Accessing a DLL function

Question

Accessing a DLL function

BigInch (Petroleum)

(OP)

30 Jul 13 05:52

I've beem trying for a week to access a dll function while running Excel/VBA. This function is contained in a 3rd party dll (not a MS product). The name of this old DLL is "sai.dll" I believe it was written in C around 1998-2000. After trying all the calling options using almost all the longs and pointers and StrPtr() and VarPtr() values I can permutate, I get error messages ranging from "Cannot find cdr entry point in the dll" to a total shutdown of Excel.

LIBRARY "Sai"
The Library export list shows only
cdr_ @1
The only description of the function in the documentation is,
void cdr(const char *case, int *ier)

The Arguments,
*case In VBA this will be a string representing an analysis case name, such as "SAramcoThermal" or similar

*ier An error value, as returned by cdr(), supposedly 0, -1, etc.

In the documented descriptions, the function is referred to as "cdr", yet in the export list and a disassembler view it shows us as "cdr_", note the trailing underscore, which confuses me. What's that about?

And my real question is, does anybody have any ideas on how I should declare this function in VBA/Excel, and perhaps make a class wrapper or do something that will give Excel that returned value?

In any case, thanks for having a look.

Independent events are seldomly independent.

IRstuff (Aerospace) · Answer 1 · 2013-07-30 15:14:48

You know, we usually send questions like this over to Tek-Tips, so that's probably still a value suggestion.

TTFN
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BigInch (Petroleum) · Answer 2 · 2013-07-31 01:08:02

Then I'll be forced to try the
new user/join/password ... not a valid user... new user/join/password .... nth time thing.
OK. I'll try it.

Independent events are seldomly independent.

xwb (Computer) · Answer 3 · 2013-07-31 01:30:42

The library export list doesn't look right. If you have two parameters, it should be cdr_@8. The number after the @ is in multiples of 4. You should get @0 for no parameters, @4 for 1 parameter etc. If cdr_@1 is from the documentation, check it using depends (http://www.dependencywalker.com/)

The reference for what you want is in MSDN

So, at a guess, in your case, it would be

CODE

declare cdr lib "sai.dll" alias "cdr_@1" (byval casestr as string, byref ier as integer)

BigInch (Petroleum) · Answer 4 · 2013-07-31 13:50:46

xwb,
Thanks a lot for that information.
I think the @1 above means the function is the first ordinal. It is the only one as well.

That Dependency Walker is a killer! I'm suffering from info overload right now, but it's great!
It shows the export function name is cdr_
I will try that declaration and let you know what happens.
Thanks again.

Independent events are seldomly independent.

BigInch (Petroleum) · Answer 5 · 2013-07-31 16:23:32

I declared and called the function,

Public Declare Function cdr Lib "d:\sai.dll" _
Alias "cdr_@1" (ByVal casename As String, ByRef ier As Integer)

dim strConnection as string
dim ier as integer

I called it as,
Ret = cdr(strConnection, ier)

Result was,
Run-time error '453': Can't find DLL entry point cdr_@1 in d:\sai.dll

VBA would only accept me writing the call as "cdr" not by the aliased name "cdr_@1".

This isn't one of those cases where strConnection has to be 144 characters long and terminated in a null, or is it? Well, the "can't find entry point" seems like a different problem then not recognizing sring variables.

Independent events are seldomly independent.

BigInch (Petroleum) · Answer 6 · 2013-07-31 23:43:46

No I figured out that it's not one of those null terminated strings. As the function does not return a string, I don't require that string to accept it.

Independent events are seldomly independent.

xwb (Computer) · Answer 7 · 2013-08-02 14:35:02

If the function name is cdr_, just change the declaration to

CODE

Public Declare Function cdr Lib "d:\sai.dll" _
Alias "cdr_" (ByVal casename As String, ByRef ier As Integer)

BigInch (Petroleum) · Answer 8 · 2013-08-03 12:08:38

OK. I'll try it.
Thanks for the continued support.

Independent events are seldomly independent.

BigInch (Petroleum) · Answer 9 · 2013-08-04 13:31:02

Tried it. "Bad calling convention"
At least it didn't knock XL down this time.

Independent events are seldomly independent.

xwb (Computer) · Answer 10 · 2013-08-05 14:05:16

It is a void function so maybe the declaration should be

CODE

Public Declare sub cdr Lib "d:\sai.dll" _
Alias "cdr_" (ByVal casename As String, ByRef ier As Integer)

If it is a function, a return type has to be specified.

BigInch (Petroleum) · Answer 11 · 2013-08-06 06:53:51

Thanks. I'll try anything at this point. I'm considering learning C!!!
Is not the ier variable returned, indicating the status of the connection?

Independent events are seldomly independent.

xwb (Computer) · Answer 12 · 2013-08-06 08:13:07

Yes but it is returned as a parameter: not as the result of the function.

BigInch (Petroleum) · Answer 13 · 2013-08-06 14:29:16

Again the "Bad calling convention" error was raised. banghead

Independent events are seldomly independent.

xwb (Computer) · Answer 14 · 2013-08-06 14:54:02

Have a look at the following

Looks like it is something to do with ByVal casename As String.

The problem is it is expecting a BSTR or wchar_t* but you've got a char*. One option is to write another DLL that calls your DLL. This will convert the wchar_t* to a char* and then pass it into cdr.

BigInch (Petroleum) · Answer 15 · 2013-08-06 16:29:10

I was thinking before that it might have been a BSTR or some string to long conversion problem and tried a number of the conversions. I'll try again, this time using these latest declare formats and see if it produces some results.

Thanks again xwb.
I'd give you another star if I could.
You're as persistent as I am.

Independent events are seldomly independent.

BigInch (Petroleum) · Answer 16 · 2013-08-06 16:32:04

Do you think VB6 will have the same variable issues as VBA?

Independent events are seldomly independent.

IDS (Civil/Environmental) · Answer 17 · 2013-08-06 18:31:49

Some suggestions that may (or may not) help:

A C Integer is equivalent to a VBA Long, so integers should be passed as Longs.

See: http://www.drivenbysteam.com/?p=158 for a table of equivalent data types.

The pages from my blog linked here: http://newtonexcelbach.wordpress.com/2012/10/16/da...
may be of some use.

They are written on the assumption that you have access to the C code, but there may be something in there that helps solve the problem.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

BigInch (Petroleum) · Answer 18 · 2013-08-17 10:31:41

Sorry about the delay posting the outcome.
The problem (I think) turned out to be trying to run a 32 bit direct memory access routine on Win7. The function crashes on Win7. Works on my oldest laptop (XPSP3) when running with Visual Basic 6. Now I must try it with VBA. I may need those variable converts as well. Thanks for that Doug.

XLB your help is greatly appreciated.

Independent events are seldomly independent.

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Accessing a DLL function