Problems with functions from a DLL

Hi all:

I don't know if you has seen YACAS (Yet Another Computer Algebra System). It has a DLL with CAS functions and evaluation and I think it was created in Visual C++ 6.0.

I would like to use that DLL (that comes with a .h header file with the functions declared to use in C++) in Visual Basic.

I tryed to declare the functions like they are in the header file, but i get some errors and I don't know what do they mean.

For example, there is a function called "yacas_init" that is declared as follow (in the C++ header file):

Code:

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YACASDLL_API void yacas_init();

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I created a VB declaration for that function like:

VB Code:

Public Declare Sub YACAS_Init Lib "yacasdll.dll" Alias "yacas_init" ()

When I call the function from VB I get no errors ;)

But, I have another function declared as follow:

Code:

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YACASDLL_API void yacas_eval(char* expression);

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And I created a VB Declaration again for that function:

VB Code:

Public Declare Sub YACAS_Evaluation Lib "yacasdll.dll" Alias "yacas_eval" (ByRef strExpression As String)

When I call that function from VB i get the following error:

"Bad DLL calling convention (Error 49)"
http://msdn.microsoft.com/library/de...allingConv.asp

I looked for many ways to solve the problem, changed ByRef to ByVal, changing String to another data type, etc.

Please help me with my problem.

Keep in touch,

Andy

Have you tried changing String to Any or Variant? I know you said you tried other data types, but didnt say which ones.

The String it's ByVal NOT ByRef, even though you use it to return data.

VB Code:

Public Declare Sub YACAS_Evaluation Lib "yacasdll.dll" Alias "yacas_eval" ([b]ByVal[/b] strExpression As String)