Importing C/C++ function from DLL in a Visual Basic application

Mattia Valassi 1

Guys,
I'm developing an application in VB which requires importing functions from a C/C++ DLL.
Now, I imported several of the functions structuring them like this:

Declare Auto Function functionName_i Lib "library.dll" Alias functionName(ByVal something, ByRef somethingElse) As ReturnClass

Public Function functionName(ByVal something, ByRef somethingElse) As ReturnClass
Return (functionName_i (something, somethingElse))
End Function

When the functions I import have parameters, either by ref or value, everything works all right.
But when I try to use a function without parameters, like a C++ function with functionName(void) as signature, it does not work, with an exception telling me it was impossible to call the function from the library.
Where is my mistake? How should I import functions without parameters correctly?

Thanks,
hope you can help me!

Xingyu Zhao-MSFT 5,366 Reputation points

2021-02-12T01:51:57.94+00:00

Hi @MattiaValassi-5943 ,

But when I try to use a function without parameters, ..., it does not work,

Is there a function without parameters defined in the C++ library?
Mattia Valassi 1 Reputation point

2021-02-12T07:15:28.007+00:00

Yes there is. I'm importing all the functions of that library, which is a Black Box API. I can only access the signatures, but not the code.
Essentially, there is one function in the DLL with a signature like return_struct noParamFunction(void); that I have to import, which upon calling won't work, even if I imported it exactly like the other ones. The only difference is that the ones working do have parameters.
Xingyu Zhao-MSFT 5,366 Reputation points

2021-02-15T08:09:54.59+00:00

Hi @MattiaValassi-5943 ,
Could you call the function without parameters successfully in C/C++?
Could you provide more details about the exception?

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