 1) will produce a 100:0 distribution
(always producing a 0 - and never the 1)...

For a zerobased coin-toss, the right Formula is Int(Rnd * 2)

Olaf

[wqweto]

Also note that Int in Int(Rnd * 20) is important. Using CLng or leaving it without explicit conversion (i.e. simple Format(Rnd * 20, "00")) will result in bias in final distribution with both end values having half the probability of the rest of outcomes.

cheers,
</wqw>

[cafeenman]

No - just play that through for a "zerobased" Coin-Toss... (a 50:50 distribution between result 0 or 1).

For that case - your proposed Int(Rnd * 1) will produce a 100:0 distribution
(always producing a 0 - and never the 1)...

For a zerobased coin-toss, the right Formula is Int(Rnd * 2)

Olaf

PS: The code below is kind of cool. You just need a VScroll1 and HScroll1 with both of them having the same min and max. That part is important.

Mine are set to min=0 and max=25
I've got that thing all over this code.

Private Sub Anger()
Dim n As Long
Dim nrnd As Long
Dim nMid As Long
Dim nMax As Long
Dim nOffset As Long

' AddToText vbCrLf & vbTab & "You have Angered the Ghost!!" & vbCrLf

'Sleep 100

With HScroll1

  nMid = .Max / 2
  nMax = .Max / 3

  For n = 0 To 49

    nrnd = Int(Rnd * nMax)

    .Value = nMid + nrnd

    .Value = nMid - nrnd

  Next n

End With

With HScroll1

  nrnd = Int(Rnd * 2)

  nOffset = .Max / 3

  If nrnd = 0 Then

    .Value = nMid + nOffset

  Else

    .Value = nMid - nOffset

  End If
  
End With

End Sub

Private Sub HScroll1_Change()

With HScroll1

  If Not .Enabled Then Exit Sub

  VScroll1.Value = .Max - .Value

End With

'lblCount.Caption = Format(HScroll1.Value, PLAY_FORMAT)

'DoARandomThing

End Sub
Private Sub HScroll1_Scroll()

HScroll1_Change

End Sub
Private Sub VScroll1_Change()

With VScroll1

  HScroll1.Value = .Max - .Value

End With

End Sub
Private Sub VScroll1_Scroll()

VScroll1_Change

End Sub

[Schmidt]

PS: The code below is kind of cool.
You just need a VScroll1 and HScroll1 with both of them having the same min and max. That part is important.

Not sure, what you want to express with the "Anger-part" of your snippet -
but it could have been written more efficiently this way:

Option Explicit

Private WithEvents H As VB.HScrollBar, WithEvents V As VB.VScrollBar

Private Sub Form_Load()
  Set V = Controls.Add("VB.VScrollBar", "V"): V.Visible = True
  Set H = Controls.Add("VB.HScrollBar", "H"): H.Visible = True

  H = H.Max / 2 + H.Max / 3 * IIf(Int(Rnd * 2), 1, -1) ' Anger
End Sub

Private Sub H_Change()
  V = H.Max - H
End Sub
Private Sub H_Scroll()
  H_Change
End Sub

Private Sub V_Change()
  H = V.Max - V
End Sub
Private Sub V_Scroll()
  V_Change
End Sub

Olaf

[The trick]

Another thing is that friend/private methods of classes do end up in runtime VTable albeit not used by codegen to make actual calls from callsites but the addresses in current process are present.

Only Friend methods, private ones is called using VTable.

[wqweto]

Only Friend methods, private ones is called using VTable.

Weird! For private methods it does codegen VTable calls.

This class:

Option Explicit

Public Function Init() As Long
    Test1
    Test2
    Test3
End Function

Public Function Test1() As Long
    Test1 = 42
End Function

Private Function Test2() As Long
    Test2 = 43
End Function

Friend Function Test3() As Long
    Test3 = Test1 + Test2
End Function

... decompiles to this:

Public Function Init() As Long
00401DA9 8D 45 E4             lea         eax,[unnamed_var1]  
00401DAC 50                   push        eax  
00401DAD 8B 45 08             mov         eax,dword ptr [Me]  
00401DB0 8B 00                mov         eax,dword ptr [eax]  
00401DB2 FF 75 08             push        dword ptr [Me]  
00401DB5 FF 50 20             call        dword ptr [eax+20h]  
00401DB8 89 45 E0             mov         dword ptr [unnamed_var1],eax  
00401DBB 83 7D E0 00          cmp         dword ptr [unnamed_var1],0  
00401DBF 7D 17                jge         Class1::Init+6Fh (401DD8h)  
00401DC1 6A 20                push        20h  
00401DC3 68 10 1A 40 00       push        offset ___vba@08C12B20 (401A10h)  
00401DC8 FF 75 08             push        dword ptr [Me]  
00401DCB FF 75 E0             push        dword ptr [unnamed_var1]  
00401DCE E8 AF F3 FF FF       call        ___vbaHresultCheckObj (401182h)  
00401DD3 89 45 D4             mov         dword ptr [ebp-2Ch],eax  
00401DD6 EB 04                jmp         Class1::Init+73h (401DDCh)  
00401DD8 83 65 D4 00          and         dword ptr [ebp-2Ch],0  
    Test1()
00401DDC 8D 45 E4             lea         eax,[unnamed_var1]  
00401DDF 50                   push        eax  
00401DE0 8B 45 08             mov         eax,dword ptr [Me]  
00401DE3 8B 00                mov         eax,dword ptr [eax]  
00401DE5 FF 75 08             push        dword ptr [Me]  
00401DE8 FF 50 24             call        dword ptr [eax+24h]  
    Test2()
00401DEB 8D 45 E4             lea         eax,[unnamed_var1]  
00401DEE 50                   push        eax  
00401DEF FF 75 08             push        dword ptr [Me]  
00401DF2 E8 B5 00 00 00       call        Class1::Test3 (401EACh)  
    Test3()
00401DF7 8B 45 08             mov         eax,dword ptr [Me]  
00401DFA 8B 00                mov         eax,dword ptr [eax]  
00401DFC FF 75 08             push        dword ptr [Me]  
00401DFF FF 50 08             call        dword ptr [eax+8]  
00401E02 8B 45 0C             mov         eax,dword ptr [Init]  
00401E05 8B 4D E8             mov         ecx,dword ptr [Init]  
00401E08 89 08                mov         dword ptr [eax],ecx  
00401E0A 8B 45 FC             mov         eax,dword ptr [ebp-4]  
00401E0D 8B 4D EC             mov         ecx,dword ptr [ebp-14h]  
00401E10 64 89 0D 00 00 00 00 mov         dword ptr fs:[0],ecx  
00401E17 5F                   pop         edi  
00401E18 5E                   pop         esi  
00401E19 5B                   pop         ebx  
00401E1A C9                   leave  
00401E1B C2 08 00             ret         8  
End Function

So private Test2 method indeed uses call dword ptr [eax+24h] indirect call through VTable but lacks HResult check.

Friend Test3 method uses call Class1::Test3 (401EACh) direct call and again no HResult check which seems to be fastest approach.

Nothing comes to mind what could possible require VTable indirect calls for private methods.

cheers,
</wqw>