[2005] Interface with C++

I'm trying to interface with a C++ app. I have everyone tlking to each other but the data that I am sending from VB seems to be byval versus byref.

From the ProbeValue_click event I am calling the C++ interface with sVal = 1.5. I can step through the code and see the 1.5 value when I reach the C++ function. I can also watch the value change to 3.444 in the C++ code.

The intent is to call byRef so the the value in VB equals the value set by C++. The ^ character in C++ (VS8) is the same as the old C/C++ reference character *. So, from what i can tell C++ is expecting a reference but VB is send a value.

What am I missing?

vb Code:

Private Sub BtnProbeValue_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnProbeValue.Click
    Dim sVar, sVal, sError As String
    Dim sts As Integer
 
    sVar = "Hoppy"
    sVal = 1.5
    sts = SimIFace.ProbeGetValue(sVar, sVal, sError)
 
  End Sub

Code:

---

int SimIFaceNET::ProbeGetValue(String^ sVar, String^ sVal, String^ sError)
{
  sVal = "3.444";
  sError = sError->Empty;
  return -1;
}

---

you need to declare your function and refernece that dll. You can then call the function.

Something like this...

vb.net Code:

Declare Function ProbeGetValue Lib "SimIFaceNET.dll" (ByVal sVar As String, _
                                ByVal sVal As String, _
                                ByRef sError As String) As Int32

Then add the dll to the app directory

Edit: I just kind of read your post again and am kind of confused. Is that c++ function doing anything besides setting sError to empty and returning -1? I am not all that familiar with c++, but I have used c++ dll's in my vb.net projects. If you want all variables to be byRef then declare them as ByRef like so

vb.net Code:

Declare Function ProbeGetValue Lib "SimIFaceNET.dll" (Byref sVar As String, _
                                ByRef sVal As String, _
                                ByRef sError As String) As Int32

Ah, that makes sense. Kind of like making a declare to an API.

Quote:

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Is that c++ function doing anything besides setting sError to empty and returning -1?

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That was a simplifed test case. We had a huge function written but it didn't work because it did not update the variables. As soon as I verify that this works, I'll return the true functionality of the code.

Thanks