Accessing C++ functions/classes (built as C++/CLI) in Visual Basic

Question

Hello,

I have source code in C++ which I want to combine with a front end built with Visual Basic 2019. I imagine that I need to build a CLR project through Visual studio. What I have been unable to find/understand is how to create a Visual Basic project which can call the functions or use objects defined in my C++ code.

I have found this page:

https://learn.microsoft.com/en-us/cpp/dotnet/walkthrough-compiling-a-cpp-program-that-targets-the-clr-in-visual-studio?view=msvc-170

However, the page only explains how to build the C++/CLI code that targets the CRL. It does not explain how to invoke the program of the code with Visual Basic.

Answer 1

Hi, @Ioannis Koutromanos

You need to create a C++ CLR Class library.
For example:

    #pragma once  
  
  
using namespace System;  
class myUnmanaged  
{  
public:  
    int a ;  
    myUnmanaged()  
    {  
        a = 2;  
    }  
};  
namespace CPPLibrary{  
    public ref class MyManagedCPP_Class  
    {  
    private:  
        myUnmanaged* myUnmanagedPtr =new myUnmanaged;  
  
    public:  
        MyManagedCPP_Class() { Console::WriteLine("hello C++!"); }  
        Void MyPrint()   
        {  
            Console::WriteLine(myUnmanagedPtr->a);  
        }  
          
    };  
}  

Call the class in VB project:

Imports System  
Imports CPPLibrary  
  
Module Program  
    Sub Main(args As String())  
        Dim m As New MyManagedCPP_Class()  
        m.MyPrint()  
        Console.WriteLine("Hello World!")  
    End Sub  
End Module  

Best regards,

Minxin Yu

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Answer 2

Hi Minxin,

Thank you for your detailed instructions.

I tried creating a solution combining the two types of projects that I need. The problem is that, when I compile, I get the warning:

warning MSB3270: There was a mismatch between the processor architecture of the project being built "MSIL" and the processor architecture of the reference "C:\Users\John\source\repos\WinFormsCallCppClass\Debug\CPPLibrary.dll", "x86". This mismatch may cause runtime failures. Please consider changing the targeted processor architecture of your project through the Configuration Manager so as to align the processor architectures between your project and references, or take a dependency on references with a processor architecture that matches the targeted processor architecture of your project.

Then, when I run my VB code (in debug mode) and I try to create an object defined in the C++ class, the execution breaks with the error message:

System.BadImageFormatException: 'Could not load file or assembly 'CPPLibrary, Version=1.0.8196.28320, Culture=neutral, PublicKeyToken=null'. An attempt was made to load a program with an incorrect format.'

Do you know what could be the reason for the specific problem, and how to resolve it?

Answer 3

Works perfectly!