Reports

@Remy
I removed all the references to "__stdcall" and uncommented the "extern "C" code in the C++ dll, so that the function should be now exported as "_add_code".

I changed the DLL declaration in:

 <DllImport("MyDll.dll", EntryPoint:="_add_code")>
   Private Shared Function _add_code(ByVal text As String) As <MarshalAs(UnmanagedType.BStr)> String
 End Function

 Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

     Dim foo As String = _add_code("ppp")

 End Sub

Noting changes, i get alway the error "System.EntryPointNotFoundException: Could not find entry point with name '_add_code' in the DLL. The Entry point is not found, so I think that eventual errors related to Strings still have to be evaluated.

Folowing your suggestion I also tried a dump to get an Export table by VS command line, and I obtain the follw answer, that confirms that the function is exported as "_add_code". So the question: "Why I can't access to it from VB??"

Microsoft (R) COFF/PE Dumper Version 14.44.35217.0
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file MyDll.dll

File Type: DLL

  Section contains the following exports fory MyDll.dll

    00000000 characteristics
    FFFFFFFF time date stamp
        0.00 version
           1 ordinal base
           1 number of functions
           1 number of names

    ordinal hint RVA      name

          1    0 00001210 add_code = _add_code

  Summary

        1000 .data
        1000 .rdata
        1000 .reloc
        1000 .rsrc
        2000 .text

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