Accessing a DLL function 1

[BigInch]

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]

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

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[BigInch]

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]

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

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

 

[BigInch]

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]

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]

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]

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

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

 

[BigInch]

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

Independent events are seldomly independent.

 

[BigInch]

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

Independent events are seldomly independent.

 

[xwb]

It is a void function so maybe the declaration should be

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]

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]

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

 

[BigInch]

Again the "Bad calling convention" error was raised.

Independent events are seldomly independent.

 

[xwb]

Have a look at the following
[ul]
[li]

http://support.microsoft.com/kb/187912

[/li]
[li]

http://msdn.microsoft.com/en-us/library/office/bb687915.aspx

[/li]
[li]

http://support.microsoft.com/kb/106553/en-us

[/li]
[/ul]
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]

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]

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

Independent events are seldomly independent.

 

[IDS]

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/daily-download-29-using-vba-linking-to-c/

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]

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.