Unamanaged call is not happening from the managed C# code

问题

I am calling unamanaged function from the managed code. But Unamanaged call is not happening.

Managed C# code: (Created a project (Sampletest) from Visual C# -> Console App) Sampletest:

namespace Sampletest
{
    class Program
    {
        const string Dllpath2 = @"C:\Users\apc\source\repos\Sampletest\SampleDll\Debug\SampleDll.dll";
        [DllImport(Dllpath2, EntryPoint = @"IsUPSPresent", CallingConvention = CallingConvention.Cdecl)]
        public static extern Boolean IsUPSPresent();
        static void Main(string[] args)
        {
            var test = IsUPSPresent();

            Console.ReadKey();
        }
    }
}

Unmanaged C++ code:

(Created a dll project (SampleDll) from Visual C++ -> Windows Desktop -> Dynamic Link Library)

"IsUPSPresent()" definition is there in SampleDll.cpp

#include "stdafx.h"

BOOL IsUPSPresent()
{
    BOOL    bRetValue = FALSE;

    return bRetValue;
}

But when we are making unmanaged call, first it is going to dllmain.cpp file present in unmanaged code.

#include "stdafx.h"

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;
}

then it is not going to

BOOL IsUPSPresent() function

and comming back to the managed call at "var test = IsUPSPresent();"

showing the error "Unhandled exception at 0x7705D6C7 (ntdll.dll) in Sampletest.exe: 0xC0000096: Privileged instruction.

Settings i Made:

For C# project,

Debug-> Selected "Enable native code debugging"

And I selected "Debug", "x86"

Please help me to resolve this issue.

回答1:

You have to declare IsUPSPresent using the __declspec(dllexport) attribute or use a .def-file. Also, to overcome C++ name mangling, your definition has to be extern "C" in C++-code.

extern "C" {
    BOOL __declspec(dllexport) IsUPSPresent()
    {
        BOOL bRetValue = FALSE;
        return bRetValue;
    }
}

来源：https://stackoverflow.com/questions/52811404/unamanaged-call-is-not-happening-from-the-managed-c-sharp-code

标签

c++

interop