DLL wrapper sample

What you would do is providing call stubs from your DLL that then are accessible via PInvoke, e.g.

//wrapper.cpp
#include "manufacturer.h"
#pragma comment(lib,"manufacturer.lib")

extern "C" __declspec(dllexport) int WrapperCallManufacturerFunc1(int a, int b)
{
    return ManufacturerFunc1(a,b);
}

extern "C" __declspec(dllexport) char* WrapperCallManufacturerFunc2(char* pString)
{
    return ManufacturerFunc2(pString);
}

extern "C" __declspec(dllexport) double WrapperCallManufacturerFunc3(double d)
{
    return ManufacturerFunc3(d);
}

extern "C" __declspec(dllexport) void WrapperCallManufacturerFunc4()
{
    ManufacturerFunc4();
}

That's basically it. The 'extern "C"' statement is used to tell the compiler to not apply C++ name mangling, i.e. the functions names are not decorated and exported 'as is'. The return types resemble the return types of the functions in the .lib you want to call, except for 'void' functions where your function is 'void' also, yet the 'return' statement is not used. Then you can access the wrapper functions like

Declare Auto Function ManufacturerFunc1  Lib "wrapper.dll" Alias "WrapperCallManufacturerFunc1 " ( _
    ByVal a As Integer, _
    ByVal b As Integer) _
    As Integer

or

Imports System.Runtime.InteropServices
Public Class Win32
    Declare Auto Function WrapperCallManufacturerFunc1 Lib "wrapper.dll" _
       (ByVal a As Integer, _
        ByVal b As Integer) As Integer
End Class

See also http://msdn2.microsoft.com/en-us/library/172wfck9(vs.80).aspx ("Walkthrough: Calling Windows APIs") and http://msdn2.microsoft.com/en-us/library/w4byd5y4(VS.80).aspx ("Creating Prototypes in Managed Code")