DLL parameters - By reference or By value???

[bavism]

I am new to alpha and I am struggling with calling functions in external dlls. Mostly I have trouble with parameters that are passed to the DLL and are then supposed to be updated by the DLL.

In Xbasic are parameters passed to the dll, by reference or by value. And how can you change this? Some of my dll functions require the values and others require the address.

Thanks for any info you can provide.

Matt

[compuaid]

Re: DLL parameters - By reference or By value???

I'm struggling with this one as well. I have a DLL from Marshallsoft that allows you to fully control an FTP session including using passive FTP which is the one major limitation I see with Alpha's built-in FTP functions but I have several methods that want a string buffer passed to them so the DLL can return information in the string buffer (altering the passed parameter) while returning a success or failure code in the function.

The Visual Basic function definition is:

Declare Function fceGetString Lib "FCE32.DLL" (ByVal fceChan As Integer, ByVal fceParamName As Integer, ByVal fceBuffer As String, ByVal fceBufLen As Integer) As Integer

I've tried using both of the following in Alpha (separately obviously) and the function executes but nothing is returned in the fceBuffer parameter:

Declare FCE32.DLL fceGetString LLLCL

or

Declarestruct _strbuffer C128sbuffer
Declare FCE32.DLL fceGetString LLL(_strbuffer)L

and I've made the call using:

Constant Global FCE_GET_SERVER_IP = 19
Dim fceBuffer as C
fceBuffer=space(128)

result=fceGetString(0,FCE_GET_SERVER_IP_ADDRESS,fcebuffer,128)

The result comes back 0 which means the DLL executed the command but fcebuffer always comes back still containing only the 128 spaces.

[bavism]

Re: DLL parameters - By reference or By value???

I think your second method is the way to go. However, you will need to define your fceBuffer variable differently.

dim fceBuffer as {_strbuffer}

you may not need to initialize fcebuffer with 128 spaces, but if you do and it shouldn't hurt to do it you would need to use
fceBuffer.sbuffer = space(128)

when you pass the variable in your function call, you would pass it exactly as you have it above.

Hope this helps.

[compuaid]

Re: DLL parameters - By reference or By value???

That was the key part I was missing! Thanks so much Matt. I've got the routine working now. I'll be posting the complete declaration function for the MarshallSoft FTP library later this week to help address some of the problems people have been having with Alpha's built-in FTP services (mainly no passive FTP). The Marshallsoft library is $130 one time charge and can be freely distributed with your apps.