Loadlibrary / Declaring dll function at runtime

[Rick H]

My software uses a Can serial card. I need to support three different types of card (PCMCIA, PCI, USB) each of these have there own dll. The dll's all contain the same function / function names.

At the moment I have to get all the users to rename their dll file to 'cancard.dll' then I am using:

Declare Function CANPC_reset_board Lib "cancard.dll" Alias "_CANPC_reset_board@0" () As Long

to delcare the function(s).

I want to get away from forcing the user to rename their DLL's and automatically detect their dll and delcare it at runtime.

I briefly looked at LoadLibrary, but it appears you need to use CallWindowProc to call the function. I still want to use the same syntax as before e.g

dim err_code as long
 
err_code = CANPC_reset_board

Any ideas?

Cheers

[Merrion]

Create an alias for each dll and call the appropriate aliased function at runtime.

[Rick H]

Have you got an example of how to do this?

Cheers

[Merrion]

Declare Function CANPC_reset_board_pmcia Lib "cancard.dll" Alias "_CANPC_reset_board@0" () As Long
Declare Function CANPC_reset_board_pci Lib "cancrd2.dll" Alias "_CANPC_reset_board@0" () As Long
Declare Function CANPC_reset_board_usb Lib "cancrd3.dll" Alias "_CANPC_reset_board@0" () As Long

Note that I don't know what the real names of the dlls are - you'll have to edit that..

[Rick H]

Thats an idea, though they would normally only have one of the DLLs one their PC so the other declares would cause an error.

[Rick H]

Actually it might work, the declarations don't cause an error unless I call the function and the dll doesn't exist. I can check which dll exists at runtime then use this:

private const PCMCIA = 1
private const PCI = 2
private const USB = 3
 
private cardtype as byte
 
public function CanPc_reset_board() as long
 
select case cardtype
case PCMCIA
   CanPc_reset_board=canpc_reset_board_pcmcia
case PCI
   CanPc_reset_board=canpc_reset_board_pci
case USB
   CanPc_reset_board=canpc_reset_board_usb
end select
 
end sub

[Spajeoly]

Just trap the error and use it to determine that the dll doesn't exist, maybe?