[Partly Resolved] DLL Problem...

[Slyke]

I want to create a DLL that any program can access.
I've had a look through the search and i've only found a few answers to my question...

First of all i found out that it needs to be an ActiveX DLL Project.

So i created one and put the following code into it.

Public Function Add_Numbers(Number1 As Integer, Number2 As Integer) As Integer
 
Add_Numbers = Number1 + Number2
 
End Function

I compiled the DLL and placed it in the Visual Basic main directory.

I then created another project and put this code into it

Private Declare Function Add_Numbers Lib "TestDll.dll" (Number1 As Integer, Number2 As Integer) As Integer
 
Private Sub Form_Load()
 
MsgBox Add_Numbers("7", "8")
 
End Sub

When i start the project it comes up with the following error

"Can't find DLL entry point Add_Numbers in TestDll.dll"

From what i can tell, it can't find the function that i placed into the dll.

I need to know what i'm doing wrong, wether i've created the dll the wrong way (so that the function is not in some way accessable outside the dll) or if i'm calling it incorrectly.

I've had a few goes at acreating ActiveX ocx files and i know that all the functions methods, properties, subs etc i wanted other programs to have access to i had to tell visual basic manually (i used a wizard when creating).

Can some one tell me what's going on, or point me in the right direction, without referecing... or is that impossible?

[smUX]

Dunno if this is the issue, but you call "MsgBox Add_Numbers("7", "8")" when you've assigned them as integer

Try MsgBox Add_Numbers(7, 8)

[randem]

That not how you use a VB dll. A VB dll is an ActiveX dll not a windows dll. You call a VB dll from your program just as you would a regular subroutine aside from that you just need to set a reference to it in your program first.

[Slyke]

Dunno if this is the issue, but you call "MsgBox Add_Numbers("7", "8")" when you've assigned them as integer

Try MsgBox Add_Numbers(7, 8)

Same error, shouldn't it come up with type mismatch or somthing lol?

And what do you mean that's not how you create a vb dll? Is there a another type? Yes, i want to call it like a function.

[RhinoBull]

ActiveX dll and standard dll work different.
While you declare function/sub from standard dll you are required to set references to an ActiveX dll.
So, go to your project's refences and point to that dll first.
Then declare object variable as YourDll.YourClass so you may access any public method from that class.

Let me know if you need some code snippet.

[Slyke]

Yeah, i will i can't find anything apart from ActiveX DLL projects There is no Standard DLL project i'm not sure if VB came with it, i have VB 2005 as well. Some code would help alot thanks.

[smUX]

I'm probably going to need to learn all this too...I've never made my own DLLs before and I plan to do so in my "pet project" :-)

[RhinoBull]

ActiveX dll only - so go ahead and set refences as we suggested.

[Slyke]

ok, will do.

I need to do something like...

Private Sub Form_Load()
 
Dim MyDLL As New TestDLL.Class1
 
MsgBox MyDLL.Add_Numbers(7, 8)
 
End Sub

(The TestDLL is the DLL's project name, not the DLL's file name).

After adding it to the references.

Which gives the result 15.

Thanks!

[RhinoBull]

@Slyke (and everybody else):

declaring object variable as New is bad habit i VB6 and here's why:

it does NOT create new instance until you actually access one of the object's properties/methods (in your case object is created when you did MyDLL.Add_Numbers). So, what you do instead is something like the following:

Dim MyDLL As TestDLL.Class1
 
Set MyDLL = New TestDLL.Class1 'this creates new instance of an object immediately
MsgBox MyDLL.Add_Numbers(7, 8)

[Slyke]

Ok, will do. Is it destroyed when the sub finishes? Or does it still linger around in the memory?

[jpritchard]

Hi,

sorry for butting in here when you are already being given good advice from the others..

but, when you sort vb dll and are finally ok with it you might like to look at the following URL

http://www.windowsdevcenter.com/pub/...reate_dll.html

I found it interesting - it takes you thru the process of turning a VB activex dll into a standard windows dll by hooking into the linker/compiler options and adding the relevant entry points manually.

I wouldn't try it till familiar with the normal vb ones though or it might get a bit confusing, but it does work..

Cheers AJP


>>Is it destroyed when the sub finishes? Or does it still linger around in the memory?

dll's are loaded into the memory space of the program that calls it. when the calling program is dropped, so is the dll.

[RhinoBull]

Ok, will do. Is it destroyed when the sub finishes? Or does it still linger around in the memory?

That depends on the scope of your variable but in any case you may always set it to Nothing explicitly so all references will be destroyed:

Set MyObjVar = Nothing