Call C++ function with parameters from VB.NET

Question

I got a c++ DLL like this:

#include "stdafx.h"
#include <string.h>
#include <iostream>
using namespace std;

BOOL booltest(string info1, string info2, DWORD dword1)
{
    if (dword1 == 5)
    {
        return FALSE;
    }
    if (!strcmp(info1.c_str(), "hello")) // check if info1 = "hello"
    {
        return FALSE; // if so return false
    }
    return TRUE; // if not return true
}

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

i have a button control on a form in a VB project and I would like to P/Invoke to call the booltest function. but I also need to pass the parameters! And obviously the data types between managed and unmanaged are different..!

Anyone have a working solution to this or useful pointers? I been tryna do this for some time now...

thanks (a sorry for english )

edit: to start?

<DllImport("mydll.dll")>
Public Shared Function booltest(...?) As Boolean
End Function

?

Answer 1

Solved the problem myself.

extern "C" {
    __declspec(dllexport) BOOL __stdcall booltest(BOOL test)
    {
        if (test)
        {
            return FALSE;
        }
        return TRUE;
    }
}

You can use it in VB.NET like this:

<DllImport("test.dll", CallingConvention:=CallingConvention.StdCall)>
Private Shared Function booltest(<MarshalAs(UnmanagedType.Bool)> ByVal test As Boolean) As Boolean
End Function

And then when you need to use it:

Dim b As Boolean = booltest(True)
If b = True Then
    MsgBox("true")
Else
    MsgBox("false")
End If

Just make sure to put the DLL in the Startup Path of the VB app so it can find the DLL, and replace "test.dll" with your own one. You can pass strings, integers, etc.. Just modify data type in the P/Invoke for the ...

good lukkk!

Answer 2

Disclaimer: I'm still learning VB.net so don't hurt me if I'm wrong.

I ran into a similar issue a couple of weeks ago. First, make sure you add a reference to your project for the DLL. Then make sure you use the 'import' statement at the head of your code. After that, you should be able to call a function normally.